ISO/DTS 24399

Thermoplastic pipes for the conveyance of fluids — Inspection of polyethylene butt fusion joints using time of flight diffraction testing

Tubes en matières thermoplastiques pour le transport des fluides - Contrôle des assemblages par soudage bout à bout en polyéthylène au moyen de la technique par diffraction des temps de vol

General Information

• Status: Not Published
• ICS: 23.040.20 - Plastics pipes
• ICS: 23.040.60 - Flanges, couplings and joints
• Technical Committee: ISO/TC 138/SC 5 - General properties of pipes, fittings and valves of plastic materials and their accessories -- Test methods and basic specifications
• Drafting Committee: ISO/TC 138/SC 5/WG 17 - Alternative test methods
• Current Stage: 5092 - FDIS referred back to TC or SC
• Completion Date: 07-Feb-2023

Standards Content (Sample)

ISO/TC 138/SC 5 N
Date:  2022-06-2707
ISO/DTS 24399:2022(E)
ISO/TC 138/SC 5/WG 17
Secretariat:  NEN
Thermoplastic pipes for the conveyance of fluids – Inspection of polyethylene
butt fusion joints using time of flight diffraction testing

Warning
This document is not an ISO International Standard. It is distributed for review and comment. It is
subject to change without notice and may not be referred to as an International Standard.
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.








Document type: Preliminarily Draft Technical Specification
Document subtype:
Document stage:  (20) Preparatory
Document language:  E


STD Version 2.7f

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ISO/DTS 24399
Copyright notice
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© ISO 2016 – All rights reserved
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ISO/DTS 24399
Content
Foreword . iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General . 3
5 Information required prior to testing . 3
5.1 Items required for test procedure development . 3
5.2 Specific information required by the operator before testing . 3
5.3 Written test procedure . 4
6 Personnel qualifications . 4
7 Equipment . 4
7.1 General . 4
7.2 Ultrasonic instrument and display . 5
7.3 Ultrasonic probes . 5
7.4 Scanning mechanisms . 5
7.5 Couplant. 5
8 Range and sensitivity settings . 6
8.1 Settings . 6
8.1.1 General . 6
8.1.2 Range setting - test volume . 6
8.1.3 Time window . 6
8.1.4   Time-to-depth
conversion………………………………………………………………………………………………. . 7
8.1.5   Sensitivity settings
………………………………………………………………………………………………………….7
8.2     Reference
sample…………………………………………………………………………………………………………… 8
8.2.1 General . 8
8.2.2 Reference block . 8
8.2.3 Reference reflectors . 8
8.3 Checking of the settings . 8
9 Equipment checks . 8
10 Test procedure . 8
10.1 Procedure qualification . 9
10.2 Scan increment . 9
10.3 Component geometry . 10
10.4 Preparation of scanning surfaces . 10
10.5 Component temperature . 10
10.6 Testing . 10
10.7 Data storage . 10
11 Interpretation and analysis of test data . 10
11.1 General . 10
11.2 Assessing the quality of the test data . 11
11.3 Identification of relevant indications . 11
11.4 Classification of relevant indications . 11
© ISO 2016 – All rights reserved
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ISO/DTS 24399
11.5 Determination of location and size of indications . 12
11.6 Assessment of indications . 12
12 Test report . 12

Annex A (Informative) Example of reference reflectors and reference blocks . 14
A.1 Reference reflectors . 14
A.2 Reference blocks . 16
A.2.1 Reference block with SDHs and a surface notch – Single block use . 16
A.2.2 Reference block with SDHs and a surface notch – Multi-block use . 17
Annex B (Informative) Example procedures for producing imperfections in butt fusion
joints . 18
B.1 Planar lack of fusion . 18
B.2 Particulate contamination. 19

Bibliography…………………………………………………………………………………………………………………………
….22
© ISO 2016 – All rights reserved
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ISO/DTS 24399
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 Electro-technicalElectrotechnical Commission (IEC) on all
matters of electro-technicalelectrotechnical 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). 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).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 onof 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: Foreword - Supplementary informationwww.iso.org/iso/foreword.html.
The main task of technical committees is to prepare International Standards.
In exceptional circumstances, when a technical committee has collected data of a different kind from that
which is normally published as an International Standard (“state of the art”, for example), it may decide
by a simple majority vote of its participating members to publish a Technical Specification.
The committee responsible for this document isThis document was prepared by Technical Committee
ISO/TC 138, Plastics pipes, fittings and valves for the transport of fluids, Subcommittee SC 5, General
properties of pipes, fittings and valves of plastic materials and their accessories — Test methods and basic
specifications.


