Non-destructive testing - Acoustic emission testing (AT) - Leak detection by means of acoustic emission (ISO 18081:2016)

This European Standard specifies the general principles required for Leak Detection by the acoustic emission (AE) testing. The Standard is addressed to the application of the methodology on structures and components, where a leak flow as result of pressure differences appears and generates AE.
It describes phenomena of the AE generation and influence of the nature of fluids, shape of the gap, wave propagation and environment.
The different application methods, instrumentation and presentation of AE results will be discussed. It also includes the guidelines for the preparation of application documents, which describe specific requirements for the application of the AE method.
Different application examples will be given.
Unless otherwise specified in the referencing documents, the minimum requirements of this standard are applicable.

Zerstörungsfreie Prüfung - Schallemission - Dichtheitsprüfung mittels Schallemission (ISO 18081:2016)

Diese Europäische Norm legt die allgemeinen Grundlagen fest, die für die Dichtheitsprüfung mittels Schallemission (en: acoustic emission, AE) erforderlich sind. Die Norm behandelt die Anwendung der Technik bei Strukturen und Bauteilen, bei denen ein Leckagestrom aufgrund von Druckdifferenzen auftritt und Schall-emission hervorruft.
Sie beschreibt Phänomene der Entstehung von Schallemission und den Einfluss der Art des Fluid, der Spaltform, der Wellenausbreitung und der Umwelt.
Es werden verschiedene Anwendungsverfahren, Messgeräte und Darstellungen der Ergebnisse der Schallemission erörtert. Die Norm enthält außerdem die Richtlinien für die Erstellung der Anwendungs-dokumente, die spezielle Anforderungen an die Anwendung der Schallemissionsprüfung beschreiben.
Die Norm enthält verschiedene Anwendungsbeispiele.
Sofern in den in Bezug genommenen Dokumenten nichts anderes festgelegt ist, gelten die Mindest-anforderungen dieser Norm.

Essais non destructif - Émission acoustique - Détection de fuite par émission acoustique (ISO 18081:2016)

La présente Norme européenne définit les principes généraux exigés pour la détection de fuites au moyen de l'essai par émission acoustique (EA). Cette norme traite de l'application de la méthodologie sur les structures et les composants, lorsqu'un écoulement de fuite dû à des différences de pression se produit, et génère une EA.
Elle décrit les phénomènes de génération d'EA et l’impact de la nature des fluides, de la forme de l'espace, de la propagation des ondes et de l'environnement.
Les différentes méthodes d'application, l'instrumentation et la présentation des résultats de l'EA vont être décrites. La présente norme contient également les lignes directrices relatives à la préparation des documents d'application, qui décrivent les exigences spécifiques pour l'application de la méthode par EA.
Différents exemples d'application vont être donnés.
Sauf spécification contraire dans les documents de référence, les exigences minimales de la présente norme sont applicables.

Neporušitveno preskušanje - Akustična emisija - Preskušanje tesnosti z akustično emisijo (ISO 18081:2016)

Ta evropski standard določa splošna načela za preskušanje tesnosti z akustično emisijo (AE). Standard je namenjen uporabi metodologije pri konstrukcijah in komponentah, pri katerih pride do uhajanja zaradi tlačne razlike, kar povzroči akustično emisijo.
Opisuje nastanek akustične emisije in njen vpliv na naravo tekočine, obliko vrzeli, širjenje valov in okolje.
Obravnavane bodo različne metode uporabe, različni instrumenti in predstavitev rezultatov akustične emisije. Vključuje tudi smernice za pripravo dokumentov za uporabo, ki opisujejo posebne zahteve za uporabo metode akustične emisije.
Navedeni bodo različni primeri uporabe.
Minimalne zahteve tega standarda so veljavne, razen če je v referenčnih dokumentih drugače določeno.

General Information

Status
Published
Public Enquiry End Date
28-Feb-2014
Publication Date
08-Feb-2017
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
02-Feb-2017
Due Date
09-Apr-2017
Completion Date
09-Feb-2017

