SIST EN 17391:2022
(Main)Non-destructive testing - Acoustic emission testing - Inservice acoustic emission monitoring of metallic pressure equipment and structures - General requirements
Non-destructive testing - Acoustic emission testing - Inservice acoustic emission monitoring of metallic pressure equipment and structures - General requirements
This standard describes acoustic emission (AE) monitoring for in service detection, location and grading of AE sources with application to metallic pressure equipment and structures. The monitoring can be periodic, temporary or continuous, on site or remote controlled, supervised or automated. The objectives of AE monitoring are to define regions which are acoustically active as a result of damage or defect evolution.
Zerstörungsfreie Prüfung - Schallemissionsprüfung - Überwachung der Schallemission von metallischen Druckgeräten und -strukturen im Betrieb - Allgemeine Grundsätze
Dieses Dokument beschreibt die Überwachung der Schallemission (AE) für die Erkennung, Lokalisierung und Einstufung von AE-Quellen im Einsatz bei der Anwendung auf metallische Druckgeräte und andere Konstruktionen, wie Brücken, Brückenseile, Krane, Speicherbehälter, Rohrleitungen, Windkrafttürme, Marineanwendungen, Offshore-Bauwerke usw. Die Überwachung kann periodisch, temporär oder konti-nuierlich, vor Ort oder ferngesteuert, überwacht oder automatisiert erfolgen. Ziel der AE-Überwachung ist es, Regionen zu definieren, die aufgrund von Schäden oder Defektentwicklungen akustisch aktiv sind.
Essais non destructifs - Contrôle par émission acoustique - Surveillance en service par émission acoustique des équipements et structures métalliques sous pression - Exigences générales
Le présent document spécifie les exigences générales relatives à la surveillance en service par émission acoustique (EA). Il porte sur la détection, la localisation et le classement des sources d’EA, avec une application aux équipements sous pression et autres structures métalliques tels que ponts, câbles de pont, grues, réservoirs de stockage, pipelines, mâts d’éoliennes, applications maritimes, structures offshore. La surveillance peut être périodique, temporaire ou continue, sur site ou à distance, supervisée ou automatisée. Les objectifs de la surveillance par EA sont de définir les zones qui sont acoustiquement actives à la suite de l’évolution d’un dommage ou d’un défaut.
Neporušitvene preiskave - Akustična emisija - Nadzorovanje akustične emisije pri uporabi kovinske tlačne opreme in drugih kovinskih struktur - Splošne zahteve
Ta standard opisuje nadzorovanje akustične emisije (AE) za ugotavljanje, iskanje in razvrščanje virov akustične emisije pri uporabi kovinske tlačne opreme in drugih kovinskih struktur. Nadzorovanje je lahko periodično, začasno ali stalno; izvaja se lahko na kraju samem ali na daljavo, pod nadzorom ali avtomatizirano. Cilj nadzorovanja akustične emisije je določitev območij, ki so akustično aktivna zaradi nastanka škode ali napak v razvoju.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 17391:2022
01-november-2022
Neporušitvene preiskave - Akustična emisija - Nadzorovanje akustične emisije pri
uporabi kovinske tlačne opreme in drugih kovinskih struktur - Splošne zahteve
Non-destructive testing - Acoustic emission testing - Inservice acoustic emission
monitoring of metallic pressure equipment and structures - General requirements
Zerstörungsfreie Prüfung - Schallemissionsprüfung - Überwachung der Schallemission
von metallischen Druckgeräten und -strukturen im Betrieb - Allgemeine Grundsätze
Essais non destructifs - Contrôle par émission acoustique - Surveillance en service par
émission acoustique des équipements et structures métalliques sous pression -
Exigences générales
Ta slovenski standard je istoveten z: EN 17391:2022
ICS:
19.100 Neporušitveno preskušanje Non-destructive testing
SIST EN 17391:2022 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 17391:2022
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SIST EN 17391:2022
EN 17391
EUROPEAN STANDARD
NORME EUROPÉENNE
June 2022
EUROPÄISCHE NORM
ICS 19.100
English Version
Non-destructive testing - Acoustic emission testing - In-
service acoustic emission monitoring of metallic pressure
equipment and structures - General requirements
Essais non destructifs - Contrôle par émission Zerstörungsfreie Prüfung - Schallemissionsprüfung -
acoustique - Surveillance en service par émission Überwachung der Schallemission von metallischen
acoustique des équipements et structures métalliques Druckgeräten und Strukturen im Betrieb - Allgemeine
sous pression - Exigences générales Grundsätze
This European Standard was approved by CEN on 5 March 2021.
