ISO 20890-5:2020

INTERNATIONAL ISO
STANDARD 20890-5
First edition
2020-06
Guidelines for in-service inspections
for primary coolant circuit
components of light water reactors —
Part 5:
Eddy current testing of steam
generator heating tubes
Lignes directrices pour les contrôles périodiques des composants du
circuit primaire des réacteurs à eau légère —
Partie 5: Essai de tuyaux de chauffage pour générateurs de vapeur
par courant de Foucault
Reference number
ISO 20890-5:2020(E)
©
ISO 2020

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ISO 20890-5:2020(E)

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© ISO 2020
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Published in Switzerland
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ISO 20890-5:2020(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Inspection technique. 3
4.1 Preliminary remark . 3
4.2 General . 4
4.3 Standard technique . 4
4.3.1 Multiple frequency technique with internal bobbin probe in differential
arrangement . 4
4.3.2 Linking the signals of multiple frequencies with internal bobbin probe in
differential arrangement (mixed technique) . 5
4.3.3 Multifrequency system with internal bobbin probe in absolute arrangement. 5
4.4 Inspection techniques for more extensive analyses . 5
5 Requirements . 6
5.1 Test personnel . 6
5.1.1 Task of NDT personnel . . 6
5.1.2 Personnel requirements . 6
5.2 Steam generator heating tubes . 7
5.3 Eddy current test equipment . 8
5.3.1 General. 8
5.3.2 Test robot . 8
5.3.3 Eddy current test system . 9
5.3.4 Assistant analysis system .10
5.4 Data storage medium .11
6 Testing .11
6.1 General .11
6.2 Preparations .11
6.3 Implementation .11
6.3.1 General.11
6.3.2 Data acquisition .12
6.3.3 Data analysis .13
6.4 Final measures .15
7 Recording .15
7.1 Test record and test report .15
7.2 Indication list .15
7.3 Findings record .15
Annex A (informative) General test procedure .17
Bibliography .19
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ISO 20890-5:2020(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 voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/ iso/ foreword .html.
This document was prepared by ISO/TC 85, Nuclear energy, nuclear technologies, and radiological
protection, Subcommittee SC 6, Reactor technology.
A list of all parts in the ISO 20890 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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INTERNATIONAL STANDARD ISO 20890-5:2020(E)
Guidelines for in-service inspections for primary coolant
circuit components of light water reactors —
Part 5:
Eddy current testing of steam generator heating tubes
1 Scope
This document gives guidelines for pre-service inspection (PSI) and in-service inspections (ISI) by eddy
current tests on non-ferromagnetic steam generator heating tubes of light water reactors, whereby the
test is carried out using mechanised test equipment outwards from the tube inner side.
An in-service eddy current test of steam generator heating tube plugs as a component of the primary
circuit is not an object of this document. Owing to the different embodiments of steam generator
heating tube plugs, the use of specially adapted test systems to be qualified is necessary.
Test systems for the localisation of inhomogeneities (surface) and requirements for test personnel, test
devices, the preparation of test and device systems, the implementation of the testing as well as the
recording are defined.
NOTE Data concerning the test section, test extent, inspection period, inspection interval and evaluation of
indications is defined in the nuclear safety standards.
It is recommended that the technical specifications are based on experience on U-tube bends with even
bend radius (similar to the S/KWU design). To test other kind of tube bends (e.g. U-tube bends with two
90° bends) further qualifications will be provided.
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.
ISO 8596, Ophthalmic optics — Visual acuity testing — Standard and clinical optotypes and their
presentation
ISO 9712:2012, Non-destructive testing — Qualification and certification of NDT personnel
ISO 12718, Non-destructive testing — Eddy current testing — Vocabulary
ISO 15548-1, Non-destructive testing — Equipment for eddy current examination — Part 1: Instrument
characteristics and verification
ISO 15548-2, Non-destructive testing — Equipment for eddy current examination — Part 2: Probe
characteristics and verification
ISO 15548-3, Non-destructive testing — Equipment for eddy current examination — Part 3: System
characteristics and verification
ISO 15549, Non-destructive testing — Eddy current testing — General principles
ISO 18490, Non-destructive testing — Evaluation of vision acuity of NDT personnel
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ISO 20890-5:2020(E)

