ISO 8149:2025

Unplasticized polyamide (PA-U) 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 unplasticized polyamide (PA-U 180) extruded pipes. NOTE 1 PA-U 180 follows ISO 16486-1 in terms of minimum strength values and covers both PA-U11 180 and PA-U12 180. NOTE 2 As there is not test data available for other types of polyamide (e.g. PA-U 160) this document does not currently contain appropriate reference lines for these materials. Future revisions will include other types of polyamide when sufficient test data becomes available.

Tubes en polyamide non plastifié (PA-U) — Influence du temps et de la température sur la résistance attendue

General Information

• Status: Published
• Publication Date: 30-Apr-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: 01-May-2025
• Due Date: 12-Jan-2026
• Completion Date: 01-May-2025

Overview

ISO 8149:2025 defines how to predict the long-term strength of extruded unplasticized polyamide (PA-U 180) pipes as a function of time and temperature. It provides reference lines (mathematical models and tabulated values) for expected hoop strength used in design and lifetime calculations of PA-U11 180 and PA-U12 180 pressure piping. The standard covers temperatures from 20 °C to 120 °C, notes hydrolytic ageing effects, and excludes other polyamide types (e.g., PA-U 160) until sufficient data are available.

Key topics and technical requirements

• Reference lines: Generic minimum long-term hydrostatic strength described by two mathematical branches (applicable models for interpolation and controlled extrapolation). The reference lines are based on ISO/TS 26873 methodology.
• Temperature and time range: Models applicable between 20 °C and 120 °C. Extrapolation limits are specified (e.g., 1 year testing at 80 °C with additional tests at 110 °C and 120 °C).
• Extrapolation time limits (minimum values from Table 1):
  • 120 °C: 0.2 years, 110 °C: 0.5 years, 100 °C: 1 year, 90 °C: 2.5 years, 80 °C: 6 years, 70 °C: 18 years, 60 °C: 50 years, ≤50 °C: 100 years.
• Hydrolysis and ageing: Tests use water; hydrolysis of amide bonds reduces molecular weight and affects ductility and strength. The standard explains kinetics and notes differing water uptake for long-chain polyamides (PA-U11/12).
• Tabulated expected hoop strengths: Table 2 provides calculated hoop stress (MPa) vs time and temperature (values are without safety or design factors). Example: at 20 °C the 1‑year expected hoop strength ≈ 20.2 MPa.
• Conformity and testing: Demonstration per Annex A requires evaluation under ISO 9080 and internal pressure tests per ISO 1167‑1/2. Tests shall be carried out at 20 °C, 60–82 °C, and 100–120 °C; at least 97.5% of experimental results must lie on or above the reference line.

Applications and who uses it

ISO 8149:2025 is intended for:

• Pipe designers and mechanical engineers performing long‑term strength and pressure‑rating calculations for PA‑U piping systems.
• Manufacturers of PA‑U 180 extruded pipes, fittings and assemblies for quality control and product certification.
• Test laboratories and conformity assessors applying ISO 9080 and ISO 1167 methods.
• Infrastructure and industrial specifiers (gas distribution, oil-field piping, above‑ground industrial lines) evaluating plastics as alternatives to metal piping. The standard helps reduce variability by providing unified reference lines for design and lifetime assessment of PA‑U 180 pressure pipes.

Related standards

• ISO 9080:2012 - Long‑term hydrostatic strength by extrapolation (referenced for evaluation).
• ISO 1167‑1 / ISO 1167‑2 - Resistance to internal pressure test methods.
• ISO 16486 series - PA‑U piping systems for gaseous fuels (PA‑U minimum strength context).

Standards Content (Sample)

International
Standard
ISO 8149
First edition
Unplasticized polyamide (PA-
2025-05
U) pipes — Effect of time and
temperature on the expected
strength
Tubes en polyamide non plastifié (PA-U) — Influence du temps et
de la température sur la résistance attendue
Reference number
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: [phone]
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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 Basic formulae . 2
5 Expected strength . 2
5.1 General .2
5.2 Extrapolation limits .3
5.3 Graphical representation .3
5.4 Tabulated value .5
6 Demonstrating conformity . 5
Annex A (normative) Demonstrating conformance to the reference lines . 6
Bibliography . 7

iii
Foreword
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bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
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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).
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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.

iv
Introduction
The first pressure piping system made of PA-U was installed as a pilot for buried gas pipes in the early
2000s. This was followed by a comprehensive number of special case installations based on different PA-U
compounds. Due to commercial applications for buried gas pipes, there is a demand for further pressure
pipe applications, which lay on ground (like oil field piping systems) or which are installed above ground
in supports (like industrial piping systems inside or outside of gas infrastructure). Using thermoplastic
piping materials instead of metallic materials (e.g. steel or cast iron) has proven successful over the last
50 years. But for many thermoplastic pipe applications, the use has been limited to a maximum operation
1)
pressure of 10 bar for buried gas piping systems or approximately 7 bar for low temperature above ground
installations. Due to their high strength, PA-U 180 compounds extend the range for operation pressures for
thermoplastic pressure piping systems with the target of replacing the use of metal-based systems.
With the market availability of PA-U 180 compounds, the option for the use of plastics materials, instead of
metallic materials, for pipes, fittings and valves, became possible for high pressure applications. As a result,
products mainly produced by extrusion and injection molding have been introduced into the market.
In the beginning, the design and the calculation for the dimensioning was based on individual ISO 9080
analyses for each individual PA-U 180 compound. The approach behind the development of this document
is the intention to align the values for the expected strength over the time (reference lines) for PA-U 180, in
order to simplify and unify all design procedures for which the expected strength over the time is needed.
At the date of publication of this document, the following International Standards dealing with PA-U pressure
piping systems had been published:
— ISO 16486 series, Plastics piping systems for the supply of gaseous fuels — Unplasticized polyamide (PA-U)
piping systems with fusion jointing and mechanical jointing
NOTE Further information can be found in the Bibliography, notably in References [6], [7], [8],[ 9], [10], [11], [12],
[13], [14], [15], [16] and [17].
5 2
1)  1 bar = 0,1 MPa = 10 Pa; 1 MPa = 1 N/mm .

v
International Standard ISO 8149:2025(en)
Unplasticized polyamide (PA-U) 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 unplasticized polyamide (PA-U 180) extruded pipes.
NOTE 1 PA-U 180 follows ISO 16486-1 in terms of minimum strength values and covers both PA-U11 180 and PA-
U12 180.
NOTE 2 As there is not test data available for other types of polyamide (e.g. PA-U 160) this document does not
currently contain appropriate reference lines for these materials. Future revisions will include other types of
polyamide when sufficient test data becomes available.
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 intern
...