ISO 8521:2009

INTERNATIONAL ISO
STANDARD 8521
Second edition
2009-08-15

Plastics piping systems —
Glass-reinforced thermosetting plastics
(GRP) pipes — Test methods for the
determination of the apparent initial
circumferential tensile strength
Systèmes de canalisations en matières plastiques — Tubes en
plastiques thermodurcissables renforcés de verre (PRV) — Méthodes
d'essai pour la détermination de la résistance en traction
circonférencielle initiale apparente




Reference number
ISO 8521:2009(E)
©
ISO 2009

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ISO 8521:2009(E)
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ii © ISO 2009 – All rights reserved

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ISO 8521:2009(E)
Contents Page
Foreword .iv
1 Scope.1
2 Terms and definitions .1
3 Principle.2
3.1 General .2
3.2 Method A .3
3.3 Method B .3
3.4 Methods C, D and E.3
3.5 Method F.3
4 Apparatus.3
4.1 For method A .3
4.2 For method B .5
4.3 For method C .6
4.4 For method D .6
4.5 For method E .6
4.6 For method F.7
5 Test pieces .8
5.1 For method A .8
5.2 For method B .8
5.3 For method C .9
5.4 For method D .10
5.5 For method E .11
5.6 For method F.12
5.7 Number of test pieces.13
6 Conditioning .14
7 Test temperature .14
8 Procedure.14
8.1 For method A .14
8.2 For method B .14
8.3 For method C .15
8.4 For method D .15
8.5 For method E .15
8.6 For method F.15
9 Calculation .16
9.1 For method A .16
9.2 For method B .16
9.3 For methods C, D and E.17
9.4 For method F.17
10 Test report.17

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ISO 8521:2009(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
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.
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 8521 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 second edition cancels and replaces the first edition (ISO 8521:1998), of which it constitutes a technical
revision.

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INTERNATIONAL STANDARD ISO 8521:2009(E)

Plastics piping systems — Glass-reinforced thermosetting
plastics (GRP) pipes — Test methods for the determination of
the apparent initial circumferential tensile strength
1 Scope
This International Standard specifies six test methods for the determination of the initial circumferential tensile
wall strength per unit of length of glass-reinforced thermosetting plastics (GRP) pipes.
NOTE Another commonly used term for “circumferential tensile strength” is “hoop tensile strength” and the two
expressions can be used interchangeably.
The burst test (method A) is suitable for all types and sizes of pipes. It is considered the reference method.
However, all the methods in this International Standard have equal validity. If correlation of any of the
methods B to F can be established by a comparative test programme, then that method can be considered as
the reference method.
The split disc test (method B) might not be suitable for pipes with helically wound reinforcing layers.
The strip test (method C), the modified strip test (method D) and the restrained strip test (method E) are
suitable for pipes with a nominal size of DN 500 and greater.
The notched plate test (method F) is primarily intended for use with helically wound pipes of nominal size
greater than DN 500 with a winding angle other than approximately 90°.
Results from one method are not necessarily equal to the results derived from any of the alternative methods.
If required, the initial circumferential tensile modulus can be determined by method A.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
initial circumferential tensile wall strength
* * * * * *
σ , σ , σ , σ , σ , σ
cA cB cC cD cE cF
ultimate circumferential tensile force per unit length in the circumferential direction (the upper-case subscripts
denote the method of test used)
NOTE It is expressed in newtons per millimetre of circumference.
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ISO 8521:2009(E)
2.2
burst pressure
p
ult
internal pressure at bursting
1)
NOTE It is expressed in bars  or megapascals.
2.3
bursting
failure by rupture of the pipe wall
2.4
ultimate tensile force
F
ult
tensile force at failure
NOTE It is expressed in newtons.
2.5
width
b
width of the test piece in the notched area
NOTE It is expressed in millimetres.
2.6
winding angle
θ
angle between the direction of the continuous reinforcement and the longitudinal axis of the pipe
NOTE It is expressed in degrees.
2.7
helical wound
cross wound
filament wound pipes made with a balanced winding angle
3 Principle
3.1 General
It is assumed that the following test parameters are set by the standard making reference to this International
Standard:
a) for method A, the length between end sealing devices (see 5.1);
b) for methods B, C, D and E, the width of the test piece (see 5.2, 5.3, 5.4 and 5.5);
c) for methods C and E, the total width of the test piece (see 5.3 and 5.5);
d) for method F, the dimensions of the plate to be tested (see 5.6);
e) the number of test pieces (see 5.7);