3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 12718 and the following 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/
3.1
analysis system
test system that is used with scanning sensors or segment sensors at steam
generator heating tubes for more precise characterisation of indications (3.2)
3.2
indication
representation or signal from a discontinuity in the format allowed by the NDT method used
[SOURCE: ISO/TS 18173:2005, 2.14]
Note 1 to entry: Signal that is initiated by operationally induced damage mechanisms, geometrical as well as
material or design induced influences.
3.3
evaluation
assessment (3.5) of indications (3.2) revealed by NDT against a predefined level
Note 1 to entry: Inspection of the recorded signals in respect to completeness and analysis capacity, localisation
and registration of indications according to defined criteria, representation of the test results.
[SOURCE: EN 1330-2:1998, 2.10]
3.4
basic frequency
test frequency that is used primarily for the localisation and analysis of indications in the standard
technique
3.5
assessment
comparison of the analysed measuring data with specified criteria
3.6
form indication
signal that is caused by geometrically induced influences
3.7
calibration
determination of the interrelation between the output measured data of the
eddy current test device and the associated indications (3.2), resulting from definite reference defects
at reference specimens
3.8
calibration block
piece of material of specified composition, surface finish, heat treatment and
geometric form, by means of which eddy current test equipment (3.15) can be assessed and calibrated
[SOURCE: ISO 5577:2017, 5.4.1]
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ISO 20890-5:2020(E)

3.9
test supervisor
responsible for application of the test method and for the individual details of the test implementation
including monitoring of the activities for preparation and implementation of the test as well as analysis
of the test results
3.10
test sensitivity
change to the initial variable of the eddy current test system (3.15) (amplitude/phase), in relation to the
change in the underlying input variable (e.g. wall thickness attenuation)
3.11
probe
body containing exciter elements (e.g. coils) and measuring elements
3.12
standard technique
test system that is carried out with internal coaxial probes (3.11) with coaxial
coils at steam generator heating tubes
3.13
interference signals
signals that impede the detection and analysis of indications
3.14
reference block
block of material representative of the material to be tested with similar
electromagnetic properties containing well-defined artificial discontinuities, used to adjust the
sensitivity and/or time base of the eddy current test equipment (3.15) in order to compare detected
discontinuity indications (3.2) with those arising from the known artificial discontinuities
Note 1 to entry: Specified metallurgical, geometrical and dimensional characteristics means for example
material, weld seam implementation, form, wall thickness with reference characteristics (e.g. notches, drill
holes) that are adapted to the test assignment.
[SOURCE: ISO 5577:2017, 5.4.2]
3.15
eddy current test equipment
eddy current test system, test robot and its measured data logging as well as the analysis unit including
software
4 Inspection technique
4.1 Preliminary remark
The suitability of the inspection technique and the test device system shall be validated corresponding
to the requirements of the applicable regulations of the nuclear safety standard.
[4]
NOTE The procedure for the qualification is described in ENIQ report nr. 31 .
A general test procedure shall be prepared. Annex A contains the items of the general test procedure.
A calibration procedure can be agreed between the contract partner and shall be documented.
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ISO 20890-5:2020(E)