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SLOVENSKI STANDARD
SIST EN ISO 18081:2017
01-marec-2017
1HSRUXãLWYHQRSUHVNXãDQMH$NXVWLþQDHPLVLMD3UHVNXãDQMHWHVQRVWL]DNXVWLþQR
HPLVLMR ,62
Non-destructive testing - Acoustic emission testing (AT) - Leak detection by means of
acoustic emission (ISO 18081:2016)
Zerstörungsfreie Prüfung - Schallemission - Dichtheitsprüfung mittels Schallemission
(ISO 18081:2016)
Essais non destructif - Émission acoustique - Détection de fuite par émission acoustique
(ISO 18081:2016)
Ta slovenski standard je istoveten z: EN ISO 18081:2016
ICS:
17.140.99 Drugi standardi v zvezi z Other standards related to
akustiko acoustics
19.100 Neporušitveno preskušanje Non-destructive testing
SIST EN ISO 18081:2017 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 18081:2017

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SIST EN ISO 18081:2017


EN ISO 18081
EUROPEAN STANDARD

NORME EUROPÉENNE

June 2016
EUROPÄISCHE NORM
ICS 19.100
English Version

Non-destructive testing - Acoustic emission testing (AT) -
Leak detection by means of acoustic emission (ISO
18081:2016)
Essais non destructifs - Contrôle par émission Zerstörungsfreie Prüfung - Schallemissionsprüfung -
acoustique - Détection de fuites par émission Dichtheitsprüfung mittels Schallemission (ISO
acoustique (ISO 18081:2016) 18081:2016)
This European Standard was approved by CEN on 22 April 2016.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.





EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2016 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 18081:2016 E
worldwide for CEN national Members.

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SIST EN ISO 18081:2017
EN ISO 18081:2016 (E)
Contents Page
European foreword . 3
2

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SIST EN ISO 18081:2017
EN ISO 18081:2016 (E)
European foreword
This document (EN ISO 18081:2016) has been prepared by Technical Committee CEN/TC 138 “Non-
destructive testing” the secretariat of which is held by AFNOR, in collaboration with Technical
Committee ISO/TC 135 “Non-destructive testing”.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by December 2016, and conflicting national standards
shall be withdrawn at the latest by December 2016.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent
rights.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 18081:2016 has been approved by CEN as EN ISO 18081:2016 without any modification.


3

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SIST EN ISO 18081:2017

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SIST EN ISO 18081:2017
INTERNATIONAL ISO
STANDARD 18081
First edition
2016-06-01
Non-destructive testing — Acoustic
emission testing (AT) — Leak
detection by means of acoustic
emission
Essais non destructifs — Contrôle par émission acoustique —
Détection de fuites par émission acoustique
Reference number
ISO 18081:2016(E)
©
ISO 2016

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SIST EN ISO 18081:2017
ISO 18081:2016(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2016 – All rights reserved

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SIST EN ISO 18081:2017
ISO 18081:2016(E)

Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Personnel qualification . 2
5 Principle of acoustic emission method . 2
5.1 The AE phenomenon. 2
5.2 Influence of different media and different phases . 3
5.3 Influence of pressure differences . 4
5.4 Influence of geometry of the leak path . 4
5.5 Influence of wave propagation . 4
6 Applications . 5
7 Instrumentation . 5
7.1 General requirements . 5
7.2 Sensors . 5
7.2.1 Typical frequency ranges (band widths) . 5
7.2.2 Mounting method . 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 AT instruments . 6
7.4 Single and multichannel AT equipment . 6
7.4.1 Single-channel systems . 6
7.4.2 Multi-channel systems . 6
7.5 Measuring features (RMS, ASL vs. hit or continuous AE vs. burst AE) . 7
7.6 Verification using artificial leak noise sources . 7
8 Test steps for leak detection . 7
8.1 Sensor application . 7
8.2 Measured features . . 8
8.3 Background noise . 8
8.3.1 Environmental noise . 8
8.3.2 Process noise . 8
8.4 Data acquisition . 8
9 Location procedures . 9
9.1 General considerations . 9
9.2 Single sensor location based on AE wave attenuation. 9
9.3 Multi-sensor location based on Δt values (linear, planar) . 9
9.3.1 Threshold level and peak level timing method. 9
9.3.2 Cross correlation method .10
9.4 Wave type and wave mode based location .11
10 Data presentation .11
10.1 Numerical data presentation (level-meter) .11
10.2 Parametric dependent function (e.g. pressure) .11
10.3 Frequency spectrum .12
11 Data interpretation .12
11.1 Leak validation .12
11.1.1 On-site (during test) and off-site (post analysis) .12
11.1.2 Correlation with pressure .12
11.1.3 Rejection of false indications .12
© ISO 2016 – All rights reserved iii

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SIST EN ISO 18081:2017
ISO 18081:2016(E)

