This part of ISO 16486 specifies the requirements of fitness for purpose of the unplasticized polyamide (PA-U) piping system, intended to be buried and used for the supply of gaseous fuels. It also specifies the definitions of electrofusion and butt fusion joints. This part of ISO 16486 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. It also specifies the test parameters for the test methods to which it refers. ISO 16486 is applicable to PA-U piping systems the components of which are connected by fusion jointing and/or mechanical jointing. In conjunction with the other parts of ISO 16486, it is applicable to PA-U fittings, their joints and to joints with components of PA-U.