A VISCOELASTIC FRACTURE-MECHANICS ASSESSMENT OF SLOW CRACK-GROWTH IN POLYETHYLENE GAS-DISTRIBUTION PIPE MATERIALS

A substantial amount of the plastic gas distribution pipe currently in service, as well as that anticipated for future use, is polyethylene (PE). While this material has an excellent record, due to a variety of abnormal loadings that can arise in long time service, some slow crack growth (SCG) related field failures have occurred. Accelerated test procedures and analysis methodologies to predict accurately the long term performance of PE gas pipes are therefore required. One such procedure is the three-point bend test conducted on a pre-cracked pipe segment that is known as the SCG test. The research reported here examines the validity of this test through the application of advanced fracture mechanics principles. Specifically, considering the viscoelastic behavior of PE materials and using the region of dominance concept, the delimitation of a linear elastic fracture mechanics (LEFM) interpretation of the SCG test was developed. Excluding the time spent in crack initiation, the long-term performance of the category of materials for which the assumptions of LEFM are valid can therefore be effectively predicted from SCG test results. Through illustrative examples, this paper demonstrates the veracity of the approach by comparing time to failure predictions for abnormal service loadings with actual gas distribution service experiences. © 1990.