ASNT NDT Handbook Volume 10 OVERVIEW

NON DESTRUCTIVE l-
TESTING HANDBOOK :s

Second Edition d
1-
VOLUME 10
NONDESTRUCTIVE TESTING OVERVIEW r-
ir
Stanley Ness
Charles N. Sherlock l-
Technical Editors al
Patrick 0. Moore ,k
Paul Mcintire
Editors :e

AMERICAN SOCIETY FOR tg
NONDESTRUCTIVE TESTING
n.
r-
rr

Copyright© 1996 TESTING, INC.
AMERICAN SOCIETY FOR NONDESTRUCTIVE
All rights reserved.

No part of this book may be reproduced, stored in a retrieval system or transmitted, in

any form or by any means - electronic, mechanical, photocopying, recording or
otherwise - without the prior written permission of the publisher.

Nothing contained in this book is to be construed as a grant of any right of manufacture,
sale or use in connection with any method, process, apparatus, product or composition,

whether or not covered by letters patent or registered trademark, nor as a defense against
liability for the infringement of letters patent or registered trademark.

The American Society for Nondestructive Testing, its employees and the contributors to
this volume are not responsible for the authenticity or accuracy of information herein, and

opinions and statements published herein do not necessarily reflect the opinion of the
American Society for Nondestructive Testing or carry its endorsement or

recommendation.

The American Society for Nondestructive Testing, its employees, and the contributors to

this volume assume no responsibility for the safety of persons using the information .in this
book

Library of Congress Cataloging-in-Publication Data

Nondestructive testing overview I Stanley Ness, Charles N. Sherlock, technical editors.

Patrick 0. Moore, Paul M. Mcintire, editors.
p. cm. - (Nondestructive testing handbook; v. 10)

Includes bibliographic references and index.
ISBN-13 978-1-57117-018-7

1. Non-destructive testing. 2. Non-destructive testing-Industrial applications.

3. Engineering inspection. I. Ness, Stanley. II. Sherlock, Charles N. III. Moore,
Patrick 0. IV. Mcintire, Paul. V. American Society for Nondestructive Testing.

VI. Series: Nondestructive testing handbook (2nd ed.); v. 10
TA418.2.N65 1996 96-25138
620.1'127-dc20
CIP

first printing 10/96

second printing 01/01
third printing 01/04

fourth printing 04/05
fifth printing O 1/07

Published by the American Society for Nondestructive Testing

PRINTED IN THE UNITED STATES OF AMERICA

ii

PRESIDENT'S FOREWORD

This book is the tenth and final volume of the second in the second edition has made productive use of ASNT'svol-
edition of the Nondestructive Testing Handbook. The Non­ unteer resources. Many hundreds of authors and reviewers
destructive Testing Handbook series again demonstrates the have donated tens of thousands of hours to this edition.
dedication of the American Society for Nondestructive Test-
ing (ASNT) to its missions of providing technical informa- Nondestructive Testing Overview was written and
tion and instructional materials and of promoting reviewed under the guidance of ASNT's Handbook Devel-
nondestructive testing technology as a profession. The opment Committee by volunteers who have shared gener-
series documents advances in research and applications in ously with us their expertise and countless hours of their
the various nondestructive testing methods and provides valuable time. A special note of thanks is extended to Hand-
reference materials for nondestructive testing educators book Development Director Roderic Stanley, to Technical
and practitioners in the field. Editors Stanley Ness and Charles Sherlock, to Handbook
Editor Patrick Moore and to his predecessor Paul Mcintire
The final volume is an appropriate place to reflect on the for their dedicated efforts and commitment in providing
second edition. The Nondestructive Testing Handbook is this outstanding book
almost as old as ASNT itself: planning for the series began in
1944. After publication of the first edition in 1959, the Tech- ASNT is now poised to begin work on the third edition.
nical Council's Handbook Committee in 1960 was charged Our hope is it will build on the successes of the past and sur-
with coordinating the preparation of the second edition. After pass them by providing current information about our
years of planning, ten volumes have been published in 1982 rapidly evolving technology.
to 1996. The collaboration between the volunteers and staff
Michael Turnbow
ASNT National President (1995-96)

iii

FOREWORD

The Aims of a Handbook Standards, specifications, recommended practices and
inspection procedures may be discussed in a handbook for
The volume you are holding in your hand is the tenth in instructional purposes, but at a level of generalization that is
the second edition of the Nondestructive Testing Handbook, illustrative rather than comprehensive. Standards writing
a series that began publication in 1982. Now, as the present bodies take great pains to ensure that their documents are
series draws to a close, is a good time to reflect on the pur- definitive in wording and technical accuracy. People writing
poses and nature of a handbook. contracts or procedures should consult real standards when
appropriate.
Handbooks exist in many disciplines of science and tech-
nology,and certain features set them apart from other refer- Those who design qualifying examinations or study for
ence works. A handbook should ideally give the basic them draw on handbooks as a quick and convenient way of
knowledge necessary for an understanding of the technol- approximating the body of knowledge. Committees and
ogy, including both scientific principles and means of appli- individuals who write or anticipate questions are selective in
cation. what they draw from any source. The parts of a handbook
that give scientific background, for instance, may have little
The typical reader may be assumed to have completed bearing on a practical examination. Other parts of a hand-
three years of college toward a degree in mechanical engi- book are specific to a certain industry. Although a handbook
neering or materials science and hence has the background does not pretend to offer a complete treatment of its sub-
of an elementary physics or mechanics course. Occasionally ject, its value and convenience are not to be denied.
an engineer may be frustrated by the difficulty of the dis-
cussion in a handbook. That happens because the assump- The present volume is a worthy member of the second
tions about the reader vary according to the subject in any edition. Because it is a multimethod volume, members of
given section. Computer science requires a different sort of nine method committees in ASNT's Technical Council par-
background from nuclear physics, for example, and it is not ticipated in the peer review. For this reason, volunteer activ-
possible for the handbook to give all the background knowl- ity was coordinated through the Handbook Development
edge that is ancillary to nondestructive testing. Committee rather than by a single method committee. The
editors, technical editors and many contributors and review-
A handbook offers a view of its subject at a certain period ers worked together to bring the project to· completion. For
in time. Even before it is published, it starts to get obsolete. their scholarship and dedication I thank them all.
The authors and editors do their best to be current but the
technology will continue to change even as the book goes to Roderic K. Stanley
press. Handbook Development Director

iv

PREFACE

The second edition of the Nondestructive Testing Hand­ articles written and published in many other countries. One
book comprises ten volumes, 17,000,000 characters, 6,573 of the consistent themes in developing each volume was
pages and more than 5,000 illustrations. Three Handbook maintenance of the series' international value. Using SI as
Development Directors (John Summers, Albert Birks and the primary measurement system w.as one result of this
Roderic Stanley) managed progress of the edition through focus, as was recruitment efforts for authors and reviewers
the Society's very active Handbook Development Commit- outside the United States. This international emphasis
tee. Fifteen technical editors undertook the task of validating allowed the Nondestructive Testing Handbook to be written
the technical content of documents covering dozens of and reviewed by British, Canadian, Dutch, French, German,
sophisticated nondestructive testing methods. Key manu- Greek, Japanese, Saudi Arabian and American volunteers.
scripts were submitted by 104 lead authors, supported by
more than 750 contributing authors. Peer reviewers num- Because of these skilled, high-reaching efforts, it turned
bered nearly 600. For the fifteen years between 1981 and out that the second edition also showed how interesting
1996, three editors-in-chief labored to establish technical nondestructive testing can be. There are uses of the tech-
protocols and to give the series a consistency of style and nology documented for virtually every industry and an
voice. Those editors were Robert C. McMaster (Volumes 1 astonishing range of materials. Here you can read about
and 2), Paul Mcintire (Volumes3 through 10) and Patrick 0. microwaving the pyramids (Vol. 4, p 546), listening to inte-
Moore (Volumes 8, 9 and 10). Their work relied completely grated circuit chips cracked in their substrates (Vol. 5,
on the efforts of those many volunteers and resulted in a sig- p 358), using alternating current underwater to do magnetic
nificant contribution to the technical literature, at an impor- particle tests (Vol. 6, p 384), or applying ultrasonic waves to
tant time for the American nondestructive testing industry. inspect the human abdomen and other kinds of plumbing
(Vol. 7, p 822 and 585). It's an impressive range of data for a
The technical accomplishments of the Nondestructive handbook series.
Testing Handbook stand as a tribute to the volunteer spirit.
ASNT could not have built the second edition without the Handbooks are expected to document the uses of their
unwavering commitment of its volunteer contributors. technology and this field guide function may be supported
Experts in every field of nondestructive testing voluntarily by text that details the pure science behind the applications.
developed outlines to cover the science and use of their The second edition of the Nondestructive Testing Handbook
nondestructive testing techniques, developed strategies for does both of these things well, while at the same time repre-
writing the chapters, reviewed, corrected and re-reviewed senting the dedication of its volunteer contributors, the
every one of those 17,000,000 characters. Volunteers have value of the peer review system and the importance of its
often expressed their reasons for doing this work: the over- international scope. With the publication of this, the second
whelming majority gave their personal time and knowledge edition's tenth and final volume, ASNT can rightly claim to
because of their abiding concern for safety, scientific credi- have documented a critical technology.
bility, the quality of American industry and the value of
ASNT's mission. Thanks are due to Jack McElhaney, who helped in word
processing of much of the text, to Edwards Brothers for
The Nondestructive Testing Handbook also validates the printing and binding, to Kevin Mulrooney for indexing and
peer review system and its ability to generate a high quality to Hollis Humphries-Black, who prepared the art and layout
product. It's true that manuscripts for the Nondestructive and made good things happen at every stage of production.
Testing Handbook arrived in all conditions within a broad
range of accuracy and consistency (one valuable contribu- Thanks are due especially to Technical Editors Stanley
tion comprised a two inch stack of yellow legal sheets hand- Ness and Charles Sherlock for overseeing the technical
written in what appeared to be lipstick). Yet, without review. The use of metric units in the text was reviewed by
exception, the positive criticism and constructive editing of Holger H. Streckert and Stanislav I. Jakuba. All the many
the peer reviewers molded the manuscripts into an accurate volunteer contributors and reviewers deserve congratula-
and practical finished product. tions for what they have accomplished.

The international stature of the Nondestructive Testing Paul Mcintire
Handbook is reflected in its frequent citation in technical Patrick Moore
Editors

v

ACKNOWLEDGMENTS

Nondestructive testing (NDT) continues to become Volume 10 of the Nondestructive Testing Handbook draws
more important in this age of increasing high technology. extensively from the preceding nine volumes of the second
Materials with compositions of greater sophistication for edition. Volunteers who were most active in the compilation
higher tensile strengths at lighter weights create the need of this volume are listed on the title page to each section.
for NDT to be performed at higher sensitivities with more Additionally, the list of contributors below acknowledges con-
accuracy and more predictability than ever before. Contin- tributors to the original sections in the second edition vol-
ued public demands for safer products at lower cost also umes from which Volume 10 was compiled. The reviewers
increase the need for better and more reliable NDT. The listed after the · contributors below, however, are those who
development of miniaturized computer chips and inte-
grated circuits with power unthinkable just a few decades participated in the preparation of Volume 10, not necessarily
ago has, in tum, spurred development of electronic NDT other volumes in the second edition.
equipment and helped create new NDT techniques. This
advancing technology and the need for increased sophistica- To acknowledge the support of scholarship by industry, a
tion in NDT methods promote each other. The results are name of a contributor or reviewer is followed by his or her
observed every day in the more reliable and safer materials affiliation at the time of most recent activity for the Nonde­
and products used in the home, in automobiles, in aircraft structive Testing Handbook, even though that person may
and the space program. have changed employers. since. Apologies are extended to
contributors, reviewers and others who helped to create this
Volume 10 of the Nondestructive Testing Handbook con- volume but may have been omitted from the list below.
tains an overview of each of the major NDT methods widely
used by industry. In a single cover, Nondestructive Testing HandbookDevelopment
Overview provides students with an introductory text and Committee
management with a readily portable reference publication.
It provides NDT and quality assurance managers with gen- Sreenivas Alampalli, New York State Department of
eral knowledge and direction to ensure the specification of Transportation
the most effective NDT for manufacturing and for in-ser-
vice inspection of existing structures. Volume 10 will prove Michael W Allgaier, GPU Nuclear
valuable to NDT practitioners whose work is limited to one
or two NDT methods but who must have a working famil- Robert A. Baker, Pennsylvania Power & Light Company
iarity with other methods, without requiring a separate vol- Albert S. Birks, AKZO Nobel Chemicals
ume for each.
Richard H. Bossi, Boeing Defense and Space Group
The second edition of ASNT's Nondestructive Testing
Handbook compiles the knowledge of many volunteers Lawrence E. Bryant, Jr., Los Alamos National Laboratory
within the NDT community, both within and outside ASNT.
Single NDT method volumes require the input of many John Stephen Cargill, Pratt & Whitney
within that single NDT discipline. However, because Vol- William C. Chedister, Circle Chemical Company
ume 10 covers all the major NDT methods, it required the
dedication and voluntary time and hard work of volunteers William D. Chevalier, Zetec, Incorporated
throughout all the NDT disciplines. The following acknowl- James L.
edgments indicate some of the hundreds of individuals and Matthew DJ. oGyoleli,sQuest Integrated, Incorporated
organizations that contributed indirectly to the preparation
of this book. As technical co-editors, we thank all those who Allen T. Green, Acoustic Technology Group
contributed to this volume as writers and reviewers.
Robert E. Green, Jr., Johns Hopkins University
Stanley Ness Grover Hardy, Materials Directorate of Wright Laboratory
Charles N. Sherlock
Technical Editors James F. Jackson
Stanislav I.Jakuba, SI Jakub Associates
John K. Keve, Westinghouse Hanford
Irvin R. Kraska, Martin Marietta

Lloyd P. Lemle, Jr.
Ronnie K. Miller, Physical Acoustics Corporation

Scott D. Miller, Aptech Engineering Services

Philip A. Oikle, Yankee Atomic Electric Company

Stanley Ness
Ronald T. Nisbet

vi

Emanuel P. Papadakis, Quality Systems Concepts Robert W Loveless, Worthington Pump Corporation
Stanislav I. Rokhlin, Ohio State University J.L. Manganaro, General Electric Company
J. Thomas Schmidt, J. Thomas Schmidt Associates J. William Marr, IBM Corporation
Kermit Skeie, Kermit Skeie Associates Ralph E. McCullough, Texas Instruments, Incorporated
Roderic K. Stanley, Quality Tubing, Incorporated Thomas G. McRae, Laser Imaging Systems
Philip J. Stolarski, California Department of Wilfred E. Nagel, Rockwell International
John A. Roberts, General Electric Company
Transportation Stanley Ruth berg, National Institute of Standards and
Holger H. Streckert, General Atomics
Stuart A. Tison, NIST Vacuum Group Technology
Noel A. Tracy, Universal Technology Corporation Charles N. Sherlock
Mark F.A. Warchol, Alcoa Technical Center Carl Waterstrat, Varian, Vacuum Products Division
George C. Wheeler, Wheeler NDT, Incorporated Robert M. Wilson, Consolidated Electrodynamics

Contributors Corporation
J.R. Worlund, Converse Environmental Consultants
Section 1, Introduction to Nondestructive Testing
Southwest
Robert C. McMaster William C. Worthington, Varian, Lexington Vacuum
Stanislav I. Jakuba, SI Jakub Associates
Stanley Ness Division
Holger H. Streckert, General Atomics
Jan van den Andel Section 3, Liquid Penetrant Testing
AlexVary, NASA Lewis Research Center
Samuel A. Wenk Bernard W. Boisvert, B&B Technical Services
Rob Hagen, NDT Europa BV
Section 2, Leak Testing Grover L. Hardy, MaterialsDirectorate of Wright

James R. Alburger, Shannon-Glow, Incorporated Laboratory
Gerald L. Anderson, American Gas & Chemical Company Vilma Holmgren, Magnaflux, Division of ITW
D.L. Ayres, The Standard Oil Company, Ohio Brian MacCracken, Pratt & Whitney
W Brewer, Argonne National Laboratory William E. Mooz, Met-L-Chek Company
Albert E. Brown, Lawrence Livermore National Laboratory Sam Robinson, Sherwin NDT Systems
John S. Buck, Acoustic Emission Leak Locators Clint E. Surber, Boeing Commercial Airplane Group
Noel A. Tracy, Universal Technology Corporation
Corporation
R. Carlson, Argonne National Laboratory Section 4, Radiation Principles and Sources
Anthony J. Carrozza, Veeco Instruments, Incorporated
David E. Center, Nooter Corporation C. Robert Emigh, Los Alamos National Laboratory
Edward E. Chait, E.I. du Pont de Nemours & Company, Frank A. Iddings
James D. Willenberg, Industrial Testing Consultants
Incorporated
Jeffrey F. Cook, JFC NDE Engineering Section 6, Radioscopy and Tomography
Lutz W. Dahlke, Sandia Laboratories
P.B. Durgin, United States Environmental Protection Richard H. Bossi, Boeing Defense and Space Group
Paul Mengers, Quantex Corporation
Agency Charles Oien, Sandia National Laboratory
A.G. Eklund, Radian Corporation
Stanley R. Goldfarb, Veeco Instruments, Incorporated Section 7, Electromagnetic Testing
J.L. Hartley, Sandia Corporation
Wesley C.L. Hemeon, Hemeon Associates Donald D. Dodge, Ford Motor Company
Charles F. Hiltner, B.P. Oil Company Emil M. Franklin, Argonne National Laboratory, Idaho
D.L. Hollinger, General Electric Company
Charles N. Jackson, Hanford Engineering Development Falls
Donald J. Hagemaier, Douglas Aircraft Company
Laboratory Tatsuo Hiroshima, Sumitomo Metals
E.F. Koch, Jet Propulsion Laboratory Nathan Ida, University of Akron
D.S. Kupperman, Argonne National Laboratory Marv Johnson, Owens Services Corporation
R. Lanham, Argonne National Laboratory Tim Kinsella, Hamilton Standard
Kenji Krzywosz,J.A. Jones Applied Research Company
Michael L. Mester, United States Steel Corporation

vii

George Mordwinkin, Sensor Corporation Robert E. Green, Johns Hopkins University
M. Pigeon, Commissariat a l'Energie Atomique, France Edmund G. Henneke, II, Virginia Polytechnic Institute
R. Saglio, Intercontrole, Incorporated
Ram P. Samy, The Timken Company and State University
Thomas R. Schmidt, Shell Development Company G. Huebschen, Fraunhofer Institut for Zerstorungsfreie
David L. Spooner, Virginia Electric and Power Company
Roderic K. Stanley, Quality Tubing, Incorporated Prufverf ahren
B.T. Khuri-Yakub, Stanford University
Section 8, Magnetic Particle Testing Bruce Maxfield, Innovative Sciences
Jean-Pierre Monchalin, Industrial Materials Research
Bernard Boisvert
Institute, Canada
Sectrion 9, Acoustic Emission Testing Emmanuel P. Papadakis, Iowa State University
W. Repplinger, Fraunhofer Institut for Zerstorungsfreie
J.A. Baron, Ontario Hydro
P.R. Blackbum, Linde Division of Union Carbide Prtifverfahren
H.J. Salzburger, Fraunhofer Institut for Zerstorungsfreie
Corporation
Albert E. Brown, Lawrence Livermore Laboratories Prufverfahren
C.E. Coleman, Atomic Energy of Canada, Chalk River R. Bruce Thompson, Iowa State University
Bruce Craig, Metallurgical Consultants
N.O. Cross, NDTech James W. Wagner, Johns Hopkins University
James Culp, Michigan Department of Transportation Ansgar Wilbrand, Fraunhofer Institut for Zerstorungsfreie
Thomas F. Drouillard
Mark Ferdinand, Hartford Steam Boiler Pntfverf ahren
Timothy J. Fowler, Felicity Group, Incorporated
Allen T. Green, Acoustic Emission Technology Corporation Section I I, Ultrasonic Pulse Echo Techniques
D. Robert Hay, Tektrend International
Phillip H. Hutton, Battelle Pacific Northwest Laboratory Glenn Andrew, Science Applications International
Min-Chung Jon, AT&T Corporation
Teruo Kishi, University of Tokyo
R.F. Klein, Battelle Pacific Northwest Laboratory Francis H. Chang, Lockheed Martin Technical Aircraft
Charles McGogney, Federal Highway Administration Systems
Ronnie K. Miller, Physical Acoustics Corporation
James R. Mitchell, Physical Acoustics Corporation Yoseph Bar-Cohen, Jet Propulsion Laboratories
Vasile Mustafa, Tektrend International Albert S. Birks, AKZO Nobel Chemicals
Hiroyasu Nakasa, Central Research Institute of Electric Matthew J. Golis
AlexVary, NASA Lewis Research Center
Power Industry
Kenneth Notvest Section I 2, Visual Testing
Adrian A. Pollock, Physical Acoustics Corporation
Dan Robinson, Hartford Steam Boiler Michael W. Allgaier, GPU Nuclear
Mansoor Saifi, Western Electric Company
E.B. Schwenk, Battelle Pacific Northwest Laboratory William H. Bailey
Jack C. Spanner, Battelle Pacific Northwest Laboratory David Casasent, Carnegie Mellon University
John Stapleton, AT&T
Sotirios J. Vahaviolos, Physical Acoustics Corporation Yen Fwu Cheu, General Motors Corporation
Governor Ware, Teletype Corporation
Peter Ying, Gilbert/Commonwealth David Clark, Global Holonetics Corporation

