ASNT NDT Handbook Volume 3 Infrared and Thermal Testing

NONDESTRUCTIVE TESTING Third Edition

HANDBOOK

Volume 3

TM Inf rared and
Therm al Test ing

Technical Editor
Xavier P.V. M aldague
Editor
Patrick O. M oore

® American Society for Nondestructive Testing

FOUNDED 1941

Copyright © 2001
AM ERICAN SOCIETY FOR NONDESTRUCTIVE TESTING, INC.
All rights reserved.

No part of th is book m ay be reproduced, stored in a retrieval system or tran sm itted, in an y form or by an y m ean s —
electron ic, m ech an ical, p h otocop yin g, record in g or oth erwise — with ou t th e p rior written p erm ission of th e p u blish er.
Noth in g con tain ed in th is book is to be con strued as a gran t of an y righ t of m an ufacture, sale or use in con n ection with
an y m eth od, process, apparatus, product or com position , wh eth er or n ot covered by letters paten t or registered
tradem ark, n or as a defen se again st liability for th e in frin gem en t of letters paten t or registered tradem ark.
Th e Am erican Society for Non d estru ctive Testin g, its em p loyees an d th e con tribu tors to th is volu m e are n ot resp on sible
for th e auth en ticity or accuracy of in form ation h erein , an d opin ion s an d statem en ts publish ed h erein do n ot n ecessarily
reflect th e op in ion of th e Am erican Society for Non d estru ctive Testin g or carry its en d orsem en t or recom m en d ation .
Th e Am erican Society for Non d estru ctive Testin g, its em p loyees, an d th e con tribu tors to th is volu m e assu m e n o
respon sibility for th e safety of person s usin g th e in form ation in th is book.

American Society for Nondestructive Testing, Incorporated
1711 Arlingate Lane
PO Box 28518
Columbus, OH 43228-0518
(614) 274-6003; fax (614) 274-6899
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Library of Congress Cataloging-in-Publication Data

Infrared and thermal testing / technical editor, Xavier P.V. Maldague ; editor,

Patrick O. Moore

p. cm. -- (Nondestructive testing handbook. Third edition ; v. 3)

Includes bibliographical references and index.

ISBN 1-57117-044-8

1. Infrared and thermal testing. I. Maldague, Xavier X.P. II. Moore,

Patrick O. III. Series: Nondestructive testing handbook (3rd ed.) ; v. 3.

TA410.N45 2001

620.1’127--dc21 00-068229

CIP

Published by the American Society for Nondestructive Testing
PRINTED IN THE UNITED STATES OF AMERICA

President ’s Forew ord

Infrared and Therm al Testing is Volu m e 3 of
th e Nondestructive Testing Handbook, th ird
ed ition . Th e con tin u in g existen ce of th e
NDT Handbook d em on strates th e
d ed ication of th e Am erican Society for
Non d estru ctive Testin g (ASNT) in
providin g n ew tech n ical in form ation in
th e field of n on destructive testin g
tech n ology an d advan cin g th e
n on d estru ctive testin g p rofession . Th is
volum e presen ts its readers with curren t
developm en ts, tech n ological
advan cem en ts an d application s of th is
n ewly an d rap id ly evolvin g tech n ology.

Th is m u ltivolu m e ed ition is bein g
written an d reviewed with in put from th e
Meth od s Division of ASNT’s Tech n ical an d
Ed u cation Cou n cil an d u n d er th e
gu id an ce of ASNT’s Han d book
Developm en t Com m ittee. I wan t to
express m y sin cere appreciation an d
th an ks to th e m an y com m ittee m em bers
an d oth er volun teers wh o provide th eir
outstan din g tech n ical in put an d support,
to th e con tributors an d reviewers, to th eir
spon sors an d particularly to series editor
Patrick Moore for th eir dedication an d
com m itm en t to th e publication of
Nondestructive Testing Handbook volu m es.

Infrared and Therm al Testing was written
an d reviewed with in put from th e
Th erm al an d In frared Com m ittee in th e
Meth ods Division . I wish to th an k
Tech n ical Ed itor Xavier Mald agu e an d h is
team of experts for th eir im portan t gift of
th is book to th e tech n ical com m u n ity.

Th e d evelop m en t of n on d estru ctive
testin g tech n ologies such as in frared an d
th erm al testin g is a con tin u ation of ASNT
an d its m ission s of providin g tech n ical
in form ation an d prom otin g
n on destructive testin g tech n ologies an d
th e profession worldwide. On beh alf of
ASNT, I welcom e th is m eth od to th e
fam ily of n on destructive testin g m eth ods
an d to th e NDT Handbook series.

Joh n A. Strin ger
ASNT Presid en t (2000-2001)

Infrared and Thermal Testing iii

Forew ord

Aims of a Handbook for in stan ce, m ay h ave little bearin g on a
practical exam in ation . Oth er parts of a
Th e volu m e you are h old in g in you r h an d h an dbook are specific to a certain
is th e th ird in th e th ird edition of th e in d u stry. Alth ou gh a h an d book d oes n ot
Nondestructive Testing Handbook. Now is a preten d to offer a com plete treatm en t of
good tim e to reflect on th e purposes an d its subject, its value an d con ven ien ce are
n ature of a h an dbook. n ot to be den ied.

Han dbooks exist in m an y disciplin es of Th e p resen t volu m e is a worth y
scien ce an d tech n ology, an d certain ad d ition to th e th ird ed ition . Th e ed itors,
features set th em apart from oth er tech n ical editors an d m an y con tributors
referen ce works. A h an dbook sh ould an d reviewers worked togeth er to brin g
ideally give th e basic kn owledge n ecessary th e p roject to com p letion . For th eir
for an u n d erstan d in g of th e tech n ology, sch olarsh ip an d dedication I th an k
in cludin g both scien tific prin ciples an d th em all.
m ean s of application .
Gary L. Workm an
Th e typ ical read er m ay be assu m ed to Han dbook Developm en t Director
h ave com pleted th ree years of college
toward a degree in m ech an ical
en gin eerin g or m aterials scien ce an d
h en ce h as th e backgroun d of an
elem en tary ph ysics or m ech an ics course.
Occasion ally an en gin eer m ay be
frustrated by th e difficulty of th e
d iscu ssion in a h an d book. Th at h ap p en s
because th e assum ption s about th e reader
vary accordin g to th e subject in an y given
ch ap ter. Com p u ter scien ce req u ires a sort
of backgroun d differen t from n uclear
ph ysics, for exam ple, an d it is n ot possible
for th e h an dbook to give all th e
backgroun d kn owledge an cillary to
n on destructive testin g.

A h an dbook offers a view of its subject
at a certain p eriod in tim e. Even before it
is p u blish ed , it starts to get obsolete. Th e
auth ors an d editors do th eir best to be
curren t but th e tech n ology will con tin ue
to ch an ge even as th e book goes to press.

Stan d ard s, sp ecification s,
recom m en ded practices an d in spection
procedures m ay be discussed in a
h an dbook for in struction al purposes, but
at a level of gen eralization th at is
illustrative rath er th an com preh en sive.
Stan d ard s writin g bod ies take great p ain s
to en sure th at th eir docum en ts are
defin itive in wordin g an d tech n ical
accu racy. Peop le writin g con tracts or
procedures sh ould con sult real stan dards
wh en appropriate.

Th ose wh o d esign q u alifyin g
exam in ation s or study for th em draw on
h an dbooks as a quick an d con ven ien t way
of approxim atin g th e body of kn owledge.
Com m ittees an d in dividuals wh o write or
an ticipate question s are selective in wh at
th ey d raw from an y sou rce. Th e p arts of a
h an dbook th at give scien tific backgroun d,

iv Infrared and Thermal Testing

Pref ace

Wh en som ebody is sick, on e of th e first m ature n on destructive testin g m eth od. In
steps for care gen erally con sists of takin g fact, an im portan t m ileston e was set
h is or h er tem perature to assess wh eth er wh en Level III certification of
or n ot th ere is a m etabolic d isord er. Su ch th erm ograp h ers by ASNT first started in
a procedure is an exam ple of passive 1993. Moreover, d evelop m en t of room
p oin t th erm ograp h y, with th e tem perature operated focal plan e array
tem perature readin g bein g an in dication in frared cam eras in th e late 1990s boosted
of th e u n seen op eration of th e bod y. As n ew ap p lication s. For in stan ce th e
th e n am e im plies, th erm ograph y is a Cad illac Seville m od el year 2000 was
m appin g of tem perature readin gs over a available with a n igh t vision system based
surface, th e m appin g bein g perform ed as on such a detector (320 × 240 pixels)
th e m easurem en t of on e or m an y poin ts en ablin g a deeper observation ran ge at
un der th e form of a lin e or a n igh t for in creased safety.
bid im en sion al im age. Su ch m ap p in g can
be obtain ed by con tact with Ap p lication s of in frared th erm ograp h y
th erm om eters, th erm ocouples or a liquid h ave been d evelop in g swiftly, as in d icated
crystal p ain t. Su ch m ap p in g can also be by th e growth of con feren ces devoted to
accom plish ed th rough in frared th at top ic — for in stan ce, Th erm osen se
m on itorin g, in wh ich case th e radiation con feren ces sin ce 1978 an d In tern ation al
em itted by th e surface of in terest is picked Con feren ces on Quan titative In frared
up by a sen sor sen sitive to th is radiation . Th erm ograp h y (QIRT) sin ce 1992.
Th is is in frared th erm ograp h y.
Su rp risin gly, all th ese d evelop m en ts
In sprin g or fall in n orth ern coun tries, were n ot supported by a rich collection of
aston ish in g n atural ph en om en a referen ce volum es on th is field of
som etim es ap p ear. For in stan ce, ligh t kn owledge. In fact books dedicated to
sn ow m eltin g on a roof m igh t reveal th e in frared th erm ograph y an d related
in n er wooden roof structure. In fact th e tech n ology can still be coun ted on th e
im ages of un derlyin g structural elem en ts fin gers of on e h an d.
m ay ap p ear, su ch as p lan k join ts an d
fram in g stu d s. Th e m orn in g su n h eats Th e Am erican Society for
m ore rapidly th e space between studs due Non d estru ctive Testin g (ASNT) is kn own
to th e reduced th ickn ess so th at at on e for its rem arkable publication s, in cludin g
poin t th e in side wooden structure is th e world fam ou s Nondestructive Testing
revealed as sn ow traces over stu d s. Th is is Handbook volu m es, bu t u n til n ow, n o
an exam ple of sim ple n atural active volum e of th is referen ce collection was
th erm ograp h y. Of cou rse, in su ch a case, solely dedicated to in frared
th e observer h as on ly a few m in utes to th erm ograp h y. (In form ation abou t
observe th e ph en om en on . in frared th erm ograph y could h owever be
foun d in th e leak testin g, special m eth ods
In frared collection of tem perature an d overview volum es.) In th e 1990s, it
im ages is n ot a n ew p roced u re. Th e first was decided to in clude a volum e fully
experim en ts with an evaporograph date d ed icated to th is tech n iq u e. Th e first step
back to th e n in eteen th cen tu ry. Th is was to appoin t a tech n ical editor
apparatus collected en ergy em itted from a respon sible for writin g th e outlin e, for
surface on a th in film of oil th at con tactin g poten tial auth ors an d
evaporated selectively at location s reviewers an d workin g in coordin ation
correspon din g to warm er target areas so both with th e ASNT staff an d with th e
th at a kin d of im age becam e visible, In frared Han d book Su bcom m ittee.
correspon din g to th e isoth erm s of th e Ru ssel T. Mack was in itially given th at
in spected surface. task an d started th e job. For variou s
reason s, h e passed m e th e flam e in 1997.
Alth ou gh it can be can said th at
m odern (in frared) th erm ograph y really Th e p rojected h an d book was ou tlin ed ,
started in 1965 with th e release by a a Web site was design ed an d lead auth ors
Swed ish com p an y of a com m ercial were con tacted to write parts an d
in frared cam era, m ilitary application s ch ap ters. Weekly con tact with ASNT’s
such as target detection were already series editor h elped speed up th e process,
active in World War II. Sin ce th en wh ich really started in 1998. Resp on se of
in frared th erm ograph y h as progressed th e com m un ity was quite en th usiastic
from a n ew an d exotic m eth od to a an d h elped keep th e flam e alive. Mon th
after m on th , texts were received from

Infrared and Thermal Testing v

au th ors, organ ized an d tu n ed by ASNT
staff an d sen t to reviewers for com m en ts,
correction s an d im p rovem en ts. Even tu ally
we started to see ligh t at th e en d of th e
tun n el.

Th e p resen t book will certain ly be
groun dbreakin g in its field of kn owledge,
coverin g m ost aspects of th erm ograph y
from fun dam en tal to very practical
con cern s. Of course im provem en ts are
still possible an d are already plan n ed for
th e n ext — fourth ! — edition . Mean wh ile
we h ope th is book will h elp to prom ote
th e developm en t of th erm ograph y
followin g rigorous procedures.

In frared th erm ograph y is m uch m ore
th an poin tin g an in frared cam era at a
surface to look at a h ot spot. Man y
adverse effects h ave to be taken in to
accoun t to obtain sign ifican t quan titative
in form ation from such m easurem en ts,
just as th e ph ysician con siders various
factors to in terp ret correctly a p atien t’s
th erm om eter read in g. Th is is th e p u rp ose
of th is book.

It is m ore th an worth wh ile to th an k all
con tributors an d reviewers wh o
volun teered an d gave th eir tim e so th at
th e task cou ld be com p leted . ASNT staff
m em ber con tribution s were also essen tial
in th e su ccess of th is en terp rise. Fin ally, a
last word to ackn owledge th e support of
m y fam ily is n ot superfluous.
Xavier P.V. Mald agu e
Tech n ical Ed itor

vi Infrared and Thermal Testing

Edit or’s Pref ace

Th e first ed ition of th e Nondestructive Acknowledgments
Testing Handbook h ad two p ages on
th erm al testin g. Th e m eth od got a ch ap ter Handbook Development
as part of th e special m eth ods volum e in Committee
th e secon d ed ition . Bu t th e th ird ed ition
is th e first edition to give an en tire Gary L. Workm an , Un iversity of Alabam a,
volum e to in frared an d th erm al testin g. Hun tsville

Th e in frared an d th erm al m eth od h as a Mich ael W. Allgaier, GPU Nu clear
lon g h istory in th e Am erican Society for Albert S. Birks, AKZO Nobel Ch em icals
Non d estru ctive Testin g (ASNT). Th e Rich ard H. Bossi, Boein g Com p an y, Seattle
m eth od attracted th e atten tion of Lisa Brasch e, Iowa State Un iversity
aerospace research ers durin g th e space Lawren ce E. Bryan t, Jr., Los Alam os
race. In th e 1960s ASNT h ad an active
in frared com m ittee th at even publish ed Nation al Laboratory
its own tran saction s. William C. Ch ed ister, Circle Ch em ical Co.
Jam es L. Doyle, North west Research
Th e com m ittee becam e in active in th e
1970s. Mean wh ile, advan ces in Associates, In c.
m icroprocessor an d video tech n ology Allen T. Green , Acou stic Tech n ology
m ade it possible for th e th erm ograph ic
in sp ection p rofession to grow. In th e Group
1980s, th ese in sp ectors tu rn ed to ASNT Robert E. Green , Jr., Th e Joh n s Hop kin s
for th e advan tages offered by qualifyin g
exam in ation s an d certification guidelin es. Un iversity
Matth ew J. Golis, Ad van ced Qu ality
Th e p lan n in g of th e p resen t volu m e
began at ASNT’s Fall Con feren ce, New Con cepts
Orlean s, Sep tem ber 1986, wh en m ore Fran k A. Id d in gs
th an 20 in spectors an d research ers Ch arles N. Jackson , Jr.
crowd ed in to a sm all room an d , as ASNT’s Joh n K. Keve, Dyn Corp Tri-Cities Services
Th erm al an d In frared Com m ittee, Lloyd P. Lem le, Jr., BP Oil Com p an y
discussed th e n eed for establish in g th e Xavier P.V. Mald agu e, Un iversity Laval
body of kn owledge for th eir youn g Pau l McIn tire, Am erican Society for
tech n ology.
Non d estru ctive Testin g
ASNT owes th an ks to Ru ssel T. Mack, Mich ael L. Mester, Th e Tim ken Com p an y
wh o, in th e early 1990s, recruited m an y Ron n ie K. Miller, Ph ysical Acou stics
of th e volun teers for th e volum e an d
wrote a prelim in ary outlin e for th e book. C o rp o rat io n
Scott D. Miller, Sau d i Aram co
In 1997 Tech n ical Ed itor Xavier P.V. Patrick O. Moore, Am erican Society for
Maldague assum ed th e respon sibility of
ed itin g th e book for tech n ical accu racy. Non d estru ctive Testin g
He also wrote th e outlin e, recruited Stan ley Ness
volun teers an d wrote text wh ere Ron ald T. Nisbet, IESCO
con tribution s from oth ers were lackin g. Lou is G. Pagliaro, Tech n ical Associates of
ASNT is in d ebted to Mald agu e an d to all
th e tech n ical experts listed at th e en d of Ch arlotte
th is foreword . (In th at list below, p eop le Em m an u el P. Pap ad akis, Qu ality System s
listed as con tributors were also reviewers
but are listed on ly on ce, as con tributors.) Con cepts
J. Th om as Sch m id t, J.T. Sch m id t
I would like to th an k staff m em bers
Hollis Hu m p h ries an d Joy Grim m for Asso cia t e s
th eir con tibution s to th e art, layout an d Fred Sep p i, William s In tern ation al
text of th e book an d also th an k Am os G. Sh erwin , Sh erwin In corp orated
Publication s Man ager Paul McIn tire for Kerm it S. Skeie, Kerm it Skeie Associates
h is support th rough out production . Rod eric K. Stan ley, Qu ality Tu bin g
Holger H. Streckert, Gen eral Atom ics
Patrick O. Moore Stu art A. Tison , Millip ore Corp oration
Ed itor Noel A. Tracy, Un iversal Tech n ology

