ISO 18211:2016

Non-destructive testing — Long-range inspection of above-ground pipelines and plant piping using guided wave testing with axial propagation

ISO 18211:2016 specifies a method for long-range testing of carbon and low-alloy steel above-ground pipelines and plant piping using guided ultrasonic waves with axial propagation applied on the entire circumferential pipe section, in order to detect corrosion or erosion damage. The guided wave testing (GWT) method allows for fast inspection of above-ground pipelines, plant piping and cased road crossings, giving a qualitative screening and localization of probable corroded and eroded areas. GWT is typically performed on operating piping systems. ISO 18211:2016 is applicable to the following types of pipes: a) above-ground painted pipelines; b) above-ground insulated pipelines; c) painted plant piping; d) insulated plant piping. NOTE Pipe sections within road crossings with external casings (without bitumen or plastic coating) are a special case of buried pipe where there is no soil pressure on the OD of the pipe. ISO 18211 :2016 applies to these cased road crossings. Other types of pipes not included in the above list need dedicated approaches due to increased complexity.

Essais non destructifs — Vérification à large échelle des réseaux de canalisations hors sol et de la tuyauterie d'usine utilisant un essai d'onde guidée à propagation axiale

General Information

• Status: Published
• Publication Date: 13-Jul-2016
• ICS: 19.100 - Non-destructive testing
• Technical Committee: IIW - International Institute of Welding
• Drafting Committee: IIW - International Institute of Welding
• Parallel Committee: ISO/TC 135/SC 3 - Ultrasonic testing
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 15-Jun-2022

Relations

• Consolidated By: ISO 177:2016 - Plastics — Determination of migration of plasticizers
• Effective Date: 06-Jun-2022

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 18211
First edition
2016-07-15
Non-destructive testing — Long-range
inspection of above-ground pipelines
and plant piping using guided wave
testing with axial propagation
Essais non destructifs — Vérification à large échelle des réseaux de
canalisations hors sol et de la tuyauterie d’usine utilisant un essai
d’onde guidée à propagation axiale
Reference number
ISO 18211:2016(E)
©
ISO 2016

---------------------- Page: 1 ----------------------
ISO 18211:2016(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. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2016 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 18211:2016(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test personnel . 3
5 General . 3
6 Factors influencing GWT performance . 4
6.1 External diameter . 4
6.2 Pipeline geometry . 4
6.3 Test range . 4
6.4 Road crossing . 5
7 Test equipment. 5
7.1 General . 5
7.2 Probe ring . 5
7.3 Signal processing and analysis system . 5
7.4 Periodic verification of equipment performance . 5
7.5 Instrument settings . 6
8 Test procedure . 6
9 Requirements for test data quality . 6
10 Testing . 7
10.1 Preparation of the test object . 7
10.1.1 Surface temperature . 7
10.1.2 Removal of insulation . 7
10.1.3 Wall thickness assessment . 7
10.1.4 Surface preparation . 7
10.2 Probe ring test position . 8
10.3 Data collection . 8
10.4 Reporting sensitivity . 8
10.5 Data interpretation . 8
10.6 Detection sensitivity . 9
10.7 Visual confirmation . 9
11 Complementary NDT to support the GWT . 9
12 Test report . 9
Annex A (informative) Selection of guided wave modes .11
Bibliography .15
© ISO 2016 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO 18211:2016(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 World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is IIW, International Institute of Welding, Commission V.
Requests for official interpretations of any aspect of this International Standard should be directed to
the ISO Central Secretariat, who will forward them to the IIW Secretariat for an official response.
iv © ISO 2016 – All rights reserved

---------------------- Page: 4 ----------------------
INTERNATIONAL STANDARD ISO 18211:2016(E)
Non-destructive testing — Long-range inspection of above-
ground pipelines and plant piping using guided wave
testing with axial propagation
1 Scope
This International Standard specifies a method for long-range testing of carbon and low-alloy steel
above-ground pipelines and plant piping using guided ultrasonic waves with axial propagation applied
on the entire circumferential pipe section, in order to detect corrosion or erosion damage.
The guided wave testing (GWT) method allows for fast inspection of above-ground pipelines, plant
piping and cased road crossings, giving a qualitative screening and localization of probable corroded
and eroded areas. GWT is typically performed on operating piping systems.
This International Standard is applicable to the following types of pipes:
a) above-ground painted pipelines;
b) above-ground insulated pipelines;
c) painted plant piping;
d) insulated plant piping.
NOTE Pipe sections within road crossings with external casings (without bitumen or plastic coating) are
a special case of buried pipe where there is no soil pressure on the OD of the pipe. This International Standard
applies to these cased road crossings.
Other types of pipes not included in the above list need dedicated approaches due to increased
complexity.
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
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
axial direction
direction along the main axis of the pipe
3.2
circumferential direction
direction around the circumference of the pipe
3.3
total pipe wall cross-section
TCS
area between the inner and outer diameters of the pipe in a plane perpendicular to the pipe axis
© ISO 2016 – All rights reserved 1

