The Prediction and Enhancement of UOE-DSAW Collapse Resistance for Deepwater Linepipe

With the increasing development of oil and gas reserves in water depths greater than 1500 m, linepipe used for deepwater and ultra-deepwater applications will require enhanced resistance to hydrostatic collapse. To support this need, Corus Tubes has been investigating methods by which increases in UOE linepipe collapse strength can be achieved. In particular, it has been theorised that modifications to the UOE manufacturing process can provide the necessary collapse strength enhancements. Pipe production trials were conducted focusing on the effect of processing parameters during UOE linepipe production, and in addition low temperature heat treatment was used to assess its effect. Full-scale collapse tests were then performed on the resulting linepipe specimens to validate the increase in collapse strength. The results of this work have demonstrated the beneficial effect of a modified UOE manufacturing approach on linepipe collapse resistance. This paper summarizes the work performed, quantifies the increase in collapse strength, and compares the test results to collapse equations found in offshore pipeline standards. It is also demonstrated that the UOE fabrication factor of 0.85 in the DNV offshore pipeline code (DNV OS-F101) may be considered to be over conservative, when linepipe is manufactured using the modified approach summarized herein.