ISO 7039:2024

Metallic materials - Tensile testing - Method for evaluating the susceptibility of materials to the effects of high-pressure gas within hollow test pieces

This document specifies the geometries and proposed finishing procedures of the inner surface of hollow test piece of metallic materials, filled with a high-pressure gaseous medium. The document specifies a tensile testing procedure to evaluate the effect of high-pressure gaseous medium compared to a high-pressure inert gas or air. The document can be used for the screening of metallic materials by evaluating mechanical property changes due to the effects of various test gases, including hydrogen. NOTE Temperature range and pressure range depend on the materials to be tested and test gas to be used.

Matériaux métalliques — Essais de traction — Méthode d'évaluation des changements de propriétés dans un environnement gazeux à haute pression en utilisant une pièce d'essai creuse

General Information

• Status: Published
• Publication Date: 21-Jul-2024
• ICS: 77.040.10 - Mechanical testing of metals
• Technical Committee: ISO/TC 164/SC 1 - Uniaxial testing
• Drafting Committee: ISO/TC 164/SC 1 - Uniaxial testing
• Current Stage: 9092 - International Standard to be revised
• Start Date: 10-Sep-2025
• Completion Date: 13-Dec-2025

Overview

ISO 7039:2024 - Metallic materials - Tensile testing - Method for evaluating the susceptibility of materials to the effects of high‑pressure gas within hollow test pieces - specifies a standardized screening method to assess how high‑pressure gases (including hydrogen) affect tensile properties of metallic materials. The method uses a cylindrical round bar with a central axial hole (a hollow test piece) that is pressurized internally during uniaxial tensile testing and compares results to the same test filled with a high‑pressure inert gas or air.

Key topics and technical requirements

• Test principle: Tensile test on a hollow specimen with its internal hole pressurized with the test gas; effects are evaluated relative to inert gas/air conditions.
• Specimen geometry: Cylindrical round bar with axial hole. Recommended outer diameter (D) of the parallel part: 3 mm to 12 mm; recommended inner diameter (d): 1 mm to 4 mm; recommended d/D < 0.33 (ratios may be agreed between parties).
• Inner surface finish: The standard specifies geometries and proposed finishing procedures for the inner surface to control factors (e.g., roughness) that affect performance under internal high pressure.
• Measured properties and metrics: Yield strength, tensile strength, percentage elongation after fracture, reduction of area at leakage and relative metrics (e.g., A_h(rel), Z_h(rel), R_p0.2h(rel), R_mh(rel)) - i.e., property with test gas divided by property with inert gas/air.
• Test conditions: Gas type, pressure, temperature and test speed influence results. ISO 7039 notes that temperature and pressure ranges depend on the material and gas used; preliminary testing is recommended to set relevant conditions.
• Limitations: Intended as a screening/selection method, not a substitute for design-level tensile values from ISO 6892 series.

Applications and who uses it

• Material screening for susceptibility to hydrogen embrittlement or other gas-induced degradation.
• R&D and qualification of alloys, welds and components intended for high‑pressure gas service (hydrogen pipelines, cylinders, compressors, valves).
• Testing laboratories and manufacturers assessing candidate materials, coatings, or surface treatments.
• Quality assurance and standards bodies using consistent evaluation protocols for high‑pressure gas environments.

Related standards

• ISO 6892‑1 / ‑2 / ‑3 (tensile testing at room / elevated / low temperature)
• ISO 21920‑2 (surface texture terminology)
• ASTM G142 and ISO 11114‑4 (related hydrogen testing approaches; referenced in the Introduction)
• ASME B31.8 (gas transmission piping - normative cross‑reference)

Keywords: ISO 7039:2024, hollow test piece, tensile testing, hydrogen embrittlement, high‑pressure gas, metallic materials, specimen geometry, inner surface finish, screening test.

Standards Content (Sample)

International
Standard
ISO 7039
First edition
Metallic materials — Tensile
2024-07
testing — Method for evaluating the
susceptibility of materials to the
effects of high-pressure gas within
hollow test pieces
Matériaux métalliques — Essais de traction — Méthode
d'évaluation des changements de propriétés dans un
environnement gazeux à haute pression en utilisant une pièce
d'essai creuse
Reference number
© ISO 2024
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
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or ISO’s member body in the country of the requester.
ISO copyright office
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Principle . 2
6 Test piece . 3
6.1 General .3
6.2 Shape and dimensions .3
6.3 Inner surface of hole .3
6.4 Number of test pieces .4
7 Measurement of original cross-sectional area . 4
8 Marking the original gauge length . 4
9 Test equipment . 4
9.1 Principle .4
9.2 Testing machine .5
9.3 Extensometer .5
9.4 Test deviation .5
10 Test conditions . 5
10.1 Test gas .5
10.2 Test temperature .6
10.3 Test pressure .6
10.4 Testing rate .6
11 Evaluation of the test results . 6
11.1 Yield strength, tensile strength, percentage elongation after fracture with hollow test
piece .6
11.2 Percentage reduction of area at leakage .7
11.3 Relative elongation after fracture with hollow test piece, A .7
h(rel)
11.4 Relative reduction of area at leakage with hollow test piece, Z .7
h(rel)
11.5 Relative 0,2 % proof strength with hollow test piece, R .7
p0,2 h(rel)
11.6 Relative tensile strength with hollow test piece, R .8
mh(rel)
12 Test report . 8
Bibliography . 9

iii
Foreword
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ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
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This document was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals, Subcommittee
SC 1, Uniaxial testing.
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.