C o rp o rat io n
Mark F.A. Warch ol, Alu m in u m Com p an y

of Am erica
Glen n A. Wash er, Tu rn er-Fairban k

High way Research Cen ter
George C. W h eeler, Materials & Processes

Con sultan ts

Infrared and Thermal Testing vii

Contributors Roberto Li Voti, Nation al In stitu te for th e
Ph ysics of Matter (INFM) an d th e
Tom m aso Astarita, Un iversità d egli stu d i Un iversity of Rom e
d i Nap oli “Fed erico II,”
Grigore L. Liakh ou , Nation al In stitu te for
Mau rice J. Bales, Bales Scien tific th e Ph ysics of Matter (INFM) an d th e
In corporated Tech n ical Un iversity of Mold avia

Jean Lou is Beau d oin , Un iversité d e Reim s Min h Ph on g Lu on g, École Polytech n iq u e
Ch am p agn e-Ard en n es Ru ssel T. Mack, Mack In sp ection &

Abd elh akim Ben d ad a, Nation al Research Th erm al Tech n ologies
Coun cil Can ada, In dustrial Materials David L. Mad er, On tario Hyd ro
In stitute
Tech n ologies
Th om as Ben ziger, Otto-von -Gu ericke Xavier P.V. Mald agu e, Un iversity Laval
Un iversität Magdeburg Sergio Marin etti, Con siglio Nazion ale

Harry Berger, In d u strial Qu ality d elle Ricerch e, Italy
In corporated Ph illip C. McMu llan , TSI Th erm o-Scan

Mario Bertolotti, Nation al In stitu te for th e In spection s
Ph ysics of Matter (INFM) an d th e Th om as G. McRae, Laser Im agin g System s
Un iversity of Rom e Erik E. Mu ller, Measu rem en t Solu tion s

Clifford C. Bish op D iv isio n
Ch ristian Bissieu x, Un iversité d e Reim s Ky T. Ngu yen , Nation al Research Cou n cil

Ch am p agn e-Ard en n es Can ada, In dustrial Materials In stitute
Leon ard J. Bon n ell, Vip era System s Step h an Offerm an n , Un iversité d e Reim s
Blair R. Bosworth , Foseco
Th om as J. Bru kilacch io, In n ovation s in Ch am p agn e-Ard en n es
Yosh izo Okam oto, East Asia Un iversity
Optics, In corporated Robert Osian d er, Joh n s Hop kin s
J.-M. Bu ch lin , In stitu t von Karm an d e
Un iversity, Ap p lied Ph ysics Laboratory
Dyn am iq u e d es Flu id es Joh n G. Pagath , Jr.
Dou glas D. Bu rleigh , Con su ltan t Stefan o Paolon i, Nation al In stitu te for th e
Gerd Bu sse, Un iversität Stu ttgart
Gen n aro Card on e, Un iversità d egli Stu d i Ph ysics of Matter (INFM) an d th e
Un iversity of Rom e
d i Nap oli “Fed erico II” Mich ael W. Pelton , Dow Ch em ical
Giovan n i M. Carlom agn o, Un iversità degli Lars Persson
Yu ri A. Plotn ikov, Gen eral Electric
Stu d i d i Nap oli “Fed erico II” Research & Develop m en t
Bryan A. Ch in , Au bu rn Un iversity Marc Prystay, Oerlikon Aerosp ace
Robert L. Cran e, Air Force Research In corporated
Nik Rajic, Aeron au tical an d Maritim e
Laboratory, Materials Directorate, Research Laboratory, Au stralia
Wrigh t-Patterson Air Force Base Raym on d R. Rayl, Con su m ers En ergy
Gen n aro Cu ccu ru llo, Un iversity of Salern o Den n is P. Red lin e, Tem p il, In corp orated
Arn old Dan iels, Coh eren t, In corp orated Elisabetta Rosin a, Politecn ico d i Milan o
E. Joh n Dickin son , Un iversity Laval An d res E. Rozlosn ik, SI Term ografia
Motoku n i Eto, Jap an Atom ic En ergy In trarroja
Research In stitu te Sam u el S. Ru ssell, Nation al Aeron au tics
Fran çois R. Galm ich e, Un iversity Laval an d Sp ace Ad m in istration
Erm an n o Grin zato, Con siglio Nazion ale R. Jam es Seffrin , In frasp ection In stitu te
d elle Ricerch e, Istitu to p er la Tecn ica Steven M. Sh ep ard , Th erm al Wave
d el Fred d o, Italy Im agin g
Pau l E. Grover, Sh elbu rn e Con cita Sibilia, Nation al In stitu te for th e
Ed m u n d G. Hen n eke, II, Virgin ia Ph ysics of Matter (INFM) an d th e
Polytech n ic an d State Un iversity Un iversity of Rom e
Hollis E. Hu m p h ries, Am erican Society for Joh n R. Sn ell, Jr., Sn ell In frared
Non d estru ctive Testin g Jan e Maclach lan Sp icer, Joh n s Hop kin s
Teru m i In agaki, Ibaraki Un iversity Un iversity
Tosh im itsu Ish ii, Jap an Atom ic En ergy Holger H. Streckert, Gen eral Atom ics
Research In stitu te An d rew C. Teich , FLIR System s
Th om as S. Jon es, In d u strial Qu ality Marvin W. Trim m , Westin gh ou se
In corporated Savan n ah River Com p an y
Herbert Kap lan , Hon eyh ill Tech n ical Ju ssi Varis, Un iversity of Helsin ki
Com pany Vlad im ir P. Vavilov, Tom sk Polytech n ic
Jean -Clau d e Krap ez, Fren ch Nation al Un iversity
Aerosp ace Research Establish m en t Jam es L. Walker, Un iversity of Alabam a
Matth ew D. Lan sin g, Un iversity of Bo Wallin , FLIR System s Swed en
Alabam a, Hu n tsville Gary J. Weil, En Tech En gin eerin g
Maria Cristin a Larcip rete, Nation al In corporated
In stitute for th e Ph ysics of Matter Stig-Björn Westberg, Vatten fall Utvecklin g
(INFM) an d th e Un iversity of Rom e Bogu slaw Wiecek, Tech n ical Un iversity of
Den n is C. Lein er, Ligh t Hou se Im agin g Lód z

viii Infrared and Thermal Testing

Gary L. Workm an , Un iversity of Alabam a Fran k J. Sattler
Pau l A. Zayicek, Electric Power Research Ed ward R. Sch au fler, In fra Red Scan n in g

In stitute Services
Peter Sh en , In frared Su rveys
Reviewers Ph ilip J. Stolarski, Californ ia Dep artm en t

Fath i Al Qad eeb, Sau d i Aram co of Tran sp ortation
Arn old Ad am s, San ta Barbara Focal Plan e Staffan L. Straat, FLIR System s Swed en
Step h en M. Ash ton , Newp ort News Rich ard Z. Stru k, Sh ellcast Fou n d ries
Carlo Ten u ta, Sh ellcast Fou n d ries
Sh ip bu ild in g Rolan d o J. Vald es, ITEQ In sp ection s
Dan iel L. Balageas, Office Nation al Mark F.A. Warch ol, Alu m in u m Com p an y

d ’Étu d es et d e Rech erch es of Am erica
Aérosp atiales Glen n A. Wash er, Un ited States
Robert D. Barton , Un ited States Air Force
Don ald E. Boren , AST Test Services Dep artm en t of Tran sp ortation
Lisa Brasch e, Iowa State Un iversity Joh n C. Watson , Dow Ch em ical Com p an y
J. Steven Cargill, Pratt & W h itn ey Th eod ore Wild i, Un iversity Laval
F. Ch arbon n ier, Office Nation al d ’Étu d es Rich ard N. Wu rzbach , Main ten an ce
et d e Rech erch es Aérosp atiales
E. Jam es Ch ern , Nation al Aeron au tics an d Reliability Grou p
Sp ace Ad m in istration , God d ard Sp ace
Fligh t Cen ter Additional Acknowledgments
An ton io Colan ton io, Pu blic Works an d
Govern m en t Services Can ad a Th is volu m e is in d ebted to m an y p eop le
Gilbert De Mey, Gh en t Un iversity, an d organ ization s. Ap ologies are exten d ed
Belgiu m to all th ose wh o gave h elp or
Dou g J. Dyck, Win n ep eg en couragem en t but are n ot m en tion ed.
Jan K. Eklu n d , Eklu n d In frared
Robert E. Fisch er, Op tics 1 For fin an cial assistan ce th e d iscu ssion
Ben oit d e Halleu x, Metrologic System s of in frared th erm ograph ic calibration is
Marcu s (Mark) R. Harty, MRH Associates in d ebted to th e Min istry of Ed u cation of
Jam es W. Hou f, Am erican Society for th e Provin ce of Quebec, Can ada.
Non d estru ctive Testin g
Th om as J. Hu rley, Hu rley an d Associates For th e d iscu ssion of in frared
Dwigh t L. Isen h ou r, Newp ort News borescopy th e en gin eerin g support is
Sh ip bu ild in g ackn owled ged of In fram etrics (n ow FLIR),
Katash i Ku rokawa, NEC San -ei Billerica, Massach u setts, an d Am ber,
Tim o Kau p p in en , VTT Bu ild in g Goleta, Californ ia.
Tech n ology
Lloyd P. Lem le, Jr. For th e d iscu ssion of lockin
Kjell M. Lin d strom , FLIR System s Swed en th erm ograp h y, th e team at Stu ttgart
Ch ee-An g Loon g, Nation al Research Un iversity is ackn owled ged : K. Breitrü ck,
Coun cil Can ada, In dustrial Materials A. Dillen z, C. Doettin ger, W. Karp en ,
In stitute N. Kroh n , X. Mald agu e, J. Ran tala,
Gregory B. McIn tosh , Sn ell In frared A. Salern o, D. Vergn e, H.G. Walth er,
Bret A. Mon roe, Mon roe In frared D. Wu an d T. Zwesch p er. Research was
Tech n ology su p p orted by Agem a; Arbeitsgem ein sch aft
Th om as B. Mu n son , Mu n son NDT In d u strieller Forsch u n gsverein igu n gen ;
Con sultan ts Deu tsch e Forsch u n gsgesellsch aft fü r
Ron Newp ort, Acad em y of In frared Oberfläch en beh an dlun g; Deutsch e
Th erm ograp h y Forsch u n gsgem ein sch aft; Deu tsch es
Ron ald T. Nisbet, IESCo Bu n d esm in isteriu m fü r Bild u n g u n d
Gary L. Orlove, FLIR System s Forsch u n g; Deu tsch es Zen tru m fü r
Ign acio M. Perez, Naval Air Warfare Lu ft- u n d Rau m fah rt (R. Aoki);
Cen ter Fairch ild -Dorn ier; Gewerblich e
Piotr Pregowski, Zobrazowan ia i Beru fssch u le Sch wäbisch -Hall; Malter
Term ografia Air-Service; an d Motoren - u n d
David W. Prin e, North western Un iversity Tu rbin en u n ion .
Joel Qu in ard , Un iversité d e Proven ce —
C N RS David Taylor Research Cen ter (Gen e
Jeff A. Register, North west Airlin es Cam p on ech i) an d th e Arm y Research
Ju kka Ran tala, Nokia Research Cen ter Office are th an ked for support of studies
Jam al Rh azi, Un iversity of Sh erbrooke in th e developm en t of
Alexan d er J. Rogovsky, Lockh eed Missiles vibroth erm ograp h y.
& Sp ace Com p an y
Jean -Fran çois Sacad u ra, Cen tre d e Research on th erm ograp h ic d etection
Th erm iq u e – CNRS of im pact dam age in graph ite epoxy
Morteza Safai, Boein g Aerosp ace Com p an y com posites was supported by Hercules
Corp oration (H. Von Jen sen ); In frared
Tech n ologies Corp oration (Carlos
Gh igliotti); Loki Data Prod u cts
rep resen tin g In sigh t Vision System s
(Coh n Byrn e); Martin Marietta Missile
System s (E.M. Crism an an d R. Cervero);
Martin NDT (T. Martin ); Joh n s Hop kin s

Infrared and Thermal Testing ix

Un iversity; Nation al In stitu te of Stan d ard s
an d Tech n ology (George Hich o); an d th e
States Arm y Materials Tech n ology
Laboratory (Ch arles Pergan tis),
Watertown , Massach usetts.

For th e d iscu ssion of th erm ograp h ic
in spection of process furn aces, th e
ph otograph y of Ph il Dollar is gratefully
ackn owledged.

Th e d iscu ssion of bu ild in g en velop es
was assisted by An il Parekh , Scan ad a
Con su ltan ts Lim ited , Ottawa, On tario,
Can ada.

For th e d iscu ssion of h istoric bu ild in gs,
th an ks are exten ded particularly to all
people collaboratin g in th e in situ tests
an d th e followin g auth ors of referen ced
p ap ers: P.G. Bison , C. Bressan , N. Lu d wig,
S. Marin etti, A. Mazzold i an d L. Rosi.

Con tribution s to th e discussion of
con servation of fin e art are gratefully
ackn owled ged : Elisabeth Mibach , d irector,
an d Lyd ia Du ll, p h otograp h er,
In term u seu m Con servation Association ;
Maryan Ain sworth , sen ior research
associate, Metrop olitan Mu seu m of Art;
William A. Real, con servator, Mu seu m of
Art, Carn egie In stitu te; Joyce Hill Ston er,
d irector, Pain tin g Con servation ,
Un iversity of Delaware.

Sou rces of illu stration s are
ackn owledged in a separate section of th is
book.

x Infrared and Thermal Testing

CO N T EN T S

Chapter 1. Introduction to Infrared Chapter 6. Errors in Infrared
and Thermal Testing . . . . . . . . . . 1 Thermography . . . . . . . . . . . . . 131

Part 1. Non d estru ctive Testin g . . . . 2 Part 1. Sou rces of Errors . . . . . . . 132
Part 2. Man agem en t of In frared Part 2. Calculation an d

an d Th erm al Testin g . . . . 12 Evalu ation of Errors . . . . 138
Part 3. History of In frared an d Part 3. Statistical Processin g of

Th erm al Testin g . . . . . . . . 20 Errors . . . . . . . . . . . . . . . 149
Part 4. Un its of Measure for
Chapter 7. Parameters in Infrared
Non d estru ctive Testin g . . 25 Thermography . . . . . . . . . . . . . 161

Chapter 2. Fundamentals of Infrared Part 1. Perform an ce Param eters
and Thermal Testing . . . . . . . . . 31 for Optical Detectors . . . 162

Part 1. Prin ciples of In frared an d Part 2. System Perform an ce
Th erm al Testin g . . . . . . . . 32 Param eters . . . . . . . . . . . 168

Part 2. Gen eral Ap p roach es an d Part 3. Effects of Atm osp h ere . . . 180
Tech n iq u es of In frared
an d Th erm al Testin g . . . . 40 Chapter 8. Noncontact Sensors for
Infrared and Thermal
Part 3. Calibration for In frared Testing . . . . . . . . . . . . . . . . . . . 185
Th erm ograp h y . . . . . . . . . 47
Part 1. Th erm al Detectors . . . . . 186
Chapter 3. Heat Transfer . . . . . . . . . . 53 Part 2. Scan n in g Rad iom etric
Part 1. Fu n d am en tals of Heat
Tran sfer . . . . . . . . . . . . . . 54 Im agin g Detectors . . . . . 194
Part 2. Heat Con d u ction in Sou n d Part 3. Sch em es for Lin e
Solid s . . . . . . . . . . . . . . . . 59
Part 3. Heat Con duction in Scan n in g . . . . . . . . . . . . 201
Solid s with Bu ried Part 4. Mu lticolor Rad iom etry
Discon tin uities . . . . . . . . 62
Part 4. Heat Diffusion in n ear Am bien t
Period ical Regim e . . . . . . 76 Tem p eratu res . . . . . . . . . 210

Chapter 4. Fundamentals of Infrared Chapter 9. Contact Sensors for
Radiometry . . . . . . . . . . . . . . . . 87 Thermal Testing and
M onitoring . . . . . . . . . . . . . . . 227
Part 1. Fu n d am en tal Laws . . . . . . 88
Part 2. Rad iative Prop erties of Part 1. Tem p eratu re
Measurem en t . . . . . . . . . 228
Materials . . . . . . . . . . . . . 91
Part 3. Tem p eratu re Part 2. Th erm ocou p les . . . . . . . . 231
Part 3. Resistan ce Tem p eratu re
Measurem en ts . . . . . . . . . 99
Detectors . . . . . . . . . . . . 248
Chapter 5. Noise in Infrared Part 4. Th erm istors . . . . . . . . . . . 252
Thermography . . . . . . . . . . . . . 107 Part 5. In tegrated Circu it Sen sors

Part 1. Defin ition , Effects an d an d Data Processin g . . . . 254
Measurem en t . . . . . . . . . 108 Part 6. Liq u id Crystals . . . . . . . . 256
Part 7. Media with Calibrated
Part 2. Noise Red u ction th rou gh
Im age Processin g . . . . . . 111 Meltin g Poin ts . . . . . . . . 262

Part 3. Tech n iq u es to In crease
Em issivity . . . . . . . . . . . 119

Part 4. Tech n iq u es to Overcom e
Low Em issivity . . . . . . . . 124

Leak Testing x i

Chapter 10. Equipment for Infrared Chapter 14. Infrared and Thermal
and Thermal Testing . . . . . . . . 271 Testing of M etals . . . . . . . . . . 441

Part 1. In frared an d Th erm al Part 1. Crystallograph y of
In strum en tation . . . . . . 272 Metals . . . . . . . . . . . . . . 442

Part 2. Th erm ograp h ic Im agers . 285 Part 2. Heat Tran sfer in Mold s
Part 3. In terpretation of In frared an d Dies for Alu m in u m
an d Plastic . . . . . . . . . . . 451
Test Resu lts . . . . . . . . . . 289
Part 4. In frared Th erm ograp h ic Part 3. On lin e Mon itorin g of Arc
Misalign m en t in Gas
Eq u ip m en t Op eration . . 293 Tu n gsten Arc Weld in g . . 458
Part 5. In frared Borescop y . . . . . 301
Part 4. Th erm al Im agin g of
Chapter 11. Techniques of Infrared Laser Weld in g . . . . . . . . 463
Thermography . . . . . . . . . . . . . 307
Part 5. In frared Tribology . . . . . . 470
Part 1. Passive Tech n iq u es . . . . . 308
Part 2. Pu lse Th erm ograp h y . . . . 310 Part 6. In frared Th erm ograp h y of
Part 3. Pulsed Ph ase Steel Wire Drawin g . . . . 478

