Identifying mechanically induced chemical changes to vintage grade high density polyethylene pipes during squeeze-off

Squeeze-off is widely used within the gas industry for temporary interruptions to supply, both when extending and repairing the polyethylene (PE) pipe network. Over the years a number of pipe failures, have been attributed to damage caused at the squeeze-off location, often linked to non-standard squeeze-off practices. The purpose of this paper is to examine PE pipes that have been squeezed in the laboratory under ASTM and non-ASTM standard conditions to determine if any changes to the PE structure can be measured. Changes in the PE due to squeeze-off was measured by FTIR at the squeeze-off ear. The carbonyl index (CI), a measure of polymer degradation, was calculated for the various squeeze-off conditions and it was found that over-compression of the PE pipe caused the greatest amount of damage to the pipe and that is directly linked to the integrity of the pipe prior to being squeezed-off.