Loop-check instrumentation and control loops

Information Sheet 5.1.1 : TESTING PROCEDURE IN LOOP CHECKING

Learning outcomes:
5. Test the loops that were checked.
Learning Activity:
5.1 Explain procedure on testing loop.

I. PROCEDURE ON INSTRUMENT PRESSURE TEST

A.) Impulse Piping/Tubing

(1) General
-All the pressure/vacuum lead piping (impulse piping/tubing) which connect
a instrument to process should be pneumatically tested for tightness. The test
fluid should be clean air or nitrogen gas.

(2) Testing Pressure
-Impulse piping/tubing shall be tested at 110% of the design pressure.

(3) Test Preparations
(3.1) Before commencing the pressure test for the differential pressure
instruments, close block valves at the process and open the bypass valve
and block valves at the instrument.
(3.2) Close block valve at the provess for pressure instruments.
(3.3) If the differential type level instrument is not equiped with bypass line, close
block valves at the vessel and add temporary bypass line between the high
pressure and low pressure sides to prevent excess differential pressure at the
instrument.
(3.4) All joint, including welds, are to be left uninsulated and exposed for examination
during the test.
(3.5) Vacuum service lines shall be tested at minimum pressure of 20 PSIG unless
limited.
(3.6) Analyzer unit shall be disconnected before pressure testing of sampling lines.

Code No. LOOP CHECK INSTRUMENTATION AND Date: Developed Date: Revised Page #
CONTROL LOOPS 1

Information Sheet 5.1.1 : TESTING PROCEDURE IN LOOP CHECKING

(4) Testing Sequence
Step 1 : Prepare piping to be tested.
Step 2 : Connect the test assembly to the impulse piping/tubing.
Step 3 : Inject preliminary test pressure upto 20 PSIG.
Step 4 : Locate major leaks and correct them.
Step 5 : Increase testing pressure gradually in steps with providing sufficient
time to allow the piping equalize the strains during test.
Step 6 : The pressure is to be reached the testing pressure.
Step 7 : The test pressure shall be maintained for a sufficient time to determine
if there are any leaks, but not less than 10 minutes.
Step 8 : Accurate records shall be maintained for all the lines tested.

B. Signal Transmission Tubing

(1) General
-All of the control and signal transmission tubing shall be tested pneumatically
prior to final loop check. Testing medium shall be instrument air or nitrogen gas.

(2) Testing Pressure
-The signal transmission tubing shall be tested at maximum pressure of the
signal range, i.e.,15 PSIG for 3 to 15 PSIG signal range.

(3) Test Preparations
(3.1) Establish the identity of each component of a given control loop and its
conformance to design specification.
(3.2) Blow air lines clean.
(3.3) Identify positively the air circuit from air supply valve through instrument
to air-operated element by setting instrument to deliver air and observing air
leakage at the disconnected air line at the air-operated element.
(3.4) Before any test of pneumatic line, instruments which would consume air
from the line must be disconnected and the line be blocked at the point of
disconnection.

Code No. LOOP CHECK INSTRUMENTATION AND Date: Developed Date: Revised Page #
CONTROL LOOPS 2

Information Sheet 5.1.1 : TESTING PROCEDURE IN LOOP CHECKING

(4) Testing Sequence
Step 1 : Disconnect air consuming pilots from the section of tubing to be tested.
Step 2 : Connect the bubbler unit to the open end of the line to be tested.
(Refer to Fig.4.2.2-1)

Step 3 : Close all three valves - A,B and C.
Step 4 : Open the air supply valve and adjust regulator so that the pressure

reach to testing pressure.
Step 5 : Open the valve A and allow the line to be fully pressurized.
Step 6 : Close valve A and open valve B and C.
Step 7 : Observe the bubbler unit. A leak on the line will cause bubbles to

appear in the unit.
Step 8 : Determine the source of the leak and correct it.
Step 9 : The line shall be considered acceptable when the bubbles are slowed

to a rate of no more than three per minute.
Step 10 : It must be stressed that air supply pressure to the bubble unit must be

stable.
Step 11 : Accurate records shall be maintained for all the lines tested.

Code No. LOOP CHECK INSTRUMENTATION AND Date: Developed Date: Revised Page #
CONTROL LOOPS 3

Information Sheet 5.1.1 : TESTING PROCEDURE IN LOOP CHECKING

C. Air Supply Piping

(1) General
-All instrument air subheaders and branch systems shall be subject to leak
and pressure testing. Main instrument air piping shall be pressure-tested by
piping group. The test medium for these tests shall be clean, oil free air. A
portable compressor may be used with dry alumina filter for this purpose,
however, main instrument air compressor shall be used if it is available.

(2) Testing Procedure
Step 1 : Operate the system instrument air compressor.
Step 2 : Put drain traps and air dryer into operation, and check quality of
instrument air at the down-stream of air dryers.
Step 3 : Test pressure shall be the maximum operation pressure of the instrument
air supply piping system.
Step 4 : Open the end of air supply pipe at the nearest union or coupling from the
instruments and blow air pipes clean removing all the foreign object and
drain trapped inside pipes.
Step 5 : After blowing is finished, reconnect all the supply piping to the instruments.
Step 6 : Apply soap solution around all the possible source of leaks (union, coupling,
etc.).
Step 7 : Check for leaks observing bubbles.
Step 8 : Mark on the leak points and depressurized the leaking section of the air
Supply piping for maintenance.
Step 9 : Repeat above steps throughout the piping system.
Step 10 : Accurate recrds shall be maintained for all the line tested.