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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, 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: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 17391:2022 E
worldwide for CEN national Members.
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SIST EN 17391:2022
EN 17391:2022 (E)
Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Personnel qualification . 6
5 Information prior to testing . 7
5.1 Structural information . 7
5.2 Operating conditions . 7
5.3 AE event mechanisms . 8
5.3.1 General. 8
5.3.2 Crack growth . 8
5.3.3 Corrosion . 9
5.3.4 Friction, fretting and cavitation erosion . 9
6 Monitoring methodology . 9
6.1 Periodic, temporary or continuous monitoring . 9
6.2 On-site or remote-controlled monitoring . 10
6.3 Supervised or automated monitoring . 11
7 Monitoring instrumentation . 11
7.1 System requirements . 11
7.2 Sensors and preamplifiers. 11
7.2.1 General requirements . 11
7.2.2 Frequency range (band width) . 12
7.2.3 Coupling agent . 13
7.2.4 Mounting method . 13
7.2.5 Temperature range, wave guide usage . 13
7.2.6 Use in explosive atmosphere . 13
7.2.7 Immersed sensors . 13
7.2.8 Integral electronics (amplifier, band-pass filter, RMS converter, ASL converter) . 13
7.2.9 Grounding . 14
7.2.10 External preamplifiers . 14
7.2.11 Sensor and preamplifier cables . 14
7.3 Portable AE equipment . 14
7.4 Single channel and multi-channel AE equipment . 14
7.5 Measured parameters . 14
7.5.1 Burst signal parameters . 14
7.5.2 Continuous signal parameters . 15
7.6 Verification of sensor sensitivity and coupling quality . 15
7.7 External parameters . 15
7.8 AE system . 15
7.9 Monitoring in hazardous areas . 16
8 Pre-monitoring measurements . 16
8.1 Wave propagation behaviour . 16
8.1.1 General. 16
8.1.2 Liquid or gas containment . 17
8.1.3 Wall thickness . 17
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8.1.4 Geometry of the structure . 17
8.1.5 Insulation . 17
8.1.6 Surface preparation . 17
8.2 Background noise measurement . 17
8.2.1 Representative location . 17
8.2.2 Process noise . 18
8.2.3 Other disturbance noise . 18
8.2.4 Noise sampling period . 18
8.3 Sensitivity of AE monitoring using linear or planar location . 18
9 Monitoring procedure . 19
9.1 Sensor positioning . 19
9.2 External parameters . 19
9.3 Instrumentation verification . 19
9.4 Data acquisition and online filtering . 19
10 Data analysis . 20
10.1 General . 20
10.2 Online analysis . 20
10.3 Data processing . 20
10.3.1 General . 20
10.3.2 Background noise analysis . 20
10.3.3 Pre-location data analysis . 21
10.3.4 AE event location . 21
10.3.5 Cluster analysis . 22
10.3.6 Pattern recognition . 22
11 AE source interpretation and evaluation . 22
11.1 Interpretation of AE results . 22
11.2 Source evaluation criteria . 23
11.3 Grading of AE sources . 25
11.4 Verification of AE sources and follow-up NDT . 26
12 Documentation and reporting . 26
Annex A (informative) Fatigue crack growth and associated acoustic emission applied to
monitoring of marine structures . 27
Bibliography . 38
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EN 17391:2022 (E)
European foreword
This document (EN 17391:2022) has been prepared by Technical Committee CEN/TC 138 “Non-
destructive testing”, the secretariat of which is held by AFNOR.