iv
Introduction
[1]
Hollow test pieces have been occasionally used for the evaluation of influence of hydrogen since the 1950’s.
But those hollow test pieces were mostly shaped with thin walls or in a tubular form, and the deformation
behaviour was different from that of solid test piece; as a result, neither the percentage elongation after
fracture (the elongation) nor the percentage reduction of area (the reduction of area) can be accurately
obtained. The influence of a high-pressure hydrogen gas environment has been conventionally evaluated
using a solid test piece within a gas-filled cylinder or vessel with the tensile force applied from outside the
[2]
vessel to evaluate the influence of the hydrogen gas on the material under test as described in ASTM G 142
[3]
or ISO 11114-4 .
Since 2005, the use of a hydrogen gas filled hollow test piece has been utilized as a method to evaluate
changes in tensile properties of metallic materials due to concurrent exposure to gaseous hydrogen. It was
[4]-[9]
found in previous studies that testing of a hollow test piece with a small diameter axial hole pressurized
with gaseous hydrogen yielded similar trends for both the elongation and the reduction of area to testing of
solid test pieces stored in a similar gaseous environment. For this reason, this method has been considered
a material screening test method for evaluation of metallic materials in gaseous hydrogen and the resulting
data are not suitable for design.
This document does not address the determination of entirely the same values of mechanical properties for
design purposes as specified by the ISO 6892 series but is suitable as a screening or first selection method
for metallic materials in a gaseous or liquid media. The hollow test piece is suitable for the evaluation of
materials used for high-pressure pipe or vessels, and can be used not only for hydrogen gas, but also for
other gaseous or corrosive media. However, the major concerns for the hollow test piece are the hoop stress
and the roughness of inner surface. In this document, the hollow test piece method is regarded for tests
filled with various media and the required preparation of the test piece, such as an inner surface finish, is
also described.
The type of the pressurized gas in the hollow test piece can affect the tensile properties in the test. Also, the
specific test conditions, e.g., test speed, test gas, internal pressure, temperature, and gas purity, can affect
the outcome. As this document describes in general the test procedure for the hollow test piece, it does not
describe the most suitable test conditions for all possible variations of the test parameters. Preliminary
tests should be conducted to identify technical relevant test conditions. Test conditions in this document
will be revised with the increase of test results.

v
International Standard ISO 7039:2024(en)
Metallic materials — Tensile testing — Method for evaluating
the susceptibility of materials to the effects of high-pressure
gas within hollow test pieces
1 Scope
This document specifies the geometries and proposed finishing procedures of the inner surface of hollow
test piece of metallic materials, filled with a high-pressure gaseous medium. The document specifies
a tensile testing procedure to evaluate the effect of high-pressure gaseous medium compared to a high-
pressure inert gas or air. The document can be used for the screening of metallic materials by evaluating
mechanical property changes due to the effects of various test gases, including hydrogen.
NOTE Temperature range and pressure range depend on the materials to be tested and test gas to be used.
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 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature
ISO 6892-2, Metallic materials — Tensile testing — Part 2: Method of test at elevated temperature
ISO 6892-3, Metallic materials — Tensile testing — Part 3: Method of test at low temperature
ISO 9513, Metallic materials — Calibration of extensometer systems used in uniaxial testing
ISO 21920-2, Geometrical product specifications (GPS) — Surface texture: Profile — Part 2: Terms, definitions
and surface texture parameters
ASME B31.8, Gas Transmission and Distribution Piping Systems for thick wall pipes
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 6892-1, ISO 21920-2 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
hollow test piece
test piece in form of round bar with a hole in its central axis
3.2
relative elongation after fracture with hollow test piece
A
h(rel)
value of the elongation after fracture obtained with a high-pressure gaseous medium divided by the
elongation after fracture obtained with a high-pressure inert gas or air with hollow test piece

3.3
relative reduction of area with hollow test piece
Z
h(rel)
value of the reduction of area at leakage obtained with a high-pressure gaseous medium divided by the
reduction of area obtained with a high-pressure inert gas or air with hollow test piece
3.4
relative 0,2 % proof strength with hollow test piece
R
p0,2 h(rel)
value of the 0,2 % proof strength obtained with a high-pressure gaseous medium divided by the 0,2 % proof
strength obtained with a high-pressure inert gas or air with hollow test piece
3.5
relative tensile strength with hollow test piece
R
mh(rel)
value of the tensile strength obtained with a high-pressure gaseous medium divided by the tensile strength
obtained with a high-pressure inert gas or air with hollow test piece
4 Symbols
The symbols and corresponding designations are given in Table 1.
Table 1 — Symbols and designations
Symbol Unit Designation
d mm original internal diameter of the parallel length
o
d mm internal diameter at the fracture section after fracture
f
D mm original outer diameter of the parallel length
o
D mm outer diameter at the fracture section after fracture
f
-1
s estimated strain rate over the parallel length
e
L
c
L mm original gauge length
o
L mm final gauge length after fracture
f
A % percentage elongation after fracture with hollow test piece:
h
LL−
fo
A = ×100
h
L
o
S mm original cross-sectional area of the parallel length
o
S mm final cross-sectional area at leakage
f
Z % percentage reduction of area at leakage with hollow test piece:
h
SS−
of
Z = ×100
h
S
o
A relative elongation after fracture with hollow test piece
h(rel)
Z relative reduction of area with hollow test piece
h(rel)
R relative 0,2 % proof strength with hollow test piece
p0,2 h(rel)
R relative tensile strength with hollow test piece
mh(rel)
5 Principle
A tensile test is carried out by pressurizing the hole of the hollow test piece with a test gas to determine the
effects of the test gas and temperature on the mechanical properties of the material under test.
The effect of the test gas is evaluated by comparing the material properties to those obtained by filling the
hole of the hollow test piece with high-pressure inert gas or air at the same test conditions.

6 Test piece
6.1 General
The shape and dimensions of inner hole of the test pieces may be adap
...