4.2 General
During the eddy current testing of steam generator heating tubes, it is the task of the evaluation to
differentiate the recorded signals according to
— operational indications (location, expansion and possibly their type, e.g. cracks, abrasions, dents),
— geometric indications (e.g. of structural parts such as spacers, tube bottom, rolled-in slugs), and
— other indications (e.g. of local fluctuations in the electrical conductivity and permeability, electrical
interference, wobble effect of the probes, impurities on the inside or outside of the tube, production
indications as well as any external parts present).
To attain a sufficiently accurate reproduction of the signal sequence, the spatial resolution shall be set
so that the required spatial resolution is ensured by the selected sampling rate and the probe speed.
The probe speed shall be dependent on the base frequency and sample rate and shall be no faster than
the speed required to obtain a clear signal from the reference standard through-wall hole, within the
calibration limitations described in 6.3.3.2.
The following inspection technique can be used for the eddy current testing of steam generator heating
tubes as part of the standard technique:
— Multiple frequency technique with internal bobbin probe (differential arrangement, see 4.3.1;
absolute arrangement, see 4.3.3);
— Linking of the signals of multiple frequencies with internal bobbin probe in differential arrangement
(see 4.3.2).
If the standard technique is inadequate for evaluation of the eddy current signals, eddy current
techniques for more extensive evaluation (see 4.4 for additional techniques, e.g. rotating scanning
probes, matrix probes with T/R technique) or other non-destructive testing methods (e.g. ultrasonic
testing, visual inspection) shall be applied.
Supplementary to the standard technique, eddy current techniques for more extensive analyses can
also be used as localisation systems in case of specific requirements (e.g. testing in the area of tube
bottom/roll-in slugs).
4.3 Standard technique
4.3.1 Multiple frequency technique with internal bobbin probe in differential arrangement
4.3.1.1 Basic frequency
The total tube circumference is recorded integrally when testing with an internal coaxial probe. The
extension of indication can therefore only be determined in the axial direction. In the undisturbed
area, evaluation of the signals of a frequency for determining location, depth and axial extension of an
operational change is sufficient.
If indications overlap (e.g. operational indications and form indications), a statement is generally only
possible with restrictions. The multifrequency technique shall then be used in the mix (linking of
multiple frequencies) (see 4.3.2).
When testing operationally indications, the test frequencies used are generally in the range from
10 kHz to 1 MHz. The basic frequency shall be selected so that the phase offset angle between a 20 %
flat-bottom hole applied on the outside of a reference specimen and a through-wall drilled hole is in the
range from 90° to 120°.
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ISO 20890-5:2020(E)

4.3.1.2 Comparison between the signals of several individual frequencies with internal
bobbin probe
If indications occur, further frequencies can be used for the differentiation of interference signals and
operationally indications in addition to the basic frequency. The individual frequencies shall be selected
so that a significant phase offset angle is reached between indications and interference signals.
4.3.2 Linking the signals of multiple frequencies with internal bobbin probe in differential
arrangement (mixed technique)
4.3.2.1 General
Two to four frequencies are used generally for this inspection technique.
Linking the signals of multiple frequencies (mix) allows a quantitative analysis of operationally
indications even when indications with interference signals overlap. However, the test sensitivity (fault
detectability) generally declines for areas in which the evaluation is conducted in the mix.
The following two mixes shall be used as a minimum:
— 2-frequency mix for the area of the spacers and the area of the tube bottom;
— 3-frequency mix for the area of tube bottom with tube expansion (roll-in).
4.3.2.2 Two-frequency mix
The frequencies shall be selected so that the interference signals of all structural parts (e.g. spacers,
corrugated iron, and oscillation limiters) are suppressed. The phase offset angle between a wall
thickness weakening of 20 % applied on the outside of a reference specimen and a wall penetrating
reference fault shall be in the range from 80° to 100°.
4.3.2.3 Three-frequency mix
The frequencies shall be selected so that the interference signals of rolling and tube bend upper edges
or support plates and “pilger effects” are suppressed simultaneously. In addition, the mix phase offset
angle for wall thickness weakening applied to the outside of a reference specimen of 60 % and 20 %
shall exhibit a difference of minimum 40°.
4.3.3 Multifrequency system with internal bobbin probe in absolute arrangement
In contrast to the multiple frequency technique in differential arrangement, the absolute arrangement
serves for localising and evaluating flat incident indications with large extension in the axial direction
(e.g. large area abrasion in the area of tube bends) or for determining the sedimentation level in the
area above the tube bottom.
4.4 Inspection techniques for more extensive analyses
To supplement the standard inspection technique, probes are specifically used for the analysis of
already localised operational indications. These probes serve for characterisation of the indications in
respect to
— circumferential expansion,
— longitudinal expansion,
— determining the number of indications both in the longitudinal and circumferential direction,
— indication orientation, and
— indication type.
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ISO 20890-5:2020(E)