Section I 0, Introduction to Ultrasonic Testing Dana Dunn

George A. Alers, Magnasonics Eugene Egger, CTS Power Services
Albert S. Birks, AKZO Nobel Chemicals Edward R. Generazio, Lewis Research Center
Dale Chimenti, Air Force Materials Laboratory Stanley Ness ·

CM.aMtth. eFworJt.uGnkolois, ElectroSonics Don J. Roth, NASA Lewis Research Center

Charles N. Sherlock

Virginia Torrey, Welch Allyn Video Division

Section I 3, Thermography and Other Special
Methods

Jorge A. Alcoz, Karta Technology
Philip D. Bondurant, Quest Integrated, Incorporated
Ronald J. Botsko, NDT Systems, Incorporated
Stephen L. Dieckman, Argonne National Laboratory
James L. Doyle, Quest Integrated, Incorporated
Steve Goldman, Goldman Machinery Dynamics

Corporation

viii

Donald J. Hagemaier, McDonnell Douglas Aerospace Timothy J. Fowler, Felicity Group, Incorporated
Matthew J. Golis
Richard L. Hannah, JP Technologies Allen T. Green, Acoustic Technology Group
E. Blair Hen:ry
Roger F. Johnson, Quest Integrated, Incorporated Robert E. Green, Jr., Johns Hopkins University
Thomas S. Jones, Industrial Quality, Incorporated Paul E. Grover, Infraspection Institute
Satish Nair, Karta Technology, San Antonio, Texas
Stanley Ness Donald J. Hagemaier, McDonnell Douglas Aerospace
Daniel Post, Virginia Polytechnic Institute and State Grover Hardy, Materials Directorate of Wright Laborato:ry
E.G. Henneke, II, Virginia Polytechnic and State
University
Martin J. Sablik, Southwest Research Institute University
Cesar A. Sciammarella, Illinois Institute of Technology Nathan Ida, Akron University
Pieter J. Sevenhuijsen, National Aerospace Laborato:ry Frank A. Iddings
John R. Snell, Jr., John Snell and Associates
Roderic K. Stanley, Quality Tubing, Incorporated James F. Jackson
John Scott Steckenrider,Argonne National Laborato:ry Stanislav I. Jakuba, SI Jakub Associates
Peter K. Stein, Stein Engineering Services Thomas S. Jones, Industrial Quality, Incorporated
Colleen M. Stuart, Technicorp John K. Keve, Westinghouse Hanford
Walter Tomasulo, Technicorp Irvin R. Kraska, Martin Marietta
AlexVary, NASA Lewis Research Center David S. Kupperman, Argonne National Laborato:ry
Ronnie K. Miller, Physical Acoustics Corporation
Volume 1 0 Reviewers Scott D. Miller, Aptech Engineering Services
Ronald T. Nisbet, Ronan Corporation
Michael W Allgaier, GPU Nuclear Philip A. Oikle, Yankee Atomic
Robert A. Baker
Yoseph Bar-Cohen, Jet Propulsion Laborato:ry Emmanuel P. Papadakis, Quality Systems Concepts
Har:ry Berger, Industrial Quality, Incorporated Morteza Safai, Quest Integrated, Incorporated
Albert S. Birks, AKZO Nobel Chemicals Ram P. Samy,The Timken Company
Bernard Boisvert Edward R. Schaufler, Infra Red Scanning Services
Richard H. Bossi, Boeing Defense and Space Group
Ronald J. Botsko, NDT Systems, Incorporated J. Thomas Schmidt, J. Thomas Schmidt Associates
John Stephen Cargill, Pratt & Whitney Paul B. Shaw, Chicago Bridge and Iron, Incorporated
Francis H. Chang, Lockheed Martin Technical Aircraft Amos G. Sherwin, Sherwin NDT Systems
Kermit Skeie, Kermit Skeie Associates
Systems
William C. Chedister, Circle Systems, Incorporated John R. Snell, Jr., John Snell and Associates
Eugene J. Chemma, Bethlehem Steel Corporation Roderic K. Stanley, Quality Tubing, Incorporated
Thomas F. Drouillard Phil Stolarski, California Department of Transportation
J.C. Duke, Jr., Virginia Polytechnic Institute and State Holger H. Streckert, General Atomics
Colleen M. Stuart, Technicorp
University Stuart A. Tison, National Institute of Standards and
Ga:ryR. Elder, Cary Elder & Associates
Todd S. Fleckenstein, Moody International Technology
Noel A. Tracy, Universal TechnologyCorporation
Mark F.A. Warchol, Aluminum Company of America
Randall D. Wasberg, American Society for Nondestructive

Testing
Carl Waterstrat, Varian Vacuum Products
George C. Wheeler, Wheeler NDT, Incorporated

ix

CONTENTS

SECTION 1: INTRODUCTION TO 1 Ensuring System Reliability through Leak . 28
NONDESTRUCTIVE TESTING Testing 28
29
Leak Testing to Detect Material Flaws . 29
29
PART 1: NATURE OF NONDESTRUCTIVE Specifying Desired Degrees of Leak . 30
Tightness 30
TESTING . 2 30
2 Avoiding Impractical Specifications for 32
Definition of Nondestructive Testing . 2 Leak Tightness . . . . . . . . . . . . . . . . . . . . . . 32
Purposes of Nondestructive Testing . . . . . . . . 32
6 Specifying Leak Testing Requirements to
Rapid Growth and Acceptance of 9 Locate Every Leak . 34
9
Nondestructive Tests . 9 Specifying Sensitivity of Leak Testing for 34
PART 2: QUALITY ASSURANCE . 10 35
11 Practical Applications . . . . . . . . . . . . . . . . . 36
Basic Concepts of Quality Assurance . 11 Definition of Leak Detector and Leak Test 36
12 37
Quality Control and Quality Assurance . 12 Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . .
Establishing Quality Levels . 14 38
Example of Sensitivity and Difficulty of 38
PART 3: TEST SPECIFICATION . 14 Bubble Leak Testing . 38
15 38
Management Policies . 15 Relation of Test Costs to Sensitivity of 39
Sources of Information . . . . . . . . . . . . . . . . . . 40
18 Leak Testing . 42
Specifying Sensitivity and Accuracy in Tests .. 18 42
Establishing the Reliability of Tests . 18 Selection of Specific Leak Testing Technique 42
20 for Various Applications .
Scheduling Tests for Maximum 21 43
Basic Categories of Leak Testing .
Effectiveness and Economy . 21 Selection of Tracer Gas Technique for Leak 44
22
Applications of Nondestructive Testing . 24 Location Only . . . . . . . . . . . . . . . . . . . . . .
Mode of Presentation .
Factors Influencing Choice between
PART 4: UNITS OF MEASURE FOR
Detector Probe and Tracer Probe Tests . .
NONDESTRUCTIVE TESTING . Selection of Technique for Leakage
Origin and Use of the SI System .
Measurement .
SI Units for Radiography .
Practical Measurement of Leakage Rates with
Fundamental SI Units Used for Leak testing .. Gaseous Tracers .

SI Units for Electrical and Magnetic Testing .. Leakage Measurements of Open Test Objects
SI Units for Other Nondestructive Testing
Accessible on Both Sides .
Methods .
Prefixes for SI Units . Selection of Test Methods for Systems

BIBLIOGRAPHY . Leaking to Atmospheric Pressure .

Purposes of Leak Testing to Locate
Individual Leaks . . . . . . . . . . . . . . . . . . . . .

SECTION 2: LEAK TESTING . 25 Classification of Methods for Locating and .
Evaluating Individual Leaks
PART 1: MANAGEMENT AND APPLICATIONS 26
26 Techniques for Locating Leaks with .
OF LEAK TESTING . 26
26 Electronic Detector Instruments .
Functions of Leak Testing . 26
27 Coordinating Overall Leakage Measurements
Relationship of Leak Testing to Product 28 with Leak Location Tests .
Serviceability . . . . . . . . . . . . . . . . . . . . . . . 28
Laser Based Leak Imaging .
Determination of Overall Leakage Rates
through Pressure Boundaries . . . . . . . . . . . Training of Leak Testing Personnel .
PART 2: SAFETY IN LEAK TESTING .
Measuring Leakage Rates to Characterize
Individual Leaks .. ; . General Safety Procedures for Test Personnel .

Quantitative Description of Leakage Rates . . PsychologicalFactors and the Safety Program .
Control of Hazards from Airborne Toxic
Examples of Practical Units Used Earlier for
Liquids, Vapors and Particles .
Measurement of Leakage .
Control of Hazards of Flammable Liquids
Units for Leakage Rates of Vacuum Systems . and Vapors .

x

Control of Electrical and Lighting Hazards . . 44 PART 10: LEAK TESTING OF STORAGE 65
Safety Precautions with Leak Testing Tracer TANKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
45 Detection of External Leaks in Underground 65
Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Storage Tanks . . . . . . . . . . . . . . . . . . . . . . .
Safety Precautions in Pressure and Vacuum 45 Leak Testing of Aboveground Storage 65
Tanks with Double Flat Bottoms . . . . . . . .
Leak Testing . . . . . . . . . . . . . . . . . . . . . . . 47 Comparison of Quantitative Leak Testing 68
Safety Precautions with Compressed Gas Techniques . . . . . . . . . . . . . . . . . . . . . . . . . 71
48
Cylinders . . . . . . . . . . . . . . . . . . . . . . . . . . 48 BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . .
PART 3: HALOGEN TRACER GAS
48 SECTION 3: LIQUID PENETRANT 75
TECHNIQUES AND LEAK DETECTORS . . . 49 TESTING..........................
Halogen Vapor Tracer Gases and Detectors . . 76
Pressure Leak Testing with Halogen (Sniffer) 49 PART 1: DEFINITION AND PURPOSE OF 76
Detector Probe . . . . . . . . . . . . . . . . . . . . . LIQUID PENETRANT TESTING . . . . . . . . . . 76
49 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PART 4: REFERENCE LEAKS . . . . . . . . . . . . . . . 49 Basic Penetrant Testing Process . . . . . . . . . . . 77
Terminology Applicable to Reference, Reasons for Selecting Liquid Penetrant
Calibrated or Standard Leaks . . . . . . . . . . 50 Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Classification of Common Types of Calibrated Disadvantages and Limitations of Liquid 79
or Standard Physical Leaks . . . . . . . . . . . . 50 Penetrant Testing . . . . . . . . . . . . . . . . . . . . 80
Modes of Gas Flow through Leaks . . . . . . . . . Equipment Requirements . . . . . . . . . . . . . . . 81
50 Personnel Requirements . . . . . . . . . . . . . . . . . 81
PART 5: PRESSURE CHANGE TESTS FOR
MEASURING LEAKAGE RATES........... 50 PART 2: CLASSIFICATIONS OF PENETRANTS . 81
Functions of Pressurizing Gases in Classification of Penetrants by Dye Type . . . . 82
Leak Testing . . . . . . . . . . . . . . . . . . . . . . . 50 Classification of Penetrants by Removal 83
Conversion of Pressure Measurements Method . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
to Systeme Internationale d'Unites 52 Types of Developers . . . . . . . . . . . . . . . . . . . . 84
(SI Units) . . . . . . . . . . . . . . . . . . . . . . . . . Qualified/Approved Penetrant Materials . . . . 84
54 Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Compressibility of Gaseous and Liquid 54
Fluids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PART 3: PENETRANT TESTING PROCESSES . . 85
55 Selection of a Penetrant Material/Process . . . 86
Pressure Change Tests for Measuring 57 Control of a Penetrant Process . . . . . . . . . . . . 88
Leakage Rates in Pressurized Systems . . . . 57 Advantages and Limitations of Penetrant 89
Materials and Techniques . . . . . . . . . . . . .
Pressure Change Tests for Measuring 57 Pretesting, Cleaning and Postcleaning . . . . . .
Leakage in Evacuated Systems . . . . . . . . . Summary... ..... . .................
58
PART 6: LEAK TESTING OF VACUUM BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . .
SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
The Nature of Vacuum . . . . . . . . . . . . . . . . . . SECTION 4: RADIATION PRINCIPLES 91
Leak Testing of Vacuum Systems with 59 AND SOURCES . . . . . . . . . . . . . . . . . . . . .
Mass Spectrometer Leak Detector 61 92
Techniques . . . . . . . . . . . . . . . . . . . . . . . . . 61 PART 1: ELECTROMAGNETIC RADIATION . . . 92
The Photon . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
PART 7: BUBBLE LEAK TESTING. . . . . . . . . . . . 61 X-Rays and Gamma Rays . . . . . . . . . . . . . . . . 93
Generation of X-Rays . . . . . . . . . . . . . . . . . . . 95
Introduction to Bubble Techniques . . . . . . . . 62 95
Bubble Testing by Liquid Film Application PART 2: RADIATION ABSORPTION . . . . . . . . . . 95
Categories of Absorption . . . . . . . . . . . . . . . . 96
Technique . . . . . . . . . . . . . . . . . . . . . . . . . Absorption of Photons . . . . . . . . . . . . . . . . . . 98
Bubble Testing by the Vacuum Box Scattering of Photons . . . . . . . . . . . . . . . . . . . 98
Attenuation Coefficients of the Elements . . . .
Technique . . . . . . . . . . . . . . . . . . . . . . . . . Neutron Irradiation . . . . . . . . . . . . . . . . . . . .
PART 8: HELIUM MASS SPECTROMETER

LEAK TESTING-. . . . . . . . . . . . . . . . . . . . . . . . .
Basic Techniques for Leak Detection with
Helium Tracer Gas . . . . . . . . . . . . . . . . . .

PART 9: ACOUSTIC LEAK TESTING . . . . . . . . . .
Principles of Acoustic Leak Testing . . . . . . . .
Instrumentation for Ultrasonic Detection of
Leaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Techniques of Leakage Monitoring with
Multiple Acoustic Emission Sensors . . . . .

xi

PART 3: BASIC GENERATOR Gamma Ray Exposure Charts . . . . . . . . . . . . . 161
CONSTRUCTION . . . . . . . . . . . . . . . . . . . . . . . 99 The Characteristic Curve . . . . . . . . . . . . . . . . 161
99 PART 5: RADIOGRAPHIC IMAGE QUALITY
X-Ray Tubes . . . . . . . . . . . . . . . . . . . . . . . . . . 103 AND DETAIL VISIBILITY . . . . . . . . . . . . . . . . 164
108 Controlling Factors . . . . . . . . . . . . . . . . . . . . . 164
High Energy Sources . . . . . . . . . . . . . . . . . . . Subject Contrast . . . . . . . . . . . . . . . . . . . . . . . 164
Control Units under 500 keV . . . . . . . . . . . . . llO Film Contrast . . . . . . . . . . . . . . . . . . . . . . . . . 164
llO Film Graininess and Screen Mottle . . . . . . . . 166
PART 4: X-RAY OPERATING 110 Penetrameters . . . . . . . . . . . . . . . . . . . . . . . . . 166
RECOMMENDATIONS . . . . . . . . . . . . . . . . . . ll l Viewing and Interpreting Radiographs . . . . . . 169
ll l PART 6: FILM HANDLING AND STORAGE . . . 170
Baseline Data . . . . . . . . . . . . . . . . . . . . . . . . . 112 170
112 Identifying Radiographs . . . . . . . . . . . . . . . . . 170
Selecting a Unit . . . . . . . . . . . . . . . . . . . . . . . 114 Shipping of Unprocessed Films . . . . . . . . . . . 170
ll 4 Storage of Unprocessed Film . . . . . . . . . . . . . 171
Tube Warmup . . . . . . . . . . . . . . . . . . . . . . . . . ll4 Storage of Exposed and Processed Film . . . . .
Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . 120
120
Electrical Safety . . . . . . . . . . . . . . . . . . . . . . . 120
120
X-Ray Safety . . . . . . . . . . . . . . . . . . . . . . . . . . 120
122
PART 5: ISOTOPES FOR RADIOGRAPHY. . . . . . 129

Radioactivity :
Selection of Radiographic Sources . . . . . . . . .

PART 6: SOURCE HANDLING EQUIPMENT . . SECTION 6: RADIOSCOPY AND
Requirements . . . . . . . . . . . . . . . . . . . . . . . . . TOMOGRAPHY . . . . . . . . . . . . . . . . . . . . . 173

Classification . . . . . . . . . . . . . . . . . . . . . . . . . . PART 1: FUNDAMENTALS OF RADIOSCOPY.. 174
Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
Manual Manipulation of Sources . . . . . . . . . . Background . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
Basic Technique . . . . . . . . . . . . . . . . . . . . . . . 175
Remote Handling Equipment . . . . . . . . . . . . Recommended Practice . . . . . . . . . . . . . . . . . 175
Safety Considerations . . . . . . . . . . . . . . . . . . . Image Intensifiers . . . . . . . . . . . . . . . . . . . . . . 175
Spectral Matching . . . . . . . . . . . . . . . . . . . . . . 177
BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
Television Cameras, Image Tubes and
SECTION 5: FILM RADIOGRAPHY . . . . . . . . 131 Peripherals . . . . . . . . . . . . . . . . . . . . . . . . . 178
Optical Coupling. . . . . . . . . . . . . . . . . . . . . . . 182
PART 1: FILM EXPOSURE . . . . . . . . . . . . . . . . . . 132 Viewing and Recording Systems . . . . . . . . . . . 183
Making a Radiograph . . . . . . . . . . . . . . . . . . . 132
Factors Governing Exposure . . . . . . . . . . . . . 133 PART 2: RADIOSCOPIC IMAGE 184
Geometric Principles . . . . . . . . . . . . . . . . . . . 134 ENHANCEMENT . . . . . . . . . . . . . . . . . . . . . . . 184
Relations of Milliamperage (Source Digital Techniques . . . . . . . . . . . . . . . . . . . . . 187
Strength), Distance and Time . . . . . . . . . . 139 Pseudocolor . . . . . . . . . . . . . . . . . . . . . . . . . . 187
The Reciprocity Law......... . . . . . . . . . . . 140 Other Techniques . . . . . . . . . . . . . . . . . . . . . . 188
Exposure Factor . . . . . . . . . . . . . . . . . . . . . . . 141 188
Determination of Exposure Factors . . . . . . . . 141 PART 3: X-RAY COMPUTED TOMOGRAPHY . . . 191
Contrast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 195
Choice of Film . . . . . . . . . . . . . . . . . . . . . . . . 142 Computed Tomography Systems . . . . . . . . . .
Radiographic Sensitivity . . . . . . . . . . . . . . . . . 143 Computed Tomography Applications . . . . . . .
144
PART 2: ABSORPTION AND SCATIERING . . . . 144 SECTION 7: ELECTROMAGNETIC TESTING 199
Radiation Absorption in the Specimen . . . . . . 146
Scattered Radiation . . . . . . . . . . . . . . . . . . . . . 146 PART 1: INTRODUCTION TO 200
Reduction of Scatter . . . . . . . . . . . . . . . . . . . . 151 ELECTROMAGNETIC TESTING . . . . . . . . . . 200
Mottling Caused by X-ray Diffraction . . . . . . . 200
Scattering in High Voltage Megavolt 151 Typical Uses of Eddy Current 200
Radiography . . . . . . . . . . . . . . . . . . . . . . . . 152 Nondestructive Tests . . . . . . . . . . . . . . . . . 201
152 201
PART 3: RADIOGRAPHIC SCREENS . . . . . . . . . . 152 Method of Induction of Eddy Currents in
Functions of Screens . . . . . . . . . . . . . . . . . . . 154 Materials . . . . . . . . . . . . . . . . . . . . . . . . . .
Lead Foil Screens . . . . . . . . . . . . . . . . . . . . . . 157
Fluorescent Screens . . . . . . . . . . . . . . . . . . . . 158 Test Material Properties Influencing Eddy
158 Current Tests . . . . . . . . . . . . . . . . . . . . . . .
PART 4: INDUSTRIAL RADIOGRAPHIC FILMS . 158
Selection of Films for Industrial Radiography . 159 Methods for Detection of Eddy Current
Photographic Density . . . . . . . . . . . . . . . . . . . Intensities and Flow Patterns . . . . . . . . . .
Densitometers . . . . . . . . . . . . . . . . . . . . . . . .
X-Ray Exposure Charts . . . . . . . . . . . . . . . . . . Analysis of Eddy Current Test Signals
(Amplitudes and Phase Angles) . . . . . . . . .