11.2 Leakage rate estimation .13
11.3 Demands on follow-up actions .13
12 Quality management documents .13
12.1 Test procedure .13
12.2 Test instruction .13
13 Test documentation and reporting .14
13.1 Test documentation .14
13.2 Test report .15
Annex A (normative) Examples of leak detection .16
Bibliography .28
iv © ISO 2016 – All rights reserved

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SIST EN ISO 18081:2017
ISO 18081:2016(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
ISO 18081 was prepared by the European Committee for Standardization (CEN) Technical Committee
CEN/TC 138, Non-destructive testing, in collaboration with ISO Technical Committee TC 135, Non-
destructive testing, Subcommittee SC 9, Acoustic emission testing, in accordance with the agreement on
technical cooperation between ISO and CEN (Vienna Agreement).
© ISO 2016 – All rights reserved v

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SIST EN ISO 18081:2017

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SIST EN ISO 18081:2017
INTERNATIONAL STANDARD ISO 18081:2016(E)
Non-destructive testing — Acoustic emission testing (AT)
— Leak detection by means of acoustic emission
1 Scope
This International Standard specifies the general principles required for leak detection by acoustic
emission testing (AT). It is addressed to the application of the methodology on structures and
components, where a leak flow as a result of pressure differences appears and generates acoustic
emission (AE).
It describes phenomena of the AE generation and influence of the nature of fluids, shape of the gap,
wave propagation and environment.
The different application methods, instrumentation and presentation of AE results is discussed.
Also included are guidelines for the preparation of application documents which describe specific
requirements for the application of the AE method.
Different application examples are given.
Unless otherwise specified in the referencing documents, the minimum requirements of this
International Standard are applicable.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
EN 1330-1, Non-destructive testing — Terminology — Part 1: General terms
EN 1330-2, Non-destructive testing — Terminology — Part 2: Terms common to the non-destructive
testing methods
EN 1330-9, Non-destructive testing — Terminology — Part 9: Terms used in acoustic emission testing
EN 13477-1, Non-destructive testing — Acoustic emission — Equipment characterisation —
Part 1: Equipment description
EN 13477-2, Non-destructive testing — Acoustic emission — Equipment characterisation —
Part 2: Verification of operating characteristics
EN 13554, Non-destructive testing — Acoustic emission testing — General principles
EN 60529, Degrees of protection provided by enclosures (IP Code)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 1330-1, EN 1330-2 and
EN 1330-9 and the following apply.
NOTE The definitions of leak, leakage rate, leak tight are those defined in EN 1330-8.
© ISO 2016 – All rights reserved 1

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SIST EN ISO 18081:2017
ISO 18081:2016(E)

4 Personnel qualification
It is assumed that acoustic emission testing is performed by qualified and capable personnel. In order
to prove this qualification, it is recommended to certify the personnel in accordance with ISO 9712.
5 Principle of acoustic emission method
5.1 The AE phenomenon
See Figure 1.
Key
1 fluid
2 AE sensor
Figure 1 — Schematic principle of acoustic emission and its detection
The continuous acoustic emission in the case of a leak, in a frequency range, looks like an apparent
increase in background noise, depending on pressure.
2 © ISO 2016 – All rights reserved

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SIST EN ISO 18081:2017
ISO 18081:2016(E)

Table 1 — Influence of the different parameters on the AE activity
Parameter Higher activity Lower activity
gas
Test media liquid
two phase
5.2 Viscosity low high
Type of flow turbulent laminar
Fluid velocity high low
5.3 Pressure difference high low
Shape of leak crack like hole
5.4 Length of leak path long short
Surface of leak path rough smooth
5.2 Influence of different media and different phases
The detectability of the leak depends on the fluid type and its physical properties. These will contribute
to the dynamic behaviour of the leak flow (laminar, turbulent) (see Table 1).
In contrast to turbulent flow, the laminar flow does not in general, produce detectable acoustic emission
signals.
Acoustic signals in conjunction with a leakage are generated by the following:
— turbulent flow of the escaping gas or liquid;
— fluid friction in the leak path;
— cavitations, during two-phase flow (gas coming out of solution) through a leaking orifice;
— the pressure surge generated when a leakage flow starts or stops;
— backwash of particles against the surface of equipment being monitored;
— gaseous or liquid jet (verification source);
— pulsating bubbles;
— explosion of bubbles;
— shock-bubbles on the walls;
— vaporization of the liquid (flashing).
The frequency content of cavitation may comprise from several kHz to several MHz.
Cavitation results in a burst emission whose energy is at least one order of magnitude higher than that
caused by turbulence.
The relative content in gas or air strongly influences the early stage of cavitation.
The acoustic waves generated by leaks can propagate by the walls of the system as well as through any
fluids inside.
Acoustic waves are generated by vibration at ultrasonic frequencies of the molecules of the fluid. The
vibrations are produced by turbulence and occur in the transition between a laminar and a turbulent
flow within the leak path and as these molecules escape from an orifice.
The acoustic waves produced by the above mentioned factors are used for leak detection and location.
© ISO 2016 – All rights reserved 3