Th erm ograp h y . . . . . . . . 313 Chapter 15. Aerospace Applications
Part 4. Lockin Th erm ograp h y . . 318 of Infrared and Thermal
Part 5. Step Heatin g . . . . . . . . . . 328 Testing . . . . . . . . . . . . . . . . . . . 489
Part 6. Vibroth erm ograp h y . . . . 334
Part 7. Th erm oelastic Stress Part 1. In frared Th erm ograp h y
of Sp ace Sh u ttle an d
An alysis . . . . . . . . . . . . . 339 Related Aerosp ace
Part 8. Th erm om ech an ical Stru ctu res . . . . . . . . . . . . 490

Cou p lin gs in Solid s . . . . 342 Part 2. Ap p lication s to Metal
Aerosp ace Stru ctu res . . . 502
Chapter 12. Data Processing and
M odeling for Infrared and Part 3. Pu lsed Th erm al In sp ection
Thermal Testing . . . . . . . . . . . . 359 of Agin g Aircraft . . . . . . 508

Part 1. Sign al Acq u isition an d Part 4. Th erm ograp h ic Detection
Processin g . . . . . . . . . . . 360 of Im pact Dam age in
Grap h ite Ep oxy
Part 2. Au tom atic Discon tin u ity Com posites . . . . . . . . . . 511
Detection . . . . . . . . . . . . 366
Part 5. In frared Scan n in g
Part 3. Quan titative In version Rad iom etry of Con vective
an d Discon tin uity Heat Tran sfer . . . . . . . . . 519
Ch aracterization . . . . . . 373
Chapter 16. Electric Power
Part 4. Th erm al Tom ograp h y . . . 386 Applications of Infrared and
Part 5. Ph ototh erm al Depth Thermal Testing . . . . . . . . . . . . 527

Profilin g by Th erm al Part 1. Th erm ograp h ic System s
Wave Backscatterin g . . . 392 for Power Gen eration
an d Distribution . . . . . . 528
Chapter 13. Thermal Contrasts
in Pulsed Infrared Part 2. In frared Th erm ograp h y
Thermography . . . . . . . . . . . . . 411 in Electrical
Main ten an ce . . . . . . . . . 531
Part 1. Backgrou n d to
Th erm al Con trasts in Part 3. Predictive Main ten an ce
Pulsed In frared for Nu clear Reactor
Th erm ograp h y . . . . . . . . 412 Com pon en ts . . . . . . . . . 534

Part 2. On e-Dim en sion al Mod el Part 4. In frared Th erm ograp h y
of Laterally Exten d ed of Nu clear Fu sion
Discon tin uity . . . . . . . . . 416 Reactor . . . . . . . . . . . . . 538

Part 3. Two-Dim en sion al Part 5. In frared Th erm ograp h y
Model of Discon tin uity of Power Gen eration
with Lim ited Lateral Su bsystem s . . . . . . . . . . 545
Exten sion . . . . . . . . . . . 422
Part 6. In frared Th erm ograp h y
for Distribution
System s . . . . . . . . . . . . . 551

Part 7. Helicop ter Based
Th erm ograp h y of
Power Lin es . . . . . . . . . . 556

x ii Infrared and Thermal Testing

Chapter 17. Chemical and Petroleum Chapter 20. Infrared and Thermal
Applications of Infrared and Testing Glossary . . . . . . . . . . . 679
Thermal Testing . . . . . . . . . . . . 571
Part 1. Term in ology . . . . . . . . . 680
Part 1. Th erm ograp h ic In sp ection Part 2. Nom en clature . . . . . . . . 699
of Process Fu rn aces . . . . 572
Index . . . . . . . . . . . . . . . . . . . . . . . . 705
Part 2. Passive Th erm ograp h ic
Detection of Ch em ical Figure Sources . . . . . . . . . . . . . . . . . . 718
Leakage from Pip elin es
an d Storage Vessels . . . . 577

Part 3. In frared Th erm ograp h y
of Steel Abovegrou n d
Storage Tan ks . . . . . . . . . 587

Part 4. Rad iom etry of Polym er
Film . . . . . . . . . . . . . . . . 591

Chapter 18. Infrastructure and
Conservation Applications
of Infrared and Thermal
Testing . . . . . . . . . . . . . . . . . . . 601

Part 1. Tech n iq u es of In frared
Th erm ograp h ic Leak
Testin g . . . . . . . . . . . . . . 602

Part 2. Th erm ograp h ic
Mod elin g of Leakage
th rough Walls . . . . . . . . 609

Part 3. Vibroth erm ograp h y of
Earth q u ake Resistan t
Stru ctu res . . . . . . . . . . . . 613

Part 4. In sp ection of Th erm al
En velop es of New
Bu ild in gs . . . . . . . . . . . . 620

Part 5. In frared an d Th erm al
Testin g for Con servation
of Historic Bu ild in gs . . . 624

Part 6. In frared an d Th erm al
Testin g for Con servation
of Fin e Art . . . . . . . . . . . 647

Chapter 19. Infrared Thermography
of Electronic
Components . . . . . . . . . 659

Part 1. Tem p eratu re Measu rem en t
of Electron ic
Com pon en ts . . . . . . . . . 660

Part 2. Tem p eratu re Measu rem en t
with In frared
Microscope . . . . . . . . . . 664

Part 3. Em issivity Evalu ation for
Electron ic Circu its an d
Com pon en ts . . . . . . . . . 667

Part 4. Sp ectral Em issivity
Evalu ation of Materials
for Microelectron ics . . . . 673

Infrared and Thermal Testing x iii

MULTIMEDIA CONTENTS

Chapter 10. Equipment for Infrared Chapter 16. Electric Power
and Thermal Testing . . . . . . . . . . 1 Applications of Infrared and
Thermal Testing . . . . . . . . . . . . 527
Movie. Hot spot located and
sp ectral filter ap p lied . . . 280 Movie. Mobile thermographic
system. . . . . . . . . . . . . . 529
Movie. Interference filter. . . . . . . 280
Movie. Apparent temperature Movie. Hot spot in transmission
station. . . . . . . . . . . . . . 551
at cross hairs. . . . . . . . . . 287
Movie. Coolant is added to Movie. High voltage
switch disconnects. . . . . 551
dewar reservoir in
camera. . . . . . . . . . . . . . 299 Movie. Hot joint in power
line. . . . . . . . . . . . . . . . . 556
Chapter 11. Techniques of Infrared
Thermography . . . . . . . . . . . . . 307 Movie. Tension joint in tower. . . 557
Movie. Tension joint in tower. . . 557
Movie. Emissivity increases Movie. Tension joint in tower. . . 557
when slag enters stream
of molten steel. . . . . . . . 309 Chapter 19. Infrared Thermography
of Electronic Components . . . . 659
Movie. Gas burner ignites. . . . . . 309
Movie. Pulse reflection setup. . . . 311 Movie. Automated thermography
Movie. Thermal pulse. . . . . . . . . 312 of printed circuit
Movie. Fluorocarbon resin board. . . . . . . . . . . . . . . 659

insert in carbon fiber Movie. Hot spots reveal thin
reinforced plastic. . . . . . 312 regions in film
Movie. Pulsed phase electrical resistor. . . . . . . 659
thermographic
system. . . . . . . . . . . . . . 312 Movie. Temperature changes in
Movie. Phase images. . . . . . . . . . 312 chip on printed
Movie. Lockin thermography circuit board. . . . . . . . . . 659
reveals thermal loss at
fatigue crack tips. . . . . . . 326 Movie. Uniformity monitoring
of wafers during
Chapter 14. Infrared and Thermal annealing. . . . . . . . . . . . 659
Testing of Metals . . . . . . . . . . 441

Movie. Friction generates heat
in grinding wheel. . . . . . 470

Movie. Friction generates heat
in drill bit. . . . . . . . . . . . 470

Chapter 15. Aerospace Applications
of Infrared and Thermal
Testing . . . . . . . . . . . . . . . . . . . 489

Movie. Space shuttle lands
at night. . . . . . . . . . . . . . 490

Movie. Leak detected in space
shuttle main engine
nozzle. . . . . . . . . . . . . . . 493

Movie. Water in honeycomb
surface. . . . . . . . . . . . . . 502

xiv Leak Testing

CHAPTER

Introduction to Infrared
and Thermal Testing

Xavier P.V. Maldague, University Laval, Quebec,
Quebec, Canada (Part 3)
Holger H. Strecker!, General Atomics, San Diego,
California (Part 4)
Marvin W. Trimm, Westinghouse Savannah River
Company, Aiken, South Carolina (Parts 1 and 2)

PART 1. Nondestructive Testing1

Nondestructi\'e testing (NDT) has been The idea of future usefulness is relevant
defined as comprising those test methods to the quality control practice of
uSed to examine or inspect a part or sampling. Sampling (that is, less than 100
material or system without impairing its percent testing to draw inferences about
future usefulness. 1 The term is generally the unsampled lots) is nondestructive
applied to nonmedical investigations of testing if the tested sample is returned to
service. If the steel is tested to verify Uw
material integrity. alloy in some bolts that can then be
Strictly speaking, this definition of returned to service, then the test is
nondestructive. In contrast, even if
nondestmctive testing includes spectroscopy used in the chemical testing
noninvasive medical diagnostics. X-rays1 of many fluids is inherently
ultrasound and endoscopes are used by nondestructive, the testing is destructive if
both medical and industrial the samples are poured down the drain
after testing.
nondestructive testing. Medical
nondestructive testing, however, has come Nondestructive testing is not confined
to be treated by a body of learning so to crack detection. Other discontinuities
separate from industrial nondestructive include porosity, wall thinning from
testing that today most physicians do not corrosion and many sorts of disbands.
use the word nondestructive. Nondestructive material characterization
is a growing field concerned with material
Nondestructive testing is used to properties including material
investigate specifically the material identification and microstructural
integrity of the test object. A number of characteristics- such as resin curing, case
other technologies- for instance, radio hardening and stress - that have a direct
astronomy, voltage and amperage influence on the service life of the test
measurement and rheometry (flow object.
measurement)- are nondestructive but
arc not used specifically to evaluate Nondestructive testing has also been
material properties. Radar and sonar are defined by listing or classifying the
classified as nondestructive testing ·when various techniques.~<l This approach
used to inspect dams, for instance, but conveys a sense of nondestructive testing
not when they are used to chart a river that is a practical sense in that it typically
bottom. highlights methods in use by industry.

Nondestructive testing asks "Is there Purposes of
something wrong v\'ith this material?" Nondestructive Testing
Various performance <md proof tests, in
contrast, ask "Does this component Since the 1920s, the art of testing without
work?" This is the reason that it is not destroying the test object has developed
considered nondestructive testing 1vhen from a laboratory curiosity to an
an inspector checks a circuit by running indispensable tool of production. No
electric current through it. Hydrostatic longer is visual testing of materials, parts
pressure testing is another form of proof and complete products the principal
testing, one that may destroy the test means of determining adequate quality.
object. Nondestmctive tests in great variety are in
worldwide use to detect variations in
Another gray area that invites various structure, minute changes in surface
interpretations in defining nondestructive finish, the presence of cracks or other
testing is future usefulness. Some material physical discontinuities, to measure the
investigations involve taking a sample of thickness of materials and coatings and to
the inspected part for testing that is determine other characteristics of
inherently destructive. A noncritical part industrial products. Scientists and
of a pressure vessel may be scraped or engineers of many countries have
shaved to get a sample for electron contributed greatly to nondestructive test
microscopy, for example. Although future development and applications.
usefulness of the vessel is not impaired by
the loss of material, the procedure is The various nondestructive testing
inherently destructive and the shaving methods are covered in detail in the
itself~- in one sense the true lest object-
has been removed from service
permanently.

2 Infrared and Thermal Testing

literature but it is always wise to consider problems. As an example, an aircraft part
objectives before details. How is was built from an alloy whose work
nondestructive testing useful? \Vhy do hardening,.notch r~sistanre rmd f;Jfigue
thousands of industrial concerns buy the life ·were not well known. After relatively
testing equipment, pay the subsequent short periods of service some of these
operating costs of the testing and even aircraft suffered disastrous failures.
reshape manufacturing processes to fit the Sufficient and proper nondestructive tests
needs and findings of nondestructive could have saved many lives.
testing?
As technology improves and as service
Modern nondestructive tests are used requirements increase, machines are
by manufacturers: (1) to ensure product subjected to greater variations and to
integrity and, in turn, reliability; (2) to wider extremes of all kinds of stress,
avoid failures, prevent accidents and save creating an increasing demand for
human life; (3) to make a profit for the stronger or more damage tolerant
user; {4) to ensure customer satisfaction materials.
and maintain the manufacturer's
reputation; (S) to aid in better product Engineering Demands for Sounder
design; (6) to control manufacturing Materials
processes; (7) to lower manufacturing
costs; (8) to maintain uniform quality Another justification for nondestructive
level; and (9) to ensure operational tests is the designer's demand for sounder
readiness. materials. As size and weight decrease and
the factor of safety is lowered, more and
These reasons for widespread and more emphasis is placed on better raw
profitable use of nondestructive testing material control and higher quality of
are sufficient in themselves but parallel materials, manufacturing processes and
developments have contributed to its workmanship.
growth and acceptance.
An interesting fact is that a producer of
Increased Demand on Machines raw material or of a finished product
sometimes does not improve quality or
In the interest of greater speed and performance until that improvement is
reduced cost for materials, the design demanded by the customer. The pressure
engineer is often under pressure to reduce of the customer is transferred to
weight. This can sometimes be done by implementation of improved design or
substituting aluminum alloys, magnesium manufacturing. Nondestructive testing is
alloys or composite materials for steel or frequently called on to deliver this new
iron but such light parts may not be the quality level.
same size or design as those they replace.
The tendency is also to reduce the size. Public Demands for Greater Safety
These pressures on the designer have
subjected parts of all sorts to increased The demands and expectations of the
stress levels. Even such commonplace public for greater safety are appar.ent
objects as sewing machines, sauce pans everywhere. Review the record of the
and luggage are also lighter and more courts in granting higher and higher
heavily loaded than ever before. The stress awards to injured persons. Consider the
to be supported is seldom static. It often outcry for greater automobile safety, as
fluctuates and reverses at low or high evidenced by the required auto safety
frequencies. Frequency of stress reversals belts and the demand for air bags,
increases with the speeds of modern blowout proof tires and antilock braking
machines and thus parts tend to fatigue systems. The publicly supported activities
and fail more rapidly. of the National Safety Council,
Underwriters Laboratories, the
Another cause of increased stress on Occupational Safety and Health
modern products is a reduction in the Administration and the Federal Aviation
safety factor. An engineer designs with Administration in the United States, as
certain known loads in mind. On the well as the work of similar agencies
supposition that materials and abroad, are only a few of the ways in
workmanship are never perfect, a safety which this demand for safety is expressed.
factor of 2, 3, 5 or 10 is applied. However, It has been expressed directly by
because of other considerations, a lower passengers who cancel reserV<ltions
factor is often used that depends on the following a serious aircraft accident. This
importance of lighter ·weight or reduced demand for personal safety has been
cost or risk to consumer. another strong force in the deve-lopment
of nondestructive tests.
New demands on machinery have also
stimulated the development and use of
new materials whose operating
characteristics and performance are not
completely known. These new materials
create greater and potentially dangerous

Introduction to Infrared and Thermal Testing 3

Rising Costs of Failure incorporates all the technology for
detection and measurement of significant
Aside from awards to the injured or to properties1 including disrontinuities, in
estates of the deceased and aside from iterns ranging from research specimens to
costs to the public (because of evacuation finished hardware and products in service.
occasioned by chemical leaks), consider By definition, nondestructive testing
briefly other factors in the rising costs of methods are means for inspecting
mechanical failure. These costs are materials and structures without
increasing for many reasons. Some disruption or impairment of serviceability.
important ones are (1) greater costs of Nondestructive testing makes it possible
materials and labor; (2) greater costs of for internal properties or hidden
complex parts; (3) greater costs because of discontinuities to be revealed or inferred
the complexity of assemblies; (4) greater by appropriate methods.
probability that failure of one part will
cause failure of others because of Nondestructive testing is becoming
overloads; (5) trend to lower factors of increasingly vital in the effective conduct
safety; (6) probability that the failure of of research1 development1 design and
one part will damage other parts of high manufacturing programs. Only with
value; and (7) part failure in an integrated appropriate nondestructive testing
automatic production machine, shutting methods can the benefits of advanced
do·wn an entire high speed production materials science be fully realized. The
line. \-\7hen production was carried out on information required for appreciating the
many separate machines1 the broken one broad scope of nondestructive testing is
could be bypassed until repaired. Today, available in many publications and
one machine is tied into the production reports.
of several others. Loss of such production
is one of the greatest losses resulting from Classification of Methods
part failure.
In a report, tile National "tvfaterials
Applications of Advisory Hoard (NMAB) Ad Hoc
Nondestructive Testing Committee on Nondestructive Evaluation
adopted a system that classified
Nondestructive testing is a branch of the technlques into six major method
materials sciences that is concerned with categories: visual, penetrating radiation,
an aspects of the uniformity, quality and magnetic-electrical, mechanical vibration,
serviceability of materials and structures.. thermal and chemical/electrochemical.3
The science of nondestructive testing A modified version is presented in
Table 1. 1

TABlE 1. Nondestructive testing method categories. Objectives
Categories

Basic Categories

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

finish; surface flaws; through-cracks

Penetrating radiation cracks; density and chemistry variations; elemental distribution; foreign objects; inclusions; microporosity;
misalignment; missing parts; segregation; service degradation; shrinkage; thickness; voids

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

Sonic~ultrasonic crack initiaion and propagation; cracks, voids; damping factor; degree of cure; degree of impregnation; degree of
sintering; delaminations; density; dimensions; elastic moduli; grain size; indusiom;
mechanical degradation; misalignment; porosity; radiation degradation; structure of composites; surface stress;
tensile, shear and compressive strength; disbands; wear

Thermal and infrared anisotropy, bonding; composition; emissivity; heat contours; plating thickness; porosity; reflectivity; stress;
thermal conductivity; thickness; voids; cracks; delaminations; heat treatment; state of cure; moisture; corrosion

Chemical-analytical alloy identification; composition; cracks; elemental analysis and distribution; grain size; inclusions;
macrostructure; porosity; segregation; surface anomalies

Image generation Auxiliary Categories
Signal image analysis
dimensional variations; dynamic performance; anomaly characterization and definition; anomaly
distribution; anomaly propagation; magnetic field configurations
data selection, processing and display; anomaly mapping, correlation and identification; image enhancement;
separation of multiple variables; signature analysis

4 Infrared and Thermal Testing

Each method can be completely holography and shearography, magnetic
characterized in terms of five principal particle and electromagnetic testing.
factors: (1) enert,'Y source or medium used ''Vhen surface or surface/near¥surface
to probe object (such as X-rays, ultrasonic methods are applied during intermediate
waves or thermal radiation); (2) nature of manufacturing processes, they provide
the signals, image and/or signature preliminary assurance that volumetric
resulting from interaction with the object methods performed on the completed
(attenuation of X-rays or reflection of object or component will reveal few
ultrasound, for example); (3) means of rejectable discontinuities. Volumetric
detecting or sensing resultant signals methods include radiography, ultrasonic
(photoemulsion, piezoelectric crystal or testing, acoustic emission testing and less
inductance coil); (4) method of indicating familiar methods such as
and/or recording signals (meter deflection, acoustoultrasonic testing and magnetic
oscilloscope trace or radiograph); and resonance imaging. Through-boundary
(S) basis for interpreting the results (direct techniques described include leak testing,
or indirect indication, qualitative or some infrared thermographic techniques,
quantitative and pertinent dependencies). airborne ultrasonic testing and certain
techniques of acoustic emission testing.
The objective of each method is to Other less easily classified methods are
provide information about the following material identification, vibration analysis
material parameters: and strain gaging.