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 2022, and conflicting national standards
shall be withdrawn at the latest by December 2022.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
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Introduction
Acoustic emission testing (AT) is well established for the detection of discontinuities in metallic
structures. Furthermore, AT is widely accepted and applied during hydraulic or pneumatic test. In-
service acoustic emission (AE) monitoring can provide global surveillance of structural details for early
detection of active cracks and damage evolution. It allows through life damage assessment guiding
subsequent non-destructive testing (NDT) for damage verification and damage sizing purposes.
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1 Scope
This document specifies general requirements for in-service acoustic emission (AE) monitoring. It
relates to detection, location and grading of AE sources with application to metallic pressure equipment
and other structures such as bridges, bridge ropes, cranes, storage tanks, pipelines, wind turbine
towers, marine applications, offshore structures. The monitoring can be periodic, temporary or
continuous, on site or remote-controlled, supervised or automated. The objectives of AE monitoring are
to define regions which are acoustically active as a result of damage or defect evolution.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 1330-1:2014, Non destructive testing — Terminology — Part 1: List of general terms
EN 1330-2:1998, Non destructive testing — Terminology — Part 2: Terms common to the non-destructive
testing methods
EN 1330-9:2017, Non-destructive testing — Terminology — Part 9: Terms used in acoustic emission
testing
EN 13477-1:2001, Non-destructive testing — Acoustic emission — Equipment characterisation — Part 1:
Equipment description
EN 13477-2:2010, Non-destructive testing — Acoustic emission — Equipment characterisation — Part 2:
Verification of operating characteristic
EN 13554:2011, Non-destructive testing — Acoustic emission testing — General principles
1
EN 60529:1991, Degrees of protection provided by enclosures (IP Code)
EN ISO/IEC 17025:2017, General requirements for the competence of testing and calibration laboratories
(ISO/IEC 17025:2017)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 1330-1:2014, EN 1330-2:1998
and EN 1330-9:2017 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
4 Personnel qualification
It is assumed that acoustic emission monitoring is performed by qualified personnel. In order to prove
this qualification, it is recommended to qualify the personnel in accordance with EN ISO 9712.
1
As impacted by EN 60529:1991/corrigendum May 1993, EN 60529:1991/A1:2000, EN 60529:1991/A2:2013,
EN 60529:1991/AC:2016-12 and EN 60529:1991/A2:2013/AC:2019-02.
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5 Information prior to testing
5.1 Structural information
The monitoring of the structure depends on the historical operational data. The knowledge of the
operating conditions (e.g. maximum load level, cycling, environmental conditions) and possible repairs
are key factors for the determination of the monitoring strategy.
The accessibility of the structure shall be considered when the monitoring task is planned, designed and
performed.
The type and size of the structure (as well as other factors) shall determine whether the monitoring can
be global or local. If damage is expected in some specific areas of the structure, the sensor configuration
shall focus on these areas to monitor for possible damage evolution. In this case the monitoring may be
restricted to:
— a known damage mechanism at a specific location from experience; or
— highly stressed areas (hot spots) of known or predicted susceptibility to failure (e.g. finite element
analysis).
5.2 Operating conditions
In the case of a potentially explosive environment, the instrumentation used and its installation should
conform to Directive 2014/34/EU (ATEX) [7]. In particular sensors and preamplifiers shall be ATEX
certified.
For structures operating above or below a certain temperature level (e.g. above +80 °C or below
−40 °C), specific high/low temperature instrumentation shall be used. Appropriate attention shall be
given to the sensor coupling agent (see 7.2.3).
A high operating temperature, either by itself or in combination with the load, can influence the damage
mechanisms in the structure (e.g. high-temperature corrosion requires a high-temperature
environment).
In case of low-temperature operating conditions, attention shall be paid to the fracture toughness
(ductile-to-brittle transition) of the structure material. If the structure is insulated, as in many cases, the
formation of frost in the insulation windows should be avoided so that cracking of the frozen product
does not disturb AE monitoring.
