ISO/TS 24399:2025

Technical
Specification
ISO/TS 24399
First edition
Thermoplastic pipes for the
2025-01
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
Reference number
© ISO 2025
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.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
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 to be defined for the procedure development . .3
5.2 Specific information required by the operator before testing .3
5.3 Written 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 General .4
7.3.2 Probe selection.4
7.3.3 Probe separation .5
7.4 Scanning mechanisms .6
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 Time-to-depth 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 Temperature of fusion joint tested .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
Annex B (informative) Example procedures for producing imperfections in butt fusion joints
[14]
.................................................................................................................................................................................................................................................. 17
Bibliography .21

iv
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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
Technical Specification ISO/TS 24399:2025(en)
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 to detect imperfections such as voids, inclusions, lack of fusions, misalignment
and particulate contamination in the BF joints. The document only applies to polyethylene pipes and fittings
without a barrier to ultrasonic waves.
This document also provides requirements for procedure qualification and guidance for personnel
qualifications, which are essential for applying this test technique.
This document covers the equipment, the preparation and performance of the test, the indication assessment
and the reporting for polyethylene BF joints.
Acceptance criteria are not covered in this document.
NOTE 1 At present, laboratory experiences exist on the use of TOFD for polyethylene butt fusion joints and/or
[1][2][3][4][5][6]
reference blocks of wall thickness between 8 mm to 100 mm. Field experience on butt fusion joints in
[7]
high density polyethylene (HDPE) pipes has been reported.
NOTE 2 Interlaboratory testing has shown that TOFD is a viable method for enhancing the integrity assessment of
[13]
butt fusion joints.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 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 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/

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, such as airborne dust, or coarse particles, such as 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 setup
TOFD setup
probe arrangement defined by probe characteristics (e.g. frequency, probe element size, beam angle, wave
mode), probe position, probe centre separation, and the number of probe pairs

3.11
probe centre separation
PCS
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 the 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 equipment, preparation and performance of the test, indication assessment, and
reporting for polyethylene butt fusion joints.
This document may be used to draft a detailed procedure for TOFD testing of polyethylene butt fusion joints.
Characterization of imperfections in the parent material adjacent to the butt fusion joint is also possible.
5 Information required prior to testing
5.1 Items to be defined for the procedure development
Information on the following items shall be provided:
a) purpose and extent of testing;
b) manufacturing or operation stage of BF joints at which the testing is to be carried out;
c) reference sample;
d) requirements for getting access to the BF joints, the surface condition of the pipe; and the
temperature range;
e) personnel qualifications;
f) reporting requirements.
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 qualified test procedure;
b) all relevant joint dimensions.
5.3 Written test procedure
For all testing, a written test procedure is required. This test procedure shall include the following
information:
a) 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.
b) equipment requirements and settings (including but not limited to frequency, sampling rate, pitch
between elements and element size);
c) evaluation of indications;
d) environmental and safety issues.
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 in the field.
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.
For selecting the system components (hardware and software), ISO/TS 16829 gives useful information.
[9]
Equipment used for TOFD testing should conform to the requirements of EN 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 A-scans are
digitized. It is recommended that the sampling rate of the A-scan should be at least six times the nominal
probe frequency.
7.3 Ultrasonic probes
7.3.1 General
Only longitudinal waves are feasible for polyethylene.
7.3.2 Probe selection
Any type of ultrasonic TOFD probe can be used provided it satisfies the requirements of Clause 8 with the
ultrasonic instrument.
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 the full
volume. These zones can be inspected simultaneously or separately. Table 2 shows examples of single and
multiple inspection zone probe setups.
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 setup Example
Single zone
Multi-zone
Key
1 TOFD setup for single zone
2  PCS
7.3.3 Probe separation
The maximum diffraction efficiency occurs when the included angle is approximately 120°.
The probes should be arranged such that the (imagined) beam centre lines intersect at approximately this
angle in the depth region where discontinuities are anticipated/sought.
Deviations of more than −35° or +45° from this value can 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 shall be used, which provides a constant transmission of
ultrasound between the probe and the tested fusion joint.
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 setup (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 general guidance, for wall thicknesses up to 100 mm, the test area
...