© ISO 2016 – All rights reserved
iv

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DRAFTTECHNICAL SPECIFICATION ISO/DTS22499



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.
© ISO 2016 – All rights reserved
2

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ISO/DTS22499
TECHNICAL SPECIFICATION ISO/DTS 24399:2022(E)

Thermoplastic pipes for the conveyance of fluids — Inspection
of polyethylene butt fusion joints using time of flight
diffraction testing
1 Scope
This document describes the time of flight diffraction (TOFD) testing of polyethylene butt fusion (BF)
joints, including pipe-to-pipe, pipe-to-fitting and fitting-to-fitting joints, used for the conveyance of fluids.
This document provides a test, whereby the presence of imperfections such as voids, inclusions, lack of
fusions, misalignment and particulate contamination in the BF joints can be detected. The document is
only applicable to polyethylene pipes and fittings without a barrier to ultrasonic waves.
This document also provides requirement for procedure qualification and guidance for personnel
qualifications which are essential for the application of this test method.
This document also covers the equipment, the preparation and performance of the test, the indication
assessment and the reporting for polyethylene BF joints. The acceptance criteria are not covered in this
document.
NOTE 1:  At the present time laboratory experiences exist on the use of TOFD for polyethylene butt fusion joints
[ ] [][ ] [][ ] [][ ] [][ ] [][ ]
and/or reference blocks of wall thickness between 8 mm to 100 mm 1 2 3 4 5 6 . Recently field
[[ ] ]
experience on butt fusion joints in HDPE pipes has been reported. 7 .
NOTE 2 Round robin testing has shown that TOFD is a viable method for enhancing the integrity assessment of
[ ]
butt-fusion joints 14 .
NOTE 3 TOFD techniques for cold fusion detection are known to be available. However further research,
verification and experience are needed to transfer the technique into an ISO Standard. This document does not
[ ]
provide any information regarding the detection of cold fusions 14 .

2 Normative references
The following referenced standards 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 5577, Non-destructive testing -— Ultrasonic inspection –testing — Vocabulary
ISO 9712, Non-destructive testing –— Qualification and certification of NDT personnel
ISO 13953, Polyethylene (PE) pipes and fittings –— Determination of the tensile strength and failure mode
of test pieces from a butt-fused joint

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ISO/DTS 24399:2022(E)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5577 and the following terms
and definitions apply.
ISO and IEC maintain terminologicalterminology databases for use in standardization at the following
addresses:
— ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/https://www.electropedia.org/
3.1
cold fusion
incomplete intermolecular diffusion of polymer chains for proper molecular entanglement at the joint
interface due to reasons other than contamination.
Note 1 to entry: Cold fusion results in insufficient joint integrity including significant reduction of joint ductility.
3.2
inclusion
foreign material trapped in the fusion joint.
3.3
lack of fusion
absence of intermolecular diffusion of polymer chains for molecular entanglement at the interface.
Note 1 to entry: A lack of fusion flaw results in complete separation at the flaw location.
3.4
melt fusion zone
MFZ
zone containing the fusion interface and having boundaries on either side of the interface which reflect
the limits of crystalline melting during the butt fusion jointing process
Note 1 to entry: The MFZ is shown in Figure 1.
3.5
misalignment
offset between the axis of the pipes/fittings to be jointed
3.6
particulate contamination
fine particles (e.g. airborne dust) or coarse particles (e.g. sand and grit) that are present at the fusion
interface
3.7
surface imperfection
imperfection on the ID or OD surface of the butt fusion joint

3.8
void
empty space (or air pocket) in a butt fusion joint
3.9
time-of-flight diffraction image / TOFD image
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ISO/DTS 24399:2022(E)
two-dimensional image, constructed by collecting adjacent A-scans while moving the time-of-flight
diffraction setup

NOTE 1 to entry: The signal amplitude of the A-scan is typically represented by grey-scale values

