This part of ISO 22621 specifies the general properties of polyamide (PA) compounds for the manufacture of pipes, fittings and valves made from these compounds, intended to be buried and used for the supply of gaseous fuels at maximum operating pressures (MOP) up to and including 20 bar1). It also specifies the test parameters for the test methods to which it refers. This part of ISO 22621 establishes a calculation and design scheme on which to base the MOP of a piping system.