Where the structure is located outside (in the open air), natural phenomena like wind, rain or hail can
disturb the AE monitoring. Such phenomena shall be taken into account during the preparation of the
monitoring methodology. If the structure cannot be protected from the environment, these natural
phenomena shall be measured as well as recorded and the data of the associated parametric inputs
correlated with the AE data.
In case of aggressive and/or corrosive environment such as exist in:
— marine or offshore structures (e.g. saline mist, waves, storms, etc.);
— chemical plant structures (e.g. acid);
— nuclear plants (e.g. radiation);
special care shall be taken for the protection of all the exposed AE instrumentation, sensors and
preamplifiers. The acquisition system shall be located as far as possible away from the above risks.
In case of high- or low-temperature operating structure, preliminary measurements shall be performed
in conditions as close as possible to real operating conditions.
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The influence of the process noise on the sensitivity of the monitoring shall be identified before starting
the monitoring itself.
All information on the various phases of the process shall be provided by the
customer/owner/operator. The severest process periods shall be taken into account to determine if the
monitoring is possible continuously or periodically.
5.3 AE event mechanisms
5.3.1 General
In technical application, detectability of early stages of structural degradation or damage, e.g. due to
fatigue and stress corrosion, is supported by material embrittlement (low temperature, hydrogen or
radiation induced embrittlement, hardened heat-affected zone of weld). Detectability can be enhanced
by major induced AE events in the material volume from secondary effects or processes. Secondary
effects are often of greater importance for early detectability compared to stable crack growth.
Simultaneously occurring secondary effects or processes can create intense sources of high AE activity
and/or higher burst signal maximum amplitudes from overlapping of many single low-energy events
e.g.:
— dislocation avalanche processes within an extended plastic zone at the tip of large cracks;
— fretting of non-corroded or corroded crack faces or stress transfer induced local interfacial friction
during opening/closure actions of fatigue cracks without any crack growth itself;
— AE emitting processes due to material morphology caused by local stress fields around/ahead of
crack tips, e.g. breakage of hard inclusions or high melting impurity phases in the ferrite grain or of
grain boundary precipitations;
— breakage of corrosion products (e.g. rust particles) internally or on corroded crack faces, etc.
5.3.2 Crack growth
Fatigue is the most common cause of mechanical failure of machinery and structures subjected to cyclic
loading. Stress corrosion cracking (SCC) is one of the common causes for failure in chemical reactors
and fluid transmission lines.
AE is sensitive to the brittle microscopic fracture events accompanying stable fatigue crack propagation
and corrosion related fracture events. The relationship between the acoustic emission from stable crack
growth in metals and the associated damage mechanisms, whether fatigue or stress corrosion cracking,
requires greater understanding of the physics of plastic deformation and fracture on the crystal
microstructure scale.
Annex A contains fracture parameters associated with acoustic emission from stable fatigue crack
growth with reference to marine structures. The driving force behind crack growth is the stress
concentration at the crack tip. Unless the crack is continually supplied with strain energy it will cease to
propagate.
Other stable crack growth mechanisms giving rise to acoustic emission include hydrogen cracking and
thermally induced cracks. AE monitoring may be used also for detection of hydrogen blistering,
delamination, creep and aging (material degradation).
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5.3.3 Corrosion
The mechanisms of corrosion are different to stable crack growth. General corrosion is usually a surface
oxidation over a large area. The AE activity and intensity depends on the severity of the ongoing
corrosion process.
Furthermore, stress due to pressure or temperature cycling usually leads to cracking and de-bonding of
the brittle oxide layer resulting in high AE activity over the corroded area.
Other localized corrosion processes may lead to damage with local stress concentration and subsequent
crack initiation (e.g. at the area of pin holes or pitting).
5.3.4 Friction, fretting and cavitation erosion
These damage mechanisms are particularly intense sources of acoustic emission.
Cavitation in a liquid leads to the implosion of bubbles that generates strong intensity (up to 1000 MPa)
and short duration (approximately µs) pressure waves. Notably AE from cavitation results in discrete
events, whose acoustic energy is at least an order of magnitude higher than those events generated by
turbulence phenomenon.