3.10
time-of flight diffraction set-up/ TOFD setup
probe arrangement defined by probe characteristics (e.g. frequency, probe element size, beam angle,
wave mode), probe position, probe centre separation (3.11) and the number of probe pairs
3.11
probe centre separation
distance between the index points of the two probes
NOTE Note 1 to entry:  The probe centre separation for two probes located on a curved surface is the straight-line,
geometric separation between the two probe indexes and not distance measured along the surface.
3.12
scan increment
distance between successive data collection points in the direction of scanning

3.13
false call
reporting an imperfection when none exists

4 General
This document covers the TOFD equipment, the preparation and performance of the test, the indication
assessment and the reporting for polyethylene butt fusion joints. The acceptance criteria are not covered
in this document.
This document may be used to draft a detailed procedure for TOFD testing of polyethylene butt fusion
joints.
Characterisation of imperfections in the parent material adjacent to the butt fusion joint is also possible.

5 Information required prior to testing
5.1 Items required for test procedure development
Information on the following items is required:
— purpose and extent of testing;
— reference sample;
— requirements for getting access to the butt fusion joints, the surface condition of the pipe; and the
temperature range
— personnel qualifications;
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ISO/DTS 24399:2022(E)
— reporting requirements;
— manufacturing or operation stage of butt fusion joints at which the testing is to be carried out.
5.2 Specific information required by the operator before testing
Before any testing of a fusion joint begins, the operator shall have access to all the information as specified
in 5.1 together with the following additional information:
a) a) written test procedure, qualified in accordance with Clause 10;
b) b) all relevant joint dimensions.
5.3 Written qualified test procedure
For all testing a written qualified test procedure is required. This test procedure shall include at least the
following information:
a) a) purpose and extent of testing;
b) b) reference sample;
c) c) requirements for access to the butt fusion joints and surface conditions and temperature;
d) d) personnel qualifications;
e) e) reporting requirements;
f) f) equipment requirements and settings (including but not limited to frequency, sampling rate and
element size, probe centre separation);
g) g) evaluation of indications;
h) h) environmental and safety issues;
i) i) documented testing strategy or scan plan.
NOTE The testing strategy gives information on the probe placement, movement, and component coverage that
provides a standardized and repeatable methodology for fusion joint testing. The scan plan gives information on
the volume tested for each butt fusion joint.
6 Personnel qualifications
Personnel performing testing in accordance with this document shall be qualified to an appropriate level
in accordance with ISO 9712 or an equivalent standard in the relevant industrial sector.
In addition to a general knowledge of ultrasonic testing, the operator shall be familiar with and have
practical experience in the use of TOFD systems on polyethylene butt fusion joints. Specific theoretical
and practical training and examination of personnel shall be performed on representative polyethylene
butt fusion joints containing natural or artificial reflectors similar to those expected. These training and
examination results shall be documented.

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ISO/DTS 24399:2022(E)
7 Equipment
7.1 General
The complete equipment, i.e. ultrasonic instrument, probe, cables and display monitor shall be capable
of the repetition of test results.
[ ]
Note NOTE 1: In selecting the system components (hardware and software) ISO TS 16829 8 give useful information.
[ ]
Note NOTE 2: Ultrasonic equipment used for TOFD testing should comply with the requirements of ISO 15626 9
[ ]
EN-12668 10 when applicable.

7.2 Ultrasonic instrument and display
The instrument shall be able to select an appropriate portion of the time base within which A-scans are
digitized. It is recommended that a sampling rate of the A-scan should be at least six times the nominal
probe frequency.

7.3 Ultrasonic probes
Only longitudinal wave mode can be used.

7.3.1 7.3.1 Probe selection
Any type of ultrasonic TOFD probe can be used if it satisfies the requirement of Section Clause 8 (Range
and sensitivity settings) with the ultrasonic equipment.
The most suitable ultrasonic probe frequency shall be selected in accordance with the pipe wall thickness.
Table 1 shows the recommended frequencies for each thickness range. However, the optimal frequency
can deviate from these values depending on the attenuation and thickness of the sample to be tested.
The gap between the test surface and the bottom of the wedge shall not be greater than 0,5 mm.

