This part of ISO 22621 specifies the requirements of fitness for purpose of the polyamide (PA) piping system, intended to be buried and used for the supply of gaseous fuels at maximum operating pressures (MOP) up to and including 2 MPa (20 bar1)). It specifies the definitions of electrofusion and butt fusion joints. It also specifies the method of preparation of test piece joints and the tests to be carried out on these joints for assessing the fitness for purpose of the system under normal and extreme conditions. In addition, it specifies the test parameters for the test methods to which it refers. In conjunction with the other parts of ISO 22621, it is applicable to PA fittings, their joints and joints with components of PA.