ISO 24033:2025

International
Standard
ISO 24033
Third edition
Polyethylene of raised temperature
2025-06
resistance (PE-RT) pipes — Effect
of time and temperature on the
expected strength
Tubes en polyéthylène de meilleure résistance à la température
(PE-RT) — Influence du temps et de la température sur la
résistance espérée
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Basic formulae . 2
5 Expected strength . 3
5.1 Extrapolation limits .3
5.2 Graphical representation .4
5.3 Tabulated values .7
6 Demonstrating conformance . 8
7 Derivation of wall thicknesses . . 8
Annex A (normative) Demonstrating conformance to the reference lines . 9
Annex B (informative) Derivation of S values . 10
calc,max
Bibliography . 14

iii
Foreword
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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.
This third edition cancels and replaces the second edition (ISO 24033:2009), which has been technically
revised.
The main changes are as follows:
— Formula (3) of the reference line for PE-RT Type 1 for 110 °C was added.
— For the procedure to demonstrate conformance to the reference lines in Annex A, the method described
in ISO 9080 was additionally implemented.
— Annex B, which gives advice for the dimensioning of piping components, was added.
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
An increasing number of types of polyethylene (PE) polymers, made in a variety of processes, are available
on the market for different applications in plastic piping and ducting systems. Many applications have their
own system standard that defines the properties and requirements for the pipes and fittings used.
The types of PE suitable for use in hot and cold-water systems are basically different from those for
applications at ambient temperatures, such as in water supply, sewage and drainage, and gaseous fuels.
Therefore, it makes sense to differentiate those PE materials having raised temperature-resistance by
terming them “PE-RT” (for polyethylene of raised temperature).
NOTE Abbreviated term based on the provisions of, and guidance for preparing new abbreviated terms for, basic
polymers, mixtures of polymers, and related terms given in ISO 1043-1.

v
International Standard ISO 24033:2025(en)
Polyethylene of raised temperature resistance (PE-RT)
pipes — Effect of time and temperature on the expected
strength
1 Scope
This document specifies the minimum values for expected strength as a function of time and temperature in
the form of reference lines, for use in calculations on pipes made of
a) polyethylene of raised temperature resistance (PE-RT) type I, and
b) polyethylene of raised temperature resistance (PE-RT) type II.
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 1167-1, Thermoplastics pipes, fittings and assemblies for the conveyance of fluids — Determination of the
resistance to internal pressure — Part 1: General method
ISO 1167-2, Thermoplastics pipes, fittings and assemblies for the conveyance of fluids — Determination of the
resistance to internal pressure — Part 2: Preparation of pipe test pieces
ISO 9080:2012, Plastics piping and ducting systems — Determination of the long-term hydrostatic strength of
thermoplastics materials in pipe form by extrapolation
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 lines
generic description of the minimum long-term hydrostatic strength to be expected from a particular
polymer.
Note 1 to entry: Reference lines are not to be considered as characteristic of a specific grade or of material from a
specific supplier.
Note 2 to entry: The lines are described by a mathematical equation which permits interpolation and extrapolation in
an unambiguous way within the applicable temperature and time ranges.
Note 3 to entry: The reference lines for PE-RT have been agreed upon by a group of ISO/TC 138/SC5 experts after
considering experimental data and have been accepted by the relevant technical committees in ISO.

4 Basic formulae
The reference lines for PE-RT in general can be applied to temperatures between 20 °C and 110 °C.
The reference lines for PE-RT Type I, described by Formulae (1) and (2), are applicable for temperatures
between 20 °C and 95 °C.
First branch:   log t= A + B /T + C log σ + (D /T) log σ (1)
10 1 1 1 10 1 10
Second branch: log t = A + B /T + C log σ + (D /T) log σ (2)
10 2 2 2 10 2 10
where
t is the time, in hours;
T is the temperature, in Kelvin;
σ is the hoop stress, in Megapascal.
The lower value obtained from Formula (1) or Formula (2), respectively, represents the expected hoop
strength.
First branch:
A = −190,481
B = 78 763,07
C = 119,877
D = -58 219,035
log t = –190,481 + 78 763,07/T + 119,877 log σ – (58 219,035/T) log σ
10 10 10
Second branch:
A = -23,795 4
B = 11 1
...