---------------------- Page: 5 ----------------------
ISO 18211:2016(E)

3.4
cross-section change
equivalent cross-section change calculated assuming that an indication is purely caused by a change in
the cross-section of the pipe wall
3.5
datum point
reference point for reporting a test position (3.16) and for correlating test results with the corresponding
position on the test object
3.6
dead zone
length of pipe on either side of the test position (3.16) where reflectors of interest cannot be detected
because they are covered by the transmitted pulse
3.7
flexural mode
non-symmetric bending type mode of guided wave propagation in pipes, with particle displacements in
axial, circumferential and radial directions
3.8
focus
concentration of guided waves at a single axial and circumferential position, achieved either by
hardware settings or by post-processing of a recorded set of signals (synthetic focus)
3.9
geometric feature
pipeline feature (e.g. weld, support, flange, bend, etc.) causing the reflection of guided waves because of
a cross-section change (3.4) or other acoustic impedance variation
3.10
guided wave mode
distinct type of guided wave with a specific vibration pattern
3.11
longitudinal mode
symmetric compression type mode of guided wave propagation in pipes, with particle displacements
predominantly in the axial direction (3.1)
3.12
primary mode
guided wave mode (3.10) which is chosen for the incident wave
3.13
probe ring
circumferential component, containing transducer elements with direct contact to the pipe
3.14
secondary mode
guided wave mode (3.10) which is different from the primary mode (3.12) and is generated by mode
conversion at pipe features or discontinuities
3.15
test frequency
centre frequency of the pulses transmitted by the probe ring (3.13)
3.16
test position
axial position on the pipe where the probe ring (3.13) is placed
2 © ISO 2016 – All rights reserved

---------------------- Page: 6 ----------------------
ISO 18211:2016(E)

3.17
test range
distance between the test position (3.16) and the furthest position for which the minimum acceptable
sensitivity of the reference signal is achieved, in each direction (positive or negative)
3.18
torsional mode
symmetric twisting type mode of guided wave propagation in pipes, with particle displacements in the
circumferential direction (3.2)
4 Test personnel
The personnel performing ultrasonic guided wave testing shall be qualified in accordance with
ISO 9712 or with any another equivalent standard of the relevant industrial sector.
Training in the use of the specific equipment is required because there are significant differences
between the available systems and diagnostic approaches.
5 General
Ultrasonic guided wave testing (GWT) uses elastic waves which are guided along the pipe wall and can
travel long distances, thus providing rapid near complete coverage of the volume of the pipe wall.
The typical test setup is comparable to conventional ultrasonic pulse-echo testing: an ultrasonic
instrument forces transducers in the probe ring to generate ultrasonic waves in the pipe wall which
are reflected by discontinuities and received by the same probe ring. The time-of-flight of the received
signal indicates the distance between the discontinuities and the probe ring. A single test with guided
waves can cover a length of pipe of tens of meters.
Within this International Standard, GWT is performed as a screening method. The reflections returning
from discontinuities and received by the ultrasonic instrument indicate the position of the discontinuity.
However, they do not give detailed quantitative information about its morphology. Therefore, GWT is
used to indicate any locations which need to be followed up with complementary detailed inspection.
More information on the nature of guided waves is given in Annex A.
Within this International Standard, GWT typically uses a frequency range between 20 kHz and 500 kHz.
If the performance of the test has been shown to have equal or better sensitivity to that obtained with
the frequency range specified above, a frequency lower than 20 kHz can be used for GWT.
The successful application of guided ultrasonic waves requires the following:
a) selective pure mode transmission and reception;
b) wave modes which are non-dispersive in the frequency range used;
c) coverage of the full cross section of the pipe wall;
d) signals coming from each direction shall be distinguished.
The amplitude of a reflected ultrasonic guided wave signal from a discontinuity varies in a complex
manner that depends on many factors such as test frequency, guided wave mode and the specific
morphology of the discontinuity. It is often possible to correlate the size of the reflected signal with
the overall cross-section change in the pipe wall resulting from wall loss, meaning that GWT can
qualitatively group discontinuities into different severity groups such as indications of low, medium and
high concern. However, usually the parameter of interest when testing piping systems with wall loss is
the remaining wall thickness in areas with discontinuities, which GWT cannot accurately provide (see
Annex A for more information).
It is recommended to perform ultrasonic guided wave testing using a range of frequencies to improve
the accuracy of the test. Also, GWT ultrasonic instruments often employ advanced approaches like
© ISO 2016 – All rights reserved 3

