ISO/TS 26873:2010

TECHNICAL ISO/TS
SPECIFICATION 26873
First edition
2010-08-15
Plastics pipes and fittings — Definition
and construction procedures for
reference lines
Tubes et accessoires en plastiques — Définition et procédure de
construction des lignes de référence

Reference number
©
ISO 2010
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ii © ISO 2010 – All rights reserved

Foreword
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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).
iv © ISO 2010 – All rights reserved

TECHNICAL SPECIFICATION ISO/TS 26873:2010(E)

Plastics pipes and fittings — Definition and construction
procedures for reference lines
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.
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:—, Plastics piping and ducting systems — Determination of the long-term hydrostatic strength of
1)
thermoplastics materials in pipe form by extrapolation
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 Reference lines can be used for the calculation of design stress. They begin and end according to limits
defined in ISO 9080.
1) Under preparation.
NOTE 2 Reference lines are defined using Equation (1):
log σ C
10 i
log tA=+B + +D log σ (1)
10 ii i 10
TT
where
t is the expected time to failure, in hours;
σ 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 Equation (1) is similar t
...