This International Standard establishes the classification of thermoplastics materials in pipe form and specifies the material designation. It also specifies a method for calculating the design stress. It is applicable to materials intended for pipes and fittings for pressure applications. NOTE 1 Classification, minimum design coefficient and calculation method are based on the resistance to internal pressure with water at 20 °C for 50 years, derived by extrapolation using the method given in ISO 9080. NOTE 2 Design coefficients for multilayer pipes are described in the appropriate product (system) standards.