Fretting and friction phenomena generate AE of high energy and these mechanisms can be produced
within a crack during loading and unloading of the structure.
6 Monitoring methodology
6.1 Periodic, temporary or continuous monitoring
The integrity or health of a structure can be investigated by AE monitoring at any time of its working
life, i.e. in-service under normal operating loads, start up and shutdowns, provided that possible
variations of operating conditions do not come into conflict with the technical specifications of the AE
instrumentation or the measurement setup during data acquisition.
Large-scale and/or complex structures, e.g. ship hulls, offshore platforms or bridges permit AE
monitoring only for areas identified as highly stressed and fatigue and/or corrosion-sensitive.
Different in-service AE monitoring methodologies can be adapted depending on the objective of the
measurement, e.g.:
— temporary (short or medium term), if the monitoring is performed for a single short (hours/days)
or medium (weeks/month) time interval;
— periodic, if the monitoring is done repeatedly on the same structure for specific time periods not
necessarily based on the same time interval;
— continuous, if the monitoring is conducted permanently on the same structure for a long duration
(months or years).
The methodology and the time period of AE monitoring shall be selected taking into account:
— type of known or expected damage mechanisms activating AE sources like crack growth, corrosion,
cavitation;
— operating conditions such as temperature, hazardous environment, rate of pressure changes, flow
of fluids, vibration or frictional noise, process cycle duration;
— environmental noise, e.g. caused by wind, rain, thermal stress release.
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The required time periods and minimum duration of AE m
...
SLOVENSKI STANDARD
oSIST prEN 17391:2019
01-julij-2019
Neporušitvene preiskave - Akustična emisija - Nadzorovanje akustične emisije pri
uporabi kovinske tlačne opreme in drugih kovinskih struktur - Splošne zahteve
Non-destructive testing - Acoustic emission testing – In-service acoustic emission
monitoring of metallic pressure equipment and structures - General requirements
Zerstörungsfreie Prüfung - Schallemissionsprüfung - Überwachung der Schallemission
von metallischen Druckgeräten und -strukturen im Betrieb - Allgemeine Grundsätze
Ta slovenski standard je istoveten z: prEN 17391
ICS:
19.100 Neporušitveno preskušanje Non-destructive testing
oSIST prEN 17391:2019 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN 17391:2019
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oSIST prEN 17391:2019
DRAFT
EUROPEAN STANDARD
prEN 17391
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2019
ICS 19.100
English Version
Non-destructive testing - Acoustic emission testing - In-
service acoustic emission monitoring of metallic pressure
equipment and structures - General requirements
Zerstörungsfreie Prüfung - Schallemissionsprüfung -
Überwachung der Schallemission von metallischen
Druckgeräten und -strukturen im Betrieb - Allgemeine
Grundsätze
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, Serbia, 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: Rue de la Science 23, B-1040 Brussels
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 17391:2019 E
worldwide for CEN national Members.
