National foreword

This British Standard is the UK implementation of ISO 4437‑3:2026. It supersedes BS ISO 4437‑3:2024, which is withdrawn.

The UK participation in its preparation was entrusted to Technical Committee PRI/88, Plastics piping systems.

A list of organizations represented on this committee can be obtained on request to its committee manager.

Contractual and legal considerations

This publication has been prepared in good faith, however no representation, warranty, assurance or undertaking (express or implied) is or will be made, and no responsibility or liability is or will be accepted by BSI in relation to the adequacy, accuracy, completeness or reasonableness of this publication. All and any such responsibility and liability is expressly disclaimed to the full extent permitted by the law.

This publication is provided as is, and is to be used at the recipient’s own risk.

The recipient is advised to consider seeking professional guidance with respect to its use of this publication.

This publication is not intended to constitute a contract. Users are responsible for its correct application.

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 October 2026.

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 138, Plastics pipes, fittings and valves for the transport of fluids, Subcommittee SC 4, Plastics pipes and fittings for the supply of gaseous fuels.

This third edition cancels and replaces the second edition (ISO 4437‑3:2024), which has been technically revised.

The main changes are as follows:

reference to information related to the suitability of PE pipe systems for 100 % hydrogen and its admixtures with natural gas has been made;
terms and definitions have been distributed over ISO 4437‑1, ISO 4437‑2 and ISO 4437‑3;
symbols and their definitions for geometrical characteristics on electrofusion socket fittings, spigot end fittings, socket fusion fittings and tapping tees have been harmonized with other standards in ISO/TC 138;
Clause 5 has been restructured;
the minimum bore for electrofusion socket fittings have been harmonized with the minimum bore of spigot end fittings;
the performance requirements for joints have been mentioned more explicitly by adding Table 8.

A list of all parts in the ISO 4437 series can be found on the ISO website.

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.

Introduction

The ISO 4437 series specifies the requirements for a piping system and its components made from polyethylene (PE) compounds, which is intended to be used for the supply of gaseous fuels.

This document covers the characteristics of fittings.

Requirements and test methods for materials and components, other than fittings, are specified in ISO 4437‑1, ISO 4437‑2 and ISO 4437‑4.

Characteristics for fitness for purpose of the system are covered in ISO 4437‑5. ISO/TS 4437‑7 gives guidance for assessment of conformity.

Recommended practice for design, handling and installation is given in ISO/TS 10839.

1 Scope

This document specifies the characteristics of fusion fittings made from polyethylene (PE) as well as of mechanical fittings for piping systems in the field of the supply of gaseous fuels.

NOTE 1 Additional information related to the installation of PE 100-RC systems is given in ISO 4437‑1:2026, Annex A.

NOTE 2 Additional information about the suitability of PE pipe systems for hydrogen and its admixtures is given in ISO 4437‑1:2026, Annex D.

It also specifies the test parameters for the test methods referred to in this document.

In conjunction with ISO 4437‑1, ISO 4437‑2, ISO 4437‑4 and ISO 4437‑5, this document is applicable to PE pipes, fittings and valves, their joints, and joints with components of PE and other materials intended to be used under the following conditions:

a maximum operating pressure (MOP) up to and including 10 bar1, at a design reference temperature of 20 °C;
an operating temperature between −20 °C and 40 °C.

For operating temperatures between 20 °C and 40 °C, derating coefficients are specified in ISO 4437‑5.

The ISO 4437 series covers a range of MOPs and gives requirements concerning colours.

This document is applicable for fittings of the following types:

electrofusion socket fittings;
electrofusion saddle fittings;
spigot end fittings (for butt fusion using heated tools and electrofusion);
socket fusion fittings;
mechanical fittings.

It is the responsibility of the purchaser or specifier to make the appropriate selections from these aspects, taking into account their particular requirements and any relevant national guidance or regulations and installation practices or codes.

NOTE 3 The fittings can be, for example, in the form of couplers, saddles, equal and reduced tees, reducers, elbows, bends or end caps.

NOTE 4 Fabricated fittings are normally not used for gas applications except for larger dimensions or in the absence of other solutions. Guidance can be found in ISO 4427‑3:2019, Annex B.

2 Normative references

3 Terms and definitions

4 Symbols and abbreviated terms

5 Material

5.1 PE compound for fittings

5.2 Material for non-polyethylene parts

6 General characteristics

6.1 Appearance

6.2 Colour

6.3 Design

6.4 Appearance of factory-made joints

6.5 Electrical characteristics for electrofusion fittings

7 Geometrical characteristics

7.1 Measurement of dimensions

7.2 Dimensions of electrofusion socket fittings

7.3 Dimensions of electrofusion saddle fittings

7.4 Dimensions of spigot end fittings

7.5 Dimensions of socket fusion fittings

7.6 Design and dimensions of mechanical fittings

8 Mechanical characteristics

8.1 General

8.2 Requirements

8.3 Modifications of the fitting

8.4 Performance requirements

9 Physical characteristics

9.1 Conditioning

9.2 Requirements

10 Performance requirements

11 Technical information

12 Marking

12.1 General

12.2 Minimum required marking of fittings

12.3 Additional marking

12.4 Fusion system recognition

13 Delivery conditions

Bibliography