SIST EN ISO 204:2023

SLOVENSKI STANDARD
01-november-2023
Kovinski materiali - Preskušanje nesoosnega lezenja pri nategu - Metoda
preskušanja (ISO 204:2023)
Metallic materials - Uniaxial creep testing in tension - Method of test (ISO 204:2023)
Metallische Werkstoffe - Einachsiger Zeitstandversuch unter Zugbeanspruchung -
Prüfverfahren (ISO 204:2023)
Matériaux métalliques - Essai de fluage uniaxial en traction - Méthode d'essai (ISO
204:2023)
Ta slovenski standard je istoveten z: EN ISO 204:2023
ICS:
77.040.10 Mehansko preskušanje kovin Mechanical testing of metals
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 204
EUROPEAN STANDARD
NORME EUROPÉENNE
August 2023
EUROPÄISCHE NORM
ICS 77.040.10 Supersedes EN ISO 204:2018
English Version
Metallic materials - Uniaxial creep testing in tension -
Method of test (ISO 204:2023)
Matériaux métalliques - Essai de fluage uniaxial en Metallische Werkstoffe - Einachsiger Zeitstandversuch
traction - Méthode d'essai (ISO 204:2023) unter Zugbeanspruchung - Prüfverfahren (ISO
204:2023)
This European Standard was approved by CEN on 25 June 2023.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2023 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 204:2023 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 204:2023) has been prepared by Technical Committee ISO/TC 164 "Mechanical
testing of metals" in collaboration with Technical Committee CEN/TC 459/SC 1 “Test methods for steel
(other than chemical analysis)” the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by February 2024, and conflicting national standards
shall be withdrawn at the latest by February 2024.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 204:2018.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 204:2023 has been approved by CEN as EN ISO 204:2023 without any modification.

INTERNATIONAL ISO
STANDARD 204
Fourth edition
2023-07
Metallic materials — Uniaxial creep
testing in tension — Method of test
Matériaux métalliques — Essai de fluage uniaxial en traction —
Méthode d'essai
Reference number
ISO 204:2023(E)
ISO 204:2023(E)
© ISO 2023
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
ISO 204:2023(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and designations . 6
5 Principle . 7
6 Apparatus . 8
6.1 Testing machine . 8
6.2 Extension and elongation measuring devices . 8
6.2.1 Extension measuring device . 8
6.2.2 Elongation measuring device . 9
6.3 Heating device, temperature measuring equipment and calibration . 9
6.3.1 Permissible temperature deviations . 9
6.3.2 Temperature measurement . 10
6.3.3 Thermocouples . 11
6.3.4 Calibration of the thermocouples . 11
7 Test pieces .12
7.1 Shape and dimensions . 12
7.1.1 Shape and dimension of smooth test pieces .12
7.1.2 Shape and dimension of notched test pieces .13
7.2 Preparation . 13
7.3 Determination of the original cross-sectional area . 13
7.4 Marking of the original gauge length, L . 14
o
7.5 Determination of the reference length, L . 14
r
8 Test procedure .15
8.1 Heating of the test piece .15
8.2 Application of the test force . 15
8.3 Test interruptions . 16
8.3.1 Planned interruptions of the test . 16
8.3.2 Multiple test piece machine with several test pieces in line . 16
8.3.3 Combined test . 16
8.3.4 Accidental interruption of the test . 16
8.4 Recording of temperature and elongation or extension . 16
8.4.1 Temperature . 16
8.4.2 Elongation and extension . 16
8.4.3 Elongation-time curve or extension-time curve . 17
9 Determination of results .17
10 Test validity .17
11 Accuracy of the results .17
11.1 Expression of the results . 17
11.2 Final uncertainty . 18
12 Test report .18
Annex A (informative) Information concerning drift of thermocouples .23
Annex B (informative) Information concerning methods of calibration of thermocouples .26
Annex C (normative) Creep testing using test pieces with V or blunt circumferential
notches . .27
iii
ISO 204:2023(E)
Annex D (informative) Method of estimating the uncertainty of the measurement in
accordance with the Guide to the expression of uncertainty in measurement (GUM) .30
Annex E (informative) Representation of results and extrapolation .36
Bibliography .45
iv
ISO 204:2023(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 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 164, Mechanical testing of metals,
Subcommittee SC 1, Uniaxial testing, in collaboration with the European Committee for Standardization
(CEN) Technical Committee CEN/TC 459/SC 1, Test methods for steel (other than chemical analysis),
in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This fourth edition cancels and replaces the third edition (ISO 204:2018), which has been technically
revised.