---------------------- Page: 7 ----------------------
ISO 18211:2016(E)

focusing or synthetic focusing to improve the sensitivity and discontinuity sizing ability of GWT. The
use of these is not specified in this International Standard, but background information is provided in
Annex A.
6 Factors influencing GWT performance
6.1 External diameter
The sensitivity of GWT depends on the cross-section change. The absolute cross-section change in a
pipe due to corrosion or erosion loss is measured in the units of area and depends on both the depth
and the circumferential extent of the discontinuity. GWT is sensitive to a minimum per cent of cross-
sectional loss, which is a function of both the absolute cross-section change and the pipe geometry. As
an example, a discontinuity in a small diameter pipe may represent a large per cent change in cross
section that is easily detectable using GWT, but the same discontinuity in a large diameter pipe may
represent a small cross-section change that cannot be detected using GWT. Because of this effective
decrease in sensitivity as pipe diameter increases, testing of pipes larger than DN 600 (24 inches in
diameter) can miss significant isolated corrosion pits, so it is recommended that complementary NDT
methods are used. When testing pipes where the known damage mechanisms result in larger cross-
section changes rather than isolated pitting, GWT is still recommended for rapid testing of pipes with
diameters larger than DN 600 (24 inches in diameter).
6.2 Pipeline geometry
The complexity of the pipe geometry can limit guided wave propagation. Below are summarized the
effects of some common pipe features which can be present in the pipes listed in Clause 1.
a) It is not possible to test beyond flanged joints or any breaks of the pipe because the guided waves
cannot propagate across them.
b) It is not permitted to test beyond an elbow fitting; instead, the tool shall be moved to a test position
on the other side of the bend. Testing beyond “pulled” bends, where a straight length of pipe is
formed into a curve of radius equal to five or more times the pipe diameter is permitted.
c) It is permitted to test beyond a branch or a tee only if the diameter of the branch is no greater than
½ the diameter of the pipe being tested. This restriction is to avoid problems with distortion of the
forward travelling guided wave by interactions with the branch.
d) It is not permitted to test beyond a support if the amplitude of reflection from it is higher than 6 dB
below the weld DAC curve. This restriction is to avoid problems of the distortion of the forward
travelling guided wave by interactions with the support.
6.3 Test range
The test range depends on many factors which are summarized below. In general, the test range is
limited by the signal-to-noise ratio (SNR) of the test data (see Clause 9, item e).
a) Geometrical features on the pipe attenuate and/or distort guided wave modes reducing test range.
b) The type of coating on the pipe can have a large effect on test range. Typically, insulation materials
like calcium silicate do not affect test range appreciably, but coatings like bitumen drastically
reduce test range by attenuating guided wave signals.
c) This International Standard only applies to above-ground pipe, but buried pipe where there is soil
in contact with the pipe surface or pipe coating is a more difficult GWT application due to high
attenuation and low signal to noise.
d) The substance contained in the pipe affects test range and it is a complex function depending on
the specific substance, ID corrosion products and the specific guided wave mode being used.
4 © ISO 2016 – All rights reserved

---------------------- Page: 8 ----------------------
ISO 18211:2016(E)

e) The presence of welds in the pipe causes reflections thereby attenuating the guided wave signal.
6.4 Road crossing
If performing GWT on a pipe passing through a road crossing with an external casing, achievement
of the test for the length of the crossing shall be proven by the test range including a reflection from a
geometrical feature (normally a weld) beyond the crossing or a reflection from a geometrical feature
(normally a weld) inside the crossing that is identifiable from both sides of the crossing.
7 Test equipment
7.1 General
The test equipment consists of the following:
a) an ultrasonic instrument to generate and receive pulses in the frequency range from 20 kHz to
500 kHz;
b) a probe ring carrying transducers for the generation of guided wave modes;
c) a probe ring carrying transducers for the reception of reflected guided waves; it can be the same
probe ring used for generating guided wave modes;
d) an electronic system for recording, processing and analysing the reflected signals.
7.2 Probe ring
The transmitting probe ring shall be capable of generating the primary guided wave mode in isolation
from other possible modes of the pipe. If more than one wave mode is used, they should be used
separately to improve the reliability of the inspection.
The receiving probe ring shall be capable of separating the individual guided wave modes which are of
interest for the analysis and to suppress the undesired modes (see Annex A for more information).
There are three different types of transducers currently available to generate and receive guided
ultrasonic waves in pipes:
— piezoelectric transducers;
— electromagnetic acoustic transducers (EMAT);
— magnetostrictive transducers.
These types of transducers are deployed on a probe ring which is placed around the pipe.
7.3 Signal processing and analysis system
The signal processing and analysis system shall produce its results in a form which can be recorded
reliably on a computer storage medium.
The results which are recorded shall be in a form such that the features in the results can be correlated
to physical locations on the piping system.
7.4 Periodic verification of equipment performance
The equipment shall be verified periodically, at intervals of no more than 12 months, to check its proper
functioning and performance, and any faults found shall be corrected.
© ISO 2016 – All rights reserved 5

