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International
Standard
ISO 18081
Second edition
Non-destructive testing — Acoustic
2024-07
emission testing (AT) — Leak
detection by means of acoustic
emission
Essais non destructifs — Essais d’émission acoustique —
Détection de fuites par émission acoustique
Reference number
© ISO 2024
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Published in Switzerland
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Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Qualification of test personnel . 2
5 Principle of acoustic emission testing . 2
5.1 The acoustic emission phenomenon .2
5.2 Influence of different media and different phases .2
5.3 Influence of pressure differences .3
5.4 Influence of geometry of the leak path .4
5.5 Influence of wave propagation .4
6 Applications . 5
7 Testing equipment . 5
7.1 General requirements .5
7.2 Sensors . .5
7.2.1 Typical frequency ranges (band widths) .5
7.2.2 Mounting technique .6
7.2.3 Temperature range, wave guide .6
7.2.4 Intrinsic safety .6
7.2.5 Immersed sensors .6
7.2.6 Integral electronics (amplifier, RMS converter, ASL converter, band pass) .6
7.3 Portable and non-portable AE instruments .7
7.4 Single and multi-channel AT instruments .7
7.4.1 Single-channel instruments .7
7.4.2 Multi-channel instruments .7
7.5 Determination of features (RMS, ASL vs. hit or continuous AE vs. burst AE) .7
7.6 System verification using artificial leak noise sources .7
8 Test procedure for leak detection . 8
8.1 Mounting of sensors .8
8.2 Additional features to be determined .9
8.3 Background noise.9
8.3.1 General .9
8.3.2 Environmental noise .9
8.3.3 Process noise .9
8.4 Data acquisition .9
9 Location procedures . 10
9.1 General .10
9.2 Single-sensor location based on AE wave attenuation .10
9.3 Multi-sensor location based on Δt values (linear, planar) .11
9.3.1 Threshold level and peak level timing technique.11
9.3.2 Cross-correlation technique .11
10 Data presentation .12
10.1 Numerical data presentation (level meter) . 12
10.2 Parametric dependent function . 12
10.3 Frequency spectrum . 13
11 Data interpretation .13
11.1 Leak validation . 13
11.1.1 On-site (during test) and off-site (post analysis) . 13
11.1.2 Correlation with pressure. 13
11.1.3 Rejection of false indications . 13
11.2 Leakage rate estimation .14
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11.3 Demand for follow-up actions .14
12 Quality management documents .15
12.1 Test procedure . 15
12.2 Test instruction . 15
13 Test documentation and reporting .16
13.1 Test documentation . .16
13.2 Test report .16
Annex A (informative) Example applications of leak detection .18
Bibliography .31
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Foreword
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