The main changes are as follows:
— Figure 1 has been corrected;
— symbols were revised;
— Formulas in Table 1 have been removed;
— the informative annex relating to computer compatible representation of standards has been
deleted;
— Bibliography has been updated.
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 204:2023(E)
Introduction
Creep is the phenomenon exhibited by materials which slowly deform when subjected to loading at
elevated temperature. This document is concerned with the method used to measure such material
behaviour.
Annexes are included concerning temperature measurement using thermocouples and their
calibration, creep testing test pieces with circumferential V and blunt (Bridgman) notches, estimation
of measurement uncertainty and methods of extrapolation of creep rupture life.
Information is still sought relating to the influence of off-axis loading or bending on the creep properties
of various materials. Based on the future availability of quantitative data, consideration can be given
as to whether the maximum amount of bending should be specified and an appropriate calibration
procedure be recommended. The decision will need to be based on the availability of quantitative
[1]
data .
This document incorporates many recommendations developed through the European Creep
Collaborative Committee (ECCC).
vi
INTERNATIONAL STANDARD ISO 204:2023(E)
Metallic materials — Uniaxial creep testing in tension —
Method of test
1 Scope
This document specifies the methods for:
a) uninterrupted creep tests with continuous monitoring of extension;
b) interrupted creep tests with periodic measurement of elongation;
c) stress rupture tests where normally only the time to fracture is measured;
d) a test to verify that a predetermined time can be exceeded under a given force, with the elongation
or extension not necessarily being reported.
NOTE A creep test can be continued until fracture has occurred or it can be stopped before fracture.
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 7500-2, Metallic materials — Verification of static uniaxial testing machines — Part 2: Tension creep
testing machines — Verification of the applied force
ISO 9513, Metallic materials — Calibration of extensometer systems used in uniaxial testing
3 Terms and definitions
For the purposes of this document, 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/
3.1
reference length
L
r
base length used for the calculation of either percentage elongation or percentage extension
Note 1 to entry: Several different gauge lengths and reference lengths are specified in this document. These
lengths reflect custom and practice used in different laboratories throughout the world. In some cases, the
lengths are physically marked on the test piece as lines or ridges; in other cases, the length can be a virtual
length based upon calculations to determine an appropriate length to be used for the determination of creep
elongation. For some test pieces, L , L and L are the same length.
r o e
Note 2 to entry: A method to calculate this value is given in 7.5.
ISO 204:2023(E)
3.2
original gauge length
L
o
length between gauge length marks on the test piece measured at ambient temperature before the test
Note 1 to entry: In general, L ≥ 5D.
o
3.3
extensometer gauge length
L
e
distance between the measuring points of the extensometer
3.4
parallel length
L
c
length of the parallel reduced section of the test piece
3.5
final gauge length after fracture
L
u
length between gauge length marks on the test piece measured after fracture, at ambient temperature,
with the pieces carefully fitted back together with their axes in a straight line
3.6
original cross-sectional area
S
o
cross-sectional area of the parallel length as determined at ambient temperature prior to testing
3.7
minimum cross-sectional area after fracture
S
u
minimum cross-sectional area of the parallel length as determined at ambient temperature after
fracture, with the pieces carefully fitted back together with their axes in a straight line
3.8
initial stress
R
o
applied force divided by the original cross-section area, S , of the test piece
o
3.9
extension
ΔL
et
increase of extensometer gauge length, L , at time t and at test temperature
e
Note 1 to entry: “Extension” is used for uninterrupted creep test with continuous measurement of the increase of
the length of the test piece by using an extensometer.
Note 2 to entry: For further information, see 6.2.
3.10
elongation
ΔL
ot
increase of original gauge length, L , at time t
o
Note 1 to entry: “Elongation” is mainly used for interrupted creep test with the manual measurement of the
increase of the length of the test piece.
Note 2 to entry: For further information, see 6.2.
ISO 204:2023(E)
3.11
percentage extension
e
extension at test temperature expressed as a percentage of the reference length, L , as given in
r
Formula (1)
ΔL
et
e=×100 (1)
L
r
Note 1 to entry: See Figure 1.