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prEN 17391:2019 (E)
Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Personnel qualification . 7
5 Preliminary information . 7
5.1 Structural information . 7
5.2 Operating conditions . 7
5.3 AE event mechanisms . 8
5.3.1 General . 8
5.3.2 Crack growth . 8
5.3.3 Corrosion . 9
5.3.4 Friction, fretting and cavitation erosion . 9
6 Monitoring methodology . 9
6.1 Periodic, temporary or continuous monitoring . 9
6.2 On-site or remote-controlled monitoring . 10
6.3 Supervised or automated monitoring . 11
7 Monitoring instrumentation . 11
7.1 General requirement . 11
7.2 Sensors and Preamplifiers . 11
7.2.1 General . 11
7.2.2 Typical frequency ranges (band width) . 12
7.2.3 Coupling agent . 12
7.2.4 Mounting method . 12
7.2.5 Temperature range, wave guide usage . 13
7.2.6 Use in explosive atmosphere . 13
7.2.7 Immersed sensors . 13
7.2.8 Integral electronics (amplifier, band pass filter, RMS converter, ASL converter) . 13
7.2.9 Grounding requirements . 13
7.2.10 External preamplifiers . 13
7.2.11 Sensor and preamplifier cables . 14
7.3 Portable AE equipment . 14
7.4 Single- and multi-channel AE equipment . 14
7.5 Measured parameters . 14
7.5.1 Burst signal parameters . 14
7.5.2 Continuous signal parameters . 14
7.6 Verification of sensor sensitivity and coupling quality . 15
7.7 External parameters . 15
7.8 AE system . 15
7.9 Monitoring in hazardous areas . 16
8 Pre-Monitoring measurements . 16
8.1 Wave propagation behaviour . 16
8.1.1 General . 16
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8.1.2 Liquid or gas containment . 16
8.1.3 Thickness of the wall (material) . 17
8.1.4 Geometry of the structure . 17
8.1.5 Insulation . 17
8.1.6 Surface preparation . 17
8.2 Background noise measurements . 17
8.2.1 Representative location . 17
8.2.2 Process noise . 17
8.2.3 Other disturbance noise . 18
8.2.4 Noise sampling period . 18
8.3 Sensitivity of AE monitoring using linear or planar location . 18
9 Monitoring procedure . 18
9.1 Sensor positioning . 18
9.2 External parameters . 19
9.3 Instrumentation verification and performance . 19
9.4 Data acquisition and online filtering . 19
10 Data analysis . 19
10.1 General . 19
10.2 Online analysis . 20
10.3 Data processing . 20
10.3.1 Background noise analysis . 20
10.3.2 Pre-location data analysis . 20
10.3.3 AE event location . 21
10.3.4 Cluster analysis . 21
10.3.5 Pattern recognition . 21
11 AE source interpretation and evaluation . 22
11.1 Interpretation of AE results . 22
11.2 Source evaluation criteria . 22
11.3 Grading and severity of AE sources . 25
11.4 Verification of AE sources and follow-up NDT . 25
12 Documentation and reporting . 26
Annex A (informative) Fatigue crack growth and associated acoustic emission applied to
monitoring of marine structures . 27
A.1 Definitions . 27
A.1.1 General . 27
A.1.2 Acoustic emission power . 27
A.1.3 Acoustic emission energy . 27
A.1.4 Acoustic emission intensity . 27
A.2 AE power and resulting waves from a micro-fracture event (AE source) . 27
A.3 AE detectability . 29
A.4 Fatigue crack growth . 30
A.5 Critical crack depth . 31
A.6 Crack growth rate and required duration of monitoring. 32
A.7 AE fatigue monitoring of ship hull structure . 35
Bibliography . 37
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European foreword
This document (prEN 17391:2019) 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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Introduction
Acoustic emission testing (AT) is well established for the detection of discontinuities in metallic
structures. Furthermore, AT is widely accepted and applied during hydraulic or pneumatic test. In
service acoustic emission (AE) monitoring can provide global surveillance of structural details for early
detection of active cracks and damage evolution. It allows through life damage assessment guiding
subsequent non-destructive testing (NDT) for damage verification and damage sizing purposes.
