ISO 24033:2025

Polyethylene of raised temperature resistance (PE-RT) pipes - Effect of time and temperature on the expected strength

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.

Tubes en polyéthylène de meilleure résistance à la température (PE-RT) — Influence du temps et de la température sur la résistance espérée

General Information

• Status: Published
• Publication Date: 10-Jun-2025
• ICS: 23.040.20 - Plastics pipes
• 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 5 - Polyolefin pipes
• Current Stage: 6060 - International Standard published
• Start Date: 11-Jun-2025
• Due Date: 15-Nov-2025
• Completion Date: 10-Jun-2025

Relations

• Revises: ISO 24033:2009 - Polyethylene of raised temperature resistance (PE-RT) pipes - Effect of time and temperature on the expected strength
• Effective Date: 18-Nov-2023

Overview

ISO 24033:2025 - Polyethylene of raised temperature resistance (PE‑RT) pipes defines how the expected long‑term strength of PE‑RT pipe materials varies with time and temperature. The standard provides mathematically defined reference lines (and tabulated/graphical values) for PE‑RT Type I and Type II over the typical service range (20 °C to 110 °C). These reference lines are intended for use in strength calculations, material qualification and design of piping systems exposed to elevated temperatures.

Key topics and requirements

• Reference lines and formulae: Expected strength is given by log‑time equations of the form log t = A + B/T + C log σ + (D/T) log σ. PE‑RT Type I uses two branches (20–95 °C) plus a separately determined 110 °C formula; Type II uses a single formula up to 110 °C.
• Temperature range: Reference lines generally apply between 20 °C and 110 °C; 110 °C data are determined from tests with water inside and air outside.
• Tabulated and graphical data: Tabled hoop stresses for various temperatures and service times (no safety factors included) and graphical plots are provided for easy lookup.
• Extrapolation limits: Minimum extrapolation time limits are specified (based on 1 year testing at 110 °C and Arrhenius extrapolation with Ea = 110 kJ/mol). Example: ≤60 °C corresponds to 100 years, while 110 °C has shorter extrapolation limits.
• Conformance testing: Annex A requires evaluation per ISO 9080 or equivalent, using internal pressure tests in accordance with ISO 1167‑1/2. At least 97.5% of test points must lie on or above the reference lines; additional checks prevent brittle “knee” failures.
• Design guidance: Annex B explains deriving maximum calculated S values and minimum wall thicknesses relative to application classes (e.g., hot water, underfloor heating), using Miner’s rule and references such as ISO 10508 and ISO 13760.

Applications and users

ISO 24033:2025 is essential for:

• Pipe and compound manufacturers qualifying PE‑RT grades for hot‑water and heating systems.
• System designers and plumbing/HVAC engineers calculating required hoop stress and wall thickness for long‑term performance.
• Test laboratories performing long‑term hydrostatic strength tests and extrapolations.
• Standards bodies and specifiers writing system standards for potable hot water, underfloor heating and high‑temperature radiator systems.

Keywords: ISO 24033:2025, PE‑RT, expected strength, reference lines, hydrostatic strength, hoop stress, extrapolation limits, ISO 9080, ISO 1167.

Related standards

• ISO 9080 (long‑term hydrostatic strength by extrapolation)
• ISO 1167‑1 / ISO 1167‑2 (internal pressure test methods)
• ISO 10508 (application classes)
• ISO 13760 (Miner’s rule guidance)
• ISO 1043‑1 (polymer terminology)

Standards Content (Sample)

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
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: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
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
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,
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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
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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.
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
...