3.12
percentage elongation
A
elongation expressed as a percentage of the reference length, L , as given in Formula (2)
r
ΔL
ot
A=×100 (2)
L
r
3.13
percentage elastic extension
e
e
extension at test temperature expressed as a percentage of the reference length, L , which is proportional
r
to the initial stress, R
o
Note 1 to entry: This value can be calculated from the stress/percentage extension values during loading. See
8.4.2.
Note 2 to entry: See Figure 1.
3.14
percentage initial total extension
e
ti
extension at test temperature expressed as a percentage of the reference length, L , at end of loading
r
with the initial stress, R
o
Note 1 to entry: See Figure 1.
3.15
percentage initial plastic extension
e
i
extension at end of loading and at test temperature with the initial stress, R , expressed as a percentage
o
of the reference length, L , and determined as the difference between the percentage initial total
r
extension, e , and the percentage elastic extension, e , as given in Formula (3)
ti e
e = e − e (3)
i ti e
Note 1 to entry: See Figure 1.
Note 2 to entry: This value represents the plastic extension during the loading phase.
3.16
percentage total extension
e
t
extension at the test force at time t and at test temperature, expressed as a percentage of the reference
length, L
r
Note 1 to entry: See Figure 1.
ISO 204:2023(E)
3.17
percentage plastic extension
e
p
extension at time t and at test temperature determined as the difference between the percentage total
extension, e , and the percentage elastic extension, e , expressed as a percentage of the reference length,
t e
L , as given in Formula (4)
r
e = e − e (4)
p t e
Note 1 to entry: See Figure 1.
3.18
percentage total ultimate extension
e
u
total extension at rupture and at test temperature, expressed as a percentage of the reference length, L
r
3.19
percentage creep extension
e
f
extension, determined under full test force and at test temperature, as the difference between the
percentage plastic extension, e , and the percentage initial plastic extension, e , expressed as a
p i
percentage of the reference length, L , as given in Formula (5)
r
e = e − e (5)
f p i
Note 1 to entry: See Figure 1.
Note 2 to entry: Suffix f originates from “fluage”, “creep” in French.
3.20
percentage anelastic extension
e
k
negative extension at end of unloading at test temperature, expressed as a percentage of the reference
length, L
r
Note 1 to entry: See Figure 1 and 8.4.
3.21
percentage permanent extension
e
per
extension at end of unloading and at test temperature determined as the difference between the
percentage total extension, e , and the sum of percentage elastic extension, e , plus the percentage
t e
anelastic extension, e , expressed as a percentage of the reference length, L , as given in Formula (6)
k r
e = e – (e + e) (6)
per t e k
Note 1 to entry: In the case of e ≈ 0, the following relationship may be used: e ≈ e .
k per p
Note 2 to entry: See Figure 1.
3.22
percentage permanent elongation
A
per
elongation expressed as a percentage of the reference length, L , at end of unloading and at room
r
temperature
ISO 204:2023(E)
3.23
percentage elongation after creep fracture
A
u
permanent elongation after fracture, L − L , expressed as a percentage of the reference length, L , as
u o r
given in Formula (7)
LL−
uo
A = ×100 (7)
u
L
r
Note 1 to entry: A may have the specified temperature, T, in degrees Celsius as superscript and the initial stress,
u
R , in megapascal as subscript; see the example in Table 1.
o
3.24
percentage reduction of area after creep fracture
Z
u
maximum change in cross-sectional area measured after fracture, S − S , expressed as a percentage of
o u
the original cross-sectional area, S , as given in Formula (8)
o
SS−
ou
Z = ×100 (8)
u
S
o
Note 1 to entry: Z may have the specified temperature, T, in degrees Celsius as superscript and the initial stress,
u
R , in megapascal as subscript; see the example in Table 1.
o
3.25
creep extension time
t
fx
time required for a strained test piece to obtain a specified percentage creep extension, x, at the
specified temperature, T, and the initial stress, R
o
EXAMPLE t
f0,2
3.26
plastic extension time
t
px
time required to obtain a specified percentage plastic extension, x, at the specified temperature, T, and
the initial stress, R
o
Note 1 to entry: An example for t is given in Figure E.2 a) (t = 100 000 h corresponds to e = 1 % at
p1 p1 p
R = 120 MPa).
o
3.27
creep rupture time
t
u
time to rupture for a test piece maintained at the specified temperature, T, and the initial stress, R
o
Note 1 to entry: The symbol t can have as superscript the specified temperature, T, in degrees Celsius and as
u
subscript the initial stress, R , in megapascal; see the example in Table 1.
o
3.28
single test piece machine
testing machine that permits straining of a single test piece
3.29
multiple test piece machine
testing machine that permits straining of more than one test piece simultaneously at the same
temperature
ISO 204:2023(E)
4 Symbols and designations
The symbols and corresponding designations are given in Table 1.