1. discontinuities and separations (cracks, No one nondestructive testing method
voids, inclusions, delaminations etc.); is all revealing. That is not to say that one
method or technique of a method is
2. structure or malstructure (crystalline rarely adequate for a specific object or
structure, grain size, segregation, component. However, in most cases it
misalignment etc.); takes a series of test methods to do a
complete nondestructive test of an object
3. dimensions and metrology (thickness, or component. For example, if surface
diameter, gap size, discontinuity size cracks must be detected and eliminated
etc.); and the object or component is made of
ferromagnetic material, then magnetic
4. physical and mechanical properties particle testing ·would be the obvious
(reflectivity, conductivity, elastic choice. If that same material is aluminum
modulus, sonic velocity etc.); or titanium, then the choice would be
liquid penetrant or electromagnetic
S. composition and chemical analysis testing. However, for either of these
(alloy identification, impurities, situations, if internal discontinuities were
elemental distributions etc.); to be detected, then ultrasonics or
radiography would be the selection. The
6. stress and dynamic response (residual exact technique in either case would
stress, crack growth, wear, vibration depend on the thickness and nature of
etc.); the material and the types of
discontinuities that must be detected.
7. signature analysis (image content,
frequency-spectrum, field Value of Nondestructive
configuration etc.); and Testing

8. abnormal sources of heat. The contribution of nondestructive
testing to profits has been ackno-wledged
Terms used in this block are further in the medical field and computer and
defined in Table 2 with respect to specific aerospace industries. However, in
objectives and specific attributes to be industries such as heavy metals, though
measured, detected and defined. nondestructive testing may be grudgingly
promoted, its contribution to profits may
The limitations of a method include not he obvious to management.
conditions required by that method: Nondestructive testing is sometimes
conditions to be met for method thought of only as a cost item. One
application (access, physical contact, possible reason is industry downsizing.
preparation etc.) and requirements to '·Vhen a company cuts costs, two
adapt the probe or probe medium to the vulnerable areas are quality and safety.
object examined. Other factors limit the '·Vhen bidding contract work, companies
detection and/or characterization of add profit margin to all cost items,
discontinuities, properties and other including nondestructive testing, so a
attributes and limit interpretation of profit should be made on the
signals and/or images generated. nondestructive testing. However, when

Classification Relative to Test
Object

Nondestructive testing techniques may be
classified according to how they detect
indications relative to the surface of a test
object. Surface methods include liquid
penetrant testing, visual testing, grid and
moire testing. Surface/near¥surface
methods include tap, potential drop,

Introduction to Infrared and Thermal Testing 5

production ls going poorly and it is attitude toward nondestructive testing is
anticipated that a job might Jose money, gradually improving as management
it seems like the first corner thn~ romes to appreciate its value.
production personnel will try to cut is
nondestructive testing. This is Nondestructive testing should be used
accomplished by subtle pressure on as a control mechanism to ensure that
nondestructive testing technicians to manufacturing processes are within design
accept a product that does not quite meet performance requirements. It should
a code or standard requirement. The never be used in an attempt to obtain
quality in a product by using

TABlE 2. Objectives of nondestructive testing methods.

Objectives Attributes Measured or Detected

Discontlnuites and separations

Surface anomalies roughness; scratches; gouges; crazing; pitting; inclusions and imbedded foreign material
Surface connected anomalies
Internal anomalies cracks; porosity; pinholes; laps; seams; folds; inclusions

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

Structure molecular structure; crystalline structure and/or strain; lattice structure; strain; dislocation; vacancy;
Microstructure deformation

Matrix structure grain structure, size, orientation and phase; sinter and porosity; impregnation; filler and/or
reinforcement distribution; anisotropy; heterogeneity; segregation
Small structural anomalies
Gross structural anomalies leaks (lack of seal or through-holes); poor fit; poor contact; loose parts; loose particles; foreign objects

assembly errors; misalignment; poor spacing or ordering; deformation; malformation; missing parts

Dimensions and metrology linear measurement; separation; gap size; discontinuity size, depth, location and orientation
unevenness; non uniformity; eccentricity; shape and contour; size and mass variations
Displacement; position film, coating, layer, plating, wall and sheet thickness; density or thickness variations
Dimensional variations
Thickness; density

Physical and mechanical properties

Electrical properties resistivity; conductiv'ity; dielectric constant and dissipation factor
Magnetic properties polarization; permeability; ferromagnetism; cohesive force
Thermal properties
Mechanical properties conductivity; thermal time constant and thermoelectric potential; diffusivity; effusivity; specific heat
compressive, shear and tensile strength (and moduli); Poisson's ratio; sonic velocity; hardness; temper and
Surface properties
embrittlement
color; reflectivity; refraction index; emissivity

Chemical composition and analysis

Elemental analysis detection; identification, distribution and/or profile
Impurity concentrations contamination; depletion; doping and diffusants
Metallurgical content variation; alloy identification, verification and sorting
Physiochemical state moisture content; degree of cure; ion concentrations and corrosion; reaction products

Stress and dynamic response heat treatment, annealing and cold work effects; residual stress and strain; fatigue damage and life (residual)
wear; spalling; erosion; friction effects
Stress; strain; fatigue corrosion; stress corrosion; phase transformation
Mechanical damage radiation damage and high frequency voltage breakdown
Chemical damage
Other damage crack initiation and propagation; plastic deformation; creep; excessive motion; vibration; damping; timing of
Dynamic performance events; any anomalous behavior

Signature analysis potential; strength; field distribution and pattern
Electromagnetic field isotherms; heat contours; temperatures; heat flow; temperature distribution; heat leaks; hot spots; contrast
Thermal field noise; vibration characteristics; frequency amplitude; harmonic spectrum and/or analysis; sonic and/or
Acoustic signature
ultrasonic emissions
Radioactive signature distribution and diffusion of isotopes and tracers
Signal or image analysis image enhancement and quantization; pattern recognition; densitometry; signal classification, separation

and correlation; discontinuity identification, definition (size and shape) and distribution analysis;
discontinuity mapping and display

6 Infrared and Thermal Testing

nondestructive testing at the end of a FIGURE 2. Section of school building roof:
manufacturing process. This approach will (a) photograph; (b) thermogram showing
ultimately increase production costs. wet insulation as warmer (lighter colored).
'A1hen used properly, nondestructive
testing saves money for the manufacturer. (a)
Rather than costing the manufacturer
money, nondestructive testing should add
profits to the manufacturing process.

Overview of Other (b)
Nondestructive Testing
Methods FIGURE 3. Visual test using borescope to
view interior of cylinder.
To optimize the use of nondestructive
testing, it is necessary first to understand
the principles and applications of all the
methods. This book features infrared and
thermal testing (Figs. 1 and 2) - only one
of the nondestmctive testing methods.
The follm\•ing section briefly describes
several other methods and the
applications associated with them.

Visual Testing

Principles. Visual testing (Fig. 3) is the
observation of a test object; either directly
with the eyes or indirectly using optical
instruments, by an inspector to evaluate
the presence of surface discontinuities and
the object's conformance to specification.
Visual testing should be the first
nondestructive testing method applied to
an item. The test procedure is to clean the
surface, provide adequate illumination
and observe. A prerequisite necessary for
competent visual testing of an item is
kno-wledge of the manufacturing processes
by which it was made, its service history,
potential failure modes and related
industry experience.
Applications. Visual testing provides a
means of detecting and examining a
variety of surface discontinuities. It is also
the most widely used method for
detecting and examining for surface
discontinuities associated with various

FIGURE 1. Thermogram of leakage in sulfur
pipeline, Carter Creek, Wyoming (1995).

Introduction to Infrared and Thermal Testing 7

structural failure mechanisms. Even when Magnetic Particle Testing
other nondestructive tests are performed,
visual tests often provide a useful Principles. Magnetic particle testing is a
supplement. For example, when the eddy method of locating surface and slightly
current testing of process tubing is subsurface discontinuities in
performed, visual testing is often ferromagnetic materials. It depends on the
performed to verify and more closely fact that ·when the material or part under
examine the surface condition. This test is magnetized, discontinuities that lie
verification process can impact the in a direction generally transverse to the
evaluation process associated with other direction of the magnetic field will cause a
nondestructive test methods being used. leakage field to be formed at and above
The following discontinuities may be the surface of the part. The presence of
detected by a simple visual test: surface this leakage field and therefore the
discontinuities, cracks, misalignment, presence of the discontinuity is detected
warping, corrosion, wear and physical by the use of finely divided ferromagnetic
damage. particles applied over the surface, with
some of the particles being gathered and
Liquid Penetrant Testing held to form an outline of the
discontinuity. This generally indicates its
Principles. Liquid penetrant testing (Fig. 4) location, size, shape and extent. Magnetic
reveals discontinuities open to the particles are applied over a surface as dry
surfaces of solid and nonporous materials. particles or as wet particles in a liquid
Indications of a wide spectrum of carrier such as water or oil.
discontinuity sizes can be found regardless
of the configuration of the workpiece and Applications. The principal industrial uses
regardless of discontinuity orientations. of magnetic particle testing are for final,
Liquid penetrants seep into various types receiving and in-process inspection; for
of minute surface openings by capillary quality control; for maintenance and
action. The cavities of interest can be very overhaul in the transportation industries;
small, often invisible to the unaided eye. for plant and machinery maintenance;
The ability of a given liquid to flow over a and for inspection of large components.
surface and enter surface cavities depends Some of the typicaBy detected
principally on the following: cleanliness discontinuities are surface discontinuities,
of the surface, surface tension of the seams, cracks and laps.
liquid, configuration of the cavity, contact
angle of the liquid, ability of the liquid to Radiographic Testing
wet the surface, cleanliness of the cavity
and size of surface opening of the cavity. Principles. Radiographic testing (Fig. 5) is
the general term given to the material test
Applications. The principal industrial uses method based on the differential
of liquid penetrant testing are final absorption of penetrating radiation -
inspection, receiving inspection,
in-process inspection and quality control, FIGURE 5. Representative setup for radiographic test.
maintenance and overhaul in the
transportation industries, in plant and Radiation source ---------4o- •
machinery maintenance and in inspection
of large components. The following are ~\
some of the typically detected
discontinuities: surface discontinuities, /~I \
seams, cracks, laps, porosity and leak
paths. /Ill \

FIGURE 4. Liquid penetrant indication of I JI I \
cracking.
II I I
II I
II
II
I II

I II I

I II I
II
Void I

/ /

Film Radiation source

8 Infrared and Thermal Testing

either electromagnetic radiation of very Eddy Current Testing
short wavelength or particulate radiation
(X-rays, gamma rays and neutron rays)- Principles. Based on electromagnetic
by the part or object being inspected. induction1 eddy current testing (Hg. 6) is
Because of differences in density and used to identify or differentiate among a
variations in thickness of the part or wide variety of physical, structural and
differences in absorption characteristics metallurgical conditions in electrically
caused by variation in composition, conductive ferromagnetic and
different portions of an object absorb nonferromagnetic metals and metal parts.
different amounts of penetrating The method is based on indirect
radiation. These variations in the measurement and on correlation between
absorption of the penetrating radiation the instrument reading and the structural
can be monitored by detecting the characteristics and serviceability of the
unabsorbed radiation that passes through parts being examined.
the object. This monitoring may be in
different forms. The traditional form is VVith a basic system, the part is placed
through radiation sensitive film. X-ray within or adjacent to an electric coil in
computed tomography is a radiographic which high frequency alternating current
technique. (AC) is flowing. This excitation current
establishes an electromagnetic field
Applications. The principal industrial uses around the coil. This primary field causes
of radiographic testing involve testing of eddy current to flow in the part because
castings and weldments1 particularly of electromagnetic induction. Inversely,
where there is a critical need to ensure the eddy currents affected by all
freedom from internal discontinuities. For characteristics (conductivity, permeability
example, radiography is often specified
for thick wall castings and weldments for 1
steam power equipment (boiler and
turbine components and assemblies). thickness, discontinuities and geometry)
Radiography can also be used on forgings of the part create a secondary magnetic
and mechanical assemblies1 although with field that opposes the primary field. The
mechanical assemblies radiography is results of this interaction affect the coil
usually limited to testing for conditions voltage and can be displayed in a variety
and proper placement of components. of methods.
Typically detected discontinuities and
conditions include inclusions, lack of Eddy currents flow in closed loops in
fusion, cracks, corrosion, porosity1 leak the part or air. Their two most important
paths, missing, incomplete components,_ characteristics, amplitude and phase, are
liquid penetration and debris. influenced by the arrangement and
characteristics of the instrumentation
FIGURE 6. Representative setup for eddy current test. and test piece. For example1 during the
test of a tube the eddy currents flow
Coil in eddy current probe Direction of symmetrically in the tube when
prim<~ry current discontinuities are not present. Hmvever,
~ when a crack is present, then the eddy
current flow is impeded and changed in
Conducting specimen Direction of eddy direction, causing significant changes in
currents the associated electromagnetic field.

Eddy current strength Applications. An important industrial use
decre<~ses with of eddy current testing is on heat
incre<~sing depth exchanger tubing. 1:or example1 eddy
current testing is often specified for thin
wall tubing in pressurized water reactors1
steam generators, turbine condensers and
air conditioning heat exchangers. Eddy
current testing is also used often in
aircraft maintenance. The following are
some of the typical material
characteristics that can be evaluated by
eddy current testing: cracks, inclusions,
dents and holes; grain size and hardness;
coating and material thickness;
dimensions and geometry; composition,
conductivity or permeability; and alloy
composition.

Ultrasonic Testing

Principles. Ultrasonic testing (Fig. 7) is a
nondestructive method in ·which beams of
high frequency sound waves are
introduced into materials for the
detection of surface and subsurface

Introduction to Infrared and Thermal Testing 9

discontinuities in the material. The sound Leaking fluids (liquid or gas) can
waves travel through the material with propagate from inside a component or
some attendant Joss of energy assembly to the outside, or vice versa, as a
(attenuation) and are reflected at result of a pressure differential between
interfaces. The reflected beam is displayed the two regions or as a result of
(or reduces the display of transmitted permeation through a barrier. The
sound) and is then analyzed to define the importance of leak testing depends on the
presence and locations of discontinuities size of the leak and on the medium being
or discontinuities. leaked. Leak testing encompasses
procedures that fall into these basic
Applications. Ultrasonic testing of metals functions: leak location, leakage
is widely used, principally for the measurement and leakage monitoring.
detection of discontinuities. This method
can be used to detect internal Applications. Like other forms of
discontinuities in most engineering nondestructive testing, leak testing has a
metals and alloys. Bonds produced by great impact on the safety and
welding, brazing soldering and adhesive performance of a product. Reliable leak
bonding can also be ultrasonically testing decreases costs by reducing
examined. In line techniques have been number of reworked products, warranty
developed for monitoring and classifying repairs and liability claims. The most
materials as acceptable, salvageable or common reasons for performing a leak
scrap and for process control. Other test are to pre\'ent the loss of costly
applications include piping and pressure materials or energy; to prevent
vessels, nuclear systems, motor vehicles, contamination of the environment; to
machinery, structures, railroad rolling ensure component or system reliability;
stock and bridges and thickness and to prevent the potential for an
measurement. explosion or fire.

Leak Testing Acoustic Emission Testing

Principles. Leak testing is concerned with Principles. Acoustic emissions are stress
the flow of liquids or gases from waves produced by sudden movement in
pressurized or into evacuated components stressed materials. The classic source of
or systems intended to hold fluids. The acoustic emission is discontinuity related
principles of leak testing involve the deformation processes such as crack
physics of fluid (liquids or gases) flowing grm,vth and plastic deformation. Sudden
through a barrier where a pressure movement at the source produces a stress
differential or capillary action exists. \Vave that radiates out into the structure

FIGURE 7. Representative setups for ultrasonic testing: (a) longitudinal wave technique; (b) shear wave
technique.

(a) (b)

-~" @ Crack

"''<®"'· Crack -~·

;,·~;.;

@

~Back surface Entry surface
Crack

/ ~ ,..