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SIST EN ISO 18081:2017
ISO 18081:2016(E)

5.3 Influence of pressure differences
The pressure difference is the primary factor affecting leak rate. However, the presence of leak
paths may depend on a threshold value of fluid temperature or pressure. Pressure dependent leaks
and temperature dependent leaks have been observed, but in extremely limited number. Pressure-
dependent or temperature-dependent leaks denote a condition where no leakage exists until threshold
pressure or temperature is reached. At this point, the leakage appears suddenly and may be detectable.
When the pressure or temperature is reversed, the leakage follows the prescribed course to the
critical point at which leakage drops to zero. Temperature and pressure are not normally applied in
the course of leak testing for the purpose of locating such leaks. Instead, they are used to force existing
discontinuities to open, so as to start or increase the leakage rate to point of detection.
An example of this effect is the reversible leakages at seals below the service temperature and/or
service pressure.
AE waves emitted by a leak will normally have a characteristic frequency spectrum depending on
the pressure difference and shape of the leak path. Therefore the detectability of the leak depends
on the frequency response of the sensor and this shall be taken into account when selecting the
instrumentation.
5.4 Influence of geometry of the leak path
The AE intensity from a natural complex leak path (e.g. pinhole corrosion, fatigue or stress corrosion
cracks) is generally greater than that produced by leakage from a standard artificial source, such as a
drilled hole used for verification. The main parameters defining the complexity are the cross section,
length and surface roughness of the leak path.
5.5 Influence of wave propagation
Acoustic emission signals are the response of a sensor to sound waves generated in solid media. These
waves are similar to the sound waves propagated in air and other fluids but are more complex because
solid media are also capable of resisting shear force.
Waves that encounter a change in media in which they are propagating may change directions or
reflect. In additions to reflection, the interface causes the wave to diverge from its original line of flight
or refract in the second medium. Also the mode of the wave may be changed in the reflection and/or
refraction process.
An incident wave upon an interface between two media will reflect or refract such that directions of
the incident, reflected and refracted waves all lie in the same plane. This plane is defined by the line
along which the incident wave is propagating and the normal to the interface.
The below factors are important to AE technology:
a) wave propagation has the most significant influence on the form of the detected signal;
b) wave velocity is key to computed source location;
c) sound attenuation governs the maximum sensor spacing that is acceptable for effective detection.
The wave propagation influences the received waveform in the following ways:
— reflections, refractions and mode conversions on the way from source to sensor result in many
different propagation paths of different lengths;
— multiple propagation paths on the way from source to sensor, even in the absence of reflecting
boundaries may be caused by the structure itself. For example, spiral paths on a cylinder;
— separation of different wave components (different modes, different frequencies) travelling at
different velocities;
4 © ISO 2016 – All rights reserved

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SIST EN ISO 18081:2017
ISO 18081:2016(E)

— sound attenuation (volumetric dispersion, absorption, as well as attenuation due to the first and
third effects listed above).
The sound attenuation is influenced by liquids inside a structure or pipe, which will assist in the
propagation of acoustic waves, while liquids (inside and outside) have a tendency to reduce the
detectable signal of the propagation of the acoustic waves. This effect will depend on the ratio of the
acoustic impedances of the different materials. The AE wave inside will be used normally for the
detection of AE sources over long distances because of the low wave sound attenuation for most liquids.
6 Applications
Acoustic emission testing provides many possibilities to detect leaks from pressurized equipment in
industry and research fields. AT is used in following areas:
a) pressure vessels;
b) pipe and piping systems;
c) storage tanks;
d) boiler drums;
e) boiler tubes;
f) autoclaves;
g) heat exchangers;
h) containments;
i) valves;
j) safety valves;
k) pumps;
l) vacuum system
...