xii

Selection of Optimum Eddy Current Test 201 PART 8: MAGNETIC FLUX LEAKAGE 242
Frequencies . . . . . . . . . . . . . . . . . . . . . . . . TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
202 Types of Parts Inspected by Magnetic Flux 242
Control of Eddy Current Penetration 202 Leakage . . . . . . . . . . . . . . . . . . . . . . . . . . .
Depths in Test Materials . . . . . . . . . . . . . . Types of Discontinuities Found by 245
202 Magnetic Flux Leakage . . . . . . . . . . . . . . . 246
Limitations of Eddy Current Tests . . . . . . . . . Effects of Discontinuities . . . . . . . . . . . . . . . .
Correlation of Eddy Current Test 202 Sensors Used in Magnetic Flux Leakage 246
203 Inspection 250
Indications with Material Properties and 204 Typical Magnetic Flux Leakage Applications . . 256
Discontinuities . . . . . . . . . . . . . . . . . . . . . .
Typical Industrial Applications of Eddy 206 BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . .
Current Tests . . . . . . . . . . . . . . . . . . . . . . . 206
Eddy Current Transducers . . . . . . . . . . . . . . . 207 SECTION 8: MAGNETIC PARTICLE
Factors Affecting Eddy Current Transducers . 208 TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . 257
PART 2: REMOTE FIELD LOW FREQUENCY 211
EDDY CURRENT INSPECTION . . . . . . . . . . . PART 1: INTRODUCTION................... 258
Remote Field Zone . . . . . . . . . . . . . . . . . . . . . 212
Eddy Currents in Pipe Wall Applications . . . . 212 Capabilities and Limitations of Magnetic
Example Applications . . . . . . . . . . . . . . . . . . . 212 Particle Techniques . . . . . . . . . . . . . . . . . . . . . 258
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . .
PART 3: ELECTROMAGNETIC SORTING 213 Principles of Magnetic Particle Testing . . . . . . 258
TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . . . . PART 2: FABRICATION PROCESSES AND
Eddy Current Impedance Plane Analysis . . . . 213
Impedance Plane . . . . . . . . . . . . . . . . . . . . . . MAGNETIC PARTICLE TEST
Liftoff and Edge Effects on Impedance 218
Plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . APPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . 259
Conductivity and Permeability Loci on 218
Impedance Plane . . . . . . . . . . . . . . . . . . . . Basic Ferromagnetic Materials Production . . . 259
PART 4: EDDY CURRENT APPLICATIONS IN 222 Inherent Discontinuities . . . . . . . . . . . . . . . . 259
THE STEEL INDUSTRY . . . . . . . . . . . . . . . . . . 223
Eddy Current Systems That Rotate the Primary Processing Discontinuities . . . . . . . . 260
Product at Ambient Temperatures . . . . . . 228
Eddy Current Systems That Rotate the 228 Forging Discontinuities . . . . . . . . . . . . . . . . . 262
Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 Casting Discontinuities . . . . . . . . . . . . . . . . . . 263
Tests at Elevated Temperatures . . . . . . . . . . . · 230
PART 5: EDDY CURRENT INSPECTION OF 231 Weldment Discontinuities . . . . . . . . . . . . . . . 263
BOLT HOLES...........................
Eddy Current Bolt Hole Inspection . . . . . . . . 232 Manufacturing and Fabrication
Reference Standards for Bolt Hole Inspection . Discontinuities . . . . . . . . . . . . . . . . . . . . . . 263
Procedure for Bolt Hole Inspection . . . . . . . . 232
Automated Bolt Hole Inspection . . . . . . . . . . Service Discontinuities . . . . . . . . . . . . . . . . . . 266
PART 6: AUTOMOTIVE APPLICATIONS OF 234
EDDY CURRENT TESTING . . . . . . . . . . . . . . 235 Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
Hardness and Case Depth Inspection of PART 3: MAGNETIC FIELD THEORY . . . . . . . . 267
Axle Shafts . . . . . . . . . . . . . . . . . . . . . . . . . 235
Crack and Porosity Detection and Magnetic Domains . . . . . . . . . . . . . . . . . . . . . 267
Machined Hole Presence in Master 236
Brake Cylinders . . . . . . . . . . . . . . . . . . . . . 237 Magnetic Poles . . . . . . . . . . . . . . . . . . . . . . . . 267
Tin Plate Thickness on Diesel Engine Piston . 239
Cold Headed Pinion Gear Blank Crack 239 Types of Magnetic Materials . . . . . . . . . . . . . . 268
Detection . . . . . . . . . . . . . . . . . . . . . . . . . . 239 Sources of Magnetism . . . . . . . . . . . . . . . . . . . 268
Hub and Spindle Hardness and Case Depth
Inspection PART 4: MAGNETIC FLUX AND FLUX
Camshaft Heat Treat Inspection . . . . . . . . . . .
PART 7: MULTIFREQUENCY TESTING . . . . . . . LEAKAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
Requirements for Multifrequency Testing . . . Circular Magnetic Fields . . . . . . . . . . . . . . . . 270
Physical Basis of the M ultifrequency Process .
Longitudinal Magnetization . . . . . . . . . . . . . . 270

Magnetic Field Strength . . . . . . . . . . . . . . . . . 271
Subsurface Discontinuities . . . . . . . . . . . . . . . 271

Effect of Discontinuity Orientation . . . . . . . . 272

Formation of Indications . . . . . . . . . . . . . . . . 272

PART 5: ELECTRICALLY INDUCED
MAGNETISM . . . . . . . . . . . . . . . . . . . . . . . . . . . 273

Circular Magnetization . . . . . . . . . . . . . . . . . . 273
Magnetic Field Direction . . . . . . . . . . . . . . . . 273

Longitudinal Magnetization . . . . . . . . . . . . . . 274

Multidirectional Magnetization . . . . . . . . . . . . 275

PART 6: MAGNETIC PARTICLE TEST
SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . · 276

Stationary Magnetic Particle Test Systems . . . 277
Power Packs . . . . . . . . . . . . . . . . . . . . . . . . . . 277

xiii

Mobile and Portable Testing Units . . . . . . . . . 277 Testing Procedures for Pressure, Storage 310
Prods and Yokes . . . . . . . . . . . . . . . . . . . . . . . 278 and Vacuum Vessels . . . . . . . . . . . . . . . . . . 310
PART 7: FERROMAGNETIC MATERIAL 312
CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . 278 Applications in the Chemical Industries . . . . .
Magnetic Flux and Units of Measure . . . . . . . 278 Composite Pipe Testing Applications . . . . . . . 314
Magnetic Hysteresis . . . . . . . . . . . . . . . . . . . . 278 Effect of Acoustic Emission Tests of Fiber 314
Magnetic Permeability . . . . . . . . . . . . . . . . . . 280 316
PART 8: TYPES OF MAGNETIZING CURRENT. 281 Reinforced Plastic Structures . . . . . . . . . .
Alternating Current . . . . . . . . . . . . . . . . . . . . 281 Zone Location in Fiber Reinforced Plastics . . 317
Half-Wave Direct Current . . . . . . . . . . . . . . . 281 Felicity Effect in Fiber Reinforced Plastics . .
Full-Wave Direct Current . . . . . . . . . . . . . . . 282 Acceptance of Acoustic Emission Techniques 318
Three-Phase Full-Wave Direct Current . . . . . 282 318
PART 9: DEMAGNETIZATION PROCEDURES . 284 for Testing of Fiber Reinforced Plastics . . 319
Justification for Demagnetizing . . . . . . . . . . . 284 PART 4: INDUSTRIAL GAS TRAILER TUBE
Methods of Demagnetization . . . . . . . . . . . . . 284 321
Demagnetization Practices . . . . . . . . . . . . . . . 286 APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . 322
PART 10: MEDIA AND PROCESSES IN Recertification of Gas Trailer Tubing . . . . . . . 322
MAGNETIC PARTICLE TESTING . . . . . . . . . 288 Test Procedure for Trailer Tubing Tests . . . . .
Magnetic Particle Properties . . . . . . . . . . . . . 288 Advantages of Acoustic Emission Testing of 323
Effects of Particle Size . . . . . . . . . . . . . . . . . . 289 Trailer Tubes . . . . . . . . . . . . . . . . . . . . . . .
Effect of Particle Shape . . . . . . . . . . . . . . . . . 289 324
Visibility and Contrast . . . . . . . . . . . . . . . . . . . 290 PART 5: RESISTANCE SPOT WELD TESTING .
Particle Mobility . . . . . . . . . . . . . . . . . . . . . . . 290 Resistance Spot Welding . . . . . . . . . . . . . . . . . 324
Media Selection . . . . . . . . . . . . . . . . . . . . . . . 291 Principles of Acoustic Emission Weld
Magnetic Particle Testing Processes . . . . . . . 291 Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . 326
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . 294 Weld Quality Parameters That Produce 327
Acoustic Emission . . . . . . . . . . . . . . . . . . .
SECTION 9: ACOUSTIC EMISSION 327
TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . 297 Acoustic Emission Instrumentation for
Resistance Spot Welding . . . . . . . . . . . . . . 329
PART 1: FUNDAMENTALS OF ACOUSTIC 298 329
EMISSION TESTING . . . . . . . . . . . . . . . . . . . . 298 Typical Applications of the Acoustic 330
The Acoustic Emission Phenomenon . . . . . . . 298 Emission Method.. . . . . . . . . . . . . . . . . . .
Acoustic Emission Nondestructive Testing . . . 300 331
Application of Acoustic Emission Tests . . . . . 300 Monitoring Coated Steel Alternating Current
Successful Applications . . . . . . . . . . . . . . . . . . 301 Welds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331
Acoustic Emission Testing Equipment . . . . . . 332
Microcomputers in Acoustic Emission 302 Alternating Current Spot Welding
Test Systems . . . . . . . . . . . . . . . . . . . . . . . Galvanized Steel . . . . . . . . . . . . . . . . . . . . 334
Characteristics of Acoustic Emission 302 339
Techniques . . . . . . . . . . . . . . . . . . . . . . . . . 303 Detecting the Size of Adjacent Alternating
Acoustic Emission Test Sensitivity . . . . . . . . . 303 Current Welds . . . . . . . . . . . . . . . . . . . . . .
Interpretation of Test Data . . . . . . . . . . . . . . . 304
The Kaiser Effect . . . . . . . . . . . . . . . . . . . . . . Control of Spot Weld Nugget Size . . . . . . . . .
305 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . .
PART 2: BUCKET TRUCK AND LIFT 305 PART 6: ACOUSTIC EMISSION APPLICATIONS
INSPECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 IN UNDERSEA REPEATER
Acoustic Emission Inspection Development . 307 MANUFACTURE
Instrumentation for Bucket Truck Inspection . 308 High Voltage Capacitor in the Repeater
Test Procedure for Bucket Truck Inspection . 309
Typical Test Data . . . . . . . . . . . . . . . . . . . . . . Circuitry Unit . . . . . . . . . . . . . . . . . . . . . .
Acceptance Criteria . . . . . . . . . . . . . . . . . . . . 310 Instrumentation and Analysis . . . . . . . . . . . . .
Tubulation Pinchweld on the Repeater
PART 3: ACOUSTIC EMISSION TESTS OF
FIBER REINFORCED PLASTIC VESSELS . . Housing . . . . . . . . . . . . . . . . . . . . . . . . . . .
BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . .

SECTION 10: INTRODUCTION TO
ULTRASONIC TESTING . . . . . . . . . . . . . . 345

PART 1: BASIC ULTRASONIC TESTING . . . . . . . 346
Advantages of Ultrasonic Tests . . . . . . . . . . . . 346
Limitations of Ultrasonic Tests . . . . . . . . . . . . 347
Criteria for Successful Testing . . . . . . . . . . . . 348
349
PART 2: ULTRASONIC WAVES IN MATERIALS. 350
Definition of Wave and Wave Properties . . . . 350
Ultrasonic Attenuation . . . . . . . . . . . . . . . . . . 350
Nonlinear Elastic Waves . . . . . . . . . . . . . . . . .

xiv

PART 3: IMPLEMENTATION OF ULTRASONIC 351 Divergence of Ultrasonic Beams in the 389
TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351 Far Field . . . . . . . . . . . . . . . . . . . . . . . . . . 390
Transmission and Reflection Techniques . . . . 351 392
Ultrasonic Test Systems . . . . . . . . . . . . . . . . . 352 Focused Beam Immersion Techniques . . . . . . 393
Ultrasonic Sources . . . . . . . . . . . . . . . . . . . . . 353 Ultrasonic Beam Attenuation by Scattering . .
Typical Transducer Characteristics . . . . . . . . . 354 Selection of Test Frequencies . . . . . . . . . . . . . 394
Through-Transmission Systems . . . . . . . . . . . . 354 Effect of Discontinuity Orientation on
Pitch and Catch Contact Testing . . . . . . . . . . 356 394
Amplitude and Transit Time Systems . . . . . . . 358 Signal Amplitude . . . . . . . . . . . . . . . . . . . . 395
B-Scan Presentation . . . . . . . . . . . . . . . . . . . . 359 Effect of Geometry of Discontinuity on Echo
C-Scan Presentation . . . . . . . . . . . . . . . . . . . . 359 395
System Calibration . . . . . . . . . . . . . . . . . . . . . 361 Signal Amplitude . . . . . . . . . . . . . . . . . . . . 395
Major System Parameters . . . . . . . . . . . . . . . . 363 Data Presentation . . . . . . . . . . . . . . . . . . . . . . 397
363 Tests of Multilayered Structures and 397
PART 4: ULTRASONIC TESTING EQUIPMENT . 364 397
Basic Ultrasonic Test Systems . . . . . . . . . . . . . Composites . . . . . . . . . . . . . . . . . . . . . . . . 398
Portable Instruments . . . . . . . . . . . . . . . . . . . 367 Dual-Transducer Methods . . . . . . . . . . . . . . . 398
367 PART 3: ANGLE BEAM CONTACT TESTING. . .
Capabilities of General Purpose Ultrasonic 368 Verification of Shear Wave Angle . . . . . . . . . . 400
Test Equipment . . . . . . . . . . . . . . . . . . . . . 369 Ranging in Shear Wave Tests . . . . . . . . . . . . . 400
370 Ultrasonic Tests of Tubes . . . . . . . . . . . . . . . . 400
Modular Ultrasonic Equipment . . . . . . . . . . . Weld Testing . . . . . . . . . . . . . . . . . . . . . . . . . . 401
Special Purpose Ultrasonic Equipment . . . . . 370 PART 4: COUPLING MEDIA FOR 401
Operation in Large Testing Systems . . . . . . . . 370 CONTACT TESTS . . . . . . . . . . . . . . . . . . . . . . . 402
PART 5: OTHER ULTRASONIC TECHNIQUES . 370 Use of Transducer Shoes . . . . . . . . . . . . . . . .
Optical Generation and Detection of 371 Use of Couplant and Membranes . . . . . . . . . . 402
371 Use of Delay Lines . . . . . . . . . . . . . . . . . . . . .
Ultrasound . . . . . . . . . . . . . . . . . . . . . . . . . 371 Selection and Use of Coupling Media . . . . . . 404
Optical Generation of Elastic Waves . . . . . . . 372 Selection of Couplants . . . . . . . . . . . . . . . . . . 404
Optical Detection of Ultrasound. . . . . . . . . . . 373 Operator Techniques to Ensure Good 405
Future Developments in Laser Ultrasonics . . 378
Air Coupled Transducers . . . . . . . . . . . . . . . . Coupling . . . . . . . . . . . . . . . . . . . . . . . . . . 407
Low Frequency Transducers . . . . . . . . . . . . . PART 5: IMAGING OF PULSE ECHO 407
High Frequency Transducers . . . . . . . . . . . . . 408
Electromagnetic Acoustic Transducers . . . . . . CONTACT TESTS . . . . . . . . . . . . . . . . . . . . . . . 410
BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . Ultrasonic Imaging Procedures . . . . . . . . . . . .
Contact Weld Tests . . . . . . . . . . . . . . . . . . . . . 411
SECTION 11: ULTRASONIC PULSE ECHO 412
TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . 379 PART 6: ULTRASONIC PULSE ECHO WATER 413
COUPLED TECHNIQUES . . . . . . . . . . . . . . . .
PART 1: ULTRASONIC TESTING Immersion Coupling . . . . . . . . . . . . . . . . . . . . 414
Immersion Coupling Devices . . . . . . . . . . . . .
TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . . . . 380 Pulse Echo Immersion Test Parameters . . . . . 419
The A-Scan Method . . . . . . . . . . . . . . . . . . . . 380 419
Test Indications Requiring Special 419
The B-Scan Method . . . . . . . . . . . . . . . . . . . . 380 Consideration. . . . . . . . . . . . . . . . . . . . . . . 420
The C-Scan Method . . . . . . . . . . . . . . . . . . . . 380 423
Location of Discontinuities . . . . . . . . . . . . . . . 423
PART 2: STRAIGHT BEAM PULSE ECHO Grain Size Discontinuities . . . . . . . . . . . . . . .
Interpretation of Indications from Rotor
TESTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
Wheels . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Instrumentation for Straight Beam Tests . . . . . 382 PART 7: IMMERSION TESTING OF
Straight Beam Test Procedures . . . . . . . . . . . . 382
COMPOSITE MATERIALS . . . . . . . . . . . . . . . .
Applications of Straight Beam Contact Tests . 384 Discontinuities in Composite Laminates . . . .
Discontinuity Discrimination . . . . . . . . . . . . . 385 Ultrasonic Testing of Composite Laminates . .
Tests of Composite Tubing . . . . . . . . . . . . . . .
Discontinuities Detected by the Straight Laminate Test Indications . . . . . . . . . . . . . . . .
Beam Method . . . . . . . . . . . . . . . . . . . . . . 386 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . .

Sizing Discontinuities _. . . . . . . . . . 386
Mechanical Scanning . . . . . . . . . . . . . . . . . . . 388
SECTION 12: VISUAL TESTING . . . . . . . . . . . 425
Selection of Ultrasonic Test Frequencies . . . . 388
PART 1: DESCRIPTION OF VISUAL AND
Effects of Ultrasonic Transducer Diameter . . 388 OPTICAL TESTS . . . . . . . . . . . . . . . . . . . . . . . . 426
Transducer Near Field . . . . . . . . . . . . . . . . . . 389

xv

Luminous Energy Tests . . . . . . . . . . . . . . . . . 426 Manual Systems . . . . . . . . . . . . . . . . . . . . . . . 465
Geometrical Optics . . . . . . . . . . . . . . . . . . . . . 426 System Selection and Application . . . . . . . . . . 466
PART 2: VISION AND LIGHT 428 PART 7: MACHINE VISION TECHNOLOGY . . . 468
The Physiology of Sight . : : : : : : : : : : : : : : : : 428 Lighting Techniques . . . . . . . . . . . . . . . . . . . . 468
Vision Acuity . . . . . . . . . . . . . . . . . . . . . . . . . . 429 Optical Filtering . . . . . . . . . . . . . . . . . . . . . . . 4 70
Vision Acuity Examinations . . . . . . . . . . . . . . . 430 Image Sensors . . . . . . . . . . . . . . . . . . . . . . . . . 4 70
Visual Angle . . . . . . . . . . . . . . . . . . . . . . . . . . 432
Color Vision . . . . . . . . . . . . . . . . . . . . . . . . . . 432 SECTION13: THERMOGRAPHYAND
Fluorescent Materials . . . . . . . . . . . . . . . . . . . 435 OTHERSPECIALMETHODS . . . . . . . . . 473
Safety for Visual and Optical Tests . . . . . . . . . 435
PART 3: BASIC VISUAL AIDS . . . . . . . . . . . . . . . . 440 PART 1: THE SPECIAL NONDESTRUCTIVE 474
Environmental Factors . . . . . . . . . . . . . . . . . . 440 TESTING METHODS . . . . . . . . . . . . . . . . . . . .
Effects of the Test Object . . . . . . . . . . . . . . . . 441 Relationship between Material Property and 475
Magnifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443 Material Behavior . . . . . . . . . . . . . . . . . . .
Low Power Microscopes . . . . . . . . . . . . . . . . . 445 478
Photographic Techniques for Recording PART 2: PRINCIPLES OF INFRARED 478
446 THERMOGRAPHY . . . . . . . . . . . . . . . . . . . . . . 482
Visual Test Results . . . . . . . . . . . . . . . . . . . 44 7 Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . 486
Image Enhancement . . . . . . . . . . . . . . . . . . . . 449 Instrumentation and Techniques . . . . . . . . . . 486
PART 4: BORESCOPES 449 490
Fiber Optic Boresco~~~ . : : : : : : : : : : : : : : : : : 450 PART 3: THERMOGR.t\PHIC APPLICATIONS . .
Rigid Borescopes . . . . . . . . . . . . . . . . . . . . . . 452 Composite Materials and Structures . . . . . . . . 491
Special Purpose Borescopes . . . . . . . . . . . . . . 452 Buildings . '. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Typical Industrial Borescope Applications . . . 453 Electric Power Distribution and 491
Borescope Optical Systems . . . . . . . . . . . . . . . 454 Transmission Systems . . . . . . . . . . . . . . . . 492
Borescope Construction . . . . . . . . . . . . . . . . . 455 Pavement, Bridge Decks and Subterranean 493
Photographic Adaptations . . . . . . . . . . . . . . . . 457 495
PART 5: VIDEO TECHNOLOGY 457 Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497
Photoelectric Devices ..... : : : : : : : : : : : : : : 457 Automotive Applications . . . . . . . . . . . . . . . . . 497
Photoemissive Devices . . . . . . . . . . . . . . . . . . 457 Bonded Materials and Structures . . . . . . . . . . 498
Photoconductive Cells or Photodiodes . . . . . 457 Diverse Applications . . . . . . . . . . . . . . . . . . . . 500
Photovoltaic Devices . . . . . . . . . . . . . . . . . . . . PART 4: OPTICAL METHODS 500
Uses of Photoelectric Detecting and 458 Grid and Moire Nondestructi~~ ·T~s~i-~g· : : : : : 503
458 503
Measuring Devices . . . . . . . . . . . . . . . . . . 459 Holography . . . . . . . . . . . . . . . . . . . . . . . . . . . 503
Photoelectric Imaging Devices . . . . . . . . . . . . 461 Shearography . . . . . . . . . . . . . . . . . . . . . . . . . 505
Video Borescopes . . . . . . . . . . . . . . . . . . . . . . 461 Point Triangulation Profilometry . . . . . . . . . . 506
Video Borescope Applications . . . . . . . . . . . . . 462 PART 5: OTHER SPECIAL METHODS . . . . . . . .
Principles of Scanning . . . . . . . . . . . . . . . . . . 462 Alloy Identification . . . . . . . . . . . . . . . . . . . . .
Television Camera Tubes . . . . . . . . . . . . . . . . 463 Electromagnetic Special Methods . . . . . . . . .
Cathode Ray Viewing Tube . . . . . . . . . . . . . . . Acoustic Methods . . . . . . . . . . . . . . . . . . . . . .
Video Resolution . . . . . . . . . . . . . . . . . . . . . . . 465 Resistance Strain Gaging . . . . . . . . . . . . . . . .
PART 6: REMOTE POSITIONING AND 465
TRANSPORT SYSTEMS . . . . . . . . . . . . . . . . . . 465 SECTION14: NONDESTRUCTIVE TESTING
Fixed Systems . . . . . . . . . . . . . . . . . . . . . . . . . GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . 515
Automated Systems . . . . . . . . . . . . . . . . . . . .
INDEX 567

