ISO 18851:2015 specifies methods of test for fittings of any form, i.e. bends, branches, tapers, intended to be used in plastics piping systems for pressure and non-pressure drainage and sewerage or water supply made of glass-reinforced thermosetting plastics (GRP). It is applicable to fittings, in order to test their structural design, but is not applicable to connecting joint systems. It assumes that the fitting either is or is not intended to be subject to the effects of hydrostatic end thrust.

The tests detailed in 8.1 to 8.4 are applicable to fittings intended to be used in buried or non-buried applications.

These test procedures are applicable to fittings of all nominal sizes specified in the referring standard. The tests are for evaluating fittings intended for use in applications conveying liquids at temperatures specified in the referring standards.

The test procedures in ISO 18851:2015 are damaging to the test piece which will not be suitable for reuse after these tests. The test procedure is applicable to type testing.