Lawrence
Testing and Processing # 1985 York
Polyethylene gas supply systems are designed for a minimum of 50 years life, but as long term data, both laboratory and field is difficult to obtain, long term assessments are based on an extrapolation of Quality Control and other short term tests. An essential requirement is that Polyethylene should be highly resistant to stress cracking and this has led to the introduction progressively of new improved material grades.
The Quality Control standards set for the earliest materials are now attained easily but it would be impractical to conduct the same Q.C. test as this would require test times of at least 1000 hrs. Since in general fatigue loading reduces the time to failure compared to stress rupture tests, a programme based on dynamic loading was designed to distinguish the significant factors affecting fatigue in pipe and to investigate the possibility of incorporating those characteristics into a routine Q.C. test.
