ISO 3213:2009 specifies the minimum values for expected strength as a function of time and temperature in the form of reference lines, for use in calculations on pipes made of:

- polypropylene homopolymer (PP-H);

- polypropylene block copolymer (PP-B) (also called heterophasic copolymer);

- polypropylene random copolymer (PP-R);

- polypropylene random copolymer (this material can be distinguished by DSC testing or another appropriate method to indicate a second melting peak) with a modified crystallinity (PP-RCT).