Both fluctuation of operation pressure and transmission halt have obvious effect on the lifetime of the pipeline. When there exist flaws in the pipes, cyclic load caused by pressure fluctuation will promote the development of such defects especially as cracks. A full-scale fatigue test was performed on the X60 Spiral Submerged Arc-Welded pipes (Outside Diameter is 660mm), which was pre-manufactured with a small outside surface crack-like flaw. The test result indicated that both defect size and cyclic load magnitude had great effect on crack propagation rate and fatigue lifetime. During the test, the artificial shallow surface defect developed only in depth direction and finally caused the leakage. Comparison of test results between small-size and full-scale fatigue tests showed that small-size test can be used for lifetime prediction of the pipeline although there was some deviation.

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