xvi

1SECTION

INTRODUCTION TO
NONDESTRUCTIVE TESTING

2 I NONDESTRUCTIVETESTINGOVERVIEW

PART 1

NATURE OF NONDESTRUCTIVE TESTING

Definitionof Nondestructive the loss of material, the procedure is inherently destructive
Testing and the shaving itself - in one sense the true "test object"
- has been removed from service permanently.
Nondestructive testing (NDT) has been defined as com-
prising those test methods used to examine or inspect a part The idea of future usefulness is relevant to the quality
or material or system without impairing its future useful- control practice of sampling. Sampling (that is, the use of
ness. The term is generally applied to nonmedical investiga- less than 100 percent inspection to draw inferences about
tions of material integrity. the unsampled lots) is nondestructive testing if the tested
sample is returned to service. If the steel is testedto verify
Strictly speaking, this definition of nondestructive test- the alloy in some bolts that can then be returned to service,
ing does include noninvasive medical diagnostics. X-rays, then the test is nondestructive. In contrast, even if spec-
ultrasound and endoscopes are used by both medical and troscopy used in the chemical testing of man)'. fluids is
industrial nondestructive testing. In the 1940s, many mem- inherently nondestructive, the testing is destructive if the
bers of the American Society for Nondestructive Testing samples are poured-down the drain after testing.
(then the Society for Industrial Radiography) were medical
X-ray professionals. Medical nondestructive testing, how- Hardness testing by indentation provides an interesting
ever, has come to be treated by a body of learning so sepa- test case for the' definition of nondestructive testing. Hard-
rate from industrial nondestructive testing that today most ness testing machines look somewhat like drill presses. The
physicians never use the word nondestructive. applied force is controlled as the bit is lowered to make a
small dent in the surface of the test piece. Then the diame-
Nondestructive testing is used to investigate specifically ter or depth of the dent is measured. The force applied is
the material integrity of the test object. A number of other correlated with the dent size to provide a measurement of
technologies - for instance, radio astronomy, voltage and surface hardness. The future usefulness of the test piece is
amperage measurement and rheometry (flow measure- not impaired except in rare cases when a high degree of sur-
ment) - are nondestructive but are not used to evaluate face quality is important. However, because the piece's con-
material properties specifically. Nondestructive testing is tour is altered, the test is rarely considered nondestructive.
concerned in a practical way with the performance of the A nondestructive alternative to this hardness test could be
test piece - how long may the piece be used and when does to use electromagnetic nondestructive testing.
it need to be checked again? Radar and sonar are classified
as nondestructive testing when used to inspect dams, for Nondestructive testing is . not confined to crack detec-
instance, but not when they are used to chart a river bottom. tion. Other discontinuities include porosity, wall thinning
from corrosion and many sorts of disbands. Nondestructive
Nondestructive testing asks "Is there something wrong material characterization is a growing field concerned with
with this material?" Various performance and proof tests, in material properties including material identification and
contrast, ask "Does this component work?" This is the rea- microstructural characteristics - such as resin curing, case
son that it is not considered nondestructive testing when an hardening and .stress - that have a direct influence on the
inspector checks a circuit by running electric current service life of the test object.
through it. Hydrostatic pressure testing is usually proof test-
ing and intrinsically not nondestructive - but acoustic emis- Nondestructive testing has also been defined by listing
sion testing used to monitor changes in a pressure vessel's or classifying the various methods.1·2 This approach is prac-
integrity during hydrostatic testing is nondestructive testing. tical in that it typically highlights methods in use by industry.

Another gray area that invites various interpretations in Purposes of NondestructiveTesting
defining nondestructive testing is that of future usefulness.
Some material investigations involve taking a sample of the Since the 1920s, the art of testing without destroying the
inspected part for testing that is inherently destructive. A test object has developed from a laboratory curiosity to an
noncritical part of a pressure vessel may be scraped or indispensable tool of production. No longer is visual exami-
shaved to get a sample for electron microscopy, for example. nation of materials, parts and complete products the princi-
Although future usefulness of the vessel is not impaired by pal means of determining adequate quality. Nondestructive

INTRODUCTOI N TO NONDESTRUCTIVE TESTING I 3

tests in great variety are in worldwide use to detect varia- manufacturing processes; (7) to lower manufacturing costs;
tions in structure, minute changes in surface finish, the (8) to maintain uniform quality level; and (9) to ensure oper-
presence of cracks or other physical discontinuities, to mea- ational readiness.
sure the thickness of materials and coatings and to deter-
mine other characteristics of industrial products. Scientists Ensuring the Integrity/Reliability of a Product
and engineers of many countries have contributed greatly to
nondestructive test development and applications. The user of a fabricated product buys it with every
expectation that it will give trouble-free service for a reason-
The various nondestructive testing methods are covered able period of usefulness. Few of today's products are
in detail in the literature but it is always wise to consider expected to deliver decades of service but they are required
objectives before plunging into the details of a method. to give reasonable unfailing value. Year by year the public
What is the use of nondestructive testing? Why do thou- has learned to expect better service and longer life, despite
sands of industrial concerns buy the testing equipment, pay the increasing complexity of our everyday electrical and
the . subsequent operating costs of the testing and even mechanical appliances.
,.reshape manufacturing processes to fit the needs and find-
ings of nondestructive testing? America has always been a nation on the move. Today
our railroads, automobiles, buses, aircraft and ships carry
Modern nondestructive tests are used by manufacturers people to more places faster than ever before. And people
(1) to ensure product integrity, and in turn, reliability; (2) to expect to get there without delays due to mechanical failure.
avoid failures, prevent accidents and save human life (see Meanwhile factories turn out more products, better, faster
Figs. 1 and 2); (3) to make a profit for the user; (4) to en- and with more automatic machinery. Management expects
sure customer satisfaction and maintain the manufacturer's machinery to operate continuously because profits depend
reputation; (5) to aid in better product design; (6) to control

FIGURE 1 . Fatigue cracks caused damage to the fuselage of this Aloha Airlines aircraft, causing the
death of a flight attendant and injury to many passengers (April 1986)

4 I NONDESTRUCTIVETESTING OVERVIEW

on such sustained output. The complexity of present-day 1.00 - 0.9057 = 0.0943 (Eq. 2)
products and the machinery which makes and transports
them requires greater reliability from every part. or almost 1 in 10. It is certain that the user of this product
will be highly dissatisfied if l out of every 10 units fails
If a product has one part that has a probability of failure prematurely. The point is that component integrity, and in
of l in 1,000 before it has served a reasonable life, it may be turn, reliability must be immensely greater than the required
satisfactory. This seems to be a very low chance of failure. reliability of the assembled product.
Now suppose that a product is assembled from 100 critical
parts of various kinds and that each part has a failure possi- Consider the ordinary V-8 automobile engine. It has only
bility of l in 1,000. What then is the possibility of failure of one crankshaft but eight connecting rods, sixteen valve
the assembled item? The overall reliability of any assembly springs and hundreds of other parts. Theoretically, failure of
is the mathematical product of the component reliability any one of these could make the motor useless. Yet how fre-
factors. Overall reliability of this example is then: quently does the car owner experience a part failure? This
amazingly low incidence of service failure during the normal
R = 0. 999100 = 0. 9057 (Eq. 1) life of an automobile is a great tribute to the ability of the
The possibility of failure of the assembly is then: automotive engineers to design well, of metallurgists to
develop the right materials, of production personnel to cast,

FIGURE2. Boilersoperatewith high internal steam pressure;matertat discontinuitiescan lead to
sudden, violent failurewith possibleinjury to peopleand property-

FROM BEN BAILEY. USED WITH PERMISSION.

INTRODUCTIONTO NONDESTRUCTIVETESTING I 5

roll, forge, machine and assemble correctly, and of inspec- revealed by such nondestructive tests as radiography, mag-
tors and quality control staff to set standards and see that netic particle or penetrant inspection of a pilot run of cast-
the product meets those standards. ings often shows the designer that design changes are
needed to produce a sounder casting in an important sec-
Preventing Accidents and Saving Lives tion. The design may then be improved and the pattern
modified to increase the quality of the product. This exam-
Ensuring product reliability is necessary because of the ple is not academic; it occurs almost daily in many plants.
general increase in performance expectancy of the public. A
homeowner. expects the refrigerator to remain in uninter- Somewhat outside the scope of discontinuity detection
rupted service, indefinitely protecting the food investment, are nondestructive tests to determine the direction, amount
or the power lawnmower to start with one pull of the rope and gradient of stresses in mechanical parts, as applied in
and to keep cutting grass for years on end. The manufac- the field of experimental stress analysis. These play a very
turer expects the lathe, punch press or fork lift to stand up important part in the design of lighter, stronger, less costly
for years of continuous work even under severe loads. and more reliable parts.

But reliability merely for convenience and profit is not Controlling Manufacturing Processes
enough. Reliability to protect human lives is a valuable end
in itself. The railroad axle must not fail at high speed. The Control is a basic concept in industry. Engineers, inspec-
front spindle of the intercity bus must not break on the tors, operators and production personnel know the prob-
curve. The aircraft landing gear must not collapse on touch- lems of keeping any manufacturing process under control.
down. The mine hoist cable must not snap with people in The process must be controlled, and the operator must be
the cab. Such critical failures are rare indeed. And this is trained and supervised. When any element of a manufactur-
most certainly not the result of mere good luck. In large part ing operation gets out of control, quality of the affected
it is the direct result of the extensive use of nondestructive product is compromised and waste may be produced.
testing and of the high order of nondestructive testing abil-
ity now available. Almost every nondestructive testing method is applied in
one way or another to assist in process control and so ensure
Ensuring Customer Satisfaction a direct profit for the manufacturer. As one example of
thousands which could be cited, consider a heat treating
While it is true that the most laudable reason for the use operation. The metallurgist sets up a procedure based on
of nondestructive tests is that of safety, it is probably also sound material of a given analysis. One nondestructive test,
true that the most common reason is that of making a profit applied to all parts or to a few from each batch of parts, tells
for the user. The sources of this profit are both tangible and whether the chemical analysis of the material is so erratic
intangible. that the procedure will fail to produce the desired hardness
or induce cracking. A second test may show when and
The intangible source of profit is ensured customer satis- where cracking has occurred. Another test may show that
faction. Its corollary is the preservation and improvement of the desired hardness has not been developed. If so, process
the manufacturer's reputation. · To this obvious advantage variables may be corrected immediately. Inthese ways, cost
may be added that of maintaining the manufacturer's com- and processing time are saved for the manufacturer.
petitive position. It is generally true that the user sets the
quality level. It is set in the market place when choosing Lowering Manufacturing Costs
among the products of several competing manufacturers.
Certainly the manufacturer's reputation for high quality is There are many other examples of both actual and
only one factor. Others may be function, appearance, pack- potential cost savings possible through the use of nonde-
aging, service and price. But in today's highly competitive structive tests. Most manufacturers could cut manufactur-
markets, actual quality and reputation for quality stand high ing costs by deciding where to apply the following cost
in the consumer's mind. reduction principle: A nondestructive test can reduce manu­
facturing cost when it locates undesirable characteristics of
Aiding in Product Design a material or component at an early stage, thus eliminating
costs of further processing or assembly. An example of this
Nondestructive testing aids significantly in better prod- principle is the testing of forging blanks before the forging
uct design. For example, the state of physical soundness as operation. The presence of seams, large inclusions or cracks
in the blanks may result in a woefully defective product.

6 I NONDESTRUCTIVETESTING OVERVIEW

Using such a blank would waste all the labor and forge ham- Rapid Growth and Acceptance of
mer time involved in forming the material into the product. NondestructiveTests

Another profit making principle is that a nondestructive The foregoing tangible and intangible reasons for
test may save manufacturing cost when it produces desirable widespread profitable use of nondestructive tests are suffi-
information at lower cost than some other destructive or cient in themselves. But parallel developments have con-
nondestructive tests. An example of this principle is the sub- tributed to their growth and acceptance.
stitution of a magnetic particle nondestructive test for acid
pickling to detect seams or cracks. As it has in many plants, a Increased Complexity of Modern Machinery
straightforward economic study of comparative costs of the
two methods may show the cost saving advantage of the non- Consider the present-day automobile. First, the manual
destructive test over the pickling examination. choke became obsolete. The old rod from the dashboard to
a butterfly valve in the carburetor has been replaced by
Maintaining Uniform Quality Level more reliable and efficient metered fuel injection. The
mechanically connected brake pedal and brake shoe have
It seems obvious that improved product quality should given way to hydraulic and antilock braking systems. The old
be an invariable aim and result of nondestructive testing. manual windshield wipers are now powered by vacuum or
Yet this is not alwaysthe case, for there is such a thing as too electricity and .complicated by washer jets and variable
high a quality level. The true function of testing is to control timers. Today's components include complex ventilation,
and maintain the quality level that engineers or design engi- heating, defrosting and air conditioning systems, power
neers establish for the particular product and circum- seats, power actuated windows and sun roofs, expanded
stances. Quality conscious engineers and manufacturers electronics, emission controls, cruise controls, stereo equip-
have long recognized that perfection is unattainable and ment, digital gaging and automatic transmissions. The auto-
that even the attempt to achieve perfection in production is mobile industry, while carrying design complexity to great
unrealistic and costly. Sound management seeks not perfec- lengths, has also tremendously raised component reliability.
tion but pursues excellence in management of workmanship Otherwise, most people would never dare to take their car
from order entry to product delivery. The desired quality from the garage for fear of serious failure.
level is the one which is most worthwhile, all things consid-
ered. Quality below the specified requirement can ruin sales As an even more startling example of component relia-
and reputation. Quality above the specified requirement bility arithmetic, consider computers. They require complex
can swallow up profits through excessive production and microprocessors, chips, resistors, wire connections, coun-
scrap losses. Management must decide what quality level it ters and other parts whose functioning demands operational
wants to produce and support. reliability in each component. The automobile and the elec-
tronic instrument industries are examples of complexity that
Once the quality level has been established, production could never have been achieved without parallel advances in
and testing personnel should aim to maintain this level and nondestructive testing.
not to depart from it. excessively either toward lower or
higher quality. In blunt language, a nondestructive test does Increased Demand on Machines
not improve quality. It can help to establish the quality level
but only management sets the quality standard. If manage- Within a lifetime, average speeds of railway passenger
ment wants to make a nearly perfect product or wants at the and freight trains have doubled. The speed of commercial
other extreme to make junk, then nondestructive tests will air transport has quintupled. Transonic speeds for rocket
help make what is wanted, no more and no less. powered missiles and for piloted aircraft are not unusual.
Automobile, bus and truck speeds have increased and their
In making a drawing for a part, the designer sets toler- engines tum twice as fast. Elevators in tall buildings are
ances on dimension and finish. If a drawing specifies acer- fully automatic and much faster, with speeds limited only by
tain dimension as 31.8 mm (1.25 in.) but fails to specify the the comfort of the passengers. The stress applied to parts in
tolerance, the machine shop supervisor rejects the drawing these vehicles often increases as the square or cube of the
as incomplete or assumes the standard tolerance. In nonde- increased velocity.
structive testing, a quality tolerance (the tolerance on the
characteristic being determined) or criteria for acceptance In the interest of greater speed and rising costs of mate-
or rejection must also be specified. The lack of appreciation rials, the design engineer is alwaysunder pressure to reduce
for this obvious requirement has caused more misunder-
standing of nondestructive testing and more objections to
nondestructive tests than any other factor. Perhaps it is the
cause of more confusion than all other factors combined.

INTRODUCTION TO NONDESTRUCTIVE TESTING I 7

weight. This can sometimes be done by substituting alu- courts in granting higher and higher awards to injured per-
minum or magnesium alloys for steel or iron, but such light sons. Consider the outcry for greater automobile safety, as
alloy parts are not of the same size or design as those they evidenced by the required use of auto safety belts and the
replace. The tendency is also to reduce the size. These pres- demand for air bags, blowout proof tires and antilock brak-
sures on the designer have subjected parts of all sorts to ing systems. The publicly supported activities of the
increased stress levels. Even such commonplace objects as National Safety Council, Underwriters Laboratories, the
sewing machines, sauce pans and luggage are also lighter Environmental Protection Agency and the Federal Aviation
and more heavily loaded than ever before. The stress to be Administration in the United States, and the work of similar
supported is seldom static. It often fluctuates and reverses agencies abroad, are only a few of the ways in which this
at low or high frequencies. Frequency of stress reversals demand for safety is expressed. It has been expressed
increases with the speeds of modern machines and thus directly by the many passengers who cancel reservations
parts tend to fatigue and fail more rapidly. immediately following a serious aircraft accident. This
demand for personal safety has been another strong force in
Another cause of increased stress on modem products is the development of nondestructive tests.
a reduction in the safety factor. An engineer designs with
certain known loads in mind. On the supposition that materi- Rising Costs of Failure
als and workmanship are never perfect, a safety factor of 2, 3,
5 or 10 is applied. Because of other considerations though, a Aside from awards to the injured or to estates of the
lower factor is often used, depending on the importance of deceased, consider briefly other factors in the rising costs of
lighter weight or reduced cost or risk to consumer. mechanical failure. These costs are increasing for many rea-
sons. Some important ones are:
New demands on machinery have also stimulated the
development and use of new materials whose operating 1. greater costs of materials and labor;
characteristics and performance are not completely known. 2. greater costs of complex parts;
These new materials create greater and potentially danger- 3. greater costs due to the complexity of assemblies;
ous problems. As an example, there is a record of an air- 4. greater probability that failure of one part will cause
craft's being built from an alloy whose work hardening,
notch resistance and fatigue life were not well known. After failure of others, due to overloads;
relatively short periods of service some of these aircraft suf- 5. trend to lower factors of safety;
fered disastrous failures. Sufficient and proper nondestruc- 6. probability that the failure of one part will damage
tive tests could have saved many lives.
other parts of high value; and
As technology improves and as service requirements 7. failure of a part within an automatic production
increase, machines are subjected to greater variations and to
wider extremes of all kinds of stress, creating an increasing machine may shut down an entire high speed, inte-
demand for stronger materials. grated, production line. When production was car-
ried out on many separate machines, the broken one
Engineering Demands for Sounder Materials could be bypassed until repaired. Today,one machine
is tied into the production of several others. Loss of
Another justification for the use of nondestructive tests such production is one of the greatest losses resulting
is the designer's demand for sounder materials. As size and from part failure.
weight decrease and the factor of safety is lowered, more
and more emphasis is placed on better raw material control Responsibilities of Production Personnel and
and higher quality of materials, manufacturing processes Inspectors
and workmanship.
Labor today often means a machinery operator. For-
An interesting fact is that a producer of raw material or merly, a laborer in a shop manually made a part and the
of a finished product frequently does not improve quality or work piece received individual attention. Today the laborer
performance until that improvement is demanded by the may be just as skilled but the skill is directed toward the
customer. The pressure of the customer is transferred to operation of a machine. The machine requires attention
implementation of improved design or manufacturing. Non- rather than the work piece. Production rates are also higher.
destructive testing is frequently called on to deliver this new This prevents paying personal attention to individual parts.
quality level.
Formerly everyone who worked on a part gave it some
Public Demands for Greater Safety sort of inspection, even if cursory. Today that is seldom the
case. Many production operations are covered by hoods,
The demands and expectations of the public for greater
safety are apparent everywhere. Review the record of the

8 I NONDESTRUCTIVETESTING OVERVIEW

FIGURE 3. Industrialorganizationchart with channels of responsibilityfor inspectionareas {chart
shows only departmentsinvolvedwith testingor inspection)

GENERAL
MANAGER

CHIEF ENGINEER OUAUlY MANAGER PURCHASING AGENT

PRODUCT DESIGN RECEIVING ----------t

MANUFACTURING STORES OUAUlY
METHODS PARTS SPECIFICATIONS
MANUFACTURING
PRODUCT ASSEMBLY CHIEF
SPECIFICATIONS INSPECTOR
FINAL TEST

TOOLS

MAINTENANCE
AND REPAIR

SAFElY
ENGINEERING

LEGEND .

