ISO/TS 26873:2010 プラスチックパイプと継手—基準線の定義と構築手順 | ページ 2

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.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.

In other circumstances, particularly when there is an urgent market requirement for such documents, a technical committee may decide to publish other types of document:

• an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in an ISO working group and is accepted for publication if it is approved by more than 50 % of the members of the parent committee casting a vote;
• an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting a vote.

An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be confirmed for a further three years, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an International Standard or be withdrawn.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO/TS 26873 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.

Introduction

This Technical Specification gives guidance to the construction of a stress rupture diagram, consisting of reference lines, giving the expected minimum required strength of plastics pipes under internal pressure as a function of time and temperature. Such lines are used for the interpolation and extrapolation of stress rupture properties and for the application of Miner's rule (see ISO 13760) in product standards (see Annex A).

1 Scope

This Technical Specification defines reference lines as the generic representation of the creep rupture properties of pipes made of thermoplastics material and gives procedures for drafting reference lines in a mathematical form.

2 Normative references

The following referenced documents are indispensable for the application 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.

3 Terms and definitions

For the purposes of this document, the following terms and definitions apply.

3.1

reference line

mathematical description of the stress rupture properties of thermoplastics materials giving the expected hoop strength of the product with a certainty of at least 97,5 % when tested in accordance with ISO 1167-1 and ISO 1167-2

Note 1 to entry: Reference lines can be used for the calculation of design stress. They begin and end according to limits defined in ISO 9080.

Note 2 to entry: Reference lines are defined using Equation (1):

(1)

where

t	is the expected time to failure, in hours;
s	is the hoop stress, in megapascals;
T	is the temperature, in kelvins (°C + 273,15);
A, B, C, D	are the parameters used in the model;
i	is 1 or 2, in the case of two separate branches (sometimes referred to as brittle and ductile).

Note 3 to entry: Equation (1) is similar to ISO 9080:—, Equation (A.1), but to avoid confusion, different symbols for the parameters have been used ( AtoD , instead of c₁ through c₄). This notation is already in general use in several International Standards dealing with reference lines (see Annex A).

Note 4 to entry: Examples of thermoplastics materials are PE, PB, PE-X, PE-RT, PP, PVC-C, PVC-U, ABS and PVDF.

Bibliography