Crack Skip distance

10 Infrared and Thermal Testing

and excites a sensitive piezoelectric sensor. FIGURE 8. Acoustic emission testing setup in which eight
As the stress in the material is raised, sensors permit computer to calculate location of crack
emissions are generated. The signals from propagation.
one or more sensors arc amplified and
measured to produce data for display and offtl~
interpretation. 0

The source of acoustic emission energy I Computer
is the elastic stress field in the material.
\".'ithout stress, there is no emission. Test
Therefore, an acoustic emission test object
(Fig. 8) is usually carried out during a
controlled loading of the structure. This
can be a proof load before service; a
controlled variation of load ·while the
structure is in service; a fatigue, pressure
or creep test; or a complex loading
program. Often, a structure is going to be
loaded hydrostatically anyway during
service and acoustic emission testing is
used because it gives valuable additional
information about the expected
performance of the structure under load.
Other times, acoustic emission testing is
selected for reasons of economy or safety
and a special loading procedure is
arranged to meet the needs of the acoustic
emission test.

Applications. Acoustic emission is a
natural phenomenon occurring in the
widest range of materials, structures and
processes. The largest scale events
observed with acoustic emission testing
are seismic and the smallest are small
dislocations in stressed metals.

The equipment used is highly sensitive
to any kind of movement in its operating
frequency (typically 20 to 1200 kHz). The
equipment can detect not only crack
growth and material deformation but also
such process as solidification, friction,
impact, fluw and phase transformations.
Therefore, acoustic emission testing
techniques are also used for in-process
weld monitoring, detecting tool touch
and tool wear during automatic
machining, detecting wear and loss of
lubrication in rotating equipment,
detecting loose parts and loose particles,
detecting and monitoring leaks,
cavitation, flow, preservice proof testing,
in-service weld monitoring and leak
testing.

Other Methods

There arc many other methods of
nondestructive testing, including optical
methods such as holography,
shearography and moire imaging; material
identification methods such as chemical
spot testing, spark testing and
spectroscopy; strain gaging; and acoustic
methods such as vibration analysis and
tapping.

Introduction to Infrared and Thermal Testing 11

PART 2. Management of Infrared and Therrrnal
Testing

Temperature is frequently considered the the condition should be well documented
key to successful plant maintenance and and trended for future evaluation.
is one of the most measured quantities in
industrial process control. Temperature On the other side of the coin and one
and thermal behavior of plant machinery, frequently overlooked application of
electrical equipment and materials in infrared thermography is identifying open
process are the factors most critical in the circuits. For instance, a common problem
maintenance of operations as well as the with a fused circuit is fuse failure. \Vhen a
manufacturing process. Infrared sensors FIGURE 9. Infrared thermography of
have become less expensive and more emergency diesel generator automatic
reliable. For this reason noncontact transfer switches: (a) hot spots are
measurement using infrared sensors has highlighted in two sections of switching;
become increasingly desirable. Now, with (b) enclosed components can be viewed.
the ever developing computer hardware (a)
and software, computer aided predictive
maintenance and full image thermal (b)
control of products and process are being

made possible.
Implementing a comprehensive

program can reduce costly equipment
outages. Infrared thermography, a
fundamental component of such
programs, uses nonintrusive techniques to
monitor the operating condition of
equipment and components.

One of the primary uses of infrared
thermography has been in the electrical
area. (See Fig. 9.) 'A'hen the resistance is
high, the power dissipated will be high for
a given current intensity. This creates the
lzot spots that are seen through the
infrared imagers. Typical problems in this
category include loose and/or corroded
connections, undersized electrical
conductors and open individual strands of
a multiple stranded conductor. A special
case of this category is phase imbalance.
The causes for a phase imbalance are
numerous but all involve the situation
where the current in one phase circuit is
significantly different from that of the
other phase(s). The difference in the
higher current phase will he seen because
of the elevated temperature. The
individual phase currents should he
measured to verify this.

Hot $pots may appear not from the
primary current but from the induced
currents. This is often the case near the
main electrical generator. Hot spots can
appear in unlikely places such as the
supporting structure of the generator. Not
all hot spots are a problem, however. In
the case of the steel structure, the hot
spots may be where the electrical fields
from the generator coincide. Hot spots are
also common on motors. In both cases

12 Infrared and Thermal Testing

fuse fails a portion, if not all, of the circuit 2. \•Viii the contract be for time ami
may appear to be cooler than other
circuits or components that are energized. materials or have a wecific scope o(

Infrared applications that do not fall work? ·
into the electrical category are usually
described as mechanical. The mechanical 3. If a time and materials contract is
area involves four major subsets:
(a) friction heating; (b) valve leakage and awarded1 who wil1 monitor the time
valve blockagei (c) insulation applications and materials charged?
and (d) building applications.
4.1f a scope a( work is required, who is
Rotating or moving equipment may
experience friction because of loss of technically qualified to develop and
lubrication or other factors. \.Yhen friction
increases, component temperature rises. approve it?
Pump and motor bearings are the first
target for the infrared survey. If a bearing S. \<\'hat products or documents (test
or coupling is worn or inadequately
lubricated, friction will increase. A reports, trending, recommendations,
misaligned shaft on a pump or motor can
result in unequal loading that in turn root cause analysis etc.) will be
increases friction. The elevated
temperature in the bearing or coupling provided once the inspections are
can be detected using infrared techniques.
completed?
Management of Infrared
and Thermal Testing 6. \.Yho will evaluate and accept the
Programs
product (test reports, trending,
Management of an infrared and thermal
testing program 'i\'ill require consideration recommendations, root cause analysis
of many items before a program can
produce the desired results. Five basic etc.) within your company?
questions must be answered before a true
direction can be charted. They are as 7. Do the service company workers
follm\'S.
possess qualifications and
1. Are regulatory requirements in place
that mandate program characteristics? certifications required by contract and

2. \·Vhat is the magnitude of the program by applicable regulations?
that will provide desired results?
8. Do the service company workers
3. \.Yhat is the performance date for a
program to be fully implemented? require site specific training (confined

4. Is there a cost benefit of infrared and space entry, electrical safety, hazardous
thermal testing?
materials etc.) or clearance to enter
S. \.Yhat are the available resources in
personnel and money? and work in the facility?

Once these questions are answered, then a 9. If quantitative tests are performed1 do
recommendation can be made to program requirements mall(J<tte
determine the best path forward. Three
primary paths are (a) service companies, equipment calibration?
(b) consultants and (c) in-house programs.
10. Does the service company retain any
Though these are primary paths, some
programs may on a routine or on liability for test results?
as-needed bases require support personnel
from a combination of two or more of Consultants
these sources. Before a final decision is
made, advantages and disadvantages of 1. \·VHI the contract be for time and
each path must be considered. Therefore, materials or have a specific scope of
the following are details that must be work?
considered.
2. If a scope o(work is required, who is
Service Companies technically qualified to develop and
approve it?
1. \.Yho will identify the components
within the facility to be examined'? 3. \".1ho will identify the required
qualifications of the consultant?

4. Is the purpose of the consultant to
develop or update a program or is it to
oversee and evaluate the performance
of an existing program?

5 \".'ill the consultant have oversight
responsibility for tests performed?

6. \·Vhat products (trending,
recommendations, root cause analysis
etc.) are provided once the tests are
completed?

7. \".1ho will evaluate the consultant's
performance (test reports, trending,
recommendations, root cause analysis
etc.) within your company?

8. Does the consultant possess
qualifications and certifications
required by contract and by applicable
regulations?

9. Does the consultant require site
specific training (confined space entry,
electrical safety, hazardous materials
etc.) or clearance to enter and work in
the facility?

Introduction to Infrared and Thermal Testing 13

10. Does the consultant retain any 4. Definitions are needed for terms and
liability for test results? abbreviations that are not common
!mowledge to people who will read the
In-House Programs procedure.

1. VVho will determine the scope S. Statements about personnel requirements
(electrical, mechanical, special address specific requirements to
applications) of the program? perform tasks in accordance with the
procedure - issues such as personnel
2. What are the regulatory requirements qualification, certification, access
associated with program development clearance etc.
and implementation?
6. Equipment characteristics, calibration
3. \'\1ho will develop a cost benefit requirements and model numbers. ~f
analysis for the program? qualified equipment must be spenfted.

4. How much time and resources are 7. The test procedure provides a sequential
available to establish the program? process to be used to conduct
inspection activities.
S. \•Vhat are the qualification
requirements (education, training, 8. Acceptance criteria establish component
experience etc.) for personnel? characteristics that will identify the
items suitable for service.
S. Do program personnel require
additional trainlng (electrical safety, 9. Reports (records) provide the means to
confined space entry, etc) and/or document specific test techniques,
qualifications? equipment used, personnel performing
activity, date performed and test
6. Are subject matter experts required to results.
provide technical guidance during
personnel development? 10. Attachments may Include (if required)
items such as report forms, instrument
7. Are procedures required to perform calibration forms, qualified equipment
work in the facility? matrix, schedules etc.

8. If procedures are required, who will Once the procedure is completed,
develop, review and approve them? typically an expert in the subject matter
performs a technical evaluation. If tl~e
9. \'\'ho ·will determine the technical procedure is deemed adequate (meet1~g
specifications for test equipment? identified requirements)1 the expert wJII
approve it for use. Some codes and
Test Procedures for standards also require the procedure to be
Infrared and Thermal qualified- that is, demonstrated to the
Testing satisfaction of a representative of a
regulatory body or jurisdictional
The conduct of facility operations authority.
(in-house or contracted) should be
performed in accordance ·with specific Test Specifications for
instructions from an expert. This is Infrared and Thermal
typically accomplished using \Vritt~n Testing4
instructions in the form of a techmcal
procedure. In many cases codes and A thermographic specification must
specifications will require the use of _a anticipate a number of issues that arise
technical procedure to perform requued during testing.
tests.
Test Condition Requirements
The procedure process can take many
forms, including general instructions that I. The heat stimulation requirements
address only major aspects of test (energy and duration) to detect the
techniques. Or a procedure may be .. target discontinuities must be
written as a step-by-step process rcqumng determined.
a supervisor's initial or signature after
each step. The following is a typical 2. The required heating rate depends on
format for an industrial procedure. the thermal and surface properties of
the subject, on the heat transfer
1. The purpose identifies the intent of the process and efficiency and on
procedure. equipment characteristics such as
speed and sensitivity.
2. The scope establishes the latitude of
items, tests and techniques covered 3. The inspector needs to know whether
and not covered by the procedure. a strippable paint or coating is needed
because of low emis:-.ivity of the test
3. References are specific documents from surface. \.Yill the customer allow a
which criteria are extracted or coating?
documents satisfied by
implementation of the procedure.

14 Infrared and Thermal Testing

4. The profile of time versus temperature Standards and·
required to reveal the target Specifications for Infrared
discontinuities must be determined. and Thermal Testing

Selection of Heat Source Standards have undergone a process of
peer review in industry and can be
1. Issues include portability, accessibility, invoked with the force of law by contract
cost, availability, pmver requirements, or by government regulation. In contrast,
safety and heating requirements. a specification represents an employer's
instructions to employees and is specific
2. If the optimum heat source is neither to a contract or work place. Specifications
practical nor available, determine an may form the basis of standards through a
alternative. review process. Standards and
specifications exist in three basic areas:
3. Does the application require testing equipment, processes and personnel.
from one side or from two?
1. Standards for equipment and materials
Selection of Detector include electronic and optical
equipment. Standardized reference
Technical specifications for the detector objects such as blackbodies would also
include noise equivalent temperature fit in this category.
differential, scan rate, field of view and
standoff. Specifications must be made for 2. The American Society for Testing and
the imaging system (if one is used) and Materials and other organizations
for detection algorithms (if the detection publish standards for test techniques.
process is automated). Other standards are for quality
assurance procedures and are not
Mechanical Considerations specific to a test Inethod or even to
inspection in general.
1. The best positions for recording
device, monitor, electrical connections 3. Qualification and certification of test
and personnel need to be determined. personnel are discussed below, with
specific reference to recommendations
2. Fixturing may be needed to support ofASNT Recommended Practice
the heat source, camera or other No. SN"l'TC-JA. 5
equipment.
Table 3 lists some of the standards used in
3. Camera position may be determined infrared and thermal testing.
by distance, fixturing, lens choice and
the spatial or thermal resolution Personnel Qualification
required to detect the target and Certification
discontinuities.
One of the most critical aspects of the test
4. Camera orientation is sometimes an process is the qualification of inspection
issue. For example, infrared cameras personnel. Nondestructive Testing is
cooled by liquid nitrogen have limited sometimes referred to as a special process.
inclination, to avoid spillage, so a The term simply means that it is very
mirror is used to achieve an inclined difficult to determine the adequacy of an
viewing path. inspection by merely observing the
process or the documentation generated
Interpretation at its conclusion. The quality of the test is
largely dependent on the skills and
Interpretation may be complex because of knowledge of the inspector.
the presence of unknown materials
(inserts, repairs) or time dependent The American Society for
contrast reversal because of thermal Nondestructive Testing (ASNT) has been a
capacitance (mass) or other thermal world leader in the qualification and
property interactions. Discontinuities may certification of nondestructive testing
be detected primarily through pattern personnel for many years. By 1999, the
recognition or image interpretation by an American Society for Nondestructive
experienced operator. Beware of the Testing had instituted three major
possibility of false or missed discontinuity programs in place for the qualification
findings caused by reflections and and certification of nondestructive testing
emissivity variations (spatial or because of personnel.
viewing angle); by surface curvature,
viewing angle or field of view; or by
environmental interference with the heat
pulse from wind, sunlight, moisture or
personnel.

Introduction to Infrared and Thermal Testing 15

TABLE 3, Standards and practi~es for infrared and thermal testing.

Prefix Issuing Organization Representative Standards
and Related Documents

ASME American Society of Mechanical Engineers PTC 19-1, Performance Test Codes, Supplement on Instruction and Apparatus:
ASNT American Society for Nondestructive Testing Part 1, Measurement Uncertainty (1985)
ASTM American Society for Testing and Materials
ASNT Recommended Practice No. SNT-TC.1A
BSI British Standards Institute
CGSB Canadian General Standards Board C 1060, Standard practice for Thermographic lmpeclion of insulation fnstal!atiom
ISO International Organization for Standardization in Envelope Cavities of Frame Buildings (1990)
International Commission on Illumination
CIE C 1153, Standard Practice forLocation of Wet lmulation in Roofing Systems
International Electrical Testing Association Using Infrared Imaging (1997)
NETA Norme Fran~aise
Nf D 4788-88, Test Method for Detecting Delamioations in Bridge Decks Using
National Fire Protection Association Infrared Thermography (1997)
NFPA Occupational Safety and Health Administration
OSHA japanese Industrial Standards E 344, Terminology Relating to Thermometry and Hydrometry (1996)
JIS British Defense Standards
MOD UK Standardization Committee of Sweden E 1213, Standard Test Metlwd for Minimum Resolvable Temperawre Difference
SIS Technical Association of the Pulp and for Thermo/Imaging Systems (1997)
TAP PI
Paper lndusty E 1256, Standard Test Methods for Radiation Thermometers (Single
Waveband Type) (1995)

E 1311-89, Standard Test Method for Minimum Detectable Temperature
Difference for Thermal Imaging Systems (1999)

E 1316, Standard Terminology for Nondestructive Examinations, S('clion J, Terms

E 1543, Test Method for Noise Equivalent Temperature Difference of T11ermal
Imaging Systems (1994)

E 1862, Test Methods for Measuring and Compensating for Reflected

Temperature Using Infrared Imaging Radiometers

E 1897, Test Methods for Measuring and Compemating for Tronsmiltance of an

Attenuating Medium Using Infrared Imaging Radiometers

E 1933, Test Method far Measuring and Compensating for Emissivity Using
Infrared Imaging Radiometers (1999)

E 1934, Standard Guide for Examining Electrical and Mechaniw/ Equipment with
Infrared Thermography (1999)

BS 1041, Temperature Measurement: Part 5, Guide to Selection and Use of
Radiation Pyrometers (1989). Amendment 8238 (1994)

149-GP-2MP, Manual for Thermographic Analysis of Building Enclosures (1986)

6781, Thermo/Insulation, Qualitative Detection of Thermo/Irregularities in

Building Envelopes, Infrared Method

9712, Nondestructive Testing- Qualification and Certification of Personnel

53, Met/Jods of Characterizing the Performance of Radiometers and Photometers
(1982)

65, Electrically Calibrated Thermal Detectors of Optical Radiation (Absolute
Radiometers) (E) (1985)

114, CIE Collection in Photometry and Radiometry (1994)

MTS-199X, Maintenance Testing of Electrical Systems

ATS-1999, Acceptance Testing of Electrical Systems

aA 09-400, Essais non Destructifs- Thermographie lnfrarouge. -- Vocabulaire
Relatif Ia Caracterisation de I'Appareilfage (December 1991)

A 04-420, Essois non Destructifs- Thermographie lnfrarauge- Caracterisation
de I'Appareil/age (April 1993)

aA 09-400, Essais non Destwctifs- Thermogropllie lnfrarouge- \locobu!aire
Relatif Ia Caracterisation de I'Apparei!lage (December 1991)
A 09-400, Norme Fran~aise de Thermographie lnfrarouge

X 07-001, Vocabulaire international des termes fondamenlaux et gim?roux de

metrologie

X 10-023-82, Isolation Thermique- Methode !nfrarouge pour Ia Detection

Qualitative d'lrrigularitis Thermiques dans Ia Structure Externe des BQtiments

(December 1982)

70-B, Recommended Practice for Electrical fquipment Maintenance

70-E, Standard for Electrical Safety Requirements for Employee Workplaces

29 CFR 1910, Occupational Safety and Health Standards [Code of Federal
Regulations: Title 29, Labor]

T 1141, Medico/Infrared Tl7ermographs (1986)

DSTAN 59·61, Semiconductor Device, Photocelf: Issue 1 (February 1973)

DSTAN 59-99, Part 01, Coolers, Infrared Detector, joule-Thompson: Part 1,
General Requirements: Issue 2 (August 1982). Amendment 1 (obsolesc.ent
December 1996)

SS02421 0, Thermo/Insulation: Thermograph}' of Buildings (1986)

TIS 0810-01 (formerly TIS 018·6}, On-Line Moisture Verification/Cofibrotion
of Infrared Moisture Sensors (1994)