Table 1 — Symbols and designations
a
Symbol Unit Designation
a mm Thickness of a test piece of square or rectangular cross-section [see Figure 2 b)]
A % Percentage permanent elongation
per
NOTE As an example, the symbol can be completed as follows:
A : percentage permanent elongation with an initial stress of 50 MPa
per 50/5000
after 5 000 h at the specified temperature of 375 °C.
A % Percentage elongation after creep fracture [see Formula (7)]
u
NOTE As an example, the symbol can be completed as follows:
A : percentage elongation after creep fracture with an initial stress of
u 50
50 MPa at the specified temperature of 375 °C.
b mm Width of the cross-section of the parallel length of a test piece of square or rec-
tangular cross-section
D mm Diameter of gauge length of a cylindrical test piece
d mm Diameter of gauge length without a notch in a combined notched/unnotched
test piece (see Figure C.1)
D mm Diameter of gauge length containing a notch
n
d mm Diameter across root of circumferential notch
n
For a combined notched/unnotched test piece d = d
n
e % Percentage extension
e % Percentage elastic extension
e
e % Percentage creep extension [see Formula (5)]
f
NOTE As an example, the symbol can be completed as follows:
e percentage creep extension with an initial stress of 50 MPa after
f 50/5000
5 000 h at the specified temperature of 375 °C.
e % Percentage creep extension at creep rupture time
fu
e % Percentage initial plastic extension
i
e % Percentage anelastic extension
k
e % Percentage plastic extension
p
e % Percentage permanent extension
per
e % Percentage plastic extension at creep rupture time
pu
e % Percentage total extension
t
e % Percentage initial total extension
ti
e % Percentage total extension at creep rupture time
u
L mm Parallel length
c
a
The main subscripts (r, o and u) of the symbols are used as follows:
r corresponds to reference;
o corresponds to original;
u corresponds to ultimate (after rupture).
NOTE 1 Index t can have different meanings, e.g. time, total or transition
NOTE 2 For the purposes of creep testing in this document, the terms "fracture" and "rupture" are interchangeable and
are used to describe when a test piece breaks.
ISO 204:2023(E)
TTabablele 1 1 ((ccoonnttiinnueuedd))
a
Symbol Unit Designation
L mm Extensometer gauge length
e
ΔL mm Extension
et
L mm Parallel gauge length containing a notch
n
L mm Original gauge length
o
ΔL mm Elongation
ot
L mm Reference length
r
L mm Final gauge length after fracture
u
n - Norton creep exponent
r mm Notch root radius
n
R MPa Initial stress
o
r mm Transition radius
t
S mm Original cross-sectional area of the parallel length
o
S mm Minimum cross-sectional area after fracture
u
t h Elapsed time from end of loading
T °C Specified temperature
T °C Corrected measured temperature
c
t h Creep extension time
fx
t h Plastic extension time
px
t h Creep rupture time
u
NOTE As an example, the symbol can be completed as follows:
t : creep rupture time with an initial stress of 50 MPa at the specified
u 50
temperature of 375 °C.
t h Creep rupture time of a notched test piece
un
x % Specified percentage creep or plastic extension
Z % Percentage reduction of area after creep fracture [see Formula (8)]
u
NOTE As an example, the symbol can be completed as follows:
Z : percentage reduction of area after creep fracture with an initial stress
u 50
of 50 MPa at the specified temperature of 375 °C.
a
The main subscripts (r, o and u) of the symbols are used as follows:
r corresponds to reference;
o corresponds to original;
u corresponds to ultimate (after rupture).
NOTE 1 Index t can have different meanings, e.g. time, total or transition
NOTE 2 For the purposes of creep testing in this document, the terms "fracture" and "rupture" are interchangeable and
are used to describe when a test piece breaks.