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1 Scope
This document describes acoustic emission (AE) monitoring for in-service detection, location and
grading of AE sources with application to metallic pressure equipment and other structures such as
bridges, bridge ropes, cranes, storage tanks, pipelines, wind turbine towers, marine applications,
offshore structures etc. The monitoring can be periodic, temporary or continuous, on site or remote-
controlled, supervised or automated. The objectives of AE monitoring are to define regions which are
acoustically active as a result of damage or defect evolution.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 1330-1:2015, Non-destructive testing - Terminology - Part 1: List of general terms
EN 1330-2:1998, Non destructive testing - Terminology - Part 2: Terms common to the non-destructive
testing methods
EN 1330-9:2017, Non-destructive testing - Terminology - Part 9: Terms used in acoustic emission testing
EN 13477-1:2001, Non-destructive testing - Acoustic emission - Equipment characterisation - Part 1:
Equipment description
EN 13477-2:2013, Non-destructive testing - Acoustic emission - Equipment characterisation - Part 2:
Verification of operating characteristics
EN 13554:2011, Non-destructive testing - Acoustic emission testing - General principles
EN 14584:2013, Non-destructive testing - Acoustic emission testing - Examination of metallic pressure
equipment during proof testing - Planar location of AE sources
EN 15495:2007, Non Destructive testing - Acoustic emission - Examination of metallic pressure equipment
during proof testing - Zone location of AE sources
EN ISO/IEC 17025:2017, Non-destructive testing - General requirements for the competence of testing
and calibration laboratories
EN 60529:2014, Degrees of protection provided by enclosures (IP Code)
3 Terms and definitions
For the purpose of this document, the terms and definitions given in EN 1330-1:2015, EN 1330-2:1998
and EN 1330-9:2017 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
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4 Personnel qualification
It is assumed that acoustic emission monitoring is performed by qualified and capable personnel. In
order to prove this qualification, it is recommended to certify the personnel in accordance with
EN ISO 9712:2013.
5 Preliminary information
5.1 Structural information
The monitoring of the structure depends on the historical operational data. The knowledge of the
operating conditions (e.g. maximum load level, cycling, environmental conditions) and possible repairs
are key factors for the determination of the monitoring strategy.
The accessibility of the structure shall be considered when the monitoring task is planned, designed and
performed.
The type and size of the structure (as well as other factors below) shall determine if the monitoring can
be global or local. If damage is expected in some specific areas of the structure, the sensor configuration
shall focus on these areas to monitor for possible damage evolution. In this case the monitoring may be
restricted to:
— a known damage mechanism at a specific location from experience; or
— highly stressed areas (hot spots) of known or predicted susceptibility to failure (e.g. finite element
analysis).
5.2 Operating conditions
In the case of a potentially explosive environment, the instrumentation used and its installation should
conform to Directive 2014/34/EU (ATEX) [1]. In particular sensors and preamplifiers shall be ATEX
certified.
For structures operating above or below a certain temperature level (e.g. above +80 °C or below
−40 °C), specific high/low temperature instrumentation shall be used. Appropriate attention shall be
given to the sensor coupling agent (see Subclause 7.2.3).
A high operating temperature, either by itself or in combination with the load, may influence the
damage mechanisms in the structure (e.g. high-temperature corrosion requires a high temperature
environment).
In case of low temperature operating conditions, attention shall be paid to the fracture toughness
(ductile-to-brittle transition) of the structure material. If the structure is insulated, as in many cases, the
formation of frost in the insulation windows should be avoided so that cracking of the frozen product
does not disturb AE monitoring.
Where the structure is located outside (in the open air), natural phenomena like wind, rain or hail can
disturb the AE monitoring. Such phenomena shall be taken into account during the preparation of the
monitoring methodology. If the structure cannot be protected from the environment, these natural
phenomena shall be measured as well as recorded and the data of the associated parametric inputs
correlated with the AE data.
In case of aggressive and/or corrosive environment such as:
— marine or offshore structures (e.g. saline mist, waves, storms…);
— chemical plant structures (e.g. acid); or
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— nuclear plants (e.g. radiation);
special care shall be taken for the protection of all the exposed AE instrumentation, sensors and
preamplifiers. The acquisition system shall be located as far as possible away from the above risks.
In case of high or low temperature operating structure, preliminary measurements shall be performed
in conditions as close as possible to real operating conditions.
The influence of the process noise on the sensitivity of the monitoring shall be identified before starting
the monitoring itself.
All information on the various phases of the process shall be provided by the
customer/owner/operator. The severest process periods shall be taken into account to determine if the
monitoring is possible continuously or periodically.
5.3 AE event mechanisms
5.3.1 General
In technical application, detectability of early stages of structural degradation or damage due to e.g.
fatigue and stress corrosion, is supported by material embrittlement (low temperature, hydrogen or
radiation induced embrittlement, hardened heat effected zone of weld, etc.). Detectability can be
enhanced by major induced AE events in the material volume from secondary effects or processes.