For thicknesses greater than 30 mm the wall thickness shall be divided into more than one inspection
zone, each zone covering a different depth region. Probe angle and frequencies shall be chosen to cover
full volume. These zones can be inspected simultaneously or separately. Table 2 shows the examples of
single and multiple inspection zone probe setup.

Table 1 — Selection of probe frequency
Centre Recommended
Wall Thickness (t) Number of  Element size
Frequency Beam angle

mm TOFD setups mm

MHz (longitudinal waves)
8 ≤t< 30 1 or 2
5 to ≤ ≤ 10 60 to ≤ ≤ 70 3 to ≤ ≤ 6
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ISO/DTS 24399:2022(E)
30 ≤t< 60 2
2,25 to ≤ ≤ 5 60 to ≤ ≤ 70 6 to ≤ ≤ 11
3 1 to ≤ ≤ 5 45 to ≤ ≤ 70 6 to ≤ ≤ 11
60≤ ≤t ≤≤ 100

NOTE 1: For multiple TOFD setups the deeper the range the lower the frequency and the smaller the beam angle.
NOTE 2 In general higher frequencies provide better resolution and lower frequencies provide better penetration.

Table 2. — Description of TOFD technique for testing butt fusion joints
TOFD set-up Example
Single zone

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ISO/DTS 24399:2022(E)
Multi-zone



7.3.2 7.3.2 Probe separation

The maximum diffraction efficiency occurs when the included angle is about 120 degrees.
The probes should be arranged such that the (imagined) beam centre lines intersect at about this angle
in the depth region where discontinuities are anticipated /sought.
o o o o
Deviations of more than -35 35 or +45 45 from this value may cause the diffracted echoes to be weak
and should not be used unless detection capabilities can be demonstrated.
Probes shall not touch the bead.

7.4 Scanning mechanisms
To achieve consistency of the images (collected data), guiding mechanisms and scan encoder(s) shall be
used.

7.5 Couplant
In order to generate proper images, a couplant should be used which provides a constant transmission
of ultrasound between the probe and the material. The same couplant used for calibration shall be used
for the testing.
NOTE Any couplant used should be cleaned off after testing.

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ISO/DTS 24399:2022(E)
8 Range and sensitivity settings
8.1 Settings
8.1.1 General
Setting of range and sensitivity shall be carried out prior to each testing period in accordance with this
document. Any change of the TOFD set-up, e.g. probe centre separation, will require a new setting.
8.1.2 Range setting - test volume
The range in the depth direction shall cover the full joint thickness in the fusion zone.
The range in the axial direction shall cover the melt fusion zone on both sides of the butt fusion centre
line. As a general guidance, for wall thicknesses up to 100 mm, the test area width is 10 mm or 1/5 of
the wall thickness from either side of the fusion zone, whichever is smaller (see Figure 1).
The range in the circumferential direction shall include the full circumference.

Key
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ISO/DTS 24399:2022(E)
1 outside of joint
2 inside of joint
3   MFZ boundary
4 test area
5   melt fusion zone (MFZ)
6   fusion interface
x width of test area
x width of test area
1 outside of joint
2 inside of joint
3 MFZ boundary
4 test area
5 melt fusion zone (MFZ)
6 fusion interface
Figure 1 – — Test area

8.1.3 Time window
The time window shall at least cover the depth range as shown in Table 1:
1) for full-thickness testing using only one setup, the time window recorded shall start at least 1 µs
prior to the time of arrival of the lateral wave, and shall extend beyond the first mode-converted to
back-wall signal;
2) if more than one setup is used, the time windows shall overlap by at least 10 % of the depth range.
The start and extent of the time windows should be verified on the test object;.

8.1.4 8.1.4 Time-to-depth conversion
Setting of time-to depth conversion shall be carried out on the reference block specified in 8.2.2
Some ultrasonic parameters are used for the time-to depth conversion such as the time of arrival of the
lateral wave, the time of arrival of back-wall reflection, probe centre separation, wedge delay, velocity
and thickness. For precise time-to depth conversion, at least four parameters have to be known correctly.
Normally, the thickness and the velocity can be measured from the reference block.

