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है”ह”ह
IS 14670 (1999): Recommended Practice for Acoustic
EmissionInspection During Hydrostatic Pressure Testing of
System[MTD 21: Non-Destructive Testing]
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lS 14670 :1999
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Indian Standard
RECOMMENDED PRACTICE FOR ACOUSTICEMISSION INSPECTION DURING
HYDROSTATIC
PRESSURE TESTING OF SYSTEM
ICS 17.140.99; 19.100
0 BIS 1999
BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR
MARG
NEW DELHI 110002
April 1999 Price Group 2
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Non-Destructive Testing Sectional Committee, MTD 21
FOREWORD
This Indian Standard was adopted by the Bureau of Indian
Standards, after the draft finalized by Non-DestructiveTesting
Sectional Committee had been approved by the Metallurgical
Engineering Division Council.
Acoustic Emission (AE) testing is of specific importance towards
non-destructive testing of systemshydrostatically pressurized, such
as pressure vessels and piping system.
The basic functions of an acoustic emission monitoring system
are to detect, locate and classify emission sources.Other methods
of NDT may be used to further evaluate the significance of acoustic
emission sources.
For the purpose of deciding whether a particular requirement of
this standard is complied with, the final value,
observed or calculated, expressing the result of a test or
analysis, shall be rounded off in accordance withIS 2:1960 ‘Rules
for rounding off numerical values (revised)’. The number of
significant places retained inthe rounded off value should be the
same as that of the specified value in this standard.
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IS 14670:1999
Indian Standard
RECOMMENDED PRACTICE FOR ACOUSTICEMISSION INSPECTION DURING
HYDROSTATIC
PRESSURE TESTING OF SYSTEM
1 SCOPE
This recommended practice guidelines for acousticemission (AE)
testing of systems, such as pressurevessels, piping systems or
other structures duringhydrostatic pressure testing of the
system.
2 PRINCIPLE
When a system is pressurized hydrostatically, the
pressurization produces changes in stresses in thestructure.
During pressurization of a structure, AE is produceddue to such
source as (a) deformation, (b) initiationand propagation of cracks,
(c) reshuffling of stresspattern at the region of high stress as
(1) fluid leak,(2) loose part motion, and (3) relative movement
between different parts of a structure. These AEsignals can be
detected by an instrumentation systemusing sensors which being
normally of thepiezoelectric type transform the mechanical
excitationstimulated by stress wave, into electrical signals.
In addition to immediate evaluation of the emissions
detected during the application of hydrostatic pressurea
permanent record of the number and location ofemitting sources and
the relative amount of acousticemission detected from each source
provides a basisfor comparison with sources detected during the
testand during subsequent pressurization.
3 PERSONNEL QUALIFICATION
The acoustic emission inspection shall be performedby qualified
personnel.
4 PREPARATION FOR INSPECTION
It shall be carried out as follows:
a)
b)
c)
Areas which bend specific monitoring suchas repaired regions,
nozzles identified highstress areas etc, should be specified.
The type of sensors and their frequencyranges should be
identified. Both sensorand couplant must be compatible with
thesurface conditions and the structural mate-rial to ensure the
signal to noise ratio.
The maximum pressure that the vessel canbe subjected to should
also be specified.
d)
e)
Q
g)
The pressurization schedule should bespecified. The
pressurization schedule shallinclude holding time at each pressure
levelin terms of percent of maximum pressure andpressure should be
continuously recorded.
There shall be proper communicationbetween acoustic emission
test control cen-tre and pressurization control point.
All potential sources of extraneous acousticnoise such as
mechanical vibrations, friction,and fluid flow should be
identified. Thesesources should be isolated and minimized .
Acoustic emission monitoring system shouldbe identified.
Calibration should at least bedone before and after the test.
Additionalcalibration checks may be performed duringthe test if so
required.
5 CALIBRATION OF EQUIPMENT
5.1 The sensitivity and locationa! accuracy of theAcoustic
Emission monitoring system -shall be
determined by using the acoustic emission simulator.
5.2 Sensitivity Calibration shall be carried out asfollows.
5.2.1 In order to set the gain for each sensor channel,locate
the acoustic emission simulator at a selecteddistance from each
sensor in turn. Monitor a sensor’sresponse to the simulated
emission and adjust thechannel again to a specified amplitude
level. Repeatthis procedure for each acoustic emission sensor onthe
structure and adjust the amplified outputs,corresponding to the
identical simulations of each tothe specified peak voltage, within
+1 dB.
5.3 Accuracy of source location shall be determinedas
follows.
5.3.1 Check the operation of the acoustic emissionsource
location function by analyzing simulatedacoustic emission signals
from several randomlocations on the structure as well as from any
specificcritical locations. For each placement of the
simulator,determine and record the precision and accuracy ofthe
acoustic emission location function.
6 INSPECTION PROCEDURE
6.1 Acoustic emission data shall be accumulated
1
\\ _.
