Specified strength, toughness, lifetime and reliability are the key requirements for PE pressure pipes in various applications such as natural gas transmission and water distribution systems. Indeed, 50 or even 100 years of reliable service is a common requirement for PE pressure pipes. It presents a challenge of a realistic lifetime assessment based on a relatively short (practical) testing time that does not exceed a few months or a year. The lifetime assessment methodology should contain (a) a test that reproduce the mechanisms of observed or expected field failure, and (b) physically justified formalism for extrapolation of test time into field life expectancy. There are different modes of PE pipes failure. A ductile failure is associated with large deformation and is observed at a relatively high stress level (in comparison with yield strength). It takes place at a relatively short time. A brittle fracture resulting from a combination of mechanical stresses and chemical degradation of polyethylene (called stress corrosion or environmental stress cracking) is more common at long time in service under low stress level. A stress driven brittle fracture is the most common mode of fracture at intermediate stresses and time in service. In the present talk we discuss the relations between the outline above modes of PE failure and fundamental thermo-mechanical properties of polyethylene such as yield strength, drawing stress and draw ratio dependency on strain rate and temperature, cold drawing (necking) and delayed necking phenomenon in PE. We also present a novel PE lifetime prediction method based on modeling of macro- and micro-mechanisms of PE failures.

Assessment of strength, toughness, and lifetime of PE pressure pipes based on testing of the material thermomechanical properties

251st National Meeting (2016)

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