I = AREAS OF INSPECTION UNDER CHIEF INSPECTOR

T = AREAS OF INSPECTION UNDER DEPARTMENT SUPERVISORS

safety devices and other mechanical fixtures so that the new answer, they find that the user has posed two new prob-
operator scarcely sees the part. This has increased the num- lems.
ber of inspectors and size and complexity of jobs (Fig. 3).
They, too, need faster, more definitive and more accurate One problem with increased use of nondestructive test-
test devices. Inspectors have become skilled specialists. ing is that some people think of nondestructive testing as a
They have progressed far beyond the individual who walked panacea. However, unless engineers design products that
down the railroad track tapping car wheels with a hammer, can be inspected, nondestructive testing will not be helpful.
scarcely knowing the purpose of the job. Today the railroad Nondestructive testing engineers must be involved early in
wheel is tested by specialists with far greater reliability and the design process so that later they can provide service the
by infinitely superior means. design engineers require and also facilitate the job of the
inspector.
To meet demands of their customers, nondestructive
testing specialists, physicists, metallurgists, chemists and In the 1930s, nondestructive testing, where it had been
electrical and mechanical engineers continually develop heard of at all, was generally considered an evil. Later it
better and more accurate tests. They find out more about became a necessary evil. For a number of years now it has
materials and components than was ever known without simply been necessary and a great aid in tens of thousands
destroying them. And when these scientists produce one of shops in a multitude of industries. Most importantly, non-
destructive testing has saved uncounted thousands of lives.

INTRODUCTION TO NONDESTRUCTIVETESTING I 9

PART 2

QUALITY ASSURANCE

Basic Concepts of Quality design control and supplier selection. Surveillancethrough
Assurance audits, in-house process control and quality checkpoints are
also specified by the quality assurance program.
To avoid misunderstanding, it is important to discussthe
meaning, interrelation and interpretation of some widely Quality control is the physical and administrative actions
used expressions. It is not uncommon to think of inspection required to ensure compliance with the quality assurance
as. a nonproductive operation. As such, it is viewed as less program. These functions include physical and chemical
valuable than direct labor. Again, it is not uncommon to tests, where appropriate, as well as nondestructive testing at
think of testing as a laboratory operation, comparable to appropriate points in the manufacturing cycle. Also
pulling of tensile test bars to determine physicalproperties. included in the quality control function are those adminis-
It is sometimes imagined that quality is something injected trative actions of documentation needed to establish a
into a product by the qesigner. record of all quality procedures and their disposition.This is
a vital element of protection againstproduct liabilityactions
In certain situations, these concepts may be true or par- and could serve as a basis for lower insurance premiums. In
tially true. Actually these terms have little real meaning many legal judgments, proof of negligence will often help
unless their place in the overall scheme of production and establish liability.
use of a product is understood.
Document control and completeness of final documen-
Product Reliability tation packages are functions of qualityassurance. This is an
activitythat requires constant attention. In major construc-
First and foremost, the goal for any product is a useful tion projects, there is frequently a considerable time lag
life. This maybe termed reliability,quality (usuallymeaning between supplier component nondestructive testing and
high quality), good value, performance and so on. Consider customer record review. In one embarrassing case, the ven-
the word reliability. The maker of the product generally dor radiographs of a valve casting that had been rejected
agrees that it should be reliable. But how reliable? That and scrapped were forwarded to the customer along with
answer is the manufacturer's responsibility.The degree of documentation showing that the casting was acceptable.
reliability must be defined as closely as possible. The Fortunately, the vendor's document control was able to ver-
demands of customers, the reliability of competitive prod- ifythat the original casting had been scrapped and also was
ucts and the market price of similar products are weighed. able to produce the radiographs of the acceptable replace-
Extensive experience and the expert advice of all depart- ment. This example illustrates another vital function of
ments within the organization guide the decision. Finally, a quality assurance: the followupand dispositionof corrective
quality level becomes company policy.Having set policy,it action.
is management's responsibility to monitor performance. It
wants assurance that its policy is being followed. It wants to Quality Assurance Program
know that the operation is under control or, if not, where
and how it is out of control. It wants assurance of quality. A good quality assurance program consists of five basic
elements.
Quality Control and Quality
Assurance 1. Prevention. A formalized plan is required for design-
ing, for inspectability and for cost effectiveness. This
Quality assurance is the establishment of a program to must be a continuing effort.
guarantee the desired quality level of a product from raw
materials through fabrication, final assemblyand delivery to 2. Control. Documented workmanship standards and
the customer. This is accomplished with judicious prepara- compatible procedures are vital for the training of
tion of specifications and procedures for material selection, production and quality personnel.

3. Assurance. Establishing quality assurance check
points and a rapid information feedback system can
prevent continuing problems.

4. Corrective action. To effectivelyimplement the feed-
back system, specialistsrapidly assessand implement
the necessary corrective action.

1 0 I NONDESTRUCTIVETESTINGOVERVIEW

5. Auditing. The quality assurance program must con- the functions of design, production, inspection and quality
tain provisions for unbiased, independent audits of all control can take over. In any case, recognition of the cus-
aspects of the program, including supplied materials tomer's stated and implied needs must be considered mini-
or components. Audits can be made on either a mum requirements.
scheduled or random basis. Quality supervisors must
have management support to audit anything, any Practical Quality Levels
time and anywhere in the manufacturing cycle and to
initiate timely corrective action. No product is perfect, whatever that word may mean.
The characteristics of a perfect part, material or product
Quality Control may be defined, but as knowledge increases, it becomes
necessary to add definitions of more characteristics. Total
Seeking quality assurance, management sets up a mech- perfection is never the true goal of nondestructive testing or
anism for obtaining it, a quality control department. Quality manufacturing. Industry desires a certain quality level
control is a more inclusive term than testing or inspection. below perfection and will even tolerate some deviation from
Notably it implies a responsibility for the control of the that level within an economic tolerance, plus or minus.
quality of the product. In the older concept, the inspection
department was responsible for checking certain aspects of Range of Test Sensitivity
the product against given specifications. Such inspection is
only part of quality control. For example, the inspector may Many do not realize the wide range of sensitivity possible
say, "The requirements for hardness (or surface finish, free- in each nondestructive test. Radiography may be made
dom from inclusions, or electrical conductivity) seem very superficial or very sensitive to many minute discontinuities
hard for our suppliers or for our own factory to meet." A by variations in X-ray tube voltage, type of film, distance
quality controller would then ask, "Is the tight specification from the tube to the part and other factors. Magnetic parti-
necessary? Can we change it? Can we do it a different way cle test sensitivity varies widely with changes in type and
and yet keep the required quality?" When inspectors think magnitude of current or with concentration and grade of the
beyond the specification to the whys and wherefore's, then particles themselves. If it is desired to locate grinding cracks
they enter into the decision about how to make a product of two hundredths of a millimeter deep, it can be done. On the
the required quality easier, cheaper and better and they may other hand, if nothing less than 2.5 mm (0.1 in.) deep is con-
truly be called quality control engineers. sidered important, the test can be made that insensitive.

Establishing Quality Levels Quality Specifications

One of the toughest problems of managers and design It should not be inferred that the depth of a discontinu-
engineers is to determine and then to define desired quality ity is a common or desirable specification. It may be used on
level in any product. This problem has no purely mathemat- primary or intermediate mill items, such as billets or
ical solution. It is not a problem for the engineer to solve nor semirolled steel, or on manufactured parts in the rough
a standard for production personnel to establish. Yet it must state where a known amount of surface material is to be
be defined as clearly and as accurately as possible. removed after inspection. Most commonly, a specification is
concerned with the direction, location or shape of a discon-
Too often management leaves this problem solely to the tinuity in the critical areas. These considerations determine
design engineer, the inspector or to production, by default. the importance of a discontinuity in causing the fatigue fail-
When that happens, the result is often less profit than ures common in mechanical parts of assemblies. Control of
expected. The designer usually wants a higher quality level test sensitivity in accordance with such specifications is
than necessary. The inspector often agrees with the designer. practical and should be practiced. For example, with mag-
Production usually focuses on producing a predetermined netic particle testing, the direction of magnetization, field
number of units within a specific time. All are sincere, all strength, bath type, concentration and other factors can
are trying to do a good job but each is affected by different control such sensitivity to desired limits.
pressures. What management wants is quality assurance
within a certain range or tolerance. Once that is made clear,

INTRODUCTION TO NONDESTRUCTIVE TESTING I 11

PART 3

TEST SPECIFICATION

ManagementPolicies 4. consulting with suppliers' inspection or test person-
nel on the types of tests or the standards or tolerances
To achieve the maximum value from any nondestructive used, to the end that both supplier and purchaser are
testing operation, it is essential to set up proper policies fully informed of the quality level required.
regarding its use. These policies include:
This receiving inspector would report to the chief
1. statements of the aims of management for develop- inspector, as shown on the accompanying organization chart
ment, management and assessment of quality systems; (Fig. 3). Similar definitions of aims and responsibility are
then set up for inspection operations following parts manu-
2. an organization chart of the entire quality manage- facture, assembly and final tests.
ment system;
In the function of chief inspector, the head of these oper-
3. description in chart or word form of the interrelation ations uses standards furnished by the company. The chief
among all departments of the company; and inspector reports to a quality manager, one of whose func-
tions is assisting in setting up realistic, well defined quality
4. establishment of skills needed for each person assigned specifications. In some plants with fewer people, the chief
responsibility within the quality system. inspector may also act as quality manager by establishing the
specifications. These quality specifications (which .include
Objectives of Nondestructive Testing more than the nondestructive testing standards) must be
drawn up with the cooperation of management, sales, engi-
A statement of the aims for a nondestructive test depart- neering and production, and must be thoroughly under-
ment may be based on one or more of the previously dis- stood by purchasing. All departments must agree to them.
cussed broad reasons for use of these methods: Thus Fig. 3 shows a dotted communication line between the
quality manager, chief engineer, chief inspector, plant man-
1. to ensure the reliability of the end product; ager and purchasing agent.
2. to save lives or prevent accidents; and
3. to save money for the user. Department of Testing or Inspection

Such a statement should, however, go into much more In Fig. 3, the letter T associated with stores, parts manu-
detail to make the wishes of management very clear to all facturing, tools, maintenance and the safety engineer indi-
levels of the organization. cates such departments may have their own nondestructive
test equipment, not under supervision of the chief inspec-
Receiving Inspection tor. A lathe operator may have a micrometer and may peri-
odically check dimensions of the product to keep the
Consider a well integrated metal goods manufacturing operation within control limits. In the same manner, there
company. It receives raw material such as bars, plate, shapes may be a magnetic particle inspection unit in the heat treat
castings, forgings, fasteners and other forms. It may have a department to ensure control of heating and quenching
receiving inspection department. The aims of such an oper- operations. That unit may be under direct control of the heat
ation may include establishing standards and saving money treat foreman. Other production departments, too, may have
for the company by: their own test equipment for internal control purposes.

1. testing incoming material to ensure that defective Similarly, in the tool room a penetrant inspection may
ensure that tools are reground or that new carbide tips are
material does not go to the shop; sound and ready for use in the machine shop. Such inspec-
tion is commonly placed under the foreman of that depart-
2. keeping quality records for each supplier and notify- ment. Also, the maintenance department may have its own
equipment for testing the production machinery in the
ing the purchasing department of the various suppli- plant. The safety engineer may have similar equipment.
ers' quality performance (the lowest cost supplier on Failure of such equipment may be very dangerous to all
plant personnel.
a per-piece basis may not give the lowest overall cost

if the quality level is much lower than that of a sup-
plier whose piece price is higher);

3. advising the purchasing department to inform suppli-

, ers of variations in p~urface protection or other
means that may reduce discontinuities or costs; and

12 I NONDESTRUCTIVETESTING OVERVIEW

Management of Inspection acceptability or rejectability, or at least a statement of the
accuracy with which discontinuities must be detected. Fur-
Inspection performed by personnel from departments thermore, it is necessary to prove that the properties to be
such as maintenance or the tool room is managed by the measured by the nondestructive tests are a reliable means of
department manager. Production line inspection functions detecting discontinuities or of predicting strength or ser-
are, however, under the chief inspector. These inspections viceability properties. In the absence of these necessary
are in the nature of audits and must be performed by per- data, it is not usually possible to intelligently specify a reli-
sonnel who are not responsible to the operation that is being able nondestructive test.
audited. Therefore, the chief inspector (or quality manager)
should not report to the plant manager but to a general Design Engineer and Stress Engineer
executive who may be responsible not only for manufactur-
ing but also for engineering or other operations that have a The design engineer and stress engineer should supply
broad bearing on the entire company performance. This is the necessary data on service loads, operating conditions
the general manager. In some situations, the title may be and the limits of performance acceptability. They should
manufacturing manager or president. In this way, the policy identify the critically stressed regions of the material and
of management may be directly applied to the determina- the probable points and types of failure to be expected in
tion and surveillance of the quality of the product. service.

Peer Contact Materials or Process Engineer

It is highly desirable for quality control and supervisory The knowledge of the design engineer may be sup-
personnel to have contacts both inside and outside the com- plemented by destructive tests on critical materials and
pany organization. As has been stated, liaison with engineer- components. Determination of the correlation between
ing and production is essential in the development of (1) strength or serviceability and (2) the discontinuities or
standards for test methods and the test interpretation. In properties measured nondestructively usually requires the
addition, frequent contacts with the sales or service depart- aid of a materials or process engineer. Often an extensive
ments will bring field reports into consideration so that test- series of controlled destructive tests is · required to prove
ing specifications can be adjusted to meet service that the test indications are a complete and reliable indica-
conditions. tion of serviceability.

It is essential that other outside contacts be maintained. Nondestructive Test Engineer
Contacts with customers give excellent information. Con-
tacts with suppliers are also important. A supplier with a Finally the job of finding a sensitive and reliable method
definite understanding of the standards and requirements of measuring the correlated property nondestructively is the
of the customer may provide better standards or a less responsibility of the nondestructive test engineer. The non-
expensive product. destructive test program must be the result of working
closely with the customer, the design engineer, the stress
Last, but also important, is peer contact for inspection and engineer and a materials or process engineer, in addition to
testing personnel of all levels. Attendance and membership the basic job of designing, developing and applying suitable
in technical societies such as the American Society for Non- nondestructive tests. As a result, nondestructive testing
destructive Testing is a valuable method of maintaining such developments will provide valuable data to design engineers
contacts and working toward better, more accurate and and manufacturers. The nondestructive test must be a reli-
more valuable quality assurance. Committee E-7 on Nonde- able measurement of properties it is designed to measure.
structive Testing of the American Society for Testing and
Materials also serves the nondestructive testing field. Many Specifying Sensitivity and Accuracy
other technical and industrial societies include committees in Tests
and research groups devoted to the application of nonde-
structive tests in their fields. Special care and caution should be used in specifying the
limits of sensitivity and accuracy required or expected in
Sources of Information nondestructive tests. The sensitivity of every type of nonde-
structive test is limited. Sensitivity adequate for testing of
Nondestructive test management engineers require full one part may be totally inadequate for another test object,
information concerning service loads and conditions of use or for a more severe service condition on the same part. In
in order to design or specify a useful nondestructive test for
a particular part. They also need clearly established limits of

INTRODUCTION TO NONDESTRUCTIVE TESTING I 1 3

general, more sensitive tests require more elaborate equip- discontinuities in symmetrical rods or bars of given shape
ment and cost more. The cost of developing, proving and and diameter.
applying a suitable nondestructive test must be considered
in each application. Nondestructive tests which cannot be Accessibility Limitations
applied economically in specific applications will usually be
abandoned, even when technically adequate. Some test methods require access to both sides of the
test specimen. In many tests, the source of the probing
Reasonable Tolerances medium is located on one side of the test object and the
detector on the opposite side, such as the X-ray tube (or
There are no simple rules for determining the most eco- gamma ray source) and film in through-wall radiography.
nomical sensitivity and accuracy of such tests. In some
cases, it is not economical to require that the accuracy of Other methods are designed or can be modified for use
nondestructive tests exceed the accuracies of the known as single-side tests. Magnetic particle inspection, ultrasonic
number and magnitude of service loads. Similarly, it is not reflection techniques and many liquid penetrant tests may
always economical to exceed the accuracy within which the be performed with single-side access.
design assumptions predict true stresses or performance.
Alternatively, it may sometimes be reasonable to limit the Size and Shape Limitations
specified test sensitivity to some fraction of the tolerance
limits in strength or serviceability. Some test methods may be applied to parts of almost any
shape or size. Portable apparatus can be used to examine
Interpretation Limitations large, fixed structures in the field. Other tests involve use of
massive testing units on fixed foundations with limited
Even well established methods of nondestructive testing maneuverability within a confined testing area. Their use is
are subject to limitations. Radiography, for example, may limited to test objects that can be brought into the test area
reliably reveal porosity, shrinkage, inclusions, dross and mis- and positioned properly with respect to the test apparatus.
runs in castings, lack of penetration in welds and similar dis-
continuities. But few indeed are the cases in which the Other tests have definite thickness limits. Beta-ray thick-
actual service life or load for failure can be predicted quan- ness gages, for example, can penetrate only very thin layers
titatively from radiographic testing. This would be difficult of most materials. Contact probe ultrasonic pulse reflection
to do even if the parts were destructively sectioned for tests require sufficient material thickness above discontinu-
detailed internal visual examination. ities to permit the pulse from the source to attenuate before
the discontinuity signal returns.
Similarly,magnetic particle inspection of ferrous materi-
als reveals surface cracks and discontinuities reliably. How- Material Limitations
ever, there are very few cases in which the fatigue strength
or the number of load applications required to produce A few tests are limited to certain kinds of materials. Mag-
fatigue failure can be predicted from these test indications. netic particle tests, for example, are useful only with ferro-
However, recognition that a surface crack or stress concen- magnetic materials. They cannot be used for nonferrous
tration may lead to premature failure under repeated load- alloys or for nonmagnetic, austenitic stainless steel alloys.
ing is generally sufficient basis for rejecting the material or
part for such service. Scanning Limitations

Geometric Limitations Some nondestructive tests permit large areas or volumes
of the test object to be inspected simultaneously in a single
In designing, specifying or applying nondestructive tests, exposure or operation. These produce large area images
it is important to recognize certain geometric limitations in (like radiography and fluoroscopy) or provide indications of
their scope and sensitivity. Some test methods are specifi- the entire exposed surface (penetrant tests). Many other
cally limited to test objects with reasonably flat or parallel test methods are essentially point tests or small area tests.
surfaces, or even to constant thickness sections. Ultrasonic These may require scanning of all small areas suspected of
resonance thickness gaging is naturally limited to walls or containing discontinuities. Because they monitor only one
plates with nearly parallel surfaces, in order that echoes may area of the material, most sheet or plate thickness gages fall
return to the sensing probe. into this category.

