ISO 8521:2020

INTERNATIONAL ISO
STANDARD 8521
Third edition
2020-07
Glass-reinforced thermosetting
plastic (GRP) pipes — Test methods
for the determination of the initial
circumferential tensile wall strength
Tubes en plastiques thermodurcissables renforcés de verre (PRV) —
Méthodes d'essai pour la détermination de la résistance à la traction
circonférentielle initiale de la paroi
Reference number
©
ISO 2020
© ISO 2020
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ii © ISO 2020 – All rights reserved

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
Foreword
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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 main changes compared to the previous edition are as follows:
— 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.
iv © ISO 2020 – All rights reserved

INTERNATIONAL STANDARD ISO 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 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 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.
...