8.1.5 8.1.5 Sensitivity settings
The sensitivity shall be set on the reference block made of the same material as the pipe with the butt
fusion joint being inspected. The gain control shall be set so that the amplitude of the lateral wave is from
40% % to 80 % of the full screen height (FSH). In cases where the use of lateral wave is not appropriate
(e.g. use of steep refraction angle), the gain control shall be set so that the material grain noise is from
5 % to 10 % of FSH.

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ISO/DTS 24399:2022(E)
8.2 Reference sample
8.2.1 General
The temperature of the reference sample shall be the same as the temperature ±10 °C of the test object
at the time of testing and shall be kept in the same environment as the test object throughout the test. A
reference block satisfying the condition in 8.2.2 shall be used as the reference sample.
8.2.2 Reference block
Reference blocks shall be used to determine the adequacy of the settings (e.g. coverage, sensitivity) and
may be used for time-to-depth conversion with known precise thickness.
A transfer correction should be applied to cover the difference in curvature and surface roughness of the
reference block and the test object.
The reference block used shall be of the same material classification as the pipe/fitting being inspected.
The thickness of the reference block shall be at least equal to the thickness of the joint to be tested. The
length and width of the reference block shall
...

FINAL
TECHNICAL ISO/DTS
DRAFT
SPECIFICATION 24399
ISO/TC 138/SC 5
Thermoplastic pipes for the
Secretariat: NEN
conveyance of fluids — Inspection of
Voting begins on:
2022-08-09 polyethylene butt fusion joints using
time of flight diffraction testing
Voting terminates on:
2022-10-04
Tubes en matières thermoplastiques pour le transport des fluides -
Contrôle des assemblages par soudage bout à bout en polyéthylène au
moyen de la technique par diffraction des temps de vol
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 SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/DTS 24399:2022(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2022

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ISO/DTS 24399:2022(E)
TECHNICAL ISO/TS
SPECIFICATION 24399
Thermoplastic pipes for the
conveyance of fluids — Inspection of
polyethylene butt fusion joints using
time of flight diffraction testing
Tubes en matières thermoplastiques pour le transport des fluides -
Contrôle des assemblages par soudage bout à bout en polyéthylène au
moyen de la technique par diffraction des temps de vol
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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.
PROOF/ÉPREUVE
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Reference number
Email: [e-mail]
ISO/TS 24399:2022(E)
Website: www.iso.org
Published in Switzerland
ii
  © ISO 2022 – All rights reserved
© ISO 2022

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ISO/TS 24399:2022(E)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General . 3
5 Information required prior to testing . 3
5.1 Items required for test procedure development . 3
5.2 Specific information required by the operator before testing . 3
5.3 Written qualified test procedure . 3
6 Personnel qualifications . .4
7 Equipment . 4
7.1 General . 4
7.2 Ultrasonic instrument and display . 4
7.3 Ultrasonic probes . 4
7.3.1 Probe selection. 4
7.3.2 Probe separation . 5
7.4 Scanning mechanisms . 5
7.5 Couplant . 6
8 Range and sensitivity settings . 6
8.1 Settings . . . 6
8.1.1 General . 6
8.1.2 Range setting ­ test volume . 6
8.1.3 Time window . 7
8.1.4 Time­to­depth conversion . 7
8.1.5 Sensitivity settings . . 7
8.2 Reference sample. 7
8.2.1 General . 7
8.2.2 Reference block . . 7
8.2.3 Reference reflectors . 8
8.3 Checking of the settings . 8
9 Equipment checks . 8
10 Test procedure .8
10.1 Procedure qualification . 8
10.2 Scan increment . 9
10.3 Component geometry . 9
10.4 Preparation of scanning surfaces . 9
10.5 Component temperature . 10
10.6 Testing . 10
10.7 Data storage . 10
11 Interpretation and analysis of test data .10
11.1 General . 10
11.2 Assessing the quality of the test data . 10
11.3 Identification of relevant indications . 11
11.4 Classification of relevant indications . 11
11.5 Determination of location and size of indications . 11
11.6 Assessment of indications . 11
12 Test report .11
Annex A (informative) Example of reference reflectors and reference blocks .13
iii
© ISO 2022 – All rights reserved

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ISO/TS 24399:2022(E)
Annex B (informative) Example procedures for producing imperfections in butt fusion
joints .18
Bibliography .22
iv
 © ISO 2022 – All rights reserved