A few types of nondestructive tests are applicable only to Limiting the Number of Properties to Be Measured
specimens of exactly identical geometry. Some electromag-
netic induction or eddy current test devices can only detect The number of properties to be measured by nondestruc-
tive tests should be limited to those of practical importance

14 I NONDESTRUCTIVETESTING OVERVIEW

in production or serviceability. For example, for given ser- proved or demonstrated. It is usually difficult, costly and time
vice conditions, a part can be weakened by several causes, consuming to obtain the data necessary to establish these cor-
such as improper material, wrong heat treatment, porosity, relations and then to design and develop a reliable nonde-
shrinkage, segregation, dross, inclusions, surface cracks, structive test method based on those data.
seams, laps and discontinuities in plating. A single nonde-
structive test should not be expected to detect and measure Costs of Inadequate Standards
all these diverse properties. Often a separate nondestructive
test is required for each general type of discontinuity. Failure to demonstrate the reliability of test correlations
before applying and depending on nondestructive tests can
Similar reasoning is true for inspection of service dam- be very costly. In most cases of doubt, inspectors using non-
age. Corrosion, repeated stressing, wear, impact, surface destructive test methods tend to be conservative, particu-
destruction and many other factors may contribute to ser- larly in the absence of reliable service data. In many cases,
vice failures of parts that were originally sound. Usually a parts rejected because of discontinuities revealed in nonde-
separate test method will be required for each of the differ- structive tests have shown no weakening when subjected to
ent general types and locations of service discontinuities. simulated service tests. The cause of these erroneous judg-
ments are inaccurate, arbitrary inspection standards, estab-
Establishing the Reliability of Tests lished more on the basis of fear or ignorance than on the
basis of careful physical tests.
Most nondestructive tests detect and evaluate disconti-
nuities or determine strength or serviceability by indirect Skill and Judgments of Inspectors
procedures. These usually involve the measurement of dif-
ferent but correlated properties. Nondestructive indication In evaluating nondestructive test methods, it is necessary
of the existence, location and extent of a discontinuity is one to discriminate between the reliability of the test method
thing. Determining the influence of that discontinuity on and the reliability of the inspectors' judgments. Lack of spe-
the strength or serviceability of the test object is quite cific data, inadequate operating experience, or bad judg-
another. ment may seriously influence the inspector's conclusions.
This situation may occur even when the nondestructive test
Validity of Test Determinations method provides excellent data concerning the condition of
the test object. Consequently it is seldom good economy to
The determination of test validity requires good engi- place elaborate and useful nondestructive testing equip-
neering judgment based on adequate service experience or ment in the hands of unskilled laborers or inspectors with
appropriate destructive tests. Typical specimens, some free little inspection experience or poor judgment. The combi-
of discontinuities and others containing discontinuities of nation of accurate test data with good judgment is essential
each basic type and extent, in each critical location, should to the success of the overall testing operation.
be available for such tests. Acquiring suitable reference
specimens is not easy. In many fields of engineering materi- The criteria the inspector uses to evaluate the test object
als, there is a lack of specific information detailing the influ- data must be developed with consideration of the service to
ence of material and fabrication discontinuities on strength which the part will be subjected. Full regard for past experi-
or serviceability. The nondestructive test cannot supply that ence obtained during operation of similar test objects under
knowledge. Such information must be obtained from the same service conditions is critical to the success of non-
destructive tests or from operating experience. destructive testing.

Validity of Inspectors' Judgments It may be particularly dangerous, however, if the inspec-
tor extrapolates conclusions from one service condition to
The necessary prerequisite for reliability in nondestruc- new and completely different service conditions. Each case
tive tests is a proven correlation between (1) the properties is specific. Unjustified generalizations can be hazardous in
actually measured by nondestructive tests and (2) the pres- most applications of nondestructive testing. Adequate expe-
ence of discontinuities or the strength and serviceability rience, adequate information concerning materials and ser-
properties being predicted from measurements. In situations vice conditions and good judgment are essential.
where such correlations have not been fully established or
where several factors influence the relationship, evaluations Scheduling Tests for Maximum
based on the experience and judgment of skilled inspectors Effectiveness and Economy
become a vitallyimportant feature of the nondestructive test
method. Such correlations are usually implied but are seldom The scheduling of nondestructive tests often has a criti-
cal influence on their cost, effectiveness and overall value.

INTRODUCTION TO NONDESTRUCTIVE TESTING I 1 5

In production, it often proves most effective to apply nonde- practical limiting importance in production or service. Only
structive tests at the earliest possible stage in which the those properties which cannot be more economically or reli-
potential discontinuities are present and detectable. In this ably controlled through other methods of process control or
way, potential rejects are eliminated before any further fab- inspection should be reserved for nondestructive testing.
rication or handling costs are incurred.
Applicationsof Nondestructive
Raw Materials Testing

It is frequently good practice to inspect raw materials as Nondestructive testing is a branch of the materials sci-
they enter the plant. Such inspection may be done by the sup- ences that is concerned with all aspects of the uniformity,
plier, an independent laboratory or in the receiving inspection quality and serviceability of materials and structures. The
department. In this way, defective raw materials cannot enter science of nondestructive testing incorporates all the tech-
production or assembly areas of the plant where they might nology for detection and measurement of significant proper-
be accidentally mixed into good production lots. ties, including discontinuities, in items ranging from research
specimens to finished hardware and products. By definition,
In some cases, discontinuities in raw material may not be nondestructive techniques are the means by which materi-
detectable until some processing steps have been com- als and structures may be inspected without disruption or
pleted. In these cases, inspection should directly follow the impairment of serviceability. Using nondestructive testing,
process step which makes their detection feasible. internal properties of hidden discontinuities are revealed or
inferred by appropriate techniques.
Processed Materials
Nondestructive testing is becoming an increasingly vital
Where processing steps may introduce discontinuities, factor in the effective conduct of research, development,
inspection can best be applied as soon after processing as design and manufacturing programs. Only with appropriate
feasible. Where fabrication is costly, it is uneconomical to use of nondestructive testing techniques can the benefits of
leave all inspection to the final, finished product stage. advanced materials science be fully realized. However, the
Here, each rejected unit is in its most expensive state. In information required for appreciating the broad scope of
addition, failure to detect rejectable discontinuities at this nondestructive testing is rather widely scattered in a multi-
point may send a defective unit into service and may cause a tude of publications and reports. Tables 1 and 2 summarize
premature failure, which is far more costly. information about nondestructive testing methods arranged
to show their purposes and similarities.
Materials in Service
The term method as used here refers to the body of spe-
The optimum interval between nondestructive tests for cialized procedures, techniques and instruments associated
damage in-service varies with the conditions of service and with each nondestructive testing approach. There are usu-
with the types of discontinuities. This period should be ally many techniques or procedures associated with each
short enough so that discontinuities not detected at the pre- method. The following text identifies, classifies and
ceding inspection do not have time to propagate to failure describes these methods without giving details on applica-
between inspections. In many types of service, there are tion or procedures, thus providing a resume of each method
natural locations or periods of time at which inspection can in a single place, for quick reference.
be made most economically. Railroad equipment and air-
planes may best be examined at a terminal or when serviced Mode of Presentation
for their next trip. Good engineering judgment, coupled
with extensive experience, usually is required for establish- Classification of Methods
ing an optimum inspecti?n schedule.
In a report, the National Materials Advisory Board
Number of Different Tests (NMAB) Ad Hoc Committee on Nondestructive Evaluation
adopted a system that classified methods into six major cate-
It is also usually difficult to answer the question of how gories: visual, penetrating radiation, magnetic-electrical, me-
many different nondestructive tests to apply at a particular chanical vibration, thermal and chemical-electrochemical.2•3
time or at a specific stage of service or production. If spe- A modified version of the classification system is presented
cific nondestructive tests for each of the potential causes of below. Additional categories have been included to cover new
failure are combined into large and complex nondestructive methods. The resulting classification system is shown in
test operations, the costs can be unreasonably high. Conse-
quently the designer, materials or process engineer and the
service engineer should determine which properties are of

16 I NONDESTRUCTIVE TESTING OVERVIEW

TABLE 1 . Nondestructivetestingmethodcategories

Categories Objectives

BasicCategories

Mechanical-optical color; cracks; dimensions; film thickness;gaging; reflectivity;strain distribution and magnitude; surface
finish; surfaceflaws; through-cracks

Penetrating radiation cracks;density and chemistryvariations; elemental distribution; foreign objects; inclusions; microporosity;
misalignment; missing parts; segregation; servicedegradation; shrinkage; thickness;voids

Electromagnetic-electronic alloy content; anisotropy; cavities; cold work; local strain, hardness;composition; contamination;
corrosion; cracks;crack depth; crystalstructure; electricaland thermal conductivities;flakes;heat
treatment; hot tears; inclusions; ion concentrations; laps; lattice strain; layer thickness; moisture content;
polarization; seams; segregation; shrinkage; state of cure; tensilestrength; thickness; disbands

Sonic-ultrasonic crack initiaion and propagation; cracks,voids; damping factor; degree of cure; degree of impregnation;
degree of sintering; delaminations; density; dimensions; elasticmoduli; grain size; inclusions;
mechanical degradation; misalignment; porosity; radiation degradation; structure of composites;surface
stress; tensile, shear and compressivestrength; disbands; wear

Thermal and infrared bonding; composition; emissivity; heat contours; plating thickness; porosity; reflectivity;stress; thermal
conductivity; thickness;voids

Chemical-analytical alloy identification; composition; cracks;elemental analysisand distribution; grain size; inclusions;
macrostructure;porosity; segregation; surfaceanomalies

Image generation AuxiliaryCategories
Signal image analysis
dimensional variations; dynamic performance; anomaly characterizationand definition; anomaly
distribution; anomaly propagation; magnetic field configurations

data selection, processingand display; anomaly mapping, correlation and identification; image
enhancement; separation of multiple variables; signature analysis

Table 1. The first six categories involve basic physical pro- 1. discontinuities and separations (cracks, voids, inclu-
cesses that require transfer of matter and/or energy with sions, delaminations etc.);
respect to the object being inspected. Two auxiliary cate-
gories describe processes that provide for transfer and accu- 2. structure or malstructure (crystalline structure, grain
mulation of information, and evaluation of the raw signals size, segregation, misalignment etc.);
and images common to nondestructive testing methods.
3. dimensions and metrology (thickness, diameter, gap
Principles size, discontinuity size etc.);

Each method can be completely characterized in terms 4. physical and mechanical properties (reflectivity, con-
of five principal factors: ductivity, elastic modulus, sonic velocity etc.);

1. energy source or medium used to probe object (such 5. composition and chemical analysis (alloy identifica-
as X-rays, ultrasonic waves or thermal radiation); tion, impurities, elemental distributions etc.);

2. nature of the signals, image and/or signature result- 6. stress and dynamic response (residual stress, crack
ing from interaction with the object (attenuation of growth, wear, vibration etc.); and
X-rays or reflection of ultrasound, for example);
7. signature analysis (image content, frequency spec:-
3. means of detecting or sensing resultant signals (photo- trum, field configuration etc.).
emulsion, piezoelectric crystal or inductance coil);
Terms used in this block are further defined in Table 2
4. method of indicating and/or recording signals (meter with respect to specific objectives and specific attributes to
deflection, oscilloscope trace or radiograph); and be measured, detected and defined.

5. basis for interpreting the results (direct or indirect The limitations of a method include conditions required
indication, qualitative or quantitative, and pertinent by that method: conditions to be met for technique applica-
dependencies). tion (access, physical contact, preparation etc.) and
requirements to adapt the probe or probe medium to the
The objective of each method is to provide information object examined. Other factors limit the detection and/or
about the following material parameters: characterization of discontinuities, properties and other
attributes and limit interpretation of signals and/or images
generated.

INTRODUCTION TO NONDESTRUCTIVE TESTING I 1 7

TABLE2. Objectivesof nondestructivetestingmethods

Objectives AttributesMeasured or Detected

Discontinuitesand separations

Surfaceanomalies roughness; scratches; gouges; crazing; pitting; inclusionsand imbedded foreign material

Surface connectedanomalies cracks; porosity; pinholes; laps; seams; folds; inclusions

Internal anomalies cracks; separations; hot tears; cold shuts; shrinkage; voids; lack of fusion; pores; cavities;
delaminations; disbands; poor bonds; inclusions;segregations

Structure

Microstructure molecular structure; crystallinestructure and/or strain; lattice structure; strain; dislocation; vacancy;
deformation
Matrix structure
grain structure, size, orientation and phase; sinter and porosity; impregnation; filler and/or
Small structural anomalies reinforcementdistribution; anisotropy; heterogeneity; segregation
Gross structural anomalies
leaks (lack of seal or through-holes); poor fit; poor contact; loose parts; loose particles;foreign objects

assemblyerrors; misalignment; poor spacing or ordering; deformation; malformation; missingparts

Dimensions and metrology

Displacement; position linear measurement; separation; gap size; discontinuity size, depth, location and orientation
Dimensionalvariations unevenness;nonuniformity; eccentricity;shape and contour; size and mass variations
Thickness; density film, coating, layer. plating. wall and sheet thickness; density or thicknessvariations

Physicaland mechanicalproperties

Electricalproperties resistivity; conductivity; dielectric constant and dissipationfactor
Magnetic properties polarization; permeability; ferromagnetism; cohesiveforce
Thermal properties conductivity; thermal time constant and thermoelectric potential
Mechanical properties compressive,shearand tensile strength (and moduli); Poisson:S ratio; sonic velocity; hardness; temper

Surfaceproperties and embrittlement
color; reflectivity; refraction index; emissivity

Chemical compositionand analysis

Elementalanalysis detection; identification, distribution and/or profile
Impurity concentrations contamination; depletion; doping and diffusants
Metallurgical content variation; alloy identification, verification and sorting
Physiochemicalstate moisturecontent degree of cure; ion concentrations and corrosion; reaction products

Stressand dynamicresponse

Stress; strain; fatigue heat-treatment,annealing and cold-work effects; residualstress and strain; fatigue damage and life
(residual)
Mechanical damage
Chemical damage wear; spalling; erosion; friction effects
Other damage
Dynamic performance corrosion; stress corrosion; phasetransformation
radiation damage and high frequency voltage breakdown

crackinitiation and propagation; plasticdeformation; creep; excessive motion; vibration; damping;
timing of events; any anomalous behavior

Signatureanalysis

Electromagneticfield potential; strength; field distribution and pattern
Thermal field
Acoustic signature isotherms; heat contours; temperatures;heat flow; temperature distribution; heat leaks; hot spots

Radioactivesignature noise; vibration characteristics; frequency amplitude; harmonic spectrum and/or analysis; sonic and/or
Signal or image analysis ultrasonic emissions

distribution and diffusion of isotopes and tracers

image enhancement and quantization; pattern recognition; densitometry; signal classification,
separationand correlation; discontinuity identification, definition (size and shape) and distribution
analysis; discontinuity mapping and display

18 I NONDESTRUCTIVETESTINGOVERVIEW

PART 4

UNITS OF MEASURE FOR
NONDESTRUCTIVE TESTING

Origin and Use of the SI System SI Units for Radiography

In 1960 the General Conference on Weights and Mea- The original discoveries of radioactivity helped establish
sures devised the International System of Units. Systeme units of measurement based on observation rather than pre-
Internationale (SI) was designed so that a single set of inter- cise physical phenomena. Later scientists who worked with
related measurement units could be used by all branches of radioactive substances (or who managed to manufacture
science, engineering and the general public. Without SI, radioactive beams) again made circumstantial observations
this Nondestructive Testing Handbook volume could have that were then used for measurement purposes. This was
contained a confusing mix of Imperial units, obsolete cen- acceptable at the time but with our broader understanding
timeter-gram-second (cgs) metric system units and the units of physics and the present tendency to use one unit for one
preferred by certain localities or scientific specialties. concept, many of the original units have been modified (see
Tables 4 and 5).
SI is the modem version of the metric system and ends
the division between metric units used by scientists and TABLE4. DerivedSI unitswith special names
metric units used by engineers. Scientists have given up
their units based on centimeter and gram and engineers Quantity Relation
made a fundamental change in abandoning the kilogram- to Other
force in favor of the newton. Electrical engineers have Units Symbol SI Unitsa
retained their amperes, volts and ohms but changed all units
related to magnetism. The main effect of SI has been the Frequency (periodic) hertz Hz J .s-1
reduction of conversion factors between units to one (l) - Force newton
in other words, to eliminate them entirely. Pressure (stress) pascal N kg·m·s-2
Energy (work) joule Pa N-m-2
Table 3 lists seven base units. Table 4 lists all of the Power watt
derived units with special names. In SI, the unit of time is Electric charge coulomb J N·m
the second (s) but hour (h) is recognized for use with SI. Electric current ampere J-s-1
Electric potential b volt w
For more information, the reader is referred to the infor- Capacitance farad Avsn-1
mation available through national standards organizations Electric resistance ohm c
and specialized information compiled by technical societies Conductance siemens w-A-1
(see ASTM E 380, Standard Practicefor Use of the Interna­ Magnetic flux weber Av
tional System of Units, for example).4 Magnetic flux density tesla nF cv-1
Inductance henry s VA-1
TABLE3. Base SI units Luminous flux lumen Av-1
llluminance lux Wb
Quantity Unit Symbol Plane angle radian Vs
Radioactivity becquerel T Wb·m-2
Length meter m Radiation absorbed dose gray Wb-A-1
Radiation dose equivalent sievert H
Mass kilogram kg Solid angle steradian cdsr
Im
Time second s tmrrr?
Ix
Electric current ampere A I
rad I -s-1
Temperature* kelvin K J·kg-1
Bq J·kg-1
Amount of substance mole mol
Gy I
Sv

sr

Luminous intensity candela Cd a. NUMBER ONE EXPRESSES DIMENSIONLESS RELATIONSHIP.
b. ELECTROMOTIVE FORCE.
=* KELVIN CAN BE EXPRESSED IN DEGREES CELSIUS f°C K - 273.1 SJ.

INTRODUCTION TO NONDESTRUCTIVETESTING I 19

TABLE5. Examples of conversionsto SI units

Quantity Measurementin Non-SI Unit Multiplyby To Get Measurementin SI Unit

Acceleration fr-s-2 I= gravity) - 9.8 meter per second per second (m·s-21)
Area square millimeter (mm2)
Distance square inch /jn.2) 645 nanometer /nm)
millimeter (mm)
Energy angstrom //\) 0.1 kilojoule /k.J)
joule (J)
Specific heat inch /jn.) 25.4 watt (W)
kilojoule per kilogram-kelvin /k.J/kg-K)
Force British thermal unit (BTU) 1.055
Force [torque. couple) newton (NJ
Force or pressure calorie /cal) 4.19 joule (J)
Frequency (cycle) kilopascal (kPa)
Frequency (revolution) British thermal unit per hour /BTU·h-1) 0.293 hertz (Hz)
II luminance l ·s-1
Luminance British thermal unit per pound 4.19 lux (Ix)
candela per square meter (cd·m-2)
Magnetic flux per degree Fahrenheit (BTU·lbm-1.°F-1) candela per square meter (cd·m-2)
Magnetic flux density candela per square meter (cd·m-2)
Magnetic field intensity pound force (lbr) 4.45 candela per square meter (cd·m-2)
Radioactivity weber (Wb)
Ionizing radiation exposure foot-pound /ft-lbr) 1.36 tesla (T)
Dose absorbed by matter ampere per square meter (A-m2)
Dose absorbed by human pound per square inch (lbrin.-2) 6.89 gigabecquerel (GBq)
Mass millicoulomb per kilogram /mC.kg-1)
Temperature (difference) cycle per minute 1/60 gray (Gy)
Temperature (scale) sievert (Sv)
revolution per minute /rpm) 1/60 kilogram (kg)
Velocity degree celsius (0()
footcandle /ftc or fc) l 0.76 degree celsius (0()
kelvin (K)
candela per square foot /cd·fr2) I 0.76 meter per second /m·s-1)
meter per second (m·s-1)
candela per square inch /jn.·fr2) 1,550

footlambert 3.426

lambert 3, 183 (= l 0,000/1t)
l x 10--s
maxwell, or line
gauss, or maxwell per square centimeter l x 10-4
4n x 10-3
oersted (Oe)

curie [Ci] 37

roentgen /R) 0.258

radiation absorbed dose (rad) 0.01

radiation equivalent man /rem) 0.01

pound (lbm) 0.454

degree Fahrenheit /°F) 0.556

degree Fahrenheit (°F) (°F - 32)/1.8

(°F - 32)/1.8) + 273. 15

inch per second (in. ·s-1) 0.0254

mile per hour (mi·h-1) 0.447

Single Unit Comparisons billions of disintegrations are required in a useful source,
the multiplier prefix giga ( 109) is nearly always necessary
The original curie was simply the radiation of one gram and the unit is normally used as gigabecquerel ( GBq).
of radium. Eventually all equivalent radiation from any
The unit for radiation dose (formerly the rad) is the gray
source was measured with this same unit. The original (Cy) in the SI system. The gray is useful because it applies
to doses which are absorbed by matter at a particular loca-
roentgen was the quantity of radiation that would ionize one tion. It is expressed in energy units per mass of matter or
cubic centimeter of air to one electrostatic unit of electricity
of either sign. It is now known that a curie is equivalent to joules per kilogram (J·kg-1). The mass is normally that of the
37 x 109 disintegrations per second and a roentgen is equiv-
alent to 258 microcoulombs per kilogram of air. This corre- absorbing body.
The SI unit for the dose absorbed by the human body
sponds to 1.61 x 1015,ion pairs per kilogram of air which has
absorbed 8.8 millijoules (formerly rem for roentgen equivalent man) is similar to the
(mJ) or 0.88 rads. gray but includes quality factors that depend on the type of
The roentgen was an intensity unit but was not represen- radiation. This absorbed dose has been given the name siev-
ert (Sv) but its dimensions are the same as the gray (J,kg-1).
tative of the dose absorbed by material in the radiation field.
Combination Units
The radiation absorbed dose, rad, was first created to mea-
sure this value and was based on ergs, an energy unit from Roentgens could be measured with an ionization cham-
ber which, when placed one meter from the radiation
the centimeter-gram-second (cgs) system. source, provided a good deal of necessary information
(roentgen per hour per curie at one meter, for example).
In SI, radiation units have been given established physi-

cal foundations and new names where necessary.
The unit for radioactivity (formerly curie) is the bec-

