ISO 8521:2020 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.