---------------------- Page: 9 ----------------------
ISO 18211:2016(E)

This verification shall be performed in accordance with a dedicated written procedure following the
manufacturer’s instructions.
7.5 Instrument settings
If no relevant standards for instrument settings are available, the following minimum requirements
shall be met.
a) Frequency and signal settings
The settings which control the frequency and bandwidth of the signal shall be chosen to be
appropriate for specific relevant guided wave modes which have been selected according to the
inspection procedure to be used for the pipe under test.
b) Pulse repetition frequency
The pulse repetition frequency shall be set sufficiently low as to allow all signals to attenuate
completely between subsequent pulses.
8 Test procedure
GWT shall be performed according to a written test procedure, which shall include at least the following:
a) a reference to this International Standard, i.e. ISO 18211;
b) background information (including standards, restrictions, safety requirements, etc.);
c) personnel qualification;
d) a description of the pipe to be tested;
e) range of the test;
f) access and environmental conditions;
g) surface preparation;
h) equipment used;
i) equipment parameters and functional testing;
j) parameters for data collection;
k) parameters for evaluation of results;
l) complementary non-destructive testing;
m) reporting requirements;
n) recording of deviations from the procedure.
9 Requirements for test data quality
The minimum requirements to assure the quality of the test data are as follows.
a) Before testing, the whole combined test system shall be checked according to the specifications
provided by the manufacturer. If the GWT instrument performs self-checks, then the results of
these shall be stored with the recorded data. Any equipment deviations from allowed specification
shall be rectified before starting the test.
6 © ISO 2016 – All rights reserved

---------------------- Page: 10 ----------------------
ISO 18211:2016(E)

b) The tolerance of range setting shall be agreed upon between the parties (due to the long wavelength
used for GWT the tolerance on distance measurement is not likely to be better than ±100 mm).
c) The probe ring coupling to the pipe surface shall be checked according to the procedures and
thresholds provided by the manufacturer. If the coupling is found not to meet the required
specification, then the surface preparation shall be improved, the probe ring re-applied and the
data re-sampled.
d) If the equipment permits an absolute amplitude calibration, then it shall be used. Otherwise,
calibration of sensitivity, using knowledge of a well-characterized reflector, such as a girth weld,
shall be used. The calibration shall also include distance amplitude correction (DAC) or time
corrected gain (TCG), in order to compensate the calibration for axial position within the range
of the test. DAC and TCG are to be understood conceptually in the same manner as is established
for conventional UT testing; a DAC provides a constant level of sensitivity as a function of range,
allowing reflections at varying ranges to be compared in a consistent manner to a known reference
level. The calibration shall be set according to the instructions provided by the manufacturer of the
GWT equipment.
e) The signal-to-noise ratio shall be estimated according to the procedure provided by the
manufacturer. For adequate interpretation of the test data, the signal-to-noise ratio shall be greater
than 6 dB; small amplitude signals below this value cannot be interpreted reliably and will lead to
noise signals being reported as discontinuities. The signal-to-noise ratio is used to determine the
range of the test (see 6.3 for more information on test range).
10 Testing
10.1 Preparation of the test object
10.1.1 Surface temperature
The surface temperature of the pipe shall be within the operating range of the test equipment used.
10.1.2 Removal of insulation
Testing on insulated pipes requires the removal of circular bands of insulation at all the points where
the probe ring shall be positioned and for a length that is sufficient to allow the fixing of the probe ring
directly on to the pipe surface.
10.1.3 Wall thickness assessment
Metal loss at the probe ring location affects the test performance of GWT. Visual testing and ultrasonic
testing shall be performed to assess the presence of external or internal metal loss. If metal loss is
detected, it is recommended that the probe ring is attached to an alternative location. The wall thickness
values shall be recorded.
GWT does not provide inspection coverage in the dead zone. One way of providing 100 % pipe
inspection coverage is to perform more than one guided wave test on a piping system where there is
sufficient overlap between tests to provide inspection coverage in all dead zones. If the dead zone is not
inspected with GWT using another test location and if the dead zone is to be tested, ultrasonic testing
(or an alternative method) shall be used.
10.1.4 Surface preparation
Testing on well-adhered painted surfaces is normally satisfactory. Loose or flaking paint, superficial
corrosion products and other coatings shall be removed at the test location prior to attaching the probe
ring if required to achieve the data quality set out in Clause 9, item e).
© ISO 2016 – All rights reserved 7

-------------------
...

