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Low cycle fatigue performance of X70 high frequency resistance welded pipe

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Document pages: 10 pages

Abstract: Strength, toughness, corrosion resistance and fatigue resistance are the main requirements for evaluating pipeline integrity. In this study, the tensile strength, impact toughness and fatigue properties of the pipe body and welded joint of X70 