PENT-Universal Test for Slow Crack Growth in Plastics

Slow crack growth (SCG) under plane strain conditions as measured by the PENT test is governed by the stress intensity, K. The PENT test, ASTM specification F 1473, which was originally designed to measure the resistance to SCG in pipes, fittings, and resins for conveying gas, can be used to measure the resistance to SCG in all polyethylene products. The resistance to SCG as measured by the PENT test in hours has been directly correlated with the lifetime of large scale gas pipe systems and is expected to be correlated with the lifetime of all polyethylene piping systems. The PENT resistance to SCG has been measured on various polyethylene products. It is now possible to specify a resistance to SCG of a PE resin as measured by the PENT test which will satisfy the commercially desired lifetime of the product. For example, a gas pipe system that contains a polyethylene resin with a PENT value of 100 h will exhibit practically no SCG failures during its first 100 years of service. It is recommended that the PENT test replace the ESCR test, ASTM D 1693, in all the ASTM specifications and that it should be used in place of the ISO specification in ISO 138/SC4, known as the British Gas Notch Test.

It is shown how the PENT test can be applied to all polymers that exhibit SCG.