Code No. LOOP CHECK INSTRUMENTATION AND Date: Developed Date: Revised Page #
CONTROL LOOPS 4

Information Sheet 5.1.1 : TESTING PROCEDURE IN LOOP CHECKING

II. TESTING ELECTRICAL CABLES AND WIRES

(1) Continuity test
-The continuity test should be performed from source of supply through utilization
equipment for each circuit. This shall also include instrument analog signal cable,
thermocouple compensation wire, switched signal cable and special cable and wire.

(2) Insulation resistance test (Megger test)
-The insulation resistance test for each electrical cable or wire shall be performed
as per electrical quality control procedure.

REFERENCE:

·ANSI - American National Standards Institute.
· API - American Petroleum Institute.
· ISA - Instrument Society of America
· Applied Instrumentation in the Process Industries, Volume I, II and III

W.G. Andrew, Gulf Publishing Company.
· Instrument Engineers'Handbook, Volume I, II and III

B.G. Liptak, Chilton Book Company.

Code No. LOOP CHECK INSTRUMENTATION AND Date: Developed Date: Revised Page #
CONTROL LOOPS 5

Operation Sheet 5.2.1: TESTING PROCEDURE IN LOOP CHECKING
Learning outcomes:
5. Test the loops that were checked.
Learning Activity:
5.1 Explain procedure on testing loop.

EQUIPMENT:
1. Pneumatic Calibrator
2. Electronic Multifunction Calibrator
3. Multi Tester
4. Insulation Tester

I. Conduct Testing for the following area. Refer to Information Sheet 5.1.1 for
step by step procedures.

A.) Impulse Piping/Tubing

B.) Signal Transmission Tubing

C.) Air Supply Piping

D.) Continuity Supply

E.) Insulation Resistance Test (Megger Test)

Warning: Always keep in mind SAFETY FIRST! You may be working on HIGH VOLTAGE SOURCE
& HIGH PRESSURE SUPPLY.

II. Record your data on Loop Check Sheet/Report provided to you.

Code No. LOOP CHECK INSTRUMENTATION Date: Developed Date: Revised Page #
AND CONTROL LOOPS

Information Sheet 5.3.1 : INSTRUMENT LOOP CHECK SHEET

Learning outcomes:
5. Test the loop that were checked
Learning Activity:
5.3 Completion of report and documents for the whole loop checking job.

SAMPLE OF INDUSTRY-BASED INSTRUMENT LOOP CHECK SHEET

Code No. LOOP CHECK INSTRUMENTATION AND Date: Developed Date: Revised Page #
CONTROL LOOPS 1

Worksheet 5.3.2 : FILL-UP INSTRUMENT LOOP CHECK SHEET

Learning outcomes:
5. Test the loop that were checked
Learning Activity:
5.3 Completion of report and documents for the whole loop checking job.

INSTRUMENT LOOP CHECK SHEET

LOOP No.: LOCATION: DRAWING No.:

MECHANICAL/ELECTRICAL CHECKS

MEASURING INSTRUMENT: □ LOCATION CORRECT □
INSTALLATION CORRECT □ MATERIALS CORRECT □
ISOLATING VALVES CORRECT □
TAPPING(S) POSITION CORRECT ORIFICE DIAMETER ______________

IMPULSE CONNECTION:

CORRECT TO HOOK-UP □ MATERIALS CORRECT □

PRESSURE TESTED □ TEST PRESSURE _______________

CONNECTION TRACED □ LAGGED □

FIELD INSTRUMENTS:

INSTALLATION CORRECT □ AIR SUPPLY CORRECT □
WEATHER PROTECTED □
POWER SUPPLY CORRECT □

PANEL INSTRUMENTS:

INSTALLATION CORRECT □ AIR SUPPLY CORRECT □
SCALE/CHART CORRECT □
POWER SUPPLY CORRECT □

CONTROL VALVES:

INSTALLATION & LOCATION CORRECT □ SIZE & TYPE CORRECT □
POSITIONER CHECKED □
STROKE TESTED □ I/P TRANSDUCER CHECKED □

LIMIT SWITCHES SET □

AIR SUPPLY:

CONNECTIONS CORRECT TO DRAWING □ BLOWN CLEAR & LEAK TESTED □

TRANSMISSION: LINES INSPECTED □
PNEU. □
ELECT. □ INSULATION CHECKED CORE TO CORE □ CORES TO EARTH □

CONTINUITY CHECKED □ LOOP IMPEDANCE CHECKED □

EARTH BONDING CHECKED □ ZENNER BARRIERS CHECKED □

TEMPERATURE LOOPS:

T/C OR RTD CHECKED □ CABLE SPECIFICATION □
CONTINUITY CHECKED □
LOOP IMPEDANCE CHECKED □

Code No. LOOP CHECK INSTRUMENTATION AND Date: Develop Date: Revised Page #

CONTROL LOOPS 1

Worksheet 5.3.2 : FILL-UP INSTRUMENT LOOP CHECK SHEET

LOOP TEST TRANSMITTER TRANSMITTER LOCAL INS. PANEL INS. REMARKS
MEASUREMENT INPUT OUPUT READING READING

CONTROLLER TRANSDUCER VALVE POSITION CONTROL REMARKS
OUTPUT OUTPUT O/P VALVE POS.

CONTROL

TEST EQUIPMENT USED MANUFACTURER MODEL SERIAL No. CERTIFICATE No. DATE

CHECKED BY: DATE: WITNESSED BY: DATE:
ACCEPTED BY: FOR: INSTRUMENT TAG No.: DATE:

PERFORMED BY:

GROUP No.:
NAMES:

Code No. LOOP CHECK INSTRUMENTATION AND Date: Develop Date: Revised Page #

CONTROL LOOPS 2