querel (Bq) which is one disintegration per second. Because

20 I NONDESTRUCTIVE TESTING OVERVIEW

The numbers, though, had limited physical meaning and milliliters ( 10-0 m3) appear in the text as exceptions for fluid
could not be used for different applications such as high- volumes.
voltage X-ray machines.
Multipliers
The roentgen per hour (R-h-1) was used to designate the
exposure to an ionizing radiation of the stated value. The SI Units that are either very large or very small are used
unit used for this is the sievert (Sv), which is 100 times as with SI multipliers that are prefixes, mostly of 103 intervals.
large as the rem it replaces. The multiplier becomes a property of the SI unit, e.g., a
centimeter (cm) is 1/100 of a meter, and the volume unit of
Because the received radiation from 1 R-h-1 was consid- a cubic centimeter (cm3) is (1/100)3 or 10-0 cubic meter
ered about equal to 1 rem, the relationship is now approxi- (m3). Note: A cm3 is not equal to 1/100 m3. Also, in equa-
tions, use of units such as centimeters (cm), decimeters
mated as 1 R-h-1 = 0.01 Cy-lr". This is better expressed as (dm) or centiliters (cL) should be avoided since such units
1 R-h-1 = 10 mGy-h-1 with higher levels of radiation in the disturb the convenient 103 or 10---3 intervals which make
equations easy to manipulate.
range of one gray.
A previously popular unit, roentgen per hour at one Scientific Notation. Leakage rates covering many orders
of magnitude have been expressed in powers of ten, e.g., 6 x
meter per curie, is expressed in SI units as millisievert per 10-5, 1 x 10-9 etc.
hour at one meter per gigabecquerel, such that:
Derived SI Units for Leak Testing
lmSv·h-1 at lm·GBq-1 = 3.7R·h-1 at lm·Ci-1 (Eq. 3)
The following derived SI units were adopted for leak
In this relationship, roentgens converts to millisieverts on a testing.
1 to 10 basis.
Gas quantity. Pascal cubic meter (Pa-m"). The quantity
Exposure charts may use curie-minutes at a source-to- of gas stored in a container or which has passed through a
film distance in inches squared. This was written min/in.2. leak is described by the derived SI unit of pascal cubic
Exposure charts made in SI use gigabecquerel-minutes for a meter, the product of pressure and volume. To be strict, the
source-to-film distance in centimeters squared, where 1 Ci- temperature should be specified for the gas volume or leak-
min-in.-2 = 50 GBq-min-cm-2. Table 5 lists some of these age measurement to define the gas quantity (sometimes
new combination units. loosely described as the mass of gas) more precisely. Often,
gas quantity is defined for standard temperature and pres-
Fundamental SI Units Used for sure, typically the standard atmospheric pressure, 101 kPa,
Leak testing and a temperature of 20 °C (293 K). Temperature correc-
tions are usually required if temperature varies significantly
Pressure during leak testing. However, small changes in temperature
may sometimes be insignificant compared with many orders
The pascal (Pa), equal to one newton per square meter of magnitude of change in gas pressure or leakage quantity.
(1 N-m-2), is used to measure a force per unit area. It is used
in place of units of pounds force per square inch (lb-In.:"), Gas leakage rate. Pascal cubic meter per second
atmospheres, millimeters of mercury (mm Hg), torr, bar, (Pa-m"-s '). The leakage rate is defined as the quantity
inches of mercury (in. Hg), inches of water and other prior (mass) of gas leaking in one second. The unit in prior use
units. It is mostly used with multipliers (prefixes) such as was the standard cubic centimeter per second (std cm3-s-1).
mega-, kilo-, milli- and micro-. No connotations shall ever Use of the word standard in units such as std cm3-s-1
be attached to SI units. SI units of pressure are normally requires that gas leakage rate be converted to standard tem-
absolute pressures. However, the text indicates whether perature and pressure conditions (293 Kand 101.325 kPa),
gage, absolute or differential pressure was meant. Negative often even during the process of collecting data during leak-
pressures might be used in heating duct technology and in age rate tests. Expressing leakage rates in the SI units of
vacuum boxes used for bubble testing, but in vacuums, used Pa-m3-s-1 provides a leakage rate valid at any pressure. Leak-
in tracer leak testing, absolute pressures are used. age rates given in SI units of Pa-m3-s-1 can be converted to
units of std cm3-s-1 at any time by simply multiplying the SI
Volume
*leakage rate by 10 or (more precisely) by 9.87. For conver-
The cubic meter (m3) is the only volume measurement
unit in SI. It takes the place of cubic feet, cubic inches, gal- sions, 1 Pa-m3·s-1 10 std cm3-s-1.
lons, pints, barrels and more. Sometimes, liters (l0-3m3) or Gas permeation rate. Pascal cubic meter per second per

square meter per meter (Pa-m3-s-1)/(m2-m-1). Permeation is

INTRODUCTION TO NONDESTRUCTIVETESTING I 21

the leakage of gas through a ( typically solid) substance that a hypothetical wire one meter (1 m) long and one square
millimeter (1 mm2) in cross section. This comparison is
is not impervious to gas flow. The permeation rate is larger immaterial because no actual wire is involved. Hence, for
conformance to SI, this unit could be changed to mJQ.m2,
with an increased exposed area, a higher pressure differen- which reduces to 1/Q,m. Because 1/Q is also conductivity in

tial across the substance (membrane, gasket etc.), and is siemens (S), material conductivity could be expressed in
Sim:
smaller with an increasing thickness of permeable sub-
stance. In vacuum testing, the pressure differential is usu- lm 106 m (Eq.6)
ally considered to be one atmosphere (101 kPa). One Q·mm2 Q.m2
sometimes finds units of permeation rate where the gas
quantity is expressed in units of mass and where the differ-
ential pressure is expressed in various units. Equation 4
expresses an equivalence for conversion of measurements:

lMS -rn "

1.0 stdcm3 ·s-1 - 0.1 Pa ·m3 ·s-1 (Eq.4) Resistivity has sometimes been given in Q,cm, where
cm2 ·cm-1 m2 ·m-1 1 n-cm = 0.01 Q.m.

Rounding. Many tables and graphs were obtained from SI Units for Other Nondestructive
researchers and scientists who did their work in the English Testing Methods
system. In the conversion, some numbers have been
rounded drastically but some were left as irrational numbers Optical Units
in the metric version, especially where quotes were made to
specific entries. Vision requires a source of illumination. The light source
is the candela (cd), defined as the luminous intensity in a
SI Units for Electricaland Magnetic given direction of a source that emits monochromatic radia-
Testing tion of 540 x 1012 hertz (Hz) at a radiant intensity of
1/683 watt per steradian (W-sr-1).
Magnetism Units
The luminous flux in a steradian (sr) is measured in
The SI unit for magnetic flux is the weber (Wb), which lumens (Im). The measurement in lumens is the product of
replaces the maxwell: 1 Wb = 108 maxwells. The density of
magnetic flux (i.e., how much flux passes perpendicularly candela and steradian (l lm = 1 cd-sr).
through a unit of area) is measured in tesla (T); 1 T =
1 Wb-m-2. The older unit is the maxwell per square cen- A light flux of one lumen (1 lm) striking one square
timeter, or gauss (G); 104 G = 1 T. The gauss meter used in meter (1 m2) on the surface of the sphere around the source
nondestructive testing is now called the tesla meter. illuminates it with one lux (l lx), the unit of illuminance. If
the source itself is scaled to one square meter ( 1 m2) and
Magnetic field strength, formerly expressed in oersted emits one candela (1 cd), the luminance (formerly called
(Oe, a nonexisting physical agent enabling analysis of com- brightness) of the source is 1 cd-m+,
plex magnetic field problems), is expressed in SI by ampere
per meter (A·m-1): Some terms have been replaced. Illumination is now
illuminance; brightness is luminance; transmission factor is
41t x lQ-3 Oe (Eq. 5) transmittance. Meter-candle is now lux and nit is candela
_ 1.257 x 10-2 Oe per square meter (cd-rrr").

Conductivity and Resistivity Units Old units are to be converted (see Table 5). Footcan-
dle (ftc) and phot now convert to lux (lx). Stilb (sb), footlam-
This text covers material conductivity measurements and bert and lambert convert to candela per sq,uare meter
favors the term m/ll-mm2, comparing material properties to (cd-nr<). Nanometer (nm) replaces angstrom (A) for wave-
length.

Decibel

The decibel is not an SI unit. It is an indication of the
ratio between two conditions of the same dimension (such

22 I NONDESTRUCTIVETESTINGOVERVIEW

as voltages or powers) and is extensively used in electronics. TABLE 6. SI multipliers
The fundamental decibel is:
Prefix Symbol Multiplier

(Eq. 7) yotta y . I 024
zetta I 021
Where: exa z I 01a
P measured power; and peta
PO reference power. tera E I 015
gig a p I 012
The power is, in a sense, a square function of voltage and mega
the decibel could also be written as: kilo T ]09
hecto* G I Q6
N,, ~ 10 log., ( :, )' (Eq. 8) deka (or deca) * M I Q3
deci* k
This in tum translates to: centi* h I 02
mi Iii da JO
NdB = 20 Iog.; --v (Eq. 9) micro d 10-1
nano c
Va pico m 10-2
femto µ
atto n I 0-3
zepto
yocto p J0-6
f 10-9
a I 0-12
z I 0-1s
y 10-18
I 0-21
I 0-24

and explains why there are often two definitions given for * AVOID THESE PREFIXES(EXCEPTIN dm3 AND cm3J FOR SCIENCEAND
the decibel (sometimes written dBV for voltage decibels). ENGINEERING.
No connotations are attached to SI units and conditions are
expressed parenthetically, such as dB(V). cubic centimeter (cm3) is (0.01)3 or 10--6 m3. Units such as
the centimeter, decimeter, dekameter (or decameter) and
Prefixes for SI Units hectometer are avoided in scientific and technical uses of SI
because of their variance from the 103 interval. However,
Very large or very small units are expressed by using the dm3 and cm3 are in use specifically because they represent a
SI multipliers, prefixes usually of 103 intervals (Table 6). 103 variance.
The multiplier becomes a property of the SI unit. For exam-
ple, a millimeter (mm) is 0.001 meter (m). The volume unit In SI, the distinction between upper and lower case let-
ters is meaningful and should be observed. For example, the
meanings of the prefix m (milli-) and the prefix M (mega-)
differ by nine orders of magnitude.

INTRODUCTION TO NONDESTRUCTIVE TESTING I 23

REFERENCES

1. Betz, C. "The Nondestructive Testing Engineer - 3. McMaster, R.C. and S.A. Wenk. A Basic Guide for
Today's Career Opportunity." Nondestructive Testing. Management's Choice of Nondestructive Tests.
Vol. 18, No. 1. Columbus, OH: American Society for Special Technical Publication No. 112. Philadel-
Nondestructive Testing (January-February 1960): phia, PA: American Society for Testing and Materi-
p 15-26. als (1951).

2. Wenk, S.A. and R.C. McMaster. Choosing NDT Appli­ 4. Standard Practicefor Use of the International Sys­
cations, Costs and Benefits of Nondestructive Testing tem of Units (SI) (The Modernized Metric System).
in Your Quality Assurance Program. Columbus, OH: ASTM E 380-93. Philadelphia, PA: American Soci-
American Society for Nondestructive Testing (1987). ety for Testing and Materials (1993).

24 I NONDESTRUCTIVE TESTING OVERVIEW

BIBLIOGRAPHY

1. ASM Handbook, ninth edition: Vol. 17, Nondestruc­ 12. Nondestructive Testing Handbook, second edition:
Vol. 2, Liquid Penetrant Tests. Columbus, OH:
tive Evaluation and Quality Control. Materials American Society for Nondestructive Testing (1982).
Park, OH: ASM International (1989).
2. Annual Book of ASTM Standards: Section 3, Metals 13. Nondestructive Testing Handbook, second edition:
Test Methods and Analytical Procedures. Vol. 03.03, Vol. 3, Radiography and Radiation Testing. Colum-
Nondestructive Testing. West Conshohocken, PA: bus, OH: American Society for Nondestructive
American Society for Testing and Materials [revised Testing (1985).
annually].
3. Bray, D.E. and D. McBride, ed. Nondestructive 14. Nondestructive Testing Handbook, second edition:
Testing Techniques. New York, NY: John Wiley & Vol. 4, Electromagnetic Testing. Columbus, OH:
Sons (1992). American Society for Nondestructive Testing (1986).
4. Bray, D.E. and R.K. Stanley. Nondestructive Evalu­
ation: A Tool in Design, Manufacturing, and Ser­ 15. Nondestructive Testing Handbook, second edition:
vice. New York, NY: McGraw-Hill (1989). Vol. 5, Acoustic Emission Testing. Columbus, OH:
American Society for Nondestructive Testing (1987).
5. Cartz, L. Nondestructive Testing: Radiography,
Ultrasonics, Liquid Penetrant, Magnetic Particle, 16. Nondestructive Testing Handbook, second edition:
Eddy Current. Materials Park, OH: ASM Interna- Vol. 6, Magnetic Particle Testing. Columbus, OH:
tional (1995). American Society for Nondestructive Testing (1989).

6. Halmshaw, R. Introduction to the Non­Destructive 17. Nondestructive Testing Handbook, second edition:
Testing of Welded Joints. Cambridge, United King- Vol. 7, Ultrasonic Testing. Columbus, OH: Ameri-
dom: Abington Publishing (1988).
can Society for Nondestructive Testing (1991).
7. Halmshaw, R. Non­Destructive Testing, second edi- 18. Nondestructive Testing Handbook, second edition:
tion. London, United Kingdom: Edward Arnold
(1991). Vol. 8, Visual and Optical Testing. Columbus, OH:
American Society for Nondestructive Testing (1993).
8. Hull, B. and V. John. Non­Destructive Testing. Bas- 19. Nondestructive Testing Handbook, second edition:
ingstoke, United Kingdom: Macmillan (1988). Vol. 9, Special Nondestructive Testing Methods.
Columbus, OH: American Society for Nondestruc-
9. McMaster, R.C., ed. Nondestructive Testing Hand­ tive Testing (1995).
book, first edition Columbus, OH: American Soci- 20. Nondestructive Testing Methods. T033B-l-l
ety for Nondestructive Testing (1959). (NAVAIROl-lA-16) TM43-0103. Washington, DC:
Department of Defense United States Air Force
10. Mathematics and Formulae in NDT, second edition, (June 1984).
revised. Northhampton, United Kingdom: British 21. Wenk, S.A. and RC. McMaster. Choosing NDT:
Institute of Non-Destructive Testing (1993). Applications, Costs and Benefits of Nondestructive
Testing in Your Quality Assurance Program.
11. Nondestructive Testing Handbook, second edition: Columbus, OH: American Society for Nondestruc-
Vol. 1, Leak Testing. Columbus, OH: American tive Testing (1987).
Society for Nondestructive Testing (1982).

LEAK TESTING 2SECTION

Charles N. Sherlock, Willis, Texas

A PORTION OF PART3 IS ADAPTED FROM THE ASTM BOOK OF STANDARDS: E 427, STANDARD PRACTICEFOR TESTINGFOR LEAKS USING THE HALOGEN LEAK
DETECTOR{ALKALI-LON DIODE/, © AMERICAN SOCIETYFOR TESTINGAND MATERIALS. REPRINTEDWITH PERM1c;;c;;10N.

26 I NONDESTRUCTIVETESTING OVERVIEW

PART 1

MANAGEMENT AND APPLICATIONS OF
LEAK TESTING

Functions of Leak Testing evaluation is indirect; the quantities measured have to be
properly correlated to the serviceability characteristics of
Leak testing is a form of nondestructive testing used for the material in question. Thus, the use of indirect tests
detection and location of leaks and for measurement of fluid depends upon the interpretation of the test results. Leak
leakage in either pressurized or evacuated systems and com- testing procedures, on the other hand, facilitate direct eval-
ponents. The word leak refers to the physical hole that exists uation. The measured leakage rate represents the physical
and does not refer to the quantity of fluid passing through effect of a faulty condition and thus requires no further
that hole. A leak may be a crack, crevice, fissure, hole, or analysis for practical assessment.
passageway that, contrary to what is intended, admits water,
air, or other fluids or lets fluids escape (as with a leak in a Determination of Overall Leakage
roof, gas pipe, or ship). The word leakage refers to the flow Rates through Pressure Boundaries
of fluid through a leak without regard to physical size of the
hole through which flow occurs. Many leak tests of large vessels or system are concerned·
with the determination of the rate at which a liquid, gas, or
Reasons for Leak Testing vapor will penetrate through their pressure boundaries.
Leakage may occur from any location within a component,
Leaks are special types of anomalies that can have tre- assembly, or system to points outside the boundary, or from
mendous importance where they influence the safety or per- external regions to points within a volume enclosed by a
formance of engineering systems. The operational reliability pressure boundary. When a fluid flows through a small leak,
of many devices is greatly reduced if sufficiently large leaks the leakage flow rate depends upon (1) the geometry of the
exist. Leak testing is performed for three basic reasons: leak, (2) the nature of the leaking fluids and (3) the prevail-
ing conditions of fluid pressure, temperature and type of
1. to prevent material leakage loss that interferes with flow. For purposes of leak testing, an easily detectable gas or
system operation; liquid tracer fluid may be used, rather than air or the system
operating fluid. Leakage typically occurs as a result of a
2. to prevent environmental contamination hazards or pressure differential between the two regions separated by
nuisances caused by accidental leakage; and the pressure boundary.

3. to detect unreliable components and those whose The term minimum detectable leakage refers to the
leakage rates exceed acceptance standards. smallest fluid flow rate that can be detected. The leakage
rate is sometimes referred to as the mass flow rate. In the
The end purpose of leak testing is to ensure reliability case of gas leakage, the leakage rate describes the number
and serviceability of components and to prevent premature of molecules leaking per unit of time, if the gas temperature
failure of systems containing fluids under pressure or vac- is constant, regardless of the nature of the tracer gas
uum. Nondestructive methods for leak testing of pressur- employed in leak testing. When the nature of the leaking gas
ized or evacuated systems and of sealed components are and the gas temperature are known, it is possible to use the
thus of great industrial and military importance. ideal gas laws to determine the actual mass of the leakage.

Relationship of Leak Testing to Measuring Leakage Rates to
Product Serviceability Characterize Individual Leaks

Most types of nondestructive tests are designed to aid in In pressurized or evacuated systems, an individual leak is
evaluating serviceability of materials, parts and assemblies. defined as a hole or porosity in the wall of an enclosure
Tests are used for determining integrity of structure, mea-
suring thickness, or indicating the presence of internal and
surface anomalies. For most nondestructive test methods

LEAKTESTING I 27

TABLE 1 . Leakage rate (mass flow) conversion TABLE2. Leakage rate comparisons in various
factors unitsof leakage

To Convertfrom To Multiplyby air at O °C
kg·yr-1
std cm3·s-1 9.87 I= 1 OJ Pa-m3-s-1 std cm3·s-1 std L/day
Pascal cubic meters per
second (Pa-m3-s-1) torrL.s'" 7.50 J JO 864 400
1.00 x 101 0.5 5 432 200
mbts'" 0.2 2 173
std ft3·h-1 1.25 0. J J 80
0.05 0.5 86.4 40
Standard cubic centimeters Pa-m3·s-1 1.01 x 10-1 0.02 0.2 43.2 20
(std cm3·s-1) 0.01 0.1 17.3
torrLs :' 7.60 x 10-1 5 x 10-3 5 x 10-2 8
2 x 10-3 2 x 10-2 8.6 4
moLs" 1.0 J J o-3 J 0-2 4.3 2
std ft3·h-1 J .7 0.8
J .27 x 10-1 5 x 1 Q-4 5 x 10-3 0.86 0.4
J0-4 10-3 0.43 0.2
Torr liters per second Pa-m3·s-1 1.33 x 10-1 5 x 10-5 86 x 10-3 4 x 10-2
(torr·L·s-1) 1.32 10-s 5 x l Q-4 43 x 10-3 2 x 10-2
std cm3·s-1 1.33 J0-4 86 x 1 Q-4 4 x 10-3
J .67 x 10-1 5 x 1 Q-6 43 x l Q-4 2 x 10-3
mbLs :' J0-6 5 x 10-5 86 x 10-5 4 x J Q-4
std ft3·h-1 10-7 10-s 86 x 10-6 4 x 10-5
J o-6 86 x 10-7 4 x J Q-6
Millibar liters per second Pa-m3·s-1 J .00 x J 0-1 10-s 10-7 86 x 1 o-s 4 x 10-7
[mb-Ls'] 9.87 x J 0-1 J o-9 86 x 10-9 4 x 10-s
std cm3·s-1 7.50 x J 0-1 J 0-10 10-s 86x 10-10 4 x 10-9
torr-Ls" 1.26 x J 0-1 10-11 J o-9 86 x 10-11 4 x J 0-10
std ft3·h-1 10-12 J 0-10 86x10-12 4 x J 0-11
10-13 J Q-11
Standard cubic feet per hour Pa-m3-s-1 0.80 J 0-12
(std ft3-h-1) 7 .87
std cm3-s-1 5.99
7.94
torr-t-s "

mb·L·s-1

capable of passing a fluid from one side of the wall to the QuantitativeDescription of
other side. The flow of fluid through the leak typically Leakage Rates
results from a pressure differential or a concentration differ-
ential of a gaseous constituent that acts across the pressure The significant quantitative measurement resulting from
boundary. The flow characteristics of a leak are often leak testing is the leakage rate or mass flow rate of fluid
described in terms of the conductance of the leak. The leak through one or more leaks. Leakage rate thus has dimensions
equivalent to pressure times volume divided by time. The
represents a physical hole with some equivalent length and units used previously for leakage rate were standard cubic
internal cross-sectional area or diameter. However, since a centimeters per second (std cm3,s-1). The Nondestructive
leak is not manufactured intentionally into a product or sys- Testing Handbook uses the international standard SI nomen-
tem, the leak hole dimensions are generally unknown and clature. In SI units, the mass of gas is measured in units of
cannot be determined by nondestructive tests. Therefore, in pascal cubic meters (Pa-rn"). The leakage rate is measured in
leak testing, the quantity used to describe the leak is the pascal cubic meters per second (Pa.m--s+). Table 1 gives fac-
measured leakage rate. · tors for conversion of leakage rates in various common units
that are gradually becoming obsolete. Table 2 provides leak-
The leakage rate depends upon the pressure differential age rate comparisons which permit a better understanding of
that forces fluid through the leak passageway.The higher this the quantities involved, when leakage rates are specified. A
pressure difference, the greater the leakage rate through a common unit of gas mass is the standard cubic meter
given leak. Therefore, leakage measurements of the same (std m3). This unit is equivalent to one million units given as
leak under differing pressure conditions can result in differ-
ing values of mass flow rate. The leak conductance is defined
both by the leakage rate and the pressure differential across
the leak. Thus, conductance or leakage rate at a given pres-
sure for a particular tracer fluid should alwaysbe specified in
reporting and interpreting the results of a leak test.