DRAFT INTERNATIONAL STANDARD ISO/DIS 18211.2
Secretariat: IIW
Voting begins on Voting terminates on

2015-06-29 2015-08-29
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION    МЕЖДУНАРОДНАЯ ОРГАНИЗАЦИЯ ПО СТАНДАРТИЗАЦИИ    ORGANISATION INTERNATIONALE DE NORMALISATION


Non-destructive testing — Long range inspection of above
ground pipelines and plant piping using guided wave testing
with axial propagation

Titre manque
Partie #: Titre de la partie
ICS 19.100











Member bodies are requested to consult relevant national interests in ISO/TC 44/SC ## before
returning their ballot to the ISO Central Secretariat.

This draft International Standard is submitted to all ISO member bodies for voting, as a
standard prepared by an international standardizing body in accordance with Council
Resolution 42/1999. The proposer, the International Institute of Welding (IIW), has been
recognized by the ISO Council as an international standardizing body for the purpose of
Council Resolution 42/1999.

To expedite distribution, this document is circulated as received from the committee
secretariat. ISO Central Secretariat work of editing and text composition will be undertaken at
publication stage.

THIS DOCUMENT IS A DRAFT CIRCULATED FOR COMMENT AND APPROVAL. IT IS THEREFORE SUBJECT TO CHANGE AND MAY NOT BE
REFERRED TO AS AN INTERNATIONAL STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS BEING ACCEPTABLE FOR INDUSTRIAL, TECHNOLOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON OCCASION HAVE TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL TO BECOME
STANDARDS TO WHICH REFERENCE MAY BE MADE IN NATIONAL REGULATIONS.
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.
©  International Organization for Standardization, 2015

---------------------- Page: 1 ----------------------
ISO/DIS 18211.2

COPYRIGHT PROTECTED DOCUMENT


©  ISO 2015
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
Case postale 56  CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail [e-mail]
Web www.iso.org
Published in Switzerland

ii © ISO 2015 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/DIS 18211.2
Contents Page
Foreword . iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test personnel . 3
5 General . 3
6 Factors influencing GWT performance . 4
6.1 External diameter . 4
6.2 Pipeline geometry . 4
6.3 Test range . 4
6.4 Road crossing . 5
7 Test equipment . 5
7.1 General . 5
7.2 Probe ring . 5
7.3 Signal processing and analysis system . 6
7.4 Periodic verification of equipment performance . 6
7.5 Settings . 6
8 Test procedure . 6
9 Requirements for test data quality . 7
10 Testing . 7
10.1 Preparation of the test object . 7
10.1.1 Surface temperature . 7
10.1.2 Removal of insulation . 7
10.1.3 Wall thickness assessment . 8
10.1.4 Surface preparation . 8
10.2 Probe ring test position . 8
10.3 Data Collection . 8
10.4 Reporting sensitivity . 8
10.5 Data interpretation . 9
10.6 Detection sensitivity . 9
10.7 Visual confirmation . 9
11 Complementary NDT to support the GWT . 9
12 Test report . 10
Annex A (informative) Selection of guided wave modes . 11
Bibliography . 15

© ISO 2015 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO/DIS 18211.2
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 18211 was prepared by IIW, the International Institute of Welding.

iv © ISO 2015 – All rights reserved

---------------------- Page: 4 ----------------------
DRAFT INTERNATIONAL STANDARD ISO/DIS 18211.2

Non-destructive testing — Long range Inspection of above
ground pipelines and plant piping using guided wave testing
with axial propagation
1 Scope
This International Standard specifies a method for long range testing of carbon and low alloy steel above
ground pipelines and plant piping using guided ultrasonic waves with axial propagation applied on the entire
circumferential pipe section, in order to detect corrosion or erosion damage.
The Guided Wave Testing (GWT) technique allows for fast inspection of above ground pipelines, plant piping
and cased road crossings, giving a qualitative screening and localization of probable corroded and eroded
areas. GWT is typically performed on operating piping systems.
This International Standard can be applied to the following types of pipes:
a) above ground painted pipelines;
b) above ground insulated pipelines;
c) pipe sections within road crossings with external casing (without bitumen or plastic coating);
d) painted plant piping;
e) insulated plant piping.
Other types of pipes not included in the above list need dedicated approaches due to increased complexity.
2 Normative references
The following referenced documents are indispensable for the application 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 9712, Non-destructive testing – Qualification and certification of personnel
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
axial direction
the direction along the main axis of the pipe
3.2
circumferential direction
the direction around the circumference of the pipe
© ISO 2015 – All rights reserved
1