SLOVENSKI STANDARD
oSIST prEN 16696:2014
01-februar-2014
1HSRUXãLWYHQRSUHVNXãDQMH$NXVWLþQDHPLVLMD3UHVNXãDQMHWHVQRVWL
Non-destructive testing - Acoustic emission - Leak detection by means of acoustic
emission
Zerstörungsfreie Prüfung - Schallemission - Dichtheitsprüfung mittels Schallemission
Essais non destructif - Émission acoustique - Détection de fuite par émission acoustique
Ta slovenski standard je istoveten z: prEN 16696
ICS:
19.100 Neporušitveno preskušanje Non-destructive testing
oSIST prEN 16696:2014 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN 16696:2014

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oSIST prEN 16696:2014

EUROPEAN STANDARD
DRAFT
prEN 16696
NORME EUROPÉENNE

EUROPÄISCHE NORM

December 2013
ICS 19.100
English Version
Non-destructive testing - Acoustic emission - Leak detection by
means of acoustic emission
Essais non destructif - Émission acoustique - Détection de Zerstörungsfreie Prüfung - Schallemission -
fuite par émission acoustique Dichtheitsprüfung mittels Schallemission
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee CEN/TC 138.

If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations which
stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other language
made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are aware and to
provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without notice and
shall not be referred to as a European Standard.


EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2013 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 16696:2013 E
worldwide for CEN national Members.

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oSIST prEN 16696:2014
prEN 16696:2013 (E)
Contents Page
Foreword .4
1 Scope .5
2 Normative references .5
3 Terms and definitions .5
4 Personnel qualification .6
5 Principle of acoustic emission method .6
5.1 The AE phenomenon .6
5.2 Influence of different media and different phases .7
5.3 Influence of pressure differences .8
5.4 Influence of geometry of the leak path .8
5.5 Influence of wave propagation .8
6 Applications .9
7 Instrumentation . 10
7.1 General requirement . 10
7.2 Sensors . 10
7.3 Portable and non-portable (fixed installed) AE equipment . 11
7.4 Single- and multichannel AE equipment . 11
7.5 Measuring features (RMS, ASL vs. Hit or continuous vs. burst) . 11
7.6 Verification using artificial leak noise sources . 11
8 Test steps for leak detection . 12
8.1 Sensor application . 12
8.2 Measured features . 12
8.3 Background noise. 12
8.4 Environmental noise . 13
8.5 Process noise . 13
8.6 Data acquisition . 13
9 Location procedures . 13
9.1 General considerations . 13
9.2 Single sensor location – based on AE wave attenuation . 13
9.3 Multi-sensor location - based on delta-T values (linear, planar) . 14
9.4 Wave type and wave mode based location . 15
10 Data presentation. 16
10.1 Numerical data presentation (level-metre) . 16
10.2 Parametric dependent function (e.g. pressure) . 16
10.3 Frequency spectrum . 17
11 Data interpretation . 17
11.1 Leak validation . 17
11.2 Leakage rate estimation . 18
11.3 Demands on follow-up actions . 18
12 QM papers . 18
12.1 Test procedure . 18
12.2 Test instruction . 19
13 Test documentation and reporting . 19
13.1 Test documentation . 19
13.2 Test report . 20
2

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oSIST prEN 16696:2014
prEN 16696:2013 (E)
Annex A (normative)  Examples of leak detection . 21
A.1 Performance test of steam traps . 21
A.2 Applications on pipelines . 23
A.3 Application of leak detection during hydrotest of nuclear pressure equipment . 25
A.4 Application on tank floors . 28
A.5 Containment structure leak tightness testing . 30
Bibliography . 33

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Foreword
This document (prEN 16696:2013) has been prepared by Technical Committee CEN/TC 138 “Non-destructive
testing”, the secretariat of which is held by AFNOR.
This document is currently submitted to the CEN Enquiry.
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1 Scope
This European Standard specifies the general principles required for Leak Detection by the acoustic emission
(AE) testing. The Standard is addressed to the application of the methodology on structures and components,
where a leak flow as result of pressure differences appears and generates AE.
It describes phenomena of the AE generation and influence of the nature of fluids, shape of the gap, wave
propagation and environment.
The different application methods, instrumentation and presentation of AE results will be discussed. It also
includes the guidelines for the preparation of application documents, which describe specific requirements for
the application of the AE method.
Different application examples will be given.
Unless otherwise specified in the referencing documents, the minimum requirements of this standard are
applicable.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
EN 473, Non-destructive testing — Qualification and certification of NDT personnel — General principles
EN 1330-1, Non-destructive testing – Terminology – Part 1: General terms
EN 1330-2, Non-destructive testing – Terminology – Part 2: Terms common to the non-destructive testing
methods
EN 1330-9, Non-destructive testing – Terminology – Part 9: Terms used in Acoustic Emission testing
EN 13477-1, Non-destructive testing — Acoustic emission — Equipment characterisation – Part 1: equipment
description
EN 13477-2, Non-destructive testing – Acoustic emission — Equipment characterisation – Part 2: verification
of operating characteristics
EN 13554, Non-destructive testing — Acoustic emission — General principles
EN ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
3 Terms and definitions
For the purpose of this document, the terms and definitions given in EN 1330-1, EN 1330-2 and EN 1330-9
apply.
The definitions of “leak”, “leakage rate”, “leak tight” are those defined in EN 1330-8 “Terms used in leak
tightness testing”.
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4 Personnel qualification
It is assumed that acoustic emission testing is performed by qualified and capable personnel. In order to prove
this qualification, it is recommended to certify the personnel in accordance with EN 473.
5 Principle of acoustic emission method
5.1 The AE phenomenon

