ISO 10471:2025

International
Standard
ISO 10471
Third edition
Glass-reinforced thermosetting
2025-08
plastics (GRP) pipes —
Determination of the long-term
ultimate bending strain and the
long-term ultimate relative ring
deflection under wet conditions
Tubes en plastiques thermodurcissables renforcés de verre
(PRV) — Détermination de l'effort à la flexion ultime à long
terme et déflexion annulaire relative ultime à long terme dans
des conditions mouillées
Reference number
© ISO 2025
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Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 3
5 Apparatus . 4
5.1 Compressive loading machine .4
5.2 Force application surfaces.5
5.2.1 General arrangement.5
5.2.2 Plates .5
5.2.3 Beam bars .5
5.3 Water container .5
5.4 Measuring devices .5
6 Test piece . 6
7 Number of test pieces . 6
8 Determination of the dimensions of the test pieces . 7
8.1 Length .7
8.2 Wall thickness .7
8.3 Mean diameter .7
9 Conditioning . 7
10 Procedure . 7
11 Calculation . 8
11.1 Extrapolation of the strain data to obtain thex-year value,ε .8
x,wet
11.2 Calculation of the long-term ultimate relative ring deflection under wet conditions,
y /d .8
u,wet,x m
12 Test report . 8
Annex A (informative) Equal increments of lg (time in h) .10

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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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 documents should be noted. This document was drafted in accordance with the editorial rules of the
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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 6, Reinforced plastics pipes and fittings for all applications.
This third edition cancels and replaces the second edition (ISO 10471:2018), which has been technically
revised.
The main changes are as follows:
— certain terms and definitions have been clarified and units have been changed from m to mm;
— a requirement on test temperature and pH of test water has been added in Clause 4;
— Figure 1 has been corrected concerning the level of water in the water container;
— the number of test lines in 8.1 has been corrected;
— an incorrect reference in 8.3 has been corrected;
— Clause 9 "Conditioning" has been aligned with ISO 23856.
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
International Standard ISO 10471:2025(en)
Glass-reinforced thermosetting plastics (GRP) pipes —
Determination of the long-term ultimate bending strain and
the long-term ultimate relative ring deflection under wet
conditions
1 Scope
This document specifies a method for determining by extrapolation the long-term ultimate ring bending
strain and for the calculation of the long-term ultimate relative ring deflection of glass-reinforced
thermosetting plastics (GRP) pipes, under wet conditions.
Two methods of loading are given, one using plates the other using beam bars.
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 3126, Plastics piping systems — Plastics components — Determination of dimensions
ISO 7685, Glass-reinforced thermosetting plastics (GRP) pipes — Determination of initial ring stiffness
ISO 10928, Plastics piping systems — Glass-reinforced thermosetting plastics (GRP) pipes and fittings —
Methods for regression analysis and their use
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
vertical compressive force
F
vertical force, applied to a horizontal pipe to cause a vertical deflection
Note 1 to entry: Vertical compressive force is expressed in newtons.
3.2
mean diameter
d
m
diameter of the circle corresponding to the middle of the pipe wall cross-section and given by either of the
following formulae:
dd=+e
mi
or
dd=−e
me
where
d is the internal diameter, in millimetres (mm);
i
d is the external diameter, in millimetres (mm);
e
e is the wall thickness of the pipe, in millimetres (mm)
Note 1 to entry: Mean diameter is expressed in millimetres.
3.3
vertical deflection
y
vertical change in diameter of a pipe in a horizontal position in response to a vertical compressive force (3.1)
Note 1 to entry: Vertical deflection is expressed in millimetres.
3.4
relative vertical deflection
y/d
m
ratio of the vertical deflection, y (3.3), to the mean diameter (3.2) of the pipe, d
m
3.5
ultimate vertical deflection under wet conditions
y
u,wet
vertical deflection (3.3) of the pipe, y, when failure occurs under wet conditions
Note 1 to entry: Ultimate vertical deflection under wet conditions is expressed in millimetres.
3.6
ultimate relative vertical deflection under wet conditions
y /d
u,wet m
ratio of the ultimate vertical deflection under wet conditions, y (3.5), to the mean diameter (3.2) of the
u,wet
pipe, d
m
3.7
long-term ultimate ring deflection under wet conditions
y
u,wet,x
extrapolated value of the ultimate vertical deflection under wet conditions (3.5) of the pipe, y , when failure
u,wet
is expected to occur at a time, x, specified in the referring standard
Note 1 to entry: Long-term ultimate ring deflection under wet conditions is expressed in millimetres.
3.8
long-term ultimate relative ring deflection under wet conditions
y /d
u,wet,x m
ratio of the long-term ultimate ring deflection under wet conditions (3.7) of the pipe, y , to the mean
u,wet,x
diameter (3.2) of the pipe, d
m
3.9
failure
loss of the structural integrity of a test piece as evidenced by the inability of the test piece to carry the load
or by significant, abrupt increase in deflection
3.10
time to failure
t
u
time elapsed until failure (3.9) occurs
Note 1 to entry: Time to failure is expressed in hours.

3.11
ring stiffness
S
physical characteristic of a pipe, that is a measure of the resistance to ring deflection per metre length under
external load and is defined by the following formula
EI×
S =
d
m
where
E is the apparent modulus of elasticity, in newtons per square metre (N/m ), determined by
testing in accordance with ISO 7685;
I is the second moment of area in the longitudinal direction per metre length, in millimetres to
the fourth power per millimetre (mm /mm), i.e.
e
I=
where
e is the wall thickness of the pipe, in millimetres (mm);
d is the mean diameter of the pipe, in millimetres (mm) (see 3.2)
m
Note 1 to entry: Ring stiffness is expressed in newtons per square metre.
3.12
initial ring stiffness
S
value of ring stiffness S (3.11), determined by testing in accordance with ISO 7685
Note 1 to entry: Initial ring stiffness is expressed in newtons per square metre.
3.13
strain factor
D
g
dimensionless factor used to transform a deflection value into a strain value
4 Principle
Each of several cut lengths of pipe is supported horizontally and loaded throughout its length to compress it
diametrically to achieve a desired level of strain. The force application surfaces are either bearing plates or
beam bars.
The pipe is immersed in water at a given temperature for a period of time during which the force remains
constant and the increasing vertical deflection is measured at intervals until failure (see 3.9) occurs. The
relative vertical deflection at failure [ultimate relative vertical deflection, y /d (see 3.6)] is converted
u,wet m
into a bending strain at failure (ultimate bending strain, ε , in percent), either calculated using Formula (1)
u,wet
or determined from a strain-deflection calibration curve (see 10.3).
The strain may also be measured directly by the use of waterproofed strain gauges.
The following strain calculations assume that the neutral axis is at the pipe wall midpoint. For pipe wall
constructions that produce an altered neutral axis position, it is necessary to evaluate results by substituting
2ȳ for the wall thickness e where ȳ is the distance from the appropriate pipe surface to the neutral axis.

ISO 1
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