TWI Industrial Member Report Summary 770/2003
C Brown and M Troughton
Background
Welded polyethylene (PE) pipe systems have been in use for nearly fifty years for the pressurised distribution of media such as potable water, sewage and domestic gas. The long-term performance of the pipes themselves is well understood from established regression analysis techniques of pressurised samples at elevated temperatures. However, the longevity of a welded pipe system also depends on the long-term performance of the joints. Numerous short-term tests are used to quantify the quality of butt fusion joints in relation to the strength of the parent material but, at the moment, these tests cannot be used to give an indication of the long-term performance of the welds. For this reason a programme of work was started in 1996 to compare the results of various short-term and long-term tests currently carried out in industry on butt fusion welds in PE pipes made using very different welding conditions.
Objectives
- To develop a long-term, whole pipe test that can be used to determine the long-term performance of butt fusion welds in PE pipes.
- To determine which, if any, short-term tests can be used to provide information about the long-term performance of butt fusion welds in PE pipes.
- To determine whether the results from standard long-term tests (coupon fatigue, coupon tensile creep rupture and hydrostatic pressure) agree with the results from the long-term, whole pipe test developed in this project.