Figure 1 — Schematic principle of acoustic emission and its detection
The continuous acoustic emission in the case of leak looks like an apparent increase in background noise.
(Transients from pressure fluctuations are very different resulting in broad band acoustic emission) Temporal
variations of pressure fluctuations are very different; the frequency spectrum of acoustic noise generated is
then very large.
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Table 1 — Influence of the different parameters on the AE activity
 Parameter Higher activity Lower activity
gas
Test media liquid
two phase
5.2 Viscosity low high
Type of flow turbulent laminar
Fluid velocity high low
5.3 Pressure difference high low
Shape of leak crack like hole
5.4 Length of leak path long short
Surface of leak path rough smooth

5.2 Influence of different media and different phases
The detectability of the leak depends on the fluid type and its physical properties. These will contribute to the
dynamic behaviour of the leak flow (laminar, turbulent) (see Table 1).
In contrast to turbulent flow the laminar flow doesn’t in general produce detectable acoustic emission signals.
Acoustic signals of leakage are generated by
— turbulent flow of the escaping gas or liquid,
— fluid friction in the leak path,
— cavitations, during two-phase flow (gas coming out of solution) through a leaking orifice,
— the pressure surge generated when a leakage flow starts or stops,
— backwash of particles against the surface of equipment being monitored,
— gaseous or liquid jet,
— pulsating bubbles,
— explosion of bubbles,
— shock-bubbles on the walls,
— vaporisation of the liquid (flashing).
The duration of an event of cavitation in water is estimated at several tens of microseconds, which implies an
emission wavelength in a frequency spectrum about several kHz to several MHz.
Cavitation results in a discrete emission whose energy is at least than one order of magnitude from that
caused by turbulence.
The content in gas or air strongly influences the early stage of cavitation.
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When it rises, it makes the leak detection easier but at the same time the noise level tends to decrease
because of wave attenuation by air bubbles
The acoustic waves generated by leaks can propagate by the walls of system as well as through any fluids
inside. The vibration at ultrasonic frequencies of fluid molecules produced by turbulence that occur in the
transition from laminar to turbulent flow within the leak path and as they escape from an orifice is the source of
the acoustic waves.
The acoustic waves produced by the above mentioned factors are used for leak detection and location.
5.3 Influence of pressure differences
The pressure difference is the primary factor affecting leak rate. However, the presence of leak paths may
depend on a threshold value of fluid temperature or pressure. Both pressure dependent leaks and
temperature dependent leaks have been observed, but in extremely limited number. Pressure-dependent or
temperature-dependent leaks denote a condition where no leakage exists until threshold pressure or
temperature is reached. At this point, the leakage appears suddenly and may be detectable. When the
pressure or temperature is reversed, the leakage follows the prescribed course to the critical point at which
leakage drops to zero. Temperature and pressure are not normally applied in the course of leak testing for the
purpose of locating such leaks. Instead, they are used to force existing discontinuities to open, so as to start
or increase the leakage rate to point of detection.
An example of this effect is the reversible leakages at seals below the service temperature and/or service
pressure.
AE waves emitted by a leak will normally have a characteristic frequency spectrum depending on the pressure
difference and shape of the leak path. Therefore the detectability of the leak depends on the frequency
response of the sensor and this shall be taken into account when selecting the instrumentation.
5.4 Influence of geometry of the leak path
The AE intensity from a natural complex leak path (e.g. pinhole corrosion, fatigue or stress corrosion cracks)
is generally greater than that produced by leakage from a standard artificial source such as a drilled hole used
for verification. The main parameters defining the complexity are the cross section, length and surface
roughness of the leak path.
5.5 Influence of wave propagation
Acoustic emission signals are response of a sensor to sound waves generated in solid media. These waves
are similar to the sound waves propagated in air and other fluids but are more complex because solid media
are capable of resisting shear force.
Waves that encounter a change in media in which they are propagating may change directions or reflect. In
additions to reflection, the interface causes the wave to diverge from its original line of flight or refract in the
second medium. Also the mode of the wave may be changed in the reflection and/or refraction process.
An incident wave upon an interface between two media will reflect or refract such that directions of the
