ISO 14828:2003

INTERNATIONAL ISO
STANDARD 14828
First edition
2003-12-01


Glass-reinforced thermosetting plastics
(GRP) pipes — Determination of the long-
term specific ring relaxation stiffness
under wet conditions and calculation of
the wet relaxation factor
Tubes en plastiques thermodurcissables renforcés de verre (PRV) —
Détermination de la rigidité annulaire spécifique à long terme en
relaxation, en conditions mouillées, et calcul du facteur de relaxation au
mouillé




Reference number
ISO 14828:2003(E)
©
ISO 2003

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ISO 14828:2003(E)
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ii © ISO 2003 — All rights reserved

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ISO 14828:2003(E)
Contents Page
Foreword. iv
1 Scope. 1
2 Normative references. 1
3 Terms and definitions. 1
4 Principle. 4
5 Apparatus. 4
5.1 Compressive loading machine . 4
5.2 Force application surfaces. 4
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 loading data . 8
11.2 Calculation of the long-term specific ring relaxation stiffness under wet conditions for
position 1 . 8
11.3 Calculation of the wet relaxation factor. 8
12 Test report. 9
Annex A (informative) Equal increments of lg(time in h) . 10


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ISO 14828:2003(E)
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
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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.
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 14828 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.

iv © ISO 2003 — All rights reserved

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INTERNATIONAL STANDARD ISO 14828:2003(E)

Glass-reinforced thermosetting plastics (GRP) pipes —
Determination of the long-term specific ring relaxation stiffness
under wet conditions and calculation of the wet relaxation
factor
1 Scope
This International Standard specifies a method for determining both the long-term specific ring relaxation
stiffness and the wet relaxation factor for glass-reinforced thermosetting plastics (GRP) pipes.
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 7685:1998, Plastics piping systems — Glass-reinforced thermosetting plastics (GRP) pipes —
Determination of initial specific ring stiffness
ISO 10928:1997, 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 International Standard the following definitions apply:
3.1
vertical compressive force
F
vertical force, expressed in newtons, applied to a horizontal pipe to cause a vertical deflection
3.2
specific ring stiffness
S
physical characteristic of a pipe, expressed in newtons per square metre, that is a measure of the resistance
to ring deflection per metre length under external load and is defined by Equation (1):
E× I
S= (1)
3
d
m
where
E is the apparent modulus of elasticity, in newtons per square metre, determined by testing in
accordance with ISO 7685;
I is the second moment of area in the longitudinal direction per metre length, in metres to the fourth
4
power per metre (m /m), i.e.
3
e
I= (2)
12
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ISO 14828:2003(E)
e being the wall thickness of the pipe, in metres;
d is the mean diameter of the pipe, in metres (see 3.3).
m
3.3
mean diameter
d
m
diameter, expressed in metres, of the circle corresponding with the middle of the pipe wall cross-section and
given by either of the following equations:
dd=+e (3)
mi
dd=−e (4)
me
where
d is the internal diameter, in metres;
i
d is the external diameter, in metres;
e
e is the wall thickness of the pipe, in metres.
3.4
initial specific ring stiffness
S
0
value of S, expressed in newtons per square metre, determined by testing in accordance with ISO 7685
3.5
long-term specific ring relaxation stiffness at position 1
S
x, 1, relax, wet
value of S, expressed in newtons per square metre, at a reference position, position 1 (see 10.2), at x years,
obtained by extrapolation of long-term force measurements at a constant deflection under wet conditions
(see 3.2 and 10.2)
3.6
calculated long-term specific ring relaxation stiffness under wet conditions
S
x, relax, wet
calculated value of S, expressed in newtons per square metre, at x years obtained using Equation (5):
SS=×α (5)
xx, relax, wet 0 , relax, wet
where
x is the elapsed time, in years, specified in the referring standard;
α is the wet relaxation factor (see 3.7);
x, relax, wet
S is the initial specific ring stiffness, in newtons per square metre.
0
3.7
wet relaxation factor
α
x, relax, wet
ratio of the long-term specific ring relaxation stiffness to the initial specific ring stiffness, both at a reference
position, position 1 (see 10.2), and given by Equation (6):
S
x,1, relax, wet
α = (6)
x, relax, wet
S
0, 1
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ISO 14828:2003(E)
where
S

is the initial specific ring stiffness at position 1, in newtons per square metre, determined in
0, 1
accordance with ISO 7685;
S is the long-term specific ring relaxation stiffness at position 1, in newtons per square metre
x, 1, relax, wet
3.8
vertical deflection
y
vertical change in diameter of a pipe in a horizontal position, expressed in metres, in response to a vertical
compressive force (see 3.1)
3.9
long-term applied force
F
x, 1, wet
value of the force F, expressed in newtons, at the reference position, position 1 (see 10.2), at x years obtained
by extrapolation of long-term applied-force measurements at a constant deflection under wet conditions
(see 3.1 and 10.2)
3.10
deflection coefficient
f
dimensionless factor which takes into account general second-order theory as applied to deflection and is
given by Equation (7):
−5

fy=+1860 2 500× /d×10 (7)
()
1m

where
is the vertical deflection at position 1, in metres;
y
1
d is the mean diameter (see 3.3) of the pipe, in metres.
m
3.11
calculated strain
ε
calc, 1
strain on the inner surface at the crown and invert of a pipe at the reference position, position 1, given in
percent by Equation (8):
e y
1
4,28×× ×100
dd
mm
ε = (8)
calc,1
2
y
1
1+

2× d
m
where
y is the vertical deflection at position 1, in metres;
1
d is the mean diameter of the pipe (see 3.3), in metres;
m
e is the wall thickness of the pipe, in metres.
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ISO 14828:2003(E)
4 Principle
A cut length of pipe supported horizontally is loaded throughout its length to compress it diametrically to a
prescribed level of strain calculated using Equation 8. 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 vertical deflection
remains constant and the force is measured at intervals. The long-term force is estimated by extrapolation.
From this force and the deflection, the long-term specific ring relaxation stiffness under wet conditions is
calculated.
The wet relaxation factor is then determined from the long-term specific ring relaxation stiffness and the initial
specific ring stiffness of the same test piece. The declared wet relaxation factor is the average of the results
from two test pieces.
NOTE It is assumed that values for the following test parameters will be set by the standard making reference to this
International Standard:
a) the method for measuring the initial specific ring stiffness, i.e. method A or B of ISO 7685:1998 (see 3.4);
b) the time to which the values are to be extrapolate
...