16 Infrared and Thermal Testing

1. ASNT Recommended Practice No. This document provides guidelines for the
SNT-TC-JA provides guidelines for establishment of a qualification and
certification program.
. ,personnel qualification and
certification in nondestructive testing. Written Practice. The employer shall
establish a written practice for the control
This Recommended Practice identifies and administration of nondestructive
the specific attributes that should be testing personnel training, examination
and certification. The employer's written
considered when qualifying practice should describe the responsibility
nondestructive testing personnel. It of each level of certification for
determining the acceptability of materials
requires the employer to develop and or components in accordance with
implement a written practice applicable codes, standards, specifications
(procedure) that details the specific and procedures.

process and any limitation in the Education, Training, Experience
qualification and certification of Requirements for initial Qualification.
nondestructive testing personnel.5 Candidates for certification in
2. ANSI/ASNT CP-189, Standard (or nondestructive testing should have
Qualification and Certification of sufficient education, training and
Nondestructil'e Testing Personnel experience to ensure qualification in
resembles SNT-TC-lA but also those nondestructive testing methods for
which they are being considered for
establishes specific attributes for the certification. Table 4 lists the
recommended training and experience
qualification and certification of factors to be considered by the employer
nondestructive testing personnel. in establishing written practices for initial
However, CP-189 is a consensus qualification of Level I and II individuals.

standard as defined by the American Training Programs. Personnel being
National Standards Institute (ANSI). It considered for initial certification should
is recognized as the American complete sufficient organized training to
Standard for Nondestructive Testing. It become thoroughly familiar with the
is not considered a recommended principles and practices of the specified
practice; it is a national standard.6 nondestructive testing method related to
3. 'l'he ASNT Central Certi{icatim1 Progra1n the level of certification desired and
(ACCP), unlike SNT-TC-lA and applicable to the processes to be used and
the products to be tested.
CP-189, is a third party certification
process. Currently it has identified Examinations. For Level I and II
personnel, a composite grade should be
qualification and certification determined by a simple averaging of the
results of the general, specific and
attributes for Level II and Level m practical examinations described belm'-.'.
Examinations administered for
nondestructive testing personnel. The qualification should result in a passing
American Society for Nondestructive composite grade of at least 80 percent,
with no individual examination having a
Testing certifies that the individual has passing grade less than 70 percent. The
the skills and knowledge for many examination for near vision acuity should

nondestructive testing method
applications. It does not remove the

responsibility for the final
determination of personnel

qualifications from the employer. The
employer evaluates an individual's

skills and knowledge for application of

company procedures using designated
techniques and identified equipment
for specific tests. 7

Sample Specifications from TABLE 4. Recommended training and experience for
SNT-TC-1A
infrared and thermal testing personnel according to
'10 give an overview of the contents of ASNT Recommended Practice No. SNT-TC-1A.5
these documents, the following items are
specified in the 1996 edition of High school graduate Level I Level II
SNT-TC-lA. (For the purpose of this Two years of collegeu
discussion the quantities cited are those Work experiencec 40 h 40 h
that address infrared and thermal te~ting 36 h 35 h
only.) 18 months
3 months
Scope. This recommended practice has
been prepared to establish guidelines for a. Or equivalent.
the qualification and certification of
nondestructive testing personnel whose b. Completion with a passing grade of at least two years of engineering or
specific jobs require appropriate
knowledge of the technical principles science study in a university, college or technical school. -
underlying the nondestructive test they
perform, witness, monitor or evaluate. c. Work lime experience per level. Note: for level !I certification, the

experience shall consist of time as level I or equivalent. If a person is
being qualified directly to Levell! with no time at level I, the required
experience shall consist of the sum of the times required for Levell and
level!! and the required tr<>ining shall consist of the sum of the hours
required for Levell and level !1.

Introduction to Infrared and Thermal Testing 17

ensure natural or corrected near distance The International Organization for
acuity in at least one eye such that Standardization is a worldwide federation
applicant can read a minimum of jaeger of national standards bodies (ISO member
size 2 or equivalent type and size letter at bodies). The work of preparing
a distance of not less than 305 mm international standards is normally carried
(12 in.) on a standard jaeger test chart. out through technical committees of the
This test should be administered annually. International Organization for
Standardization. Each member body
Written Examination for NDT Levels I interested in a subject for which a
and II. The minimum number of technical committee has been established
questions that should be administered in has the right to be represented on that
the written examination for infrared and committee. International organizations,
thermal test personnel is as follows: 40 governmental and nongovernmental, in
questions in the general examination and liaison with tlle International
20 questions in the specific examination. Organization for Standardization, also
The number of questions is the same for take part in the work. The International
Level I and Level II. Organization for Standardization
collaborates closely \Vith International
Practical Examination for NDT Levell Electrotechnical Commission (IEC) on all
and II. The candidate should demonstrate matters of electrotechnical
familiarity with the ability to operate the standardization.
necessary nondestructive test equipment,
record and analyze the resultant Technical Committee ISO/TC 135,
information to the degree required. At N01z-Destruclive Testing Subcommittee
least one selected specimen should be SC 7, Personnel Qualification, prepared
tested and the results of the international standard ISO 9712,
nondestructive test analyzed by the Nondestructive Testing- Qualification and
candidate. Certification o(Personnel.Bln its statement
of scope, ISO 9712 states that it
Certification. Certification of all levels of 11establishes a system for the qualification
nondestructive testing personnel is the and certification, by a certification body,
responsibility of the employer. of personnel to perform industrial
Certification of nondestructive testing nondestructive testing (NDT) using any of
personnel shall be based on the following methods: {a) eddy current
demonstration of satisfactory qualification testing; (b) liquid penetrant testing;
in accordance with sections on education, {c) magnetic particle testing;
training, experience and examinations, as (d) radiographic testing; (e) ultrasonic
modified by the employer's written testing11 and that the 11system described in
practice. Personnel certification records this International Standard may also
shall be maintained on file by the apply to visual testing (VT), leak testing
employer. (LT), neutron radiography (NR), acoustic
emission (AE) and other nondestructive
Recertification, All levels of test methods where independent
nondestructive testing personnel shall be certification programs exist. The
recertified periodically in accordance ·with applicability of ISO 9712 to infrared
the following: evidence of continuing thermography therefore depends on
satisfactory performancei reexamination activity of the national certifying body.
in those portions of examinations in
Section 8 deemed necessary by the The American Society for
employer's NDT Level Ill. Nondestructive Testing as of 1999 has the
ASNT NOT Level III Certification Program
Recommended maximum that includes infrared thermography. If
recertification intervals are three years for industry requirements evolve and leaders
Levell and Level 11 and five years for of the thermal and infrared testing
Level III. industry evolve or request a third
party/ISO compliant certification, the
These recommendations from American Society for Nondestructive
SNT-TC-lA are cited only to provide a Testing is prepared to develop and
flavor of the specific items that must be implement this certification within the
considered in the development of an ASNT Central Certification Program
in-house nondestructive testing program. (ACCP).
However, if an outside agency is
contracted for infrared and thermal test Safety in Thermal and
services, then the contractor must have a Infrared Testing
qu(llification and certification program to
satisfy most codes and standards. To manage a thermal or infrared test
program, as with any test program, the
Central Certification first obligation is to ensure safe working

Another standard that may be a source for
compliance is contained in the
requirements of the International
Organization for Standardization (JSO).

18 Infrared and Thermal Testing

conditions. The following arc components Most facilities in the United States aTe
of a safety program that may be required required by law to follow the
or at least deserve serious consideration. requirements in the applicable standard.
Two Occupational Safety and Health
1. Identify the safety and operational Standards in the United States that should
rules/codes applicable to the areas, be reviewed are Occupational Safety and
equipment and/or processes being Health Standards for general industry9 and
examined before work is to begin. the Occupational Safety and Health
Standards {in tile Constmction Industry. 10
2. Provide proper safety equipment
(safety glasses1 hard hat, safety Personnel safety is always the first
harnesses, steel toed shoes, hearing consideration for every job.
protection etc.).
Ensuring Reliability of Test
3. If needed1 obtain a qualified assistant Results
who knows the plant's electrical,
mechanical or process systems. \Vhen a test is performed, there are four
possible outcomes: (l) a discontinuity can
4. Before the test, perform a thorough be found when a discontinuity is present;
visual survey to determine all the (2) a discontinuity can be missed even
hazards and identify necessary when a discontinuity is present; (3) a
safeguards to protect test personnel discontinuity can be found when none is
and equipment. presenti and (4) no discontinuity is found
when none is present. A reliable testing
5. Notify operative personnel to identify process and a reliable inspector should
the location and specific equipment find all discontinuities of concern with no
that will be examined. In addition, a discontinuities missed (no errors as in
determination must be made if signs case 21 above) and no false callouts
or locks restrict access by personnel. (case 3, above).
Be aware of equipment that may be
operated remotely or may started by To achieve this goal, the probability of
time delay. finding a discontinuity must be high and
the inspector must be both proficient in
6. Be aware of any potentially explosive the testing process and motivated to
atmospheres. Determine whether it is perform a maximum efficiency. A reckless
safe to take your equipment into the inspector may accept parts that contain
area. discontinuities, with the resultant
consequences of possible inservice part
7. Do not enter any roped off or no entry failure. A conservative inspector may
areas without permission and reject parts that co'ntain discOntinuities
approval. but the inspector also may reject parts
that do not contain discontinuities, with
8. Determine if electrical safety courses the resultant consequences of unnecessary
are required for the performance of scrap and repair. Neither inspector is
electrical surveys. doing a good job.

9. When working on or around electrical Summary
equipment, remove pens, watches,
rings or objects in your pockets that As noted in this discussion, many factors
may touch (or fall into) energized must be considered before a program of
equipment. thermal and infrared testing can begin at
a facility. 'Ib manage a nondestructive
10. Know interplant communication and testing program many options must be
evacuation systems. considered. The final decision for a path
fonvard must be based on requirement
11. Never let unqualified personnel documents (codes, standards or
operate equipment. specifications) and what is best for your
company. If you Jack the expertise for this
12. Keep a safe distance between you and critical decision, the industry has many
any energized equipment. In the talented individuals that are willing to
United States, these distances can be assist. The American Society for
found in documents from the Nondestructive Testing is a place to begin
Occupational Safety and Health the decision making process.
Administration, the National Fire
Prevention Association (National
Electric Code), the Institute of Electrical
and Electronics Engineers (National
Electrical Sa(et)' Code) and other
organizations.

B. Be aware of the personnel
responsibilities before entering a
confined space. All such areas must be
tested satisfactorily for gas and oxygen
levels before entry and periodically
thereafter. If odors are noticed, or
unusual sensations such as earaches,
dizziness or difficulty in breathing are
experienced, leave the area
immediately.

Introduction to Infrared and Thermal Testing 19

PART 3. History of Infrared and Thermal
Testing11

Scientific Discoveries Stefads law gives the peak wavelength
},ma"- (in micrometer) of the thermal
William Herschel radiation from a graybody at temperature
T (in units kelvin). For example observing
Infrared technology started in 1800 with a red hot steel plate having a temperature
William Herschel (1738-1822) and a
famous experiment that revealed the of about 1000 K (700 oc = -1300 °1°) the
existence of the infrared radiation
spectrum. The royal astronomer for King peak wavelength would be about 3 pm. In
George Ill of England, Herschel (Fig. I 0) this case Herschel 1S thermometer would
accidentally discovered Uranus on indicate a peak temperature far from the
13 March 1793. This accident led to his red light band (red light wavelength is
discovery of infrared rays. At first he around 0.7 p.m). In fact Herschel 's
wanted to protect his eyes when finding can be summarized in three
observing the sun. For his experiment he directions:
used a prism that separated the various
colors from blue to red. Using a mercury FIGURE 11. Herschel's experiment leading to
thermometer, he noted that the discovery of infrared radiation:
maximum elevation of temperature (a) thermometer placed in shadow near red
occurred beyond the red band where no side of color spectrum; (b) prism used by
radiation was visible (Fig. 11). 12-J.S Herschel.

In fact this experiment had been done (a)
before but Herschel was the first to notice
that the heating is located in a specific
part of the spectrum and therefore
depends on wavelength. It is now known
that this is related to Planck's and Stefan's
laws, discussed elsewhere in this volume.

fiGURE 10. Portrait of William Herschel.

(b)

20 Infrared and Thermal Testing

I. Herschel was concerned with the FiGURE 12. Investigation of propagation laws of infrared
similarity between heat and light. He
called his discovery "invisible rays" or radiation: (a) Macedonia Melloni; (b) optical bench used by
"rays that occasion heat''. It is now
known that heat (infrared radiation} Melloni. ·
and light are both forms of
electromagnetic radiation of different (a)
wavelength and frequency. The
electromagnetic spectrum includes (b)
both visible and infrared radiation.
whose electrical conductivity cl1anges
2. Herschel demonstrated also that when heated by an impinging radiation.)
quantitative measurements are
possible in this newly discovered part Twentieth Century
of the electromagnetic spectrum using
the mercury thermometer (imagined 1vfuch of what is known of industrial
by Galilee in the 16th century). innovations in the infrared and thermal
method of nondestructive testing was
3. Herschel showed that transmission of gathered in a search of United States
those invisible rays is affected by patents and literature conducted by
material properties. For this reason Robert lvld.·faster and colleagues during
germanium lenses are widely used in the 1940s.2n.2! Tables 5 and 6 include all
infrared equipment rather than of the patents surveyed.2n-29
conventional optic glass, which poorly
transmits the infrared. In his In 1917 Case set up a photoconducting
experiments, he found that sodium detector. Instead of being sensitive to the
chloride (table salt) is a good infrared increase of temperature caused by the
transmitter. He also noticed that the incident radiation, the signal came from
lleatius m}'S are reflected following the the direct interaction with photons. Those
same rules as visible rays. detectors were faster and more sensitive

After Herschel

After Herschel were further
milestones.I2,I6·IB

In 1829, Leopold Nobili (1784-1835),
inventor of the astatic galvanometer,
invented the first thermocouple, based on
the thermoelectric effect discovered in
1821 by Thomas Seebeck (1770-1831). A
thermocouple is a contact sensor formed
of two distinct metals junctions. When
one junction is set at a different
temperature \Vith respect to the other, a
proportional difference of voltage is
generated and is related to the
temperature difference between the two
junctions.

In 1833, Macedonio lvfelloni
(1798-1854) made the first thermopile by
connecting many thermocouples together,
the increased sensitivity achieved allowed,
by focussing the incoming radiation on
one side of the junctions, to detect the
presence of a person at a 10m (33ft)
distance (the focused radiation heats the
junction). Figure 12 shows the optical
bench used by 1'v1elloni.

In 1840, John EW. Herschel
(1792-1871), son of \'\'illiam Herschel,
produced the first infrared image using an
evaporograph, a device in which the
infrared image is formed by differential
evaporation of a thin film of oif.l'J

In 1880, The bolometer is invented by
Samuel Pierpont Langley (1834-1906) and
perfected by Charles Greeley Abbot
(1872-1973), who used it to sense the
heat from a cow some 400 m (1300 ft)
away. (A bolometer is a thermal detector

Introduction to Infrared and Thermal Testing 21

than the other thermal detectors available McNutt used externally applied
at that time. oxyacetylene flames.25 Kuehni used an
external resistance heater.28 Internal
Thermal tests in the first half of the resistance heating was proposed by
twentieth century were characterized by MacDonald and DeForest. 2,26 DeForest24
heat flow in a test object and and Somes29 list advantages in induction
measurement of the associated heating. (See Tables 5 and 6.) Resultant
temperature conditions. The heat may be temperature indications may be detected
introduced into the test object from an by visible glow, by radiant heat detectors,
external heat source through direct by contact thermocouples or resistance
thermal contacts or intermediate heat thermometers, by melting of wax or other
conductors or may be developed in the temperature indicators or by formation of
test object through electric current characteristic oxides.
heating, magnetic losses or other energy
transformations. The useful literature on Surface Film Temperature
thermal techniques was limited to articles Indicator
on thickness testing30,31 and information
on development of more sensitive thermal Surface temperatures may be revea1cd by
detectors.32·38 the melting of wax coatings, lines or
pellets. Del'orest used stearin to indicate
An early infrared nondestructive discontinuities in tubes and welds.24
testing application dates back to 1935 Lacquers and crayons calibrated to change
when Nichols used a radiometer to verify
the uniformity at ·which steel slabs are
reheated in a steel rolling mill (Fig. 13).39

TABLE 5. Functionality of selected thermal nondestructive testing inventions, 1920-1944.

Patent (Year) Quantity Measured Required Access Typical Application

1 327 341 (1920) unquantified indication one .side tube or bar testing
1 681 991 (1928) polarized heat radiation two opposite sides measuring strain in opaque glass
1 869 336 (1932) temperature one or two sides tube or weld testing
2 008 793 (1935) temperature one side plate and sheet testing
2260186(1941) temperature one side plate and tube testing
2264968 (1941) unquantified indication one side only plate and pipe thickness testing
2 278 936 (1942) radiant heat one .side only radiant heat detection; burglar alarm
2 323 715 (1943) rate of heat transmission one .side ~mly spot weld testing
2 340 150 (1944) temperature inside only tube testing

TABLE 6. Operational features of selected thermal nondestructive testing inventions, 1920-1944.

Patent (Year) Energy Source Energy Input Energy Output Pickup and Detector Indicator

1 327 341 (1920) heavy current generator electric, current conduction thermal visual visual

1 681 991 (1928) oven thermal, polarized thermal, heat radiometer, bolometer, galvanometer
heat radiation radiation thermopile etc.

1 869 336 (1932) AC~ generator or electromagnetic thermal thermal; stearin stearin
transformer induction

2 008 793 (1935) battery unspecified thermal radiation pyrometer ammeter

2 260186 (1941) oxyacetylene flame thermal temperature oxide color, visible glow visual

effects, thermal thermocouples etc.

2 264 968 (1941) heavy Ac~ generator eddy current, current thermal contact thermocouple and galvanometric
or transformer conduction galvanometric instrument instrument

2 278 936 (1942) unspecified unspecified thermal- charred organic gas; amplifier and
radiant heat piezoelectric crystal meter
gas (pressure detector)

2 323 715 (1943) resistance heater thermal differential heal thermocouples or galvanometer
flow
temperature sensitive

resistors; resistance bridge

and rectifier

2 340 150 (1944) induction heating electromagnetic induction thermal visual visual or audible
generator alarm

a. Alternating current.