Secondary effects are often of greater importance for early detectability compared to stable crack
growth.
Simultaneously occurring secondary effects or processes can create intense sources of high AE activity
and/or higher burst signal maximum amplitudes from overlapping of many single low energy events
e.g.:
— dislocation avalanche processes within an extended plastic zone at the tip of large cracks;
— fretting of (non-corroded or corroded) crack faces or stress transfer induced local interfacial
friction during opening/closure actions of fatigue cracks without any crack growth itself;
— AE emitting processes due to material morphology caused by local stress fields around/ahead of
crack tips, e.g. breakage of hard inclusions or high melting impurity phases in the ferrite grain or of
grain boundary precipitations;
— breakage of corrosion products (e.g. rust particles) internally or on corroded crack faces etc.
5.3.2 Crack growth
Fatigue is the most common cause of mechanical failure of e.g. machinery and structures subjected to
cyclic loading. Stress corrosion cracking (SCC) is one of the common causes for failure in e.g. chemical
reactors and fluid transmission lines.
AE is sensitive to the brittle microscopic fracture events accompanying stable fatigue crack propagation
and corrosion related fracture events. The relationship between the acoustic emission from stable crack
growth in metals and the associated damage mechanisms, whether fatigue or stress corrosion cracking,
requires greater understanding of the physics of plastic deformation and fracture on the crystal
microstructure scale.
Annex A gives expressions for the key deformation and fracture parameters associated with acoustic
emission from stable fatigue crack growth. The driving force behind crack growth is the stress
concentration at the crack tip. Unless the crack is continually supplied with strain energy it will cease to
propagate.
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Other stable crack growth mechanisms giving rise to acoustic emission include hydrogen cracking and
thermally induced cracks. AE monitoring may be used also for detection of hydrogen blistering,
delamination, creep and aging (material degradation).
5.3.3 Corrosion
The mechanisms of corrosion are different to stable crack growth. General corrosion is usually a surface
oxidation over a large area. The AE activity and intensity depends on the severity of the ongoing
corrosion process.
Furthermore, stress due to pressure or temperature cycling usually leads to cracking and de-bonding of
the brittle oxide layer resulting in high AE activity over the corroded area.
Other localized corrosion processes may lead to damage with local stress concentration and subsequent
crack initiation (e.g. at the area of pin holes or pitting).
5.3.4 Friction, fretting and cavitation erosion
These damage mechanisms are particularly intense sources of acoustic emission.
Cavitation in a liquid leads to the implosion of bubbles that generates strong intensity (up to 1000 MPa)
and short duration (approximately µs) pressure waves. Notably AE from cavitation results in discrete
events, whose acoustic energy is at least an order of magnitude higher than those events generated by
turbulence phenomenon.
Fretting and friction phenomena generate AE of high energy and these mechanisms can be produced
within a crack during loading and unloading of the structure.
6 Monitoring methodology
6.1 Periodic, temporary or continuous monitoring
The integrity or health of a structure can be investigated by AE monitoring at any time of its working
life (i.e. in-service under normal operating loads, start up and shutdowns, etc.) provided that possible
variations of operating conditions do not come into conflict with the technical specifications of the AE
instrumentation or the measurement setup during data acquisition.
Large-scale and/or complex structures, e.g. ship hulls, offshore platforms or bridges permit AE
monitoring only for areas identified as highly stressed and fatigue and/or corrosion sensitive.
Different in-service AE monitoring methodologies can be adapted depending on the objective of the
measurement, e.g.:
— temporary (short or medium term), if the monitoring is performed for a single short (hours/days)
or medium (weeks/month) time interval;
— periodic, if the monitoring is done repeatedly on the same structure for specific time periods not
necessarily based on the same time interval;
— continuous, if the monitoring is conducted permanently on the same structure for a long duration
(months or years).
The methodology and the time period of AE monitoring are selected taking into account:
— type of known or expected d
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