---------------------- Page: 5 ----------------------
ISO/DIS 18211.2
3.3
total pipe wall cross-section (TCS)
the area between the inner and outer diameters of the pipe in a plane perpendicular to the pipe axis
3.4
cross-section change
the equivalent cross-section change calculated assuming that an indication is purely caused by a change in
the cross-section of the pipe wall
3.5
datum point
reference point for reporting a test position and for correlating test results with the corresponding position on
the test object
3.6
dead zone
length of pipe on either side of the test position where reflectors of interest cannot be detected because they
are covered by the transmitted pulse
3.7
flexural mode
a non-symmetric bending type mode of guided wave propagation in pipes, with particle displacements in axial,
circumferential and radial directions
3.8
focus
concentration of guided waves at a single axial and circumferential position, achieved either by hardware
settings or by post-processing of a recorded set of signals (synthetic focus)
3.9
geometric feature
pipeline feature (i.e. weld, support, flange, bend, etc.) causing the reflection of guided waves because of a
cross section change or other acoustic impedance variation
3.10
guided wave mode
distinct type of guided wave with a specific vibration pattern
3.11
longitudinal mode
a symmetric compression type mode of guided wave propagation in pipes, with particle displacements
predominantly in the axial direction
3.12
primary mode
guided wave mode which is chosen for the incident wave
3.13
probe ring
circumferential component, containing transducer elements with direct contact to the pipe
3.14
secondary mode
guided wave mode which is different from the primary mode and is generated by mode conversion at pipe
features or discontinuities
3.15
test frequency
centre frequency of the pulses transmitted by the probe ring
© ISO 2015 – All rights reserved
2

---------------------- Page: 6 ----------------------
ISO/DIS 18211.2
3.16
test position
axial position on the pipe where the probe ring is place
3.17
test range
the distance between the test position and the furthest position for which the minimum acceptable sensitivity
of the reference signal is achieved, in each direction (positive or negative)
3.18
torsional mode
a symmetric twisting type mode of guided wave propagation in pipes, with particle displacements in the
circumferential direction

4 Test personnel
The personnel performing ultrasonic guided wave testing shall be qualified in accordance with ISO 9712 or
with any another equivalent standard of the relevant industrial sector.
Training in the use of the specific equipment is required because there are significant differences between the
available systems and diagnostic approaches.
5 General
Ultrasonic Guided Wave Testing (GWT) uses elastic waves which are guided along the pipe wall and can
travel long distances, thus providing rapid near complete coverage of the volume of the pipe wall.
The typical test setup is comparable to conventional ultrasonic pulse-echo testing: an ultrasonic instrument
forces transducers in the probe ring to generate ultrasonic waves in the pipe wall which are reflected by
discontinuities and received by the same probe ring. The time-of-flight of the received signal indicates the
distance between the discontinuities and the probe ring. A single test with guided waves can cover a length of
pipe of tens of meters.
Within this standard, GWT is performed as a screening method. The reflections returning from discontinuities
and received by the ultrasonic instrument indicate the position of the discontinuity. However, they do not give
detailed quantitative information about its morphology. Therefore, GWT is used to indicate any locations which
need to be followed up with complementary detailed inspection. More information on the nature of guided
waves is given in Annex A.
Within this standard, GWT typically uses a frequency range between 20 kHz and 500 kHz. If the performance
of the test has been shown to have equal or better sensitivity to that obtained with the frequency range
specified above, a frequency lower than 20 kHz can be used for GWT.
The successful application of guided ultrasonic waves requires:
a) selective pure mode transmission and reception;
b) wave modes which are non dispersive in the frequency range used;
c) coverage of the full cross section of the pipe wall;
d) signals coming from each direction shall be distinguished.
© ISO 2015 – All rights reserved
3