incident, reflected and refracted waves all lie in the same plane. This plane is defined by the line along which
the incident wave is propagating and the normal to the interface.
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Below are presented important factors to AE technology:
a) wave propagation has the most significant influence on the form of the detected signal;
b) wave velocity is key to computed source location;
c) attenuation governs the sensor spacing that is needed for effective detection.
The wave propagation influences the received waveform in the following ways.
— Reflections, refractions and mode conversions on the way from source to sensor result in many different
propagation paths of different lengths.
— Multiple propagation paths on the way from source to sensor - even in the absence of reflecting
boundaries may be caused by the structure itself. For example, spiral paths on a cylinder.
— Separation of different wave components (different modes, different frequencies) travelling at different
velocities.
— Attenuation (volumetric dispersion, absorption as well as attenuation due to the first and third effects
listed above).
The attenuation is influenced by liquids inside a system or pipe, which will assist in the propagation of acoustic
waves, while liquids outside (such as moisture in the soil) have a tendency to reduce detectable signal the
propagation of the acoustic waves. This effect will depend on the relative acoustic impedances of the different
materials.
6 Applications
Acoustic emission testing provides many possibilities to detect leaks from pressurised volumes in industry and
research fields. AT is used in following areas:
a) pressure vessels
b) pipe and piping systems
c) storage tanks
d) boiler drums
e) boiler tubes
f) autoclaves
g) heat exchangers
h) containments
i) valves
j) safety valves
k) pumps
l) vacuum systems
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7 Instrumentation
7.1 General requirement
Instrumentation components (hard and software) shall conform to the requirements of EN 13477-1 and
EN 13477-2.
7.2 Sensors
7.2.1 Typical frequency ranges (band width)
The optimum frequency range for leak detection depends very much on the application, e.g. the fluid type,
pressure difference at the leak, the leak rate, and the sensor to source distance and more. For example, the
optimum frequency range for tank floor leak detection of atmospheric tanks is around 20 kHz – 80 kHz,
because the source to sensor distance can be large and at these frequencies the attenuation is low. The
preferred frequency range for high pressure piping leak detection may go up to 400 kHz for optimum signal to
noise ratio in presence of disturbing sources. Leak detection at pipes for low pressure (e.g. water supply) is
usually performed at or below 5 kHz.
Usually a sensor is in direct contact to a test object. Then a coupling agent must be used between the sensor
and the test object for optimum and stable wave transfer. Durability, consistency, and chemical composition of
the coupling agent must comply with the duration of the monitoring, the temperature range and the corrosion
resistance of the test object.
7.2.2 Mounting method
The mounting method is influenced by the duration of the monitoring. For a temporary installation at a
ferromagnetic test object, a magnetic holder may be the preferred mounting tool. For permanent installations,
sensors might be fastened by metallic clamps or bonded to the test object using a suitable adhering coupling.
7.2.3 Temperature range, Wave guide
The specified temperature range of the AE sensor must meet the temperature conditions of the test object,
otherwise waveguides must be used between sensor and test object.
7.2.4 Intrinsic safety
If the sensor will be installed in a potentially explosive atmosphere, the sensor shall be intrinsically safe and
should usually be ATEX certified in accordance the classified hazard at the location where it shall be used.
See EN 60079-0, EN 60079-11 and EN 60079-14 for explosion proof installations.
7.2.5 Immersed sensors
If the sensor shall be immersed into a liquid, the sensor's IP-code (defined in EN 60529) shall be specified to
at least IP68. Sensor and other immersed accessories must be tight for the maximum possible pressure of the
liquid.
7.2.6 Integral electronics (amplifier, RMS converter, ASL converter, band pass)
Passive sensors and sensors with an integral preamplifier of suitable bandwidth are available. Sensors with
built-in electronics are less susceptible to electromagnetic disturbances, due to the elimination of a sensor-to-
preamplifier cable. These sensors are usually a little larger in size and weight and have a more limited
temperature range.
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Sensors may also include a signal to RMS converter, a signal to ASL converter and /or a limit-comparator with
digital output.
7.3 Portable and non-portable (fixed installed) AE equipment
An acoustic emission leak detection instrument designed for portable use contains usually one or a few
channels. The choice of a portable device is generally based on several factors such as cost, test duration,
