This Standard is based on ISO 4437 and specifies dimensions and general requirements for two classes of pipe for use in gas mains and services for direct burial and reliner applications, for the distribution of natural gas at pressures up to 400 kPa and of LP gas and mixtures of LP gas and air where the partial pressure of the LP gas component does not exceed 200 kPa. ISO 161-1 outside diameter series of tensions are used with a size range of 50 to 220.