ISO 21138-1:2007 specifies the definitions and requirements for pipes, fittings and the system based on unplasticized poly(vinyl chloride) (PVC-U), polypropylene (PP) and polyethylene (PE) structured-wall piping systems in the field of non-pressure underground systems for underground drainage and sewerage. ISO 21138-1:2007 specifically refers to PVC, PP and PE materials. ISO 21138-1:2007 covers a range of pipe and fitting sizes, materials, pipe constructions, nominal ring stiffnesses, and gives recommendations concerning colours. In conjunction with ISO 21138-2 and ISO 21138-3, it is applicable to PVC-U, PP and PE structured-wall pipes and fittings, to their joints and to joints with components of other plastics and non-plastics materials intended to be used for buried piping systems for the transport of drainage and sewerage. ISO 21138-1:2007 is applicable to PVC-U, PP and PE structured-wall pipes and fittings with or without an integral socket with elastomeric ring seal joints as well as welded and fused joints. For dimensions larger than DN/OD 1200 or DN/ID 1200, ISO 21138-1:2007 can serve as a general guide regarding appearance, colour, physical and mechanical characteristics as well as performance requirement