This Part of EN 12666 specifies the requirements for pipes, fittings and the system of polyethylene (PE) piping systems intended to be used for - non-pressure underground drainage and sewerage outside the building structure (application area code "U"), and - non-pressure underground drainage and sewerage for both buried in the ground within the building structure (application area code "D") and outside the building structure. This is reflected in the marking of products by "U" and "UD". It also specifies the test parameters for the test methods referred to in this European Standard. This European Standard covers a range of nominal sizes, a range of pipe series/stiffness classes and gives recommendations concerning colours. NOTE 1 It is the responsibility of the purchaser or specifier to make the appropriate selection from these aspects, taking into account their particular requirements and any relevant national regulations and installation practices or codes. In conjunction with CEN/TS 12666-2 [1] it is applicable to PE pipes and fittings, their joints and to joints with components of other plastics and non-plastics materials intended to be used for buried piping systems for non-pressure drainage and sewerage. This European Standard is applicable to PE pipes with or without an integral socket. The fittings can be manufactured by injection-moulding or be fabricated from pipes and/or mouldings. This European Standard is applicable to PE pipes and fittings for the following types of joints: - elastomeric ring seal joints; - butt fused joints; - electrofusion joints; - mechanical joints.