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Understanding, then avoiding in-service failures linked to the use of the squeeze-off flow stopping technique

 

Papers # 2010 Vancouver

Polyethylene pipes are widely used across the utilities sector for the safe, reliable, transportation of gas or water under pressure. The success of the material in being adopted is partly due to the ability to treat it as an engineering polymer whose properties and failure modes are well understood, predictable, and in the case of failure designed out of field installations. In the recent past, a new failure mode has been observed on field installations made in the United Kingdom, manifesting itself during the application of the squeeze off flow-stopping technique. Type testing of materials and their suitability for use with the squeeze-off technique concentrates on the performance of the seal made (measurement of let-by rates), and on the effect on long term failure modes – ductile strength and also the onset of stress crack related failures in particular. This additional mode is evident during the initial application of the squeeze tool and manifests itself as a ductile tear, either partial or full through the pipe wall adjacent the squeeze point. This has been investigated and probable root causes established, together with preventative measures that can be taken to avoid in-service failures – key to maintaining an enviable track record of predictable performance.

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