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ISO/TS 24399:2022(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 non­governmental, 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 of 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 www.iso.org/
iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 138, Plastics pipes, fittings and valves
for the transport of fluids, Subcommittee SC 5, General properties of pipes, fittings and valves of plastic
materials and their accessories — Test methods and basic specifications.
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.
v
© ISO 2022 – All rights reserved

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TECHNICAL SPECIFICATION ISO/TS 24399:2022(E)
Thermoplastic pipes for the conveyance of fluids —
Inspection of polyethylene butt fusion joints using time of
flight diffraction testing
1 Scope
This document describes the time of flight diffraction (TOFD) testing of polyethylene butt fusion (BF)
joints, including pipe-to-pipe, pipe-to-fitting and fitting-to-fitting joints, used for the conveyance of
fluids. This document provides a test, whereby the presence of imperfections such as voids, inclusions,
lack of fusions, misalignment and particulate contamination in the BF joints can be detected. The
document is only applicable to polyethylene pipes and fittings without a barrier to ultrasonic waves.
This document also provides requirement for procedure qualification and guidance for personnel
qualifications which are essential for the application of this test method.
This document also covers the equipment, the preparation and performance of the test, the indication
assessment and the reporting for polyethylene BF joints. The acceptance criteria are not covered in this
document.
NOTE 1 At the present time laboratory experiences exist on the use of TOFD for polyethylene butt fusion joints
[1][2][3][4][5][6]
and/or reference blocks of wall thickness between 8 mm to 100 mm . Recently field experience on
[7]
butt fusion joints in HDPE pipes has been reported .
NOTE 2 Round robin testing has shown that TOFD is a viable method for enhancing the integrity assessment
[14]
of butt-fusion joints .
NOTE 3 TOFD techniques for cold fusion detection are known to be available. However further research,
verification and experience are needed to transfer the technique into an ISO Standard. This document does not
[14]
provide any information regarding the detection of cold fusions .
2 Normative references
The following referenced standards 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 5577, Non-destructive testing — Ultrasonic testing — Vocabulary
ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel
ISO 13953, Polyethylene (PE) pipes and fittings — Determination of the tensile strength and failure mode of
test pieces from a butt-fused joint
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5577 and the following terms
and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
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ISO/TS 24399:2022(E)
3.1
cold fusion
incomplete intermolecular diffusion of polymer chains for proper molecular entanglement at the joint
interface due to reasons other than contamination
Note 1 to entry: Cold fusion results in insufficient joint integrity including significant reduction of joint ductility.
3.2
inclusion
foreign material trapped in the fusion joint
3.3
lack of fusion
absence of intermolecular diffusion of polymer chains for molecular entanglement at the interface
Note 1 to entry: A lack of fusion flaw results in complete separation at the flaw location.
3.4
melt fusion zone
MFZ
zone containing the fusion interface and having boundaries on either side of the interface which reflect
the limits of crystalline melting during the butt fusion jointing process
Note 1 to entry: The MFZ is shown in Figure 1.
3.5
misalignment
offset between the axis of the pipes/fittings to be jointed
3.6
particulate contamination
fine particles (e.g. airborne dust) or coarse particles (e.g. sand and grit) that are present at the fusion
interface
3.7
surface imperfection
imperfection on the ID or OD surface of the butt fusion joint
3.8
void
empty space (or air pocket) in a butt fusion joint
3.9
time-of-flight diffraction image / TOFD image
two-dimensional image, constructed by collecting adjacent A-scans while moving the time-of-flight
diffraction setup
Note 1 to entry: The signal amplitude of the A-scan is typically represented by grey-scale values
3.10
time-of flight diffraction set-up/ TOFD setup
probe arrangement defined by probe characteristics (e.g. frequency, probe element size, beam angle,
wave mode), probe position, probe centre separation (3.11) and the number of probe pairs
3.11
probe centre separation
distance between the index points of the two probes
Note 1 to entry: The probe centre separation for two probes located on a curved surface is the straight-line,
geometric separation between the two probe indexes and not distance measured along the surface.