5 2 2
1) 1 bar = 0,1 MPa 10 N/m = 0,1 N/mm .
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ISO 8521:2009(E)
f) the requirements for conditioning (see Clause 6);
g) the test temperature (see Clause 7).
3.2 Method A
*
The initial circumferential tensile wall strength, σ , is determined by an internal pressure test.
cA
Cut lengths of pipe are subjected to an increasing internal pressure which, within a specified time, causes
bursting (see 2.3). The test conditions are such that a mainly uniaxial circumferential stress is obtained.
3.3 Method B
*
The initial circumferential tensile wall strength, σ , is determined by a split disc test.
cB
Rings cut from the pipe are subjected to an increasing tensile force, by means of a split disc positioned within
the ring, until rupture occurs within a specified time.
3.4 Methods C, D and E
* * *
The initial circumferential wall strength, σ or σ or σ , is determined by a strip test.
cC cD cE
Strips cut from the pipe wall in the circumferential direction, and if necessary, shaped to incorporate notches
at defined locations, are subjected to an increasing tensile force until rupture occurs within a specified time.
3.5 Method F
*
The apparent initial circumferential wall strength, σ , is determined by a notched plate test.
cF
Plates cut from the pipe wall are subjected to an increasing tensile force until rupture occurs within a specified
time.
4 Apparatus
4.1 For method A
4.1.1 Hydrostatic pressurizing system, capable, for pipes up to DN 500, of causing failure of the test
piece between 1 min and 3 min after commencing the pressurization.
For some nominal sizes greater than DN 500, the duration of the test will, for practical equipment reasons,
need to be increased. Where increasing the testing time results in lower burst pressures, this shall be
evaluated by comparing results of different test durations.
The pressurizing system shall prevent air from entering the test piece during pressurization to failure.
4.1.2 Pressure measuring device, capable of measuring the applied internal pressure to an accuracy of
± 2,0 %.
4.1.3 End sealing devices for the test pieces, capable of inducing in the test piece, during the test, a
mainly uniaxial state of stress in the circumferential direction in the test piece (see Figure 1).
4.1.4 Dimension measurement devices, capable of measuring the necessary dimensions of the test piece
to an accuracy of ± 0,1 mm.
4.1.5 Test piece support, if needed, to minimize deformation due to the weight of the test piece and its
contents.
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ISO 8521:2009(E)
4.1.6 Strain measurement, if circumferential tensile modulus of the pipe wall is to be determined, strain
gauges of the foil type, single element suitable for the anticipated strain level and of a length appropriate for
the pipe diameter.
4.1.7 Flexible membrane (if used as a barrier system to prevent weeping), which does not reduce the
stress in the pipe wall by more than 1 %. The flexible membrane may be of a different material from the pipe,
e.g. elastomeric or thermoplastic sheet or a flexible coating.

Key
1 end sealing device
2 elastomeric seal
3 test piece
4 tie bar for carrying end thrust
Figure 1 — Typical arrangement for pressure testing pipes (method A)
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ISO 8521:2009(E)
4.2 For method B
4.2.1 Test machine, of the type capable of producing a progressive separation of the split disc and
incorporating the following components:
a) a fixed or virtually fixed part;
b) a moveable part;
c) a drive mechanism, capable of imparting a constant speed to the moving part so that rupture can be
reached between 1 min and 3 min after initial loading;
d) a load indicator, capable of measuring the force applied. This shall be virtually free from inertia at the
specified rate of testing and shall indicate the force to an accuracy of within 1 % of the measured value.
4.2.2 Rigid split discs, as shown in Figure 2, capable of making even contact with the internal diameter of
the test piece. The diameter of the two segments of the split disc shall be not less than 98 % of the internal
diameter of the pipe with which they are intended to be used.
4.2.3 Dimension measuring devices, capable of measuring the necessary dimensions of the test piece to
an accuracy of ± 0,1 mm.

Key
1 toggle
2 saddle
3 shear pin
a
Direction of loading.
b
Separation.
c
Rounded edges.
Figure 2 — Typical arrangement for the split disc test (method B)
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ISO 8521:2009(E)
4.3 For method C
4.3.1 Test machine, of the type with constant separating speed, incorporating the following components:
a) a fixed, or virtually fixed, part with a grip to hold one end of a test piece;
b) a moveable part, incorporating a second grip to hold the other end of the test piece. The grips holding the
ends of the test piece shall do so as far as possible without slipping and/or crushing;
NOTE Grips that tighten automatically can be used.
c) the fixed and moving parts and their associated grips shall enable the test piece to be aligned when a
force is applied, so that the axis of the test piece is coincident with that of the force;
d) a drive mechanism capable of imparting a constant speed to the moving part, so that failure can be
reached between 1 min and 3
...