5 Principle
The test consists of heating a test piece to the specified temperature and of straining it by means of
a constant tensile force or constant tensile stress (see Note) applied along its longitudinal axis for a
period of time to obtain any of the following:
— a specified creep extension (uninterrupted test) with continuous extension measurement;
— values of permanent elongation at suitable intervals throughout the test (interrupted test);
ISO 204:2023(E)
— the creep rupture time (uninterrupted and interrupted test).
NOTE “Constant stress” or ”true stress” means that the ratio of the force to the instantaneous cross-section
remains constant throughout the test. The results obtained with constant stress are generally different from
[2]
those obtained with constant force .
6 Apparatus
6.1 Testing machine
The testing machine shall apply a force along the axis of the test piece while keeping inadvertent bending
or torsion of the test piece to a minimum. Prior to test, the machine should be visually examined to
ensure that loading bars, grips, universal joints and associated equipment are in a good state of repair.
The force shall be applied to the test piece without shock.
The machine should be isolated from external vibration and shock. The machine should be equipped
with a device which minimizes shock when the test piece fractures.
The machine shall be verified and shall meet the requirements of at least class 1 in ISO 7500-2.
6.2 Extension and elongation measuring devices
6.2.1 Extension measuring device
In uninterrupted tests, the extension shall be measured using an extensometer which meets the
performance requirements of class 1 or better of ISO 9513 or by other means which ensure the same
accuracy without interruption of the test. The extensometer can either be directly attached to the test
piece or be non-contacting (e.g. a non-contacting optical or laser extensometer).
It is recommended that the extensometer be calibrated over an appropriate range based upon the
expected creep strain.
The extensometer shall be calibrated at intervals not exceeding 3 years, unless the test duration
is longer than 3 years. If the predicted test duration exceeds the date of the expiry of the calibration
certificate, then the extensometer shall be recalibrated prior to commencement of the creep test.
The extensometer gauge length shall not be less than 10 mm.
The extensometer shall be capable of measuring extension of one side of the test piece or, preferably, on
opposite sides of the test piece.
The type of extensometer used (e.g. single-sided, double-sided, axial, diametral) should be reported.
When the extension is measured on the opposite sides, the average extension should be reported.
When the extension is measured with an extensometer attached to the grip ends of the test piece, the
ends shall be of such shape and size that it can be assumed that the observed extension has occurred
completely within the reference length of the test piece. Percentage creep extension is measured over
L .
r
A gauge length as long as possible should be used to improve the accuracy of measurements.
Care should be taken to avoid spurious negative creep when using nickel base alloy extensometers. See
[3]
the Code of Practice .
ISO 204:2023(E)
For low creep strain measurements, e.g. ≤1 % strain, on test pieces with short gauge lengths, careful
consideration should be given to ensure that the measuring device used has sufficient resolution and
accuracy over the range of use.
NOTE 1 Information on the long-term stability of transducers used for creep testing and accreditation issues
is given in References [4] and [5].
NOTE 2 No extensometer is required if only the percentage elongation after creep fracture or the percentage
creep elongation for a specified test duration is determined.
6.2.2 Elongation measuring device
In interrupted tests, periodically unload the test piece, cool it to ambient temperature and measure the
permanent elongation on the gauge length with an appropriate device. The precision of this device shall
be 0,01 ΔL or 0,01 mm, whichever is the greater. After this measurement, the test piece may be first
r
reheated and then reloaded.
6.3 Heating device, temperature measuring equipment and calibration
6.3.1 Permissible temperature deviations
The heating device shall heat the test piece to the specified temperature, T. The permitted deviations
between the corrected measured temperature, T , and the specified temperature, T, and the permitted
c
maximum temperature variation along the test piece shall be as given in Table 2.
Table 2 — Permitted deviations between T and T and maximum permissible temperature
c
variation along the test piece
Specified temperature Permitted deviation between Maximum permissible temperature
T T and T variation along the test piece
c
°C °C °C
T ≤ 600 ±3 3
600 < T ≤ 800 ±4 4
800 < T ≤ 1 000 ±5 5
1 000 < T ≤ 1 100 ±6 6
For specified temperatures greater than 1 100 °C, the permitted values, including drift, shall be
specified by agreement between the parties concerned.
The corrected measured temperatures, T , are the temperatures measured at the surface of the parallel
c
length of the test piece, errors from all sources, including drift (see Annex A), being taken into account
and any systematic errors having been corrected.