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ISO/TS 24399:2022(E)
3.12
scan increment
distance between successive data collection points in the direction of scanning
3.13
false call
reporting an imperfection when none exists
4 General
This document covers the TOFD equipment, the preparation and performance of the test, the indication
assessment and the reporting for polyethylene butt fusion joints. The acceptance criteria are not
covered in this document.
This document may be used to draft a detailed procedure for TOFD testing of polyethylene butt fusion
joints.
Characterisation of imperfections in the parent material adjacent to the butt fusion joint is also possible.
5 Information required prior to testing
5.1 Items required for test procedure development
Information on the following items is required:
— purpose and extent of testing;
— reference sample;
— requirements for getting access to the butt fusion joints, the surface condition of the pipe; and the
temperature range
— personnel qualifications;
— reporting requirements;
— manufacturing or operation stage of butt fusion joints at which the testing is to be carried out.
5.2 Specific information required by the operator before testing
Before any testing of a fusion joint begins, the operator shall have access to all the information as
specified in 5.1 together with the following additional information:
a) written test procedure, qualified in accordance with Clause 10;
b) all relevant joint dimensions.
5.3 Written qualified test procedure
For all testing a written qualified test procedure is required. This test procedure shall include at least
the following information:
a) purpose and extent of testing;
b) reference sample;
c) requirements for access to the butt fusion joints and surface conditions and temperature;
d) personnel qualifications;
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ISO/TS 24399:2022(E)
e) reporting requirements;
f) equipment requirements and settings (including but not limited to frequency, sampling rate and
element size, probe centre separation);
g) evaluation of indications;
h) environmental and safety issues;
i) documented testing strategy or scan plan.
NOTE The testing strategy gives information on the probe placement, movement, and component coverage
that provides a standardized and repeatable methodology for fusion joint testing. The scan plan gives information
on the volume tested for each butt fusion joint.
6 Personnel qualifications
Personnel performing testing in accordance with this document shall be qualified to an appropriate
level in accordance with ISO 9712 or an equivalent standard in the relevant industrial sector.
In addition to a general knowledge of ultrasonic testing, the operator shall be familiar with and have
practical experience in the use of TOFD systems on polyethylene butt fusion joints. Specific theoretical
and practical training and examination of personnel shall be performed on representative polyethylene
butt fusion joints containing natural or artificial reflectors similar to those expected. These training
and examination results shall be documented.
7 Equipment
7.1 General
The complete equipment, i.e. ultrasonic instrument, probe, cables and display monitor shall be capable
of the repetition of test results.
[8]
NOTE 1 In selecting the system components (hardware and software) ISO TS 16829 give useful information.
[9]
NOTE 2 Ultrasonic equipment used for TOFD testing should comply with the requirements of ISO 15626 EN­
[10]
12668 when applicable.
7.2 Ultrasonic instrument and display
The instrument shall be able to select an appropriate portion of the time base within which A­scans are
digitized. It is recommended that a sampling rate of the A-scan should be at least six times the nominal
probe frequency.
7.3 Ultrasonic probes
Only longitudinal wave mode can be used.
7.3.1 Probe selection
Any type of ultrasonic TOFD probe can be used if it satisfies the requirement of Clause 8 (Range and
sensitivity settings) with the ultrasonic equipment.
The most suitable ultrasonic probe frequency shall be selected in accordance with the pipe wall
thickness. Table 1 shows the recommended frequencies for each thickness range. However, the optimal
frequency can deviate from these values depending on the attenuation and thickness of the sample to
be tested.
The gap between the test surface and the bottom of the wedge shall not be greater than 0,5 mm.
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ISO/TS 24399:2022(E)
For thicknesses greater than 30 mm the wall thickness shall be divided into more than one inspection
zone, each zone covering a different depth region. Probe angle and frequencies shall be chosen to cover
full volume. These zones can be inspected simultaneously or separately. Table 2 shows the examples of
single and multiple inspection zone probe setup.
Table 1 — Selection of probe frequency
Centre Recommended
Wall Thickness (t) Number of Element size
Frequency Beam angle
mm TOFD setups mm