Here a detailed determination of the indication position in relation to structural parts can be made.
Owing to the smaller coil length of coverage, the smaller zone of interaction or the width of coverage,
the test sensitivity is increased in the longitudinal direction and in the circumferential direction (i.e. in
the entire range of the tube circumference). The multiple frequency technique is usually used here in
the same way as the standard inspection technique. The following are typically used as analysis probes:
— Rotating scanning probes;
— Segmentcoils;
— Matrix probes (array probes).
The following clauses in this document define the requirements for the standard inspection techniques
and shall be applied correspondingly to the analysis techniques used. Special requirements for the
analysis techniques require separate definition.
5 Requirements
5.1 Test personnel
5.1.1 Task of NDT personnel
[4]
NDT personnel have a great responsibility, not only with respect to their employers or contractors
but also under the rules of good workmanship. The NDT personnel may be independent and free from
economic influences with regard to his test results, otherwise the results are compromised. The NDT
personnel shall be aware of the importance of his signature and the consequences of incorrect test
results for safety, health and environment. Under legal aspects, the falsification of certificates is an
offence and judged according to the national legal regulations. A tester may find himself in a conflicting
situation about his findings with his employer, the responsible authorities or legal requirements.
Finally, the NDT personnel is responsible for all interpretations of test results carrying his signature.
NDT personnel should never sign test reports beyond their certification (see Table 1).
NOTE For reasons of readability, the male form is used with personal names, however the female form is
also always intended.
5.1.2 Personnel requirements
The test personnel comprise operating personnel for test robots, operating personnel for eddy current
test devices and analysts as well as the test supervisor.
Those personnel, using qualified non-destructive testing (NDT) procedures and equipment, should be
qualified through one or any combination of the following:
— certification through a national NDT personnel certification scheme;
— theoretical and/or open trials;
— blind trials.
Any personnel certification requirements invoking relevant national NDT personnel certification
schemes (e.g. ISO 9712) should be validated according to Table 1. Any additional personnel training
requirements should also be specified in the qualification dossier.
If no relevant scheme exists or if extra personnel qualification is needed, the qualification body should
determine the additional practical and theoretical examinations needed beyond those in the national
certification scheme, include these in the qualification procedure and ensure that the NDT procedure also
includes the necessary requirements. The qualification procedure should describe the proposed system.
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ISO 20890-5:2020(E)

The test supervisor is responsible for the application of the NDT qualified system and shall have the
knowledge required for his tasks as well as sufficient knowledge of the application options and limits
of the test methods and have knowledge about the characteristic appearances of operationally induced
defects. Indications beyond the evaluation limit shall be evaluated by the test supervisor, who has the
requisite experience in respect to the test object, test assignment, test method and device system.
The operating personnel for test robots and eddy current test devices shall be trained for the special
requirements of the work to be performed. In particular, they shall have adequate experience in the
implementation of eddy current tests and knowledge about the test object in respect to this testing.
The analysts shall be trained for the special requirements of the work to be performed and have
experience in the analysis and evaluation of indications as well as knowledge of the test object and the
characteristic appearance of indications.
Test personnel performing NDT and the evaluation of the results shall be qualified in accordance with
ISO 9712 or equivalent at an appropriate level in the relevant industrial sector.
Table 1 — Minimum requirements for the test personnel
Test personnel Qualification
Operating personnel for test robots Validation by training
Operating personnel for eddy current Certified with at least level 2 according to ISO 9712 or comparable
test devices qualification
Analysts Certified with at least level 2 according to ISO 9712 or comparable
qualification
Test supervisor Certified with level 3 according to ISO 9712
The test personnel shall fulfil the vision requirements of ISO 9712:2012, 7.4
The test personnel shall provide annual validation of their visual ability, which has been determined by
an ophthalmologist, ophthalmic optician or other medically recognised person. The vision requirements
of ISO 9712 shall be fulfilled. The following modifications can be used as a substitute to ISO 9712.
a) The visual acuity testing shall be conducted using standard symbols in accordance with ISO 8596
(Landolt rings) or ISO 18490 (E shaped character). Here a near vision acuity of 1,0 at a test dista
...