This standard specifies a method for preparation of samples for the determination of the viscosity number and calculation of the K-value. The standard is directed at manufacturers, test facilities and users of thermoplastic fittings. This document is intended to provide the user with an internationally recognised test standard for preparation of samples for the determination of the viscosity number and calculation of the K-value. The standard contains in particular aspects of quality and product safety. DIN EN ISO 13229 is the German version of the standard prepared by Technical Committee ISO/TC 138 "Plastics pipes, fittings and valves for the transport of fluids", in collaboration with Technical Committee CEN/TC 155 "Plastics piping systems and ducting systems". The committee responsible for DIN EN ISO 13229 is NA 054-05-02 AA "Prüfverfahren für Rohre" ("Test methods for plastic pipes") at DIN.