---------------------- Page: 7 ----------------------
ISO/DIS 18211.2
The amplitude of a reflected ultrasonic guided wave signal from a discontinuity varies in a complex manner
that depends on many factors such as test frequency, guided wave mode and the specific morphology of the
discontinuity. It is often possible to correlate the size of the reflected signal with the overall cross section
change in the pipe wall resulting from wall loss, meaning that GWT can qualitatively group discontinuities into
different severity groups such as indications of low, medium and high concern. However, usually the
parameter of interest when testing piping systems with wall loss is the remaining wall thickness in areas with
discontinuities, which GWT cannot accurately provide (see Annex A for more information).
It is recommended to perform ultrasonic guided wave testing using a range of frequencies to improve the
accuracy of the test. Also, GWT ultrasonic instruments often employ advanced approaches like focusing or
synthetic focusing to improve the sensitivity and discontinuity sizing ability of GWT. The use of these is not
specified in this standard, but background information is provided in Annex A.
6 Factors influencing GWT performance
6.1 External diameter
The sensitivity of GWT depends on the cross section change. The absolute cross section change in a pipe
due to corrosion or erosion loss is measured in the units of area, and depends on both the depth and the
circumferential extent of the discontinuity. GWT is sensitive to a minimum percent of cross sectional loss,
which is a function of both the absolute cross section change and the pipe geometry. As an example, a
discontinuity in a small diameter pipe may represent a large percent change in cross section that is easily
detectable using GWT, but the same discontinuity in a large diameter pipe may represent a small cross
section change that cannot be detected using GWT. Because of this effective decrease in sensitivity as pipe
diameter increases, testing of pipes larger than DN 600 (24 inches diameter) can miss significant isolated
corrosion pits, so it is recommended that complementary NDT methods are used. When testing pipes where
the known damage mechanisms result in larger cross section changes rather than isolated pitting, GWT is still
recommended for rapid testing of pipes with diameters larger than DN600 (24 inches diameter).
6.2 Pipeline geometry
The complexity of the pipe geometry can limit guided wave propagation. Below are summarized the effects of
some common pipe features which can be present in the pipes listed in clause 1:
a) it is not possible to test beyond flanged joints or any breaks of the pipe because the guided waves
cannot propagate across them;
b) it is not permitted to test beyond an elbow fitting; instead the tool shall be moved to a test position on
the other side of the bend. Testing beyond ‘pulled’ bends, where a straight length of pipe is formed
into a curve of radius equal to 5 or more times the pipe diameter is permitted;
c) it is permitted to test beyond a branch or a tee only if the diameter of the branch is no greater than ½
the diameter of the pipe being tested. This restriction is to avoid problems with distortion of the
forward travelling guided wave by interactions with the branch;
d) it is not permitted to test beyond a support if the amplitude of reflection from it is higher than 6 dB
below the weld DAC curve. This restriction is to avoid problems of the distortion of the forward
travelling guided wave by interactions with the support.
6.3 Test range
The test range depends on many factors which are summarized below. In general, the test range is limited by
the signal/noise ratio (SNR) of the test data (see clause 9, item e).
a) geometrical features on the pipe attenuate and/or distort guided wave modes reducing test range;
© ISO 2015 – All rights reserved
4

---------------------- Page: 8 ----------------------
ISO/DIS 18211.2
b) the type of coating on the pipe can have a large effect on test range. Typically, insulation materials
like calcium silicate do not affect test range appreciably, but coatings like bitumen drastically reduce
test range by attenuating guided wave signals;
c) this standard only applies to above ground pipe, but buried pipe where there is soil in contact with the
pipe surface or pipe coating is a more difficult GWT application due to high attenuation and low signal
to noise;
d) the substance contained in the pipe effects test range, and it is a complex function depending on the
specific substance, ID corrosion products and the specific guided wave mode being used;
e) the presence of welds in the pipe cause reflections thereby attenuating the guided wave signal.
6.4 Road crossing
If performing GWT on a pipe passing through a road crossing with an external casing, achievement of the test
for the length of the crossing shall be proven by the test range including a reflection from a geometrical feature
(normally a weld) beyond the crossing, or a reflection from a geometrical feature (normally a weld) inside the
crossing that is identifiable from both sides of the crossing.
7 Test equipment
7.1 General
The test equipment consists of:
a) an ultrasonic instrument to generate and receive pulses in the frequency range from 20 kHz to 500
kHz;
b) a probe ring carrying transducers for the generation of guided wave modes;
c) a probe ring carrying transducers for the reception of reflected guided waves. It can be the same
probe ring used for generating guided wave modes;
d) an electronic system for recording, processing and analysing the reflected signals.
7.2 Probe ring
The transmitting probe ring shall be capable of generating the primary guided wave mode in isolation from
other possible modes of the pipe. If more than one wave mode is used, they should be used separately to
improve the reliability of the inspection.
The receiving probe ring shall be capable of separating the individual guided wave modes which are of
interest for the analysis and to suppress the undesired modes (see Annex A for more information).
There are three different types of transducers currently available to generate and receive guided ultrasonic
waves in pipes:
⎯ piezoelectric transducers;
⎯ electromagnetic acoustic transducers (EMAT);
⎯ magnetostrictive transducers.
These types of transducers are deployed on a probe ring which is placed around the pipe.
© ISO 2015 – All rights reserved
5

---------------------- Page: 9 ----------------------
ISO/DIS 18211.2
7.3 Signal processing and analysis system
The signal processing and analysis system shall produce its results in a form which can be recorded reliably
on a computer storage medium.
The results which are recorded shall be in a form such that the features in the results can be correlated to
physical locations on the piping system.
7.4 Periodic verification of equipment performance
The equipment shall be verified periodically, at intervals of no more than 12 months, to check its proper
functioning and performance, and any faults found shall be corrected.
This verification shall be performed in accordance with a dedicated written procedure following the
manufacturer's instructions.
7.5 Settings
If no relevant standards for equipment settings are available, the following minimum requirements shall be
met:
a) Frequency and signal settings
The settings which control the frequency and bandwidth of the signal shall be chosen to be appropriate for
specific relevant guided wave modes which have been selected according to the inspection procedure to be
used for the pipe under test.
b) Pulse repetition frequency
The pulse repetition frequency shall be set sufficiently low as to allow all signals to attenuate completely
between subsequent pulses.
8 Test procedure
GWT shall be performed according to a written test procedure, which shall include at least the following:
a) a reference to this standard;
b) background information (including standards, restrictions, safety requirements, etc.);
c) personnel qualification;
d) a description of the pipe to be tested;
e) range of the test;
f) access and environmental conditions;
g) surface preparation;
h) equipment used;
i) equipment parameters and functional testing;
j) parameters for data collection;
© ISO 2015 – All rights reserved
6

