ISO 8521:2020

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 8521
ISO/TC 138/SC 6
Glass-reinforced thermosetting
Secretariat: ASI
plastic (GRP) pipes — Test methods
Voting begins on:
2020­04­20 for the determination of the initial
circumferential tensile wall strength
Voting terminates on:
2020­06­15
RECIPIENTS OF THIS DRAFT ARE INVITED TO
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OF ANY RELEVANT PATENT RIGHTS OF WHICH
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DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 8521:2020(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
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DARDS TO WHICH REFERENCE MAY BE MADE IN
©
NATIONAL REGULATIONS. ISO 2020

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ISO/FDIS 8521:2020(E)

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© ISO 2020
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ISO/FDIS 8521:2020(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
4.1 General . 2
4.2 Method A . 3
4.3 Method B . 3
4.4 Methods C, D and E . 3
4.5 Method F . 3
5 Apparatus . 3
5.1 For method A . 3
5.2 For method B . 4
5.3 For method C . 6
5.4 For method D . 7
5.5 For method E . 7
5.6 For method F . 8
6 Test pieces . 9
6.1 For method A . 9
6.2 For method B . 9
6.3 For method C .10
6.4 For method D .11
6.5 For method E .12
6.6 For method F .13
6.7 Number of test pieces .15
7 Conditioning .15
8 Test temperature .15
9 Procedure.16
9.1 For method A .16
9.2 For method B .16
9.3 For method C .17
9.4 For method D .17
9.5 For method E .17
9.6 For method F .17
10 Calculation .18
10.1 For method A .18
10.2 For method B .18
10.3 For methods C, D and E .19
10.4 For method F .19
11 Test report .19
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ISO/FDIS 8521:2020(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 non­governmental, 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.
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 ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade 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 8521:2009), which has been technically
revised.
The major changes to this edition include:
— For methods C and D, an allowance for using a notched specimen has been added.
— The way to grip samples for methods C and D has been clarified.
— For method D, an alternative allowed splitting of samples lengthwise has been added.
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.
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 8521:2020(E)
Glass-reinforced thermosetting plastic (GRP) pipes —
Test methods for the determination of the initial
circumferential tensile wall strength
1 Scope
This document specifies six test methods for the determination of the initial circumferential tensile
wall strength per unit of length of glass­reinforced 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 document 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) is not always 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 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
initial circumferential tensile wall strength
∗∗ ∗∗ ∗∗
σσ,,σσ,,σσ,
cA cB cC cD cE cF
ultimate tensile force (3.4) per unit length in the circumferential direction
Note 1 to entry: The upper-case subscripts denote the method of test used.
Note 2 to entry: It is expressed in newtons per millimetre of circumference.
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ISO/FDIS 8521:2020(E)

3.2
burst pressure
p
ult
internal pressure at bursting (3.3)
1)
Note 1 to entry: It is expressed in bars or megapascals.
3.3
bursting
failure by rupture of the pipe wall
3.4
ultimate tensile force
F
ult
tensile force at failure
Note 1 to entry: It is expressed in newtons.
3.5
test width
b
width of the test piece in the notched area
Note 1 to entry: It is expressed in millimetres.
3.6
total width
b
tot
total width of the test piece
Note 1 to entry: It is expressed in millimetres.
3.7
winding angle
θ
angle between the direction of the continuous reinforcement and the longitudinal axis of the pipe
Note 1 to entry: It is expressed in degrees.
3.8
helically wound
filament wound pipes made with a balanced winding angle (3.7)
4 Principle
4.1 General
It is assumed that the following test parameters are set by the referring standard:
a) for method A, the distance between end sealing devices (see 6.1);
b) the number of test pieces (see 6.7);
c) the requirements for conditioning (see Clause 7);
d) the test temperature (see Clause 8).
5 2 2
1)  1 bar = 0,1 MPa 10 N/m = 0,1 N/mm .
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ISO/FDIS 8521:2020(E)

4.2 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 3.3). The test conditions are such that a mainly uniaxial circumferential stress is
obtained.
4.3 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.
4.4 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.
4.5 Method F
∗
The 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.
5 Apparatus
5.1 For method A
5.1.1 Hydrostatic pressurising 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 pressurising system shall prevent air from entering the test piece during pressurization to failure.
5.1.2 Pressure measuring device, calibrated within an accuracy of ±2,0 %.
5.1.3 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).
5.1.4 Dimension measurement devices, calibrated within an accuracy of ±0,1 mm.
5.1.5 Test piece support, if needed, to minimize deformation due to the weight of the test piece and
its contents.
5.1.6 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.
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ISO/FDIS 8521:2020(E)

5.1.7 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 3 test piece
2 elastomeric seal 4 tie bar for carrying end thrust
Figure 1 — Typical arrangement for pressure testing pipes (method A)
5.2 For method B
5.2.1 Test machine, capable of producing a progressive separation of the split disc and incorporating
the following components:
a) a fixed or virtually fixed part;
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ISO/FDIS 8521:2020(E)

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.
5.2.2 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.
5.2.3 Dimension measuring devices, calibrated within an accuracy of ±0,1 mm.

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ISO/FDIS 8521:2020(E)

Key
a
1 toggle Direction of loading.
b
2 saddle Separation
...