MHz (longitudinal waves)
8 ≤t< 30 1 or 2 5 to ≤ 10 60 to ≤ 70 3 to ≤ 6
30 ≤t< 60 2 2,25 to ≤ 5 60 to ≤ 70 6 to ≤ 11
60 ≤t≤ 100 3 1 to ≤ 5 45 to ≤ 70 6 to ≤ 11
NOTE 1 For multiple TOFD setups the deeper the range the lower the frequency and the smaller the beam
angle.
NOTE 2 In general higher frequencies provide better resolution and lower frequencies provide better
penetration.
Table 2 — Description of TOFD technique for testing butt fusion joints
TOFD set-up Example
Single zone
Multi­zone
7.3.2 Probe separation
The maximum diffraction efficiency occurs when the included angle is about 120 degrees.
The probes should be arranged such that the (imagined) beam centre lines intersect at about this angle
in the depth region where discontinuities are anticipated/sought.
o o
Deviations of more than ­35 or +45 from this value may cause the diffracted echoes to be weak and
should not be used unless detection capabilities can be demonstrated.
Probes shall not touch the bead.
7.4 Scanning mechanisms
To achieve consistency of the images (collected data), guiding mechanisms and scan encoder(s) shall be
used.
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ISO/TS 24399:2022(E)
7.5 Couplant
In order to generate proper images, a couplant should be used which provides a constant transmission
of ultrasound between the probe and the material. The same couplant used for calibration shall be used
for the testing.
Any couplant used should be cleaned off after testing.
8 Range and sensitivity settings
8.1 Settings
8.1.1 General
Setting of range and sensitivity shall be carried out prior to each testing period in accordance with this
document. Any change of the TOFD set-up, e.g. probe centre separation, will require a new setting.
8.1.2 Range setting - test volume
The range in the depth direction shall cover the full joint thickness in the fusion zone.
The range in the axial direction shall cover the melt fusion zone on both sides of the butt fusion centre
line. As a general guidance, for wall thicknesses up to 100 mm, the test area width is 10 mm or 1/5 of
the wall thickness from either side of the fusion zone, whichever is smaller (see Figure 1).
The range in the circumferential direction shall include the full circumference.
Key
x width of test area
1 outside of joint
2 inside of joint
3 MFZ boundary
4 test area
5 melt fusion zone (MFZ)
6 fusion interface
Figure 1 — Test area
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ISO/TS 24399:2022(E)
8.1.3 Time window
The time window shall at least cover the depth range as shown in Table 1:
1) for full-thickness testing using only one setup, the time window recorded shall start at least 1 µs
prior to the time of arrival of the lateral wave, and shall extend beyond the first mode-converted to
back-wall signal;
2) if more than one setup is used, the time windows shall overlap by at least 10 % of the depth range.
The start and extent of the time windows should be verified on the test object.
8.1.4 Time-to-depth conversion
Setting of time-to depth conversion shall be carried out on the reference block specified in 8.2.2
Some ultrasonic parameters are used for the time­to depth conversion such as the time of arrival of
the lateral wave, the time of arrival of back-wall reflection, probe centre separation, wedge delay,
velocity and thickness. For precise time-to depth conversion, at least four parameters have to be known
correctly.
Normally, the thickness and the velocity can be measured from the reference block.
8.1.5 Sensitivity settings
The sensitivity shall be set on the reference block made of the same material as the pipe with the butt
fusion joint being inspected. The gain control shall be set so that the amplitude of the lateral wave
is from 40 % to 80 % of the full screen height (FSH). In cases where the use of lateral wave is not
appropriate (e.g. use of steep refraction angle), the gain control shall be set so that the material grain
noise is from 5 % to 10 % of FSH.
8.2 Reference sample
8.2.1 General
The temperature of the reference sample shall be the same as the temperature ±10 °C of the test object
at the time of testing and shall be kept in the same environment as the test object throughout the test. A
reference block satisfying the condition in 8.2.2 shall be used as the reference sample.
8.2.2 Reference block
Reference blocks shall be used to determine the adequacy of the settings (e.g. coverage, sensitivity) and
may be used for time-to-depth conversion with known precise thickness.
A transfer correction should be applied to cover the difference in curvature and surface roughness of
the reference block and the test object.
The reference block used shall be of the same material classification as the pipe/fitting being inspected.
The thickness of the reference block shall be at least equal to the thickness of the joint to be tested. The
length and width of the reference block shall be chosen such that all relevant reflectors can be properly
scanned.
The width of the reference block shall be suff
...