It is permitted to carry out indirect measurement of the temperature of each heating zone of the furnace
provided that it is demonstrated that the tolerance specified above is fulfilled on the test piece instead
of measuring the temperature at the surface of each individual test piece.
If an extensometer is used, the parts of this instrument outside the furnace shall be designed and
protected in such a way that the temperature variations in the air around the furnace do not significantly
affect the measurements of the variations in length.
Variations in temperature of the air surrounding the test machine should not exceed ±3 °C.
In the interrupted test, the variation of the room temperature during all measurements of the gauge
length should not exceed ±2 °C. If this range is exceeded, corrections for ambient temperature variations
shall be applied.
ISO 204:2023(E)
6.3.2 Temperature measurement
6.3.2.1 General
The temperature indicator shall have a resolution of at least 0,5 °C. The temperature measuring
equipment shall have an accuracy equal to or better than ±1 °C.
For thermocouples, in the absence of measuring instruments with cold junction compensation, cold
junction temperatures, normally at 0 °C, shall be measured to within 0,5 °C.
Many laboratories maintain the cold junction above ambient temperature. Whatever its temperature,
it shall remain stable and appropriate compensation shall be applied to determine the temperature
measured by the thermocouple.
NOTE Information concerning drift of thermocouples is given in Annex A and methods of calibration of
thermocouples are given in Annex B.
For indirect methods of temperature measurement e.g. pyrometry, thermal cameras or resistivity
techniques, it shall be demonstrated that traceability is provided to the SI System of temperature
measurement and that the above criteria for accuracy and resolution can be achieved.
6.3.2.2 Calibration of the temperature measuring equipment
The calibration of the temperature measuring equipment (including the cable, the connection, the cold
junction, the indicator or the recorder, the data line, etc.) shall be carried out by a method traceable to
the international unit (SI) of temperature.
If practicable, this calibration should be carried out annually over the range of temperatures measured
by the equipment and the readings shall be given in the calibration report.
6.3.2.3 Single test piece machines
In single test piece machines, with thermocouples used for temperature measurement, at least two
thermocouples should be used for test pieces with a parallel length less than or equal to 50 mm. For test
pieces with a parallel length greater than 50 mm, at least three thermocouples should be used. In all
cases, a thermocouple should be placed at each end of the parallel length and, if a third thermocouple is
used, it should be placed in the middle region of the parallel length.
The number of thermocouples may be reduced to one if it can be demonstrated that the conditions
of the furnace and the test piece are such that the variation of temperature of the test piece does not
exceed the values specified in 6.3.1.
6.3.2.4 Multiple test piece machines
In multiple test piece machines, with thermocouples used for temperature measurement, at least one
thermocouple should be used for each test piece. If only one thermocouple is used, it shall be positioned
at the middle of the parallel length. Three thermocouples may only be used if located at appropriate
positions within the furnace, and if there is supporting data to demonstrate that for all test pieces the
temperature conforms to the requirements of 6.3.1.
In the case of indirect temperature measurement, regular control measurements are required to
determine differences between the thermocouple(s) of each heating zone and a significant number of
test pieces within a given zone. The non-systematic components of the temperature differences shall
not exceed ±2 °C up to 800 °C and ±3 °C above 800 °C.
ISO 204:2023(E)
6.3.2.5 Notched test pieces
Temperature measurement of notched test pieces shall be in accordance with either 6.3.2.3 or 6.3.2.4. It
is recommended that one thermocouple be placed close to the notch.
NOTE Details about testing notched test pieces are given in Annex C.
6.3.3 Thermocouples
The thermocouple junctions shall make good thermal contact with the surface of the test piece and
shall be screened from direct radiation from the heating source. The remaining portions of the wires
within the furnace shall be thermally shielded and electrically insulated.
Precautions shall be taken to minimize contamination and physical damage of thermocouples.
Insulators and/or insulation shall be maintained in a clean state to also minimise contamination and
prevent conduction.
[6]
Information concerning different types of thermocouples is given in IEC 60584-1 .
The use of rare metal thermocouples, preferentially of type S or R, is recommended for temperatures
[7]
equal to or greater than 400 °C .
Base metal thermocouples of type K should only be used either for temperatures lower than 400 °C
or for times less than 1 000 h at higher temperatures and should not be re-used without cutting back
exposed wire and re-calibrating.
Base metal thermocouples of type N may be used eit
...