---------------------- Page: 10 ----------------------
ISO/DIS 18211.2
k) parameters for evaluation of results;
l) complementary non-destructive testing;
m) reporting requirements;
n) recording of deviations from procedure.
9 Requirements for test data quality
The minimum requirements to assure the quality of the test data are:
a) Before testing, the whole combined test system shall be checked according to the specifications provided
by the manufacturer. If the GWT instrument performs self-checks, then the results of these shall be stored
with the recorded data. Any equipment deviations from allowed specification shall be rectified before
starting the test.
b) The tolerance of range setting shall be agreed between the parties (due to the long wavelength used for
GWT the tolerance on distance measurement is not likely to be better than ± 100 mm);
c) The probe ring coupling to the pipe surface shall be checked according to the procedures and thresholds
provided by the manufacturer. If the coupling is found not to meet the required specification, then the
surface preparation shall be improved, the probe ring re-applied and the data re-sampled.
d) If the equipment permits an absolute amplitude calibration, then it shall be used. Otherwise, calibration of
sensitivity, using knowledge of a well-characterised reflector, such as a girth weld, shall be used. The
calibration shall also include Distance Amplitude Correction (DAC) or Time Corrected Gain (TCG), in
order to compensate the calibration for axial position within the range of the test. DAC and TCG are to be
understood conceptually in the same manner as is established for conventional UT testing, as in
ISO 16811; a DAC provides a constant level of sensitivity as a function of range, allowing reflections at
varying ranges to be compared in a consistent manner to a known reference level. The calibration shall
be set according to the instructions provided by the manufacturer of the GWT equipment.
e) The signal-to-noise ratio shall be estimated according to the procedure provided by the manufacturer. For
adequate interpretation of the test data the signal-to-noise ratio shall be greater than 6 dB; small
amplitude signals below this value cannot be interpreted reliably and will lead to noise signals being
reported as discontinuities. The signal-to-noise ratio is used to determine the range of the test (see clause
6.3 for more information on test range).
10 Testing
10.1 Preparation of the test object
10.1.1 Surface temperature
The surface temperature of the pipe shall be within the operating range of the test equipment used.
10.1.2 Removal of insulation
Testing on insulated pipes requires the removal of circular bands of insulation at all the points where the probe
ring shall be positioned, and for a length sufficient to allow the fixing of the probe ring directly to the pipe
surface.
© ISO 2015 – All rights reserved
7

---------------------- Page: 11 ----------------------
ISO/DIS 18211.2
10.1.3 Wall thickness assessment
Metal loss at the probe ring location affects the test performance of GWT. Visual testing and ultrasonic testing
shall be performed to assess the presence of external or internal metal loss. If metal loss is detected it is
recommended that the probe ring is attached to an alternative location. The wall thickness values shall be
recorded.
GWT does not provide inspection coverage in the dead zone. One way of providing 100% pipe inspection
coverage is to perform more than one guided wave test on a piping system where there is sufficient overlap
between tests to provide inspection coverage in all dead zones. If the dead zone is not inspected with GWT
using another test location, and if the dead zone must be tested, ultrasonic testing (or an alternative method)
shall be used.
10.1.4 Surface preparation
Testing on well adhered painted surfaces is normally satisfactory. Loose or flaking paint, superficial corrosion
products and other coatings shall be removed at the test location prior to attaching the probe ring if required to
achieve the data quality set out in clause 9, item e.
10.2 Probe ring test position
In a typical piping system, it is normal to require many different probe ring test positions to provide full
inspection coverage of the entire piping system. The choice of these locations for the probe ring is critical in
order to provide adequate inspection of the entire piping system (see clause 6.2 for more information). The
position(s) of the probe ring on the piping system shall be recorded with reference to a known physical datum
or on a piping drawing to allow repeatability.
10.3 Data Collection
Data shall be collected according to the instructions provided by the equipment manufacturer and to a
dedicated procedure. This procedure shall include instruction on the following:
a) ensuring proper probe ring coupling to the pipe surface;
b) ensuring proper electrical connection between system components;
c) setting test equipment parameters;
d) setting test equipment range;
e) setting test equipment sensitivity;
f) verifying data quality.
10.4 Reporting sensitivity
Prior to GWT data interpretation, DAC or TCG curves shall be applied to establish sensitivity using the
requirements in clause 9, item d. In practice, it is typically not possible to perform an absolute amplitude
cal
...