Fatigue Behaviour of Skelp End Welds in Spiral Welded Oil and Gas Pipes

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The oil and gas industry plays a critical role for the Canadian economy. Pipeline operators use buried steel pipelines as the primary mode for transporting oil, gas, and various petroleum products. Manufacturing these pipes uses steel strips which are deformed and welded using two different seam welds: straight seam weld and spiral seam weld. Spiral seam welded pipe offers many technical advantages and economic benefits as compared to straight seam welded pipe. However, the manufacturing process of spiral seam welded pipe requires feeding multiple coils of steel strip. The ends of two consecutive strips are welded together before feeding them into the forming machine and as result, a skelp end weld (SEW) forms where ends of two successive coils are joined. Though spiral welded pipe is now well accepted as a cheaper and better alternative to straight seam welded pipe for construction and replacement pipelines, the portion of the spiral welded pipe that contains the SEW is discarded. This is because the pipeline operators are not confident in using it as the fatigue behaviour of SEW pipe section is not known. This cropping process results in a yield loss of 1% to 5% for the Canadian pipe mills making them less competitive in the global market. Hence, this research project is aimed at determining the effect of spiral weld and SEW on the structural integrity and safety of a field pipeline under fatigue loads develop primarily from the fluctuations in the operating pressure. The results of this study will provide an insight in the structural integrity of spiral welded pipes which can ultimately be transferred and used by the pipeline operators and engineering consulting companies. Therefore, Canadian pipe manufacturing mills and pipeline operators, as well as the Canadian economy in general, are expected to benefit from this research project. In particular, Evraz and the local economy of Regina will benefit from this research, since Evraz's production facilities in Regina alone employ 500 people. Completion of this study will require a large number of full-scale fatigue tests on 36 inch (915 mm) straight and seam spiral welded pipes with and without SEW.