22 Infrared and Thermal Testing

colors at specified temperatures are Radiation Detection Techniques
commercially available.
Radiation detectors, together with
Contact Thermocouple and polarized infrared waves, arc integral to
Resistance Thermometer Littleton's technique if measuring and
detecting strains in opaque glass sheets.2:t
Contact thermocouples were suggested by He suggested the use of any well known
DeForest for thermal tests of tubes and radiometer, such as the bolometer,
plates. Many such indicators 'Were thermopile or galvanometer. Lindsay and
mentioned in McNutt's description of a Pears<:n27 described a novel radiant energy
t~1be and plate tester.25 Kuehni proposed receivmg system comprising a closed
either thermocouples or temperature chamber containing hydrocarbons formed
sensitive resistance elements that might by destructive distillation of organic
form arms of a bridge circuit in his fibers. These materials can absorh large
thermal spot .weld tester. He specifically quantities of gas released as the materials
suggested resistance materials such as are heated. They absorb a large proportion
baked sodium silicate or a baked mixture of incident radiation, their thermal
of iron oxide and borax that have capacities are negligible and their specific
negative temperature coefficients of densities are low. The closed chamber
resistance -that is, their resistance drops containing the heat sensitive gas
rapidly with increasing temperature and absorbers is provided with a rock salt
increases rapidly when the temperature whidow that transmits infrared radiation.
drops.2l:l The rise in gas pressure is detected with
piezoelectric crystal pressure indicators.

~~)us~~~ ~ie~~i:mal test system in Nichols' 1935 patent proposes scanning pyrometry of sheet or plate mat~rial: (a) end view;

(a) (b)

[J /0
ll

7 4

T ,J4 ,'(0) I

legend 6. Photoelectric unit. 11. Variable resistance in power circuit
7. lens. 12. Variable reshtance in ind'tcator circuH.
1. Work piece. 8. Reflector. 13. Battery.
2. Conveyor. 9. Motor to make reflector rotate. 14. Three-element tube.
3. Conveyor motor. 10. Power lines.
4. Roller conveyor. 15. Indicator or recorder.
5. Sensor housing. 16. Battery for indicator or recorder.

Introduction to Infrared and Thermal Testing 23

World War II

There was much progress during 'florid
\'Var II and many patents were released.
Applications include detection of soldiers,
machinery, ships and icebergs;
communicationsi and guidance of
torpedoes.

This last application is particularly
interesting because of the success of
infrared and photonics devices in attacks
during the Persian Gulf War in 1991. The
1940s torpedo weapon used an active
illumination scheme and was sensitive in
near infrared '\Vavelengths (< 1 pm). The
target was irradiated with a tungsten lamp
filtered to block visible radiation and the
reflected infrared radiation served to guide
the torpedo. During this period, the
Germans found that performance can be
improved by cooling the detectors. This
development was of major importance:
cooling is now widely used in infrared
detection devices.

After World War II

The postwar period was very fruitful in
research and development because the
war clearly demonstrated the usefulness
and great potential of infrared and
thermal techniques1 at least for military
applications. Although many spins off
found applications in other areas1 it was
estimated as late as 1995 that 80 percent
of the infrared market was still for
military applications.

Other early nondestructive testing
investigations dealt with analysis of
temperature distribution in brake shoes,40
inspection of soldered seam on a tin
can/ti power transmission line surveys42
and detection of overheated components
on circuit boards.43 More complete
reviews of these "pioneers" in infrared
nondestructive testing applications can be
found in the Iiterature.44.4S

The availability of commercial infrared
cameras in the 1960s saw a flourishing of
applications in medical1 environmental1
industrial, scientific and military
industries. An infrared committee was
established in the American Society for
Nondestructive Testing. 4o After a period of
inactivity starting in the 1970s, personnel
certification initiatives encouraged the
committee to become active again at the
Fall Conference in New Orleans, LA,
November 1986. The 1992 edition of
ASNT Recommended Practice
No. SNT-TC:-JA5 included provision for
infrared and thermal testing. In the same
year1 members of the Therma1/lnfrared
Committee drafted an oulline for an
infrared volume in the Nondestructive
Testing Handbook series.

24 Infrared and Thermal Testing

PART 4. Units of Measure for Nondestructive
Testing

Origin and Use of the Sl For more information, the reader is
System referred to the information available
through national standards organizations
In 1960 the General Conference on and specialized information compiled by
\'\'eights and h.,feasures devised the technical organizations.47,4R
International System of Units. Le SystCme
Jutemational d'Uniti's (SI) was designed so Multipliers
that a single set of interrelated
measurement units could be used by all Very large or very small numbers with
branches of science, engineering and the units are expressed by using the Sl
general public. Vv'ithout SI, this multipliers, prefixes of 101 intervals
Nondestructive Testing Handbook volume (Table 10) in science and engineering. The
could have contained a confusing mix of multiplier becomes a property of the SI
Imperial units, obsolete unit. For example1 a millimeter {mm) is
centimeter-gram-second (cgs) metric 0.001 meter (m). The volume unit cubic
system version units and the units centimeter (cm3) is (0.01)3 or lQ-6 m3.
preferred by certain localities or scientific Unit submultiples such as the centimeter,
specialties. decimeter, dekameter (or decameter) and
hectometer are avoided in scientific and
SI is the modern version of the metric technical uses of Sl because of their
system and ends the division between
metric units used by scientists and metric TABlE 8. Derived Sl units with special names.
units used by engineers and the public.
Scientists have given up their units based Quantity Units Symbol Relation
on centimeter and gram and engineers to Other
made a fundamental change in Sl Units"
abandoning the kilogram-force in favor of
the newton. Electrical engineers have Frequency (periodic) hertz Hz l·s-1
retained their ampere1 volt and ohm but
changed all units related to magnetism. Force newton N kg·m·s-2
The main effect of Sl has been the
reduction of conversion factors between Pressure (stress) pascal Pa N·m-2
units to one (1)- in other words1 to
eliminate them entirely. Energy joule w N·m
Power watt J·s·l
Table 7 lists seven base units. Table 8 Electric charge coulomb c
lists derived units with special names. Electric potentialh volt As
Table 9 gives examples of conversions to v w.A-1
SI units. In Sl1 the unit of time is the
second (s) but hour (h) is recognized for Capacitance farad f C-V-1
use with Sl.
Electric resistance ohm !l V·A-1
Conductance siemens 5 AV-1

Magnetic flux weber Wb V·s

TABLE 7. Base Sf units. Magnetic flux densily tesla T Wb·m-2
Inductance henry
H Wb·k1

Quantity Unit Symbol luminous flux lumen lm cd·sr
m
length meter kg Illuminance lux lx lm·nr2
Mass kilogram
Time second A Plane angle radian rad 1
Electric current ampere K
Temperaturea kelvin mol Radioactivity becquerel Bq 1·s-1
Amount of substance mole cd
luminous intensity candela Radiation absorbed dose gray Gy )·kg 1

Radialion dose equivalent sievert Sv J·kg·l

Solid angle steradian " 1
Time hour 3600 s
h

Volumec liter l dm 3

a. Kelvin can be expressed in degrees celsius a. Number one expresse~ dimensionless relationship.
("C = K- 273.15). b. Electromotive force.
c. For science and engineering, the only prefixes that should be used with

liter are milti (m) and micro (~l).

Introduction to Infrared and Thermal Testing 25

TABlE 9. Examples of conversions to Sl units.

Quantity Measurement in Non-SI Unit Multiply by To Get Measurement in Sl Unit

Area square inch (in,2) 645 square millimeter (mm2)
Distance nanometer (nm)
angstrom (A) 0.1 millimeter (mm)
Energy kilojoule (kJ)
inch (in.) 25.4 joule (J)
Power watt 0N)
Specific heat British thermal unit (BTU) 1.055 kilojoule per kilogram per kelvin (kJ-kg-1-K-1)

Force (torque, couple) calorie (cal), thermochemical 4.184 joule (J)
Pressure k"ilopascal (kPa)
Frequency (cycle) British thermal unit per hour (BTU-h-1) 0.293 hertz (Hz)
Illuminance lux (lx)
British thermal unit per pound 4.19 lux (lx)
Luminance per degree Fahrenheit (BTU-Ibm- 1-"F-1) candela per square meter (cd-m-2)
candela per square meter (cd-m-2)
Radioactivity foot-pound (ft-lb1) inch (lb,.in.-2) 1.36 candela per square meter (cd-m-2)
Ionizing radiation exposure pound force per square 6.89 candela per square meter (cd-m-2)
Mass candela per square meter (cd-m·2)
Temperature (difference) cycle per minute 1/60 candela per square meter (cd-m..2)
Temperature (scale) gigabecquerel (GBq)
footcandle (ftc) 10.76 millicoulomb per kilogram (mC-kg-1)
kilogram (kg)
phot (ph) 10000 degree celsius ("C)

candela per square foot (cd-ft-2) 10.76 eFdegree celsius ("C)

candela per square inch (cd-in.-2) 1 550 ~ 32)/1.8) + 273.15 kelvin (K)

footlambert 3.426

lambert 3 183 (= 10000/rr)

nit (nt) 1

stilb (sb) 10000

curie (Ci) 37

roentgen (R) 0.258

pound (Ibm) 0.454

degree fahrenheit eF) 0.556

degree fahrenheit eF) (°F ~ 32)/1.8

variance from the 103 interval. However, TABLE 10. Sl multipliers.
dmJ and cm3 are in use specifically
because they represent a 103 variance. Prefix Symbol Multiplier
Note that 1 cm3 is not equal to 0.01 m3.
Also, in equations, submultiples such as yotta y 1 Q24
centimeter (em) or decimeter (dm) should zetta 1 Q21
be avoided because they disturb the exa z 1Q18
convenient 103 or 10-3 intervals that peta 1Q15
make equations easy to manipulate. tera E
giga p 1012
In SJ, the distinction between upper mega 109
and lower case letters is meaningful and kilo T 1O'
should be observed. For example, the hecto3 103
meanings of the prefix 1n (milli) and the deka (or deca)a G 102
prefix i\1 (mega) differ by nine orders of M 10
magnitude. ded~ k 1D-'
h 1Q-2
Sl Units to Express centia da 1 Q-3
Particular Quantities in d
Nondestructive Testing m"illi c 10-6
micro m
Old units are to be converted (Table 9). nano 1D-'
British thermal unit (BTU) and calorie pico ~ 1Q-12
convert to joule 0). British thermal unit femto 1 Q-15
per hour converts to watt (\-\1). For atto n lQ-18
measurement of wavelength, nanometer zepto p lQ-21
yocto f 1Q-24
(nm) obviates angstrom (A): 10 A= 1 nm. a

Volume z
y
The cubic meter (m·~) is the only volume
measurement unit in SI. It takes the place a. Avoid these prefixes (except in drn1 and crn3} for
of cubic foot, cubic inch, gallon, pint, science and engineering.
barrel and more. In Sl, the liter (L) is also
approved for use. The liter is a special 1 dnr'~ = 10-:~ m 3). Only the milli (m) and
name for cubic decimeter (1 L =
micro (p) prefixes may be used with liter.
The fundamental units of lime,

temperature, pressure and volume are
expressed every time movement of a fluid
(liquid or gas) is measur('d.

26 Infrared and Thermal Testing

TABlE 11. Compound units used in infrared and thermal testing.

Thernlal Sl' 51'
Quantity Units Symbols

Heat capacity, or entropy joule per cubic meter kelvin J·m-3 ·K-1
Heat density joule per square meter J·m-2
Heat flow rate watt (1 W ~ 1 )·s-')
Heat irradiance, or heat flux density watt per square meter w
Heat transfer coefficient watt per square meter kelvin
Radiance watt per square meter kelvin w.m-2
Radiant intensity watt per steradian
Specific heat joule per kilogram kelvin W·m-2·K-1
Thermal conductance watt per square meter kelvin W · m -2 ·K- 1
Thermal conductivity watt per meter kelvin W·sr 1
Thermal diffusivity square meter per second J·kg- 1 ·K- 1
Thermal expansion meter per meter kelvin W·m-2·K-1
Thermal resistance square meter kelvin per watt
Thermal resistivity meter kelvin per watt w.m-1·K-1
Thermal transmittance watt per square meter kelvin
m2.s-'

m · m · 1 · K -1
m2·K·W-1
m·K·W-1
W·m-l.K-1

a. International System of Units (51).

Heat, Temperature and Thermal
Radiation

Heat can be described as the energy
transfer associated with the random and
chaotic motions of the atomic particles
from which matter is composed. The unit
of heat is the joule U), equal to about
0.24 calorie (cal) or 9.481 x lQ-4 British
thermal units (BTUs).

Temperature is a measure of the
intensity of particle motion (or vibration)
in degrees celsius (C) or fahrenheit (°F)
or, in the absolute scale, kelvin (K) or
rankine (0 R), \Vhere per increment
I K = I oc ~ 1.8 oR ~ 1.8 °F. Fahrenheit

and rankine are obsolete units, almost
never used in scientific work. All materials
(hot or cold) transfer heat and radiate
infrared energy. As a material is cooled, it
continuously loses heat and radiation
power. At absolute zero (0 K = 0 oR =
-273.16 oc = -459.69 oF), all energy

content, radiation and particle motion
cease to exist. It has been physically
impossible to create the temperature of
absolute zero.

Quantities in infrared and thermal
testing are measured and expressed by
using a variety of compound units. Some
of the more common are listed in
Table 11. Thermal conductivity is a body's
relative ability to carry heat by
conduction in a static temperature
gradient. A material's thermal resistance is
its resistance to the flow of thermal
energy and is inversely proportional to
the materiaJis thermal conductivity.

Introduction to Infrared and Thermal Testing 27

References

1. Nondestructiw Testing Handbook, 12. Hudson, R.D. In(raml System
second edition: Vol. 10, Nondestmctil't' Engineering. New York, NY: VViley
Testing Ot'elvicw. Columbus, OH: lnterscience (1969).
American Society for Nondestructive
Testing (1996). 13. Herschel, \'\'. "Experiments on the
Solar and on the Terrestrial Rays That
2. \•Venk, S.;\, and R.C. !vki\·faster. Occasion Heat; with a Comparative
View of the Laws to \o\1hich Light and
Choosing NDT: Applications, Costs and Heat, or Rather the Rays Which
Benefits of Nondestrucliw Testing in Your
Occasion Them, Are Subject, in Order
Quality Assurance Program. Columbus, to Determine \o\'hether They Are. the
Same or Different." Pltilosopllical
OH: American Society for Transactions. Vol. 90. London, United
Kingdom: Royal Society (1800):
Nondestructive Testing (1987).
3. Nondestructive Testing Methods. p 293-437.
14. Herschel,\-\'. "Investigation of the
T03:JB-I-1 (NAVAIR 01-JA-16)
TM43-0103. Washington, DC: Pmvers of the Prismatic Colours to
Heat and Illuminate Objects; with
Department of Defense Uune 1984). Remarks, that Prove the Different
4. Burleigh, D.D. "Practical Hefrangibility of Radiant Heat. To
\o\1hich Is Added, an Inquiry into the
(Nontechnical) Aspects of NDl~ Using Method of Viewing the Sun
Thermographic NDT as an Example .11 Advantageously, \Vith Telescopes of
Materials Evaluation. Vol. 53, No. 11. Large Apertures and High Magnifying
Powers." Pllilosopllical Trausactions.
Columbus, OH: American Society for Vol. 90. London, United Kingdom:
Nondestructive Testing (November Royal Society (1800): p 255.
1996): p 1266-1269.
5. ASNT Recommended Practice No. IS. Niro, L.N. "Herschel's Discovery of
SNT~TC-JA. Columbus, OH: American Infrared Solar Hays." Materials
Society for Nondestructive Testing. Emluativn. Vol. 45, No.4. Columbus,
OH: American Society for
6. ANSI/ASNT CP-189, Standard for Nondestructive Testing (April 1987):
Qualification and Certification of p 434-435.
Nondestructive Testing Personnel.
Columbus, OH: Ainerican Society for 16. Cornell, E.S. "Early Studies in Hadiant
Nondestructive Testing. Heat." Annals ufScieuce. Vol. 1.
London, United Kingdom: Taylor and
7. ASNT Central Certification Program Francis Group (1936): p 217-225.

(ACCP), Revision 3 (November 1997). 17. Cornell, E.S. 11 Radiant Heat Spectrum
from HerschcJ to Melloni - I. The
Columbus, OH: American Society for H'ork of Herschel and His
Nondestructive Testing (1998). Contemporaries." Annals o(Sciettce.
8. ISO 9712, Nondestructive Testing- Vol. 3. London, United Kingdom:
Qualification and Certification of 'I~1ylor and Francis Group (1938):
Personnel. Geneva, Switzerland:
International Organization for p 119-37.
Standardization. 18. Cornell, E.S. 11 Radiant Heat Spectrum

9. 29 CFR 1910, Ocwpotional Safet)' and from Herschel to Mel!oni- II. The
Health Standards [Code ofFederal \o\'ork of !\·felloni and His
Regulatiom: Title 29, Labor.] Contemporaries." Annals of Sciellrc.
\Vashington, DC: United States Vol. 3. London, United Kingdom:
Department of Labor, Occupational Taylor and Francis Group (1938):
Safety and Health Administration; p 402-16.
Government Printing Office. 19. Czerny, ~vf.Z. Physik. Vol. 53, No.1
(1929).
10. 29 CFR 1926, Occupational Safe!}' and
Health Standards for tile Construction 20. jackson, L.l{., H.}...f. Banta, R.C.
lnduslt)' [Code ofFederal Regulations: Mclvfastcr and T.P. Nordin." A Survey
Title 29, Laborj. \·Vashington, DC: of Patents, Publications on
United States Department of Labor, Non-Destructive Tests." The Drilling
Occupational Safety and Health Contractor. Houston, TX: International
Administration; Government Printing Association of Drilling Contractors
Office. (April and June !948).

11. Maldague, X.P.V. "Instrumentation for
the Infrared." Infrared Methodology and
Technology. Langhorne, PA: Gordon
and Breach Science Publishers (1995).