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IS 14670:1999—.- ..—
during and if only after pressurization, then how toplotthe
dataassuggested in Fig. l after pressurizationof the system or
both.
6.1.1 During application ofhydrostatic pressure thelocations of
acoustic sources are usually determinedthrough analysis of the
difference in time of arrival ofAcoustic Emission signals at
acoustic sensors. Suchanalysis may be performed through the use of
an analogor digital computer. The computer accumulates andanalyses
data over a specified pressure range. As thepressure is applied
record the number and location ofemitting source and the amount of
acoustic emissiondetected from each source. The acoustic emission
activityat one or more sensors maybe monitored and displayedin
realtime during pressurization. If the acoustic emissioncount rate
in the form of acoustic emission, count rate,event rate, energy or
a-similar acoustic emission quantityshows an appreciable increase
noti~ the owner of thestructure or his representative immediately.
It shall behis decision to reduce, hold or stop the test. The cause
ofacoustic emission increase shall be investigated beforecontinuing
the test.
6.1.2 Calibration shall be repeated after the test andchanges
recorded in gain setting and source location
performance. Appropriate compensation shall bemade during data
interpretation.
7 INTERPRETATION OF RESULTS
7.1 All results shall be summarized on an appropriatelayout map,
displayed or tabulated or both for readyreference and
interpretation. This layout or tabulation
shall display the location and classification of each
source with pertinent comments,
7.2 Source Location
All locations data resulting from analysis shal! bepresented in
a manner consistent with the previously
established calibration accuracy.
7.3 Source Classification
Sources shall be classified with respect to their
acousticactivity and intensity.
7.3.1 Activity of a source shall be measured by eventcount or
emission count. Source is considered to beactive if its event count
or emission count continuesto increase with increasing or constant
stimulation.A source is considered to be critically active if
thederivative of its event count or emission count withrespect to
stimulus continuously increases withincreasing pressurization or
with time under constantpressure (see Fig. 1).
7.3.2 An intensity measure of a source is its averageamplitude
per event also, the emission count per event,the emission energy
per event or other quantities thatcan be shown to be related to the
amplitude of thesignal, can be used as intensity measures. A source
isconsidered to be intense if it is active and its intensitymeasure
consistently exceeds, by a specified amount,the average intensity
of active source. The intensityof a source can be calculated for
increments of thestimulus or of events. An intense source is
consideredto be critically intense if its intensity
continuouslyincrease with increasing stimulation or with time
under constant stimulus (see Fig. 2).
SOURCE 3
1/’
PRE5WK-i
NOTE — To the right of the vertical line, Source 1 is inactive,
Source 2 is active and Source 3 is critically active,
FIG. 1 SCHEMATICREPRESENTATIONOFTHREEDIFFERENTTYPES
2
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7.4 Evaluation of classified source shall be as givenbelow:
a)
b)
c)
d)
Sources considered to be critically active orcritically intense
or both are indicative ofquestionable structural intensity and,
ifpossible, shall be evaluated by other NDTmethods.
Sources considered to be int&se are indica-tive of possible
flaw growth and, if possibleshould be evaluated by other NDT
methods.
Sources considered to b; active but not intenseshall be recorded
for comparison with sourcesdetected during subsequent
examination.
Sources considered to be of.low activity andintensity are not
usually required to be fur-ther evaluated for subsequent
correlation.
8 REPORT
A“ll calibration data and instrument adjustmentincluding
equipment description and performance
IS 14670:1999
data, shall be included in the records of the inspectionand be
signed by the inspecting authority. Theinformation recorded shall
be sufficient to permitcomplete re-analysis of the results. This
informationshall include the following:
a)
b)
c)
d)
e)
f)
Complete identification of vessel, material,method of
fabrication, manufacturer’s name,previous history and maintenance
as well asits maximum operating pressure prior to AEinspection;
Details of AE equipment, manufacturersname, Model No.;
Sensor specification, sensitivity, frequency,type of
couplant;
Vessel sketch with number of sensors withtheir locations;
Inspector’s name and his qualification; and
Suspect areas to be shown on a sketch ofves-sel along with data
of AE signals and inter-pretation of results.
Ik10
1
NOTE — Four different regions are shown prior to S., the source
was inactive between .S. and ,S,, the source was of low
intensitybetween S; and SZ,tie source is classified as critically
in”tense. ‘
FIG. 2 SOURCEINTENSITYI DIVIDEDBY A WEIGHTEDAVERAGEINTENSITYOF
ALLSOURCES,kIo PLOTTEDAGAINSTTHEPRESSURE
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Bureau of Indian Standards
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Amendments are issued to standards as the need arises on the
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amendments or edition by referring to the latest issueof ‘BIS
Handbook’ and ‘Standards Monthly Additions’
This Indian Standard has been developed from Dot: No. MTD21
(3614).
Amendments Issued Since Publication
Amend No. Date of-Issue Text Affected
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