ISO/TC 138/SC 5/WG 20 - Slow crack growth (SCG)

This document specifies a test method for determining the resistance to slow crack growth of polyolefin pipes, expressed in terms of time to failure in a hydrostatic pressure test on a pipe with machined longitudinal notches in the outside surface. The test is applicable to pipes of wall thickness greater than 5 mm.

ISO 18489:2015 specifies a method to determine the resistance to slow crack growth (SCG) of polyethylene materials, pipes, and fittings. The test is applicable to samples taken from compression moulded sheet or extruded pipes and injection moulded fittings of suitable thickness. ISO 18489:2015 provides a method that is suitable for an accelerated fracture-mechanics characterization at ambient temperatures of 23 °C of different polyethylene grades, especially for PE 80 and PE 100 types for pipe applications. NOTE This test method could be adapted for other thermoplastics materials by developing the procedure using different test parameters.

ISO 18488:2015 specifies a method for the determination of the strain hardening modulus which is used as a measure for the resistance to slow crack growth of polyethylene. The strain hardening modulus is obtained from stress-strain curves on compression moulded samples. This International Standard describes how such measurement is performed and how the strain hardening modulus shall be determined from such a curve. Details of the required equipment, precision, and sample preparation for the generation of meaningful data are given. ISO 18488:2015 provides a method that is valid for all types of polyethylene, independent from the manufacturing technology, comonomer, catalyst type, that are used for pipes and fittings applications. NOTE This method could be developed for materials for other applications.