Users' guide on squeeze-off of polyethylene gas pipes. Plastic pipes research results. Volume 1. Topical report, August 1989-February 1992

Squeeze-Offs are routinely performed on polyethylene (PE) gas pipes to stop gas flow to conduct downstream repairs. Occasionally damage is initiated so that failure occurs by a slow crack growth mechanism some time later. To prevent such problems the natural gas distribution industry needs to know which conditions induce damage, how to identify materials susceptible to squeeze-off induced damage, what are guidelines for good squeeze-off procedures, and which tool designs avoid or minimize damage. It is shown that if squeeze-off related damage is not initiated during squeeze-off, it is unlikely to be initiated subsequently. If damage is initiated, Slow-Crack-Growth (SCG) resistant materials have much longer life than less-SCG resistant materials. For the materials that were tested, the data show that the main variables that affect damage formation are wall compression, size of the squeeze tool, pipe wall thickness, and pipe material. For materials that were not tested, or may be introduced in future, a recommended qualification procedure is defined. Recommended guidelines to minimize damage due to squeeze-off are itemized, features of tool designs that minimize damage are outlined, and key features for retrofit procedures are identified.