28 Infrared and Thermal Testing

2l.lvfcMaster, R.C. and S.A. \1\'enk. "A 36. Ellickson, R.'J: 1'Recent Developments
Basic Guide for Management's Choice
of Nondestructive Tests." Symposium in the Detection of Infrared
on the Rule of Non-Destructive Testing if1 Radiation." American Journal ofPhysics.
tile Economics of Production. Special Vol. 15. (May and June 1947):
Technical Publication 112. \Vest
p 199-202.
Conshohocken, PA: American Society 37. Billings, ll.H. E. E. Barr and W.L. Hyde.
for Testing and Materials (1951).
"Construction and Characteristics of
22. MacDonald, A.S. and H.P. MacDonald. Evaporated Nickel Bolometers." Review
Metllod of Developing Defects in Metallic of Scientific Instnmwnts. Vol. 18.
Objects. United States Patent 1 327 341 Melville, NY: American Institute of
(January 1920).
Physics Oune 194 7): p 429-435.
23. Littleton, j."L Method of Detecting and 38. Hornig, D.F. and B.j. O'Keefe. 11The
Measuring Strains. United States Patent
1681991 (August 1928). Design of Fast Thermopiles and the
Ultimate Sensitivity of Thermal
24. DeForest. A.V. Thermal Method of Detectors.'' Re\'iew of Scientific
Testing Bimetallic Bodies, United States Instruments. Vol. 18, No. 7. Melville,
Patent 1869 336 (July 1932).
NY: American Institute of Physics
25. McNutt, L.C. .Method o{ Examining (July 1947): p 474-482.
Metal for Subsurface Defects. United 39. Nichols, ].T. Temperature Measuring.
States Patent 2 260 186 (October 1941). United States Patent 2 008 793
(July 1935).
26. DeForest. A. V. Apparatus for Measurins 40. Parker, R.C. and P.R. Marshall. 11The
1¥all Thickness. United States Patent Measurement of the Temperature of
2 264 968 (Decem1m 1941).
Sliding Surfaces with Particular
27. Lindsay, M.H.A. and H.J. Pearson. Reference to Railway Brake Blocks and
Radiant Energy Receil•ing System. United Shoes." Proceedings of the Institution of
States Patent 2 278 936 (February lvfeclwnical Engineers. Vol. 158.
1942).
London1 United Kingdom: Institution
28. Kuehni, H.P. Thermal Testing Apparatus. of Mechanical Engineers (1948): p 209.
United States Patent 2 323 715 (July 41. Gorrill, \•V.S. 11Industrial High-Speed
Infrared Pyrometer to Measure the
1943).
29. Somes, H.E. FaulVfesting Articles of Temperature of a Soldered Seam on a
Tin Can." Electronics. Vol. 22. New
Electrically Conductive Material. York, NY: McGraw-Hill (1949): p 112.
United States Patent 2 340 150 42. leslie, ].R. and ].R. \'\7ait. 11 Detection of

(January 1944). Overheated Transmission Line Joints
30. DeForest, A.V. "Thermoflux Measures by Means of a Bolometer." Transactions
of tile American Jmlitute of Electrical
Plate Thickness." Iron Age. Vol. 144. Engineers. Vol. 68. New York, NY:
Newton, MA: Cahners Business American Institute of Electrical

Information, Division of Reed Elsevier Engineers (1964): p 64.
43. Anonymous. 11 lnfrared Camera Spots
(13 July 1939): p 82-85.
31. Berthjold, R. "A New Method of ~...Jalfunction." Electronic Design. Vol. 9.
New York, NY: Microwaves (1961):
Non-Destructive Testing.'' Bulletin.
Vol. 147. London, United Kingdom: p 12.
44. VVilburn, D.K. 11Survey of Infrared
British Non-Ferrous Metals Research
Association (September 1941): p 273. Inspection and Measuring
Techniques." i\Jaterials Research and
32. Anonymous. "Thermal Detectors." Standards. Vol. 1. VVest Conshohocken,
Electronic lndustTies. Vol. 5. New York, PA: American Society for Testing and
NY: Caldwell-Clements (September Materials (1961): p 528.

1946): p 97, 116, 118. 45. 1\.fcGonnagle, VV. and F. Park.
33. 'Neller, C.T. "Characteristics of //Nondestructive Testing.'' Intemntimwl
Science and Teclmolugy. Nev York, NY:
Thermocouples." General Electric International Communications
Rel'iew. Vol. 49, No. 11. Schenectady, !previously Conver Mast Publications]
NY: General Electric Company
(November 1946): p 50-53. (July 1964): p 14.
46. Current Infrared Papers Pres£'1/ted at tile
34. Niven, C.D. "The Organic Thermistor
Bolometer." Canadian Journal of lR & T Sessions (Detroit, Ml, October
Researc/1: Section A, Physical Sciences. 1965; Los Angeles, CA, March 1966;
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Columbus, Oil: American Society for
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47.1EEE/ASTM Sl 10-1997, Sta11dard for Use
1946): p 93·1 02. of the International System of Units (SJ):
35. ~·filton, R.M. "A Superconducting The Modernized AJelric System. \·Vest
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OH: American Chemical Society

(December 1946): p 419-433.

Introduction to Infrared and Thermal Testing 29

48. Taylor, B.N. Guide for tile Use of llze
International System of UnUs (51). NIST
Special Publication 811, 1995 edition.
\•Vashington, DC: United States
Government Printing Office (1995).

30 Infrared and Thermal Testing

' ' '~ -

CHAPTER

Fundamentals of Infrared
and Thermal Testing

Xavier P.V. Maldague, University Laval, Quebec,
Quebec, Canada (Parts 2 and 3)
Thomas S. )ones, Industrial Quality Incorporated,
Gaithersburg, Maryland (Part 1)
Herbert Kaplan, Honeyhill Technical Company,
Norwalk, Connecticut (Part 1)
Sergio Marinetti, Consiglio Nazionale delle Ricerche,
Padua, Italy (Part 3)
Marc Prystay, National Research Council of Canada,
Boucherville, Quebec, Canada (Part 3)

PART 1. Principles of Infrared and Thermal
Testing 1

Infrared and thermal testing involves The terms inf'mretl and thermal are used
interchangeably in many contexts.
temperature and heat flow measurement Thermal refers to the physical
to predict or diagnose failure. This may phenomenon of heat1 involving the
involve contacting or noncontacting movement of molecules. I11{rared (beyond
devices or a combination of both. A the color red) denotes radiation between
the visible and microwave regions of the
fundamental knowledge of heat flow and electromagnetic spectrum. The intensity
the thermal behavior of materials is and frequency/wavelength of the
necessary to understand the significance radiation can be correlated closely with
of temperature and temperature changes the heat of the radiator. It follows that
on a test sample. radiation sensors can ten us about the
physical condition of the test object. This
Contacting devices include is the basis of the technology of
thermometers of various types, thermography.
thermocouples, thermopiles and
thermochromic coatings. Noncontacting Thermography can be practiced by
devices include convection (heat flux) various techniques. One technique
devices, optical pyrometers, infrared involves the direct application of
radiation thermometers, infrared line temperature sensitive materials (usually
scanners and infrared thermal imaging coatings) to the test surface. This
(thermographic) equipment. approach relies upon thermal conduction
to the temperature sensing medium. Note
Infrared thermography is the that although this technology may be
nondestructive1 nonintrusive, noncontact referred to as thermal, the term infrared
mapping of thermal patterns on the does not apply. Techniques monitoring
surface of objects. 1t is usually used to the infrared radiation emitted by the test
diagnose thermal behavior and, thereby, surface were developed in the 1960s and
to assess the performance of equipment 1970s and digitized in the 1980s. The
and the integrity of materials, products temperature patterns on the material
and processes. The infrared thermal surface produce corresponding radiation
imaging equipment used in infrared patterns. Thus, heat flow by both
thermography is available in numerous conduction and radiation may be
configurations and \Vith varying degrees observed to locate materjaJ
of complexity. discontinuities. Heat flow is the key
mechanism.
The thermal maps produced by
infrared thermal imaging instruments are Heat can be described as the energy
called thermograms. To understand and associated with the random and chaotic
interpret thermograms, the motions of the atomic particles from
thermographer must be familiar with the which matter is composed. The unit of
fundamentals of temperature and heat heat is the joule 0), equal to about 0.24
transfer, infrared radiative heat flow and calorie (cal) or 9.481 x 10-4 British thermal
the performance of infrared thermal unit (BTU). Temperature is a measure of
imaging instruments and other thermal the intensity of particle motion (or
instruments. vibration) in degrees celsius CC) or
fahrenheit CF) or, in the absolute scale,
An understanding of the equipment, kelvin (K) or rankine (0 R), where each
materials and processes being observed is
also important to effectively assess the full increment of 1 K ::: 1 oc = 1.8 oR = 1.8 T
significance of infrared/thermal
measurements. A more detailed discussion All materials (hot or cold) contain heat
of the performance parameters of infrared and radiate infrared energy. As a material
thennal imaging instruments is provided is cooled, it continuously loses heat and
else\vhere. radiation power. At absolute zero (0 K ==
-273.16 oc ~ -459.69 oF~ 0 oR), all heat
Infrared and thermal methods for
nondestructive testing are based on the content, radiation and particle motion
principle that heat flow in a material is cease to exist. Of course, it has been
altered by the presence of some types of physically impossible to create the
anomalies. These changes in heat flow temperatures of absolute zero.
cause localized temperature differences in
the material surface. The imaging or study
of such thermal patterns is known as
thermography.

32 Infrared and Thermal Testing

Infrared Radiation radiation (that is, radiation of frequencies
beyond red). The quantum energy of
Heat transfer can occur hy conduction, infrared produces wave frequencies in tlw
radiation, convection or a combination of electromagnetic spectrum between
these. Conduction occurs when warmer microwaves and visible light (see Fig. 1).
atomic particles collide with~ and thus These frequencies involve wavelengths
impart some of their l1eat energy to ~ extending just beyond the visible range,
adjacent cooler (slower moving) particles. at ahout 750 nm to the microwave region,
This action is passed on from one atom which starts at about 1 mm. The infrared
(or free electron) to the next in the range is further broken dmvn into near
direction of cooler regions. Thus, heat infrared, with wavelengths shorter than
always flows from a warmer to a cooler 1 pm, and far infrared, with longer
region. The term convection denotes the wavelengths. Most infrared
transfer of heat by mass displacement of a nondestructive testing takes place in near
heated material, especially a gas or liquid. infrared and slightly beyond it, up to
For example, heated air can be blown to
another region by forced convection or -15 fllll.
can rise, as a result of its lower density, by Infrared radiation behaves like light at
natural (free) convection. Heat transfer hy
radiation occurs through the emission of visible frequencies. lt travels in straight
electromagnetic waves from the material lines, reflects, refracts, is absorbed,
interferes, exhibits beam spreading, can be
surface. focused and travels in a vacuum at the
Heat transfer is measured in watts per speed of Hgllt, -3 x 108 m·s-1 (6.7 x 108
mi·h-1). The techniques of geometric
square meter (\t\'·m-2). Heat transfer is optics apply, with some modifications for
discussed in more detaH in another longer wavelengths, lens materials and
chapter of this book. sensors. V\'hen infrared radiation falls on a
surface, the absorbed part of the energy is
Surface temperature patterns can be converted into heat.
remotely observed by sensing the
radiation emitted from the surface. All 'J'he infrared radiation emitted by a
bodies above the temperature of absolute
zero emit electromagnetic radiation by heated solid body normally contains a
virtue of the motion of the constituent continuous band of ·wavelengths over a
atoms.2,3 Electromagnetic radiation occurs specific range. The band of wavelengths
when an electric charge is accelerated or results from the chaotic motion .and
decelerated. The spectrum and intensity interaction of the constrained atomic
of the radiation depend on the particles in the solid. The radiation
temperature and nature of the surface. intensity (\V·m-2) emitted by the solid
depends upon the temperature and nat me
\•Vhen a surface is heated, there is an of the surface. At lower temperatures the
increase in energy of the atomic particles radiation intensity is low and consists
leading to a corresponding increase in chiefly of longer wavelengths. At higher
temperature and emitted energy. The temperatures, the radiation intensity
chaotic thermal agitation of atomic rapidly increases while the wavelength
particles produces a form of radiant band shifts toward shorter values. These
electromagnetic energy known as infrared behaviors are described in relevant
chapters of this book.

FIGURE 1. Electromagnetic spectrum.

Frequency (Hz)

10' 10' 10' 10' ton 101$ 1017 1Q19 10 21 1023

II III
Ultraviolet
I
..._Infrared v

I X-rays
s

Radio waves I Gamma ray~

B

l

Mkwwavcs ' Cosmic ray~

10' 10' 100 10' 10- 4 10 • 10' ]0-10 JQ-12 lQ-H II

]0-16

Wavelength (m)

Fundamentals of Infrared and Thermal Testing 33

Instrumentation Radiometry

Infrared nondestructive testing is Infrared testing measures surface
performed by either active or passive temperatures by means of device::. l ..Hed
techniques. Active techniques involve radiometers or infrared cameras. A
heating or cooling the materia} to radiometer basically consists of optics that
generate the required heat flow and collect and focus or image the received
thermal gradients. Transient heat flow infrared radiation on a sensitive detector.
usually is used during active testing. The detector converts the infrared
Passive techniques involve applications radiation into an electrical signaL :~vfany
where the material already contains its radiometers are scanning or imaging
own internal source of heat (such as an cameras that provide the operator with a
inservice heater element or the human thermographic image of the test surface. A
body).4 Thus, steady state conditions microprocessor processes the image and
normally apply to passive tests.
FIGURE 2. Block diagram of typical infrared inspection
Active tests are conducted by heating system.
the material to observe the development
of the transient state thermogram. Heat of Video tape recorder Test
a given intensity and a given duration is panel
applied by hot gas jets, infrared lamps,
electrical induction (of metals), dielectric D
heating (of nonmetals), direct contact
(conduction heating) or baking (soaking) Computer image
the test piece in an oven. processing system

The size of the heated spot can be a
few millimeters (about 0.1 in.) in diameter

or much larger, depending on the

thermographic detection scheme. Small
heat spots are distributed across the
surface and the thermographic pattern
they leave is observed.

FIGURE 3. Functional sketch of radiometer showing one optical scanning technique for producing infrared
images (about 1990). Not shown is an internal reference temperature sensed by the detector.

Vertical synchrOnization signal

Horizontal synchronization signal

Motor 1 Photocell Photocell Motor 2 Dewar flask
pickup pickup
Video
-16 cycles signal to
display unit
pN second

GHmaniurn lens
Germanium lens

Oscillating
plane mirror

34 Infrared and Thermal Testing

presents it on a television screen or digital thermal image from the surface of the test
output display. Variations of the image material is focused on a photoconductive
intensity are related to the corresponding retina plane next to the receiving face of
surface temperatures on the material the tube, converting the thermal image
under test. Typical sensitivity of the into a conductivity pattern by the
instruments is 0.05 K (0.05 oc ~ 0.1 oF) or photoconductive action of the retina. An
electron beam focused from the other end
better. figure 2 shows the components of of the tube is raster scanned across the
a typical infrared inspection system. entire inside surface of the retina, usually
at a rate of 30 frames per second. During
Pyrometry. The word pyrometry means electron scanning, an electrical charge
"fire measmement. 11 As the name implies, pattern corresponding to the conductivity
pyrometers are for hot applications, such pattern is developed on the inside surface
as the monitoring of furnace or foundry of the retina. This action causes an
conditions. A pyrometer is a kind of instantaneous modulation of electron
radiation thermometer, giving readings backscatter, whose intensity depends on
for one point at a time, rather than the thermal information at the particular
imaging a scene the way an infrared video point being scanned. The backscatter
camera would. Pyrometers since 1990 intensity is detected by a high sensitivity
have been digital devices with liquid electron multiplier, mounted coaxially
crystal temperature readouts. They may be around the electron gun. The amplified
mounted in place and hand held units are current signal is then fed through
also available. processing circuits to a synchronized
television monitor. The result is a
Video Radiometry. Standard infrared video standard television image of the
camera systems can resolve temperature thermogram.
variations of 0.05 oc (0.1 °F) and display
images with temperature gradients of 256 Detector Arrays. The greatest advantage of
colors or levels of gray. l)'pical operating an array detector over a scanned detector
ranges begin at -50 oc to 0 °C (-60 to is that each element of a detector array
32 °F) and may go as high· as 2273 K can monitor the emissions from the
(+2000 °C ~ 3600 °F). object's surface for the full duration of the
video frame exposure whereas the
Scanning Radiometry. The test surface can scanned detector has to collect
be optically scanned at high speed by
mechanical deflection of mirrors and information on the fly. Where objects are
prisms in the radiometer. For example, the
horizontal trace on the raster is provided near room temperature, as is often the
by a rotating prism and the vertical trace case for nondestructive testing, the
by a nodding mirror. This action monitors intensity for infrared emissions can be
an area 0.75 to 3.2 mm (0.030 to very low and the increased dwell time of
0.125 in.) in diameter. Moving back and the detector in the full field array
forth and up and down on the surface, dramatically improves the level of photon
the scan covers the surface completely in noise. Linear detector arrays are suited for
a small fraction of a second, producing production environments, \Vhere they
the thermographic image. A variety of provide data from a cross section of
optimizing adjustments are provided to product as it passes by on line; full field
select spot size, scan area, scan rate, focus, arrays, however, offer the familiar scenic
sensitivity (contrast) etc. Figure 3 shows a
functional sketch of an optical scanning FIGURE 4. Functional sketch of infrared vidicon tube.
radiometer. Note that the indium
antimonide detector requires cooling, a Retina
normal situation for high sensitivity
infrared detector materials. Forward beam

Some scanning radiometers will yield Electron multiplier mage
an image several inches wide and several
inches high or surface area sizes Signal Cooling finger
determined by the optics. A field of view current
of 5 to 30 degrees is common. Detection
distances are usually from about 1 m (a from
fe'iv feet) to infinity. Standard frame anode
speeds of 30 frames per second will
produce flicker free images, especially
advantageous for visually observing static
or moving objects.

Real Time Radiometry. Radiometers of one
type feature real time image readout by
incorporating an infrared sensitive
vidicon tube. Mechanical manipulation of
the optics is replaced with a scanning
electron beam. As shown in Fig. 4, the

Fundamentals of Infrared and Thermal Testing 35