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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]

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

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.

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/’

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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

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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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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