hazard and availability of external power.
Portable devices are used e.g. for valve leak detection.
7.4 Single- and multichannel AE equipment
7.4.1 Single-channel systems
Single-channel systems are usually used for a point by point search mode, the sensor being moved to areas
of interest over the structure.
7.4.2 Multi-channel systems
Multi-channel systems are mainly used for large structures where the sensor positions are fixed and one of
the location procedures in 9.2 may be applied.
Also, permanently installed instruments for continuous remote structural health monitoring, e.g. for leak
detection in the piping network of nuclear plants, are often used in multi-channel configurations.
7.5 Measuring features (RMS, ASL vs. Hit or continuous vs. burst)
Simple instruments measure continuously only the ASL (the arithmetic average of the logarithm of the rectified
AE signal over a specified period of time) and/or RMS (the square root of the average of squared AE signal
over a specified period of time) and/or peak amplitudes within a specified period of time, and display the
results.
On some of the instruments the resulting functions over time can be shown for each channel numerically or
graphically and be compared against static or computed alarm levels so alarm conditions may automatically
and trigger an alarm.
More sophisticated instruments also may acquire and store waveform data for determination of time
differences by delta-t-measurement or cross correlation method.
7.6 Verification using artificial leak noise sources
An artificial leak noise source should be used for system verification.
A setup using an air jet or a test block/ pipe with a drilled hole passing a controlled flow of gas or liquid may be
used to determine the dependency of stimulation amplitude versus stimulated flow of gas or liquid and
amplitude measured at a certain distance from emitter.
Beside the same artificial leak noise source, which was used for the system verification, a well reproducible
artificial leak noise source, like a passive sensor stimulated by electrical white noise or a sine wave of a
certain frequency from a function generator, may be used for periodic system verification.
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8 Test steps for leak detection
8.1 Sensor application
For aboveground structures surface-mounted AE sensors with fixed positions are attached in direct contact to
the test object or via acoustic waveguides. The mounting method and useful coupling materials mainly depend
on temperature and duration of measurement (see 7.1).
The quality of sensor coupling can be enhanced by special shoes that conform to the diameter / curvature of
the tested structure.
In case of, for e.g. leak detection pigs for buried pipelines, the AE sensors are mounted on the pig and
measurements made during the pig run (see A.2). The position of the respective pig can be measured on the
basis of an encoder and/ or acoustic markers positioned on the outside of the pipe.
The sensors shall be positioned so as to ensure leak location based on appropriate location procedure (see
Clause 9) and to achieve the required location accuracy. Their positions on the structure shall take into
consideration welds, changes of shape that affect flow characteristics, shadowing effects of nozzles and
ancillary attachments etc.
For preparing the periodic system verification, appropriate locations for artificial stimulation shall be defined at
the test object and the response of certain sensors in various distances to the stimulation shall be determined
and periodically verified.
Prior to the test wave propagation and attenuation measurements using, e.g. Hsu-Nielsen source or artificial
leak noise sources (see 7.5) shall be performed on the structure in order to determine the effective wave
velocity and to calculate the maximum allowed sensor distance needed for leak detection with predefined
sensitivity. The maximum sensor spacing for detection and location of leaks is influenced by many factors
such as surface covering by coating, cladding or insulation, background noise level, system pressure, type of
fluid, type of leak etc.
8.2 Measured features
In its simplest form leak detection will comprise measurement of the RMS/ASL at each defined sensor position
as a function of pressure to estimate the approximate location of the leak. At the estimated position it is
recommended the RMS/ASL is measured as a function of increasing or decreasing pressure for verification
purposes.
For more complex situations for improved diagnosis other features may be measured, such as
— crest factor
— arrival time
— wave form
— frequency (spectrum
— other parametric inputs (e.g. temperature).
8.3 Background noise
The background noise is usually a combination of environmental and process noise.
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8.4 Environmental noise
Sometimes it is unavoidable that environmental noise, even airborne noise, is picked up in addition to the
sound of interest. This can be noise from weather conditions, road traf
...

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