28 I NONDESTRUCTIVETESTING OVERVIEW

atmospheric cubic centimeters (atm cm3). Both units indi- Leakage is not simply the volume of air entering the vac-
cate the quantity of gas (air) contained in a unit volume at uum chamber. Instead, the critical factor is the number of
average sea level atmospheric pressure. The average atmo- gaseous molecules entering the vacuum system. This num-
spheric pressure at sea level is 101.3 kPa (760 mm of mer- ber of molecules, in turn, depends upon the external pres-
cury or 760 torr). The SI unit of pressure, the pascal, is sure, temperature and the volume of gas at this pressure
equivalent to newton per square meter (N-m-2). that leaks into the vacuum system. The leakage rate is
expressed in terms of the product of this pressure difference
Examples of Practical Units Used multiplied by the gas volume passing through the leak, per
Earlier for Measurement of unit of time. Thus, the leakage rate is directly proportional
Leakage to the number of molecules leaking into the vacuum system
per unit of time.
Various units have been used for measurement of leak-
age, including many related to English units commonly used Ensuring System Reliability through
in engineering. Justification for prior use of this diversity of Leak Testing
units lies in the relative ease with which these common units
can be adapted for many practical engineering problems. One important reason for leak testing is to measure the
For example, suppose that an operator has a gas cylinder reliability of the system under test. Leak testing is not a
with a pressure gage calibrated in units of pounds per direct measure of reliability, but it might show a fundamen-
square inch (lbj-in.r"). With daily gage readings, it is conve- tal fault of the system by a higher than expected leakage rate
nient for the operator to express leakage as the gage pres- measurement. A high rate of leakage from mechanical con-
sure change multiplied by cylinder volume, divided by the nections might indicate that a gasket is improperly aligned
leakage time period (days). This simple calculation results in or missing. In the same manner, a high leakage value might
leakage rate measurement in units of lb-m." ft3/day. This show the presence of a misaligned or misthreaded flange.
leakage rate has dimensions of (pressure) x (volume) + Therefore, it is possible to detect installation errors by high
(time). To have expressed the leakage merely as the volume leakage values. (However, the absence of high leakage does
of gas lost is insufficient since the volume of gas that leaves not necessarily indicate the absence of improperly installed
daily at high cylinder pressure will be considerably larger components.) Leakage measurements to detect installation
than the volume leaking to the atmosphere each day when errors need not be extremely sensitive, since the leakage
the internal pressure of the cylinder is lower. Many combi- rates to be expected from serious error will be relatively
nations of units for pressure, volume and time are possible. high (10-3 to 10-6 Pa-m3-s-1 or 10-2 to 10-5 std cm3-s-1). Thus,
The preferred SI leakage rate unit pascal cubic meter per leak locations can usually be detected readily.
second (Pa-rn'<s") is used throughout this section.
Leak Testing to Detect Material
Units for Leakage Rates of Vacuum Flaws
Systems
Many leaks are caused by material anomalies such as
As another example, suppose that leakage of air into a cracks and fissures. Some of these can be detected by mea-
vacuum system has an undesired effect upon the pressure surement of leakage rates. Other leaks can be detected by
within the vacuum system. The operator of the vacuum sys- discontinuity detection techniques that identify leak loca-
tem can read vacuum pressure in pascals or torr from gages tions. However, neither of these two leak testing technique
permanently installed in the system. (The pressure unit categories will detect all anomalies. Leak testing is therefore
known as a torr is defined as l/760th of a standard atmo- complementary to other nondestructive testing methods
sphere. It differs only by one part in seven million from the that are used to find and evaluate basic material anomalies.
well known barometric pressure unit of millimeters of mer-
cury.) In the past, the leakage rate in vacuum systems was Because service reliability is not necessarily a direct
measured in scientific units of torr-liters per second. If the function of the leakage in a system, it is difficult to establish
volume of the vacuum chamber had been measured in cubic an acceptance level for leakage rate. The decision may be
meters, the operator might find it easier to measure leakage influenced by the fact that increased leak testing sensitivity
rate in units of pascal cubic meters per day or per second. may detect only a small number of additional leaks at con-
siderable added cost. This is because most leaks in welded,
brazed and mechanical joints tend to be relatively large.

LEAK TESTING I 29

This is partly due to the clogging of smaller leaks by water 1. no detectable leakage;
vapor and liquids that occurs in parts exposed to industrial 2. no measureable leakage;
processes or to the atmosphere. The only case where small 3. noleakage;and
leaks of less than 10-8 Pam+s' (10-7 std cm+s') are 4. zero leakage.
encountered is in parts that receive special clean room
treatment during manufacture. Impractical leak testing specifications are expensive to
implement. They are also very confusing unless the leak
Specifying Desired Degrees of Leak testing method is precisely described. With specifications in
Tightness impractical 'terms, the leak testing operator is always work-
ing against background instrument noise. He must then
In industry, the term leaktight has taken on a variety of decide whether the leakage reading obtained is caused by
meanings. A water bucket is tight if it does not allow easily the random fluctuations of test instruments or by the actual
detectable quantities of water to leak out. A high vacuum detection of specific leakage. It is much easier to discrimi-
vessel is tight if the rate of apparent leakage into the system nate whether a measured leakage rate is above or below a
cannot be indicated with the equipment on hand. One given standard than to discriminate leakage from random
might even consider that a gravel truck is leaktight so long as instrument noise. It is therefore suggested that, when spec-
there are no openings in the truck bed large enough to allow ified, zero leakage be defined as a measurable quantitative
the smallest nugget to escape. The degree of leak tightness value of leakage rate that is insignificant in the operation of
depends on the individual situation. Leak tightness requires the system. Such a definition allows the system or the mea-
that the leakage flow be too small to be detected. However, surement sensitivity to be compared with a flow through a
leak tightness is a relative term. Therefore, it becomes a standard physical leak In this way, a qualification of the sys-
necessity to establish a practical level ofleak testing sensitiv- tem performance acceptability can be made during the test
ity for any given component under test. Thus, nothing is operation.
leaktight except by comparison to a standard or specifica-
tion. Even then, the measured degree of leak tightness can Specifying Leak Testing
be ensured only at the time of leak testing and under spe- Requirements to Locate Every Leak
cific leak testing conditions. Later operation at higher pres-
sures might open up leaks. Occasionally it is desirable to locate every existing leak
irrespective of size for the following reasons.
Avoiding Impractical Specifications
for Leak Tightness 1. Stress leaks have a habit of growing, i.e., very small
leaks may become very troublesome later, after
Aiming at absolute tightness is an academic endeavor. In repeated stressing.
practice, all that can be asked for is a more or less stringent
degree of tightness selected according to the application 2. High temperature leaks may be very small at test
requirements. Nothing made by man can truly be consid- temperature but may have higher leakage rates at sys-
ered to be absolutely leaktight. Even in the absence of tem operating temperatures.
minute porosities, the permeation of certain gases through
metals, crystals, polymers and glasses still exists. 3. Temperature cycling to either high or cryogenic lev-
els usually creates stress that results in change of
Thus, it is necessary to establish a practical leakage rate leakage rates.
that is acceptable for a given component under test. A pre-
liminary decision has to be made concerning the definition The criterion whereby a decision is made whether or not
of leak tightness for the particular situation. Because leak to seek greater reliability should be the ratio of cost of the
tightness is a relative term and has no absolute meaning, the leak testing procedure to the number of leaks found. For
sensitivity of the available leak testing equipment is a practi- example, improving leak testing reliability from lQ-6 Pa-m3-s-1
cal guide to attainable levels of leak testing sensitivity. Any (lo-S std cm3-s-1) to a reliability of 10-7 Pa-m3-s-1
increase in required sensitivity of leak testing increases the (10-6 std cm3-s-1) may not be justified. The cost of obtaining
time required for leak testing and increases test cost. This the small increase in reliability may be prohibitive in relation
increase in cost of leak testing reaches a maximum when the to the value of the increase in detection reliability.
leakage specification is given in such impractical term as:
The expected leak tightness of sealing operations that will
be used to isolate the system during leak testing must also be
considered. The leak testing specification should be written
with advice from an experienced engineer who makes a

30 I NONDESTRUCTIVE TESTING OVERVIEW

judgment of the reasonable value of allowable leakage rate. be defined. For example, if some decision can be made as to
Factors to be considered include the leak testing method the allowable amount of reaction between the oxidizer and
and technique; type, size and complexity of the system the rocket engine parts, the maximum acceptable rate of
under test; and the service requirements and operating con- total leakage of oxidizer from the storage tank can be
ditions under which the tested system will be used. defined. Similarly, in an electronic component, if failure
results from adsorption of a monolayer of leaking molecules
Specifying Sensitivity of Leak on the surface, then knowing that 1015 molecules form one
Testing for Practical Applications monolayer on a square centimeter of surface makes it possi-
ble to calculate the allowable leakage rate for this particular
In specifying the sensitivity of the leak testing technique, component. If failure results from a pressure rise, then the
an optimum leakage sensitivity value should be sought first. maximum allowable pressure, the planned system operation
Large deviations from this optimum value could increase time and system volume are all that are necessary for calcu-
the cost and the difficulty of measuring the leakage rate. lation of the allowable leakage rate.
Secondly, any increase in the sensitivity specified for a par-
ticular leakage test automatically increases the cost of leak Specifying Tightness Required to Avoid Personnel
testing. Therefore, a compromise has to be reached Hazard Caused by Fluid Leakage
between testing cost and leakage tolerance. Thirdly, the sen-
sitivity required in leak testing depends upon the particular Material leakage can cause personnel hazard during sys-
effects of leakage that must be controlled or eliminated, as tem operation. If the tolerable concentrations are known, and
illustrated in the following examples. Finally, the language these are often reported in literature, it is again quite easy to
in which the leak testing specification is written should be calculate the maximum tolerable equipment leakage rate.
easy to interpret and to implement in testing, to ensure that
management's goals are achieved by the leak test. Specifying Tightness Required to Avoid Undesirable
Appearance Caused by Leakage
Specifying Tightness Required to Control Material
Loss by Leakage An appearance specification is a specification for maxi-
mum leakage that is made because leakage of a higher value
The first consideration in specifying the leak tightness will spoil the appearance of the system. Appearance is often
required of a fluid containment system is to ensure that the specified when no more stringent specification is necessary.
system does not leak sufficient material to cause system fail- A specification for leakage of oil out of the oil pan of a new
ure during the operational life of the system. The greatest car is a good example. This leakage specification may not be
allowable leakage rate would then be the allowable total caused by concern that too much oil will be lost or that dam-
leakage divided by the operational life of the system. Of age to the . car motor will occur; instead, it is specified
course, conversion might have to be made between numeri- because the prospective buyer would not be inclined to buy
cal values for the tracer gas leakage during leak testing and a car that would immediately dirty his driveway and that, at
those for the material leakage under system operation con- the time of sale, was dripping oil onto the showroom floor.
ditions.
Specifying Tightness Required to Avoid Nuisance
Specifying Tightness Required to Control Caused by Leakage
Environmental Contamination by Leakage
When appearance sets the allowable leakage of the sys-
Contamination failure of a system might cause environ- tem, the leakage is often only a nuisance. However, even
mental damage, personnel hazard, or degraded appearance. leaks that are largely a nuisance may alter the effectiveness
The environmental damage to a system may be caused by of the total system. For example, during the East Coast
material leaking either into or out of the system. For exam- power blackout in the United States on November 9, 1965,
ple, system damage may be caused to a liquid rocket motor a large steam generator failed during the shutdown because
when the oxidizer leaks out of the storage tank and reacts the auxiliary steam supply used for lubrication purposes was
with parts of the motor. On the other hand, electronic com- not available. This steam supply had been shut off earlier by
ponents can fail when air or water vapor enters a hermeti- workers who were bothered by excessive leakage of steam
cally sealed protective container. It is often difficult to through some valve packing. This steam leakage was not
calculate the very small amount of material necessary to critical, but it was enough of a nuisance that the system was
cause a contamination failure to occur. However, in most shut down for repair. The repair did not take place in time
cases, such calculations are not impossible if the failure can and the bearings of the generator burned out during emer-
gency shutdown of the system.

LEAK TESTING I 31

Definition of Leak Detector and FIGURE 1 . Ease of test operationas a function
Leak Test Sensitivity of leak testingsensitivity

A leak detector's sensitivity is a measure of the concen- GREAT
tration or flow rate of tracer gas that gives a minimum mea-
sureable leak signal. Sensitivity depends on the minimum z
detectable number of tracer gas molecules entering the
detector. The sensitivity of a leak detector is independent of 0
the pressure in the system being tested, provided that time
is ignored as a test factor. ~

Leak test sensitivity refers to the minimum detectable ua.i.
amount of leakage that will occur in a specific period of time 0
under specified leak test conditions. It is necessary to state 0LL
both the leakage rate and the prevailing test conditions to w
properly define leak test sensitivity in terms of the smallest
physical size leak that can be detected. To avoid confusion, a ~
set of standard leak test conditions is required.
LOW-+-~~~~~~~~~~~~~~~~~~ HIGH
Standard Conditions for Leak Testing LOW

The set of standard conditions most commonly accepted LEAK TESTING SENSITIVITY
is that of dry air at 25 °C, for a pressure differential between
one standard atmosphere and a vacuum (a standard atmo- Bubble testing by immersion in water is an example of how
sphere is 101.325 kPa). For practical purposes, the vacuum the optimum value affects the ease of performing the test.
need be no better than 0.01 of an atmosphere or 1 kPa.
When a leak is being described and only the leakage rate is The bubble testing sensitivity range extends from 10-2 to
given, it is assumed that the leakage rate refers to leakage at 10-5 Pa-m3-s-1 (10-1 to lQ-4 std cm3-s-1 ). In measuring for
standard conditions. The sensitivity of a leak testing instru-
ment is synonymous with the minimum detectable leakage 10-2 Pa-m3-s-1 (10-1 std cm3-s-1) leaks, a component may be
or minimum flow rate the instrument can detect. These
minima are independent of leak testing conditions. When placed in water and observed quickly. Bubbles may emerge
the instrument is applied to a test, the leak testing sensitivity from the pressurized component at such a rapid rate that
depends on existing conditions of pressure differential, tem- there is no question of the existence of a leak. When check-
perature and fluid type in addition to the instrument sensi- ing for leaks in the range of 10-J to lQ-4 Pa-m3-s-1 (10-2 to
tivity. However, the leak test instrument should be more
sensitive by at least a factor of 2 than the minimum leakage lQ-3 std cm3-s-1 ), the operator must be sure that the test
to be detected, to ensure reliability and reproducibility of
measurements. object or component is submerged long enough for any
bubbles coming from crevices to have a chance to collect
Example of Sensitivity and and rise. When locating leaks in the 10-5 Pa-m3-s-1
Difficulty of Bubble Leak Testing (10-4 std cm3-s-1) range, the component, after being

Each modification of a leak testing procedure has an opti- immersed, has to be completely stripped of attached air
mum sensitivityvalue at which it is most readily used. Devia- bubbles so that the bubble formed by leaking gas may be
tion from this optimum value of sensitivity makes it more detected. The lQ-5 Pa-m3-s-1 (10-4 std cm3-s-1) leakage range
difficult to perform the measurement and decreases confi-
dence in the results. Figure 1 shows the influence ofleak test- is near the limit of detectability of the bubble technique,
ing sensitivity level on the ease of operation of test although longer waiting periods theoretically could obtain
equipment. In most cases, after reaching a plateau, further higher sensitivity. Longer waiting periods become impracti-
increase of sensitivityrapidly decreases the ease of operation. cal when the rate of bubble evolution approaches the rate at
which tracer gas is dissolving in the test fluid.

Specifying sensitivity much greater than lQ-5 Pa-m3-s-1
(10-4 std cm3-s-1) makes bubble testing exceedingly difficult.
For instance, bubble testing could be used at higher sensi-
tivity by saturating the immersion liquid with the tracer gas
used in leak testing. However, it would be better to change
to a different leak testing method that is more effective at
that higher sensitivity. Bubble testing to detect leaks greater
than 10-2 Pa-m3-s-1 (10-1 std cm3-s-1) becomes difficult

because of rapid gas evolution and rapid decay of pressure

32 I NONDESTRUCTIVETESTING OVERVIEW

in the system under test. However, difficulties in the less Basic Categories of Leak Testing
sensitive test range are usually not so great as in the more
stringent sensitivity range. Types of Fluid Media Used in Leak Testing

Relation of Test Costs to Sensitivity Leak testing can be divided into three main categories:
of Leak Testing (1) leak detection, (2) leak location and (3) leakage measure-
ment. Each method in all categories involves a fluid leak
Leak testing instrumentation costs increase as required tracer and some means for establishing a pressure differen-
test sensitivity increases, as sketched in Fig. 2. The test tial or other means for causing fluid flow through the leak or
equipment investment for determining a leakage rate of leaks. Possible fluid media include gases, vapors and liquids
10-4 Pa-m3,s-1 (10-3 std cm3-s-1) is negligible compared with or combinations of these physical states of fluid probing
that for a sensitivity of 10-13 Pa-m3-s-1 (10-12 std cm3,s-1 ), media. Selection of the desired fluid probing medium for
whose cost is 10,000 times higher. Even after a test tech- leak testing depends on operator or engineering judgment
nique has been selected, raising leak sensitivity require- involving factors such as:
ments within this technique will result in an increase in
measurement cost. This increase is usually caused by FIGURE2. Effectof requiredsensitivityon leak
greater complexity of leak tests with increased sensitivity. detectionequipmentcost
Cost increases become particularly drastic when the
required sensitivity is higher than the optimum operating LEAKAGE MEASUREMENT SENSITIVITY I 0-12
range shown in Fig. 1. standard cubic centimeter per second

Selection of Specific Leak Testing I o-6
Technique for Various Applications
t;:j
Figure 3 provides a graphical guide to selection of leak 0
testing methods and techniques for various applications. It
shows a decision tree with which the choice of a leak testing U 5,000 -
method becomes a step-by-step process. The selection pro-
cesses suggested by Fig. 3 serve as a basic guide. Further zf--
consideration of specific leak testing requirements may sug-
gest other methods or techniques for test selection, or cause w
the test engineer to modify leak testing procedures. The
final selection of the leak testing method will typically be 5o2,
made from perhaps only three or four possible test meth-
ods. The special conditions under which tests must be made 0w
can become a major factor in this final test selection.
~~ 500 -
The first question to be asked when choosing the best
leak testing method, or technique of a method, is "Should Vuil
this test reveal the presence of a suspected leak, or is its pur- f--
pose to show the location of a known leak?" The second :,.::
question to be answered is, "Is it necessary to measure the
rate of leakage at the specific leak?" If leakage measurement ;'.S
is essential, use of calibrated or reference leaks or other
means to provide quantitative leakage measurement is _J
required. In the decision tree of Fig. 3, the first branch (or
decision point) answers the preceding questions and deter- w>
mines if the purpose or requirements of the test lead to the w~a,::
upper branch of leak location only, or to the lower branch of
leakage rate measurements. I

I 0-4 I 0-10 10-13

LEAKAGE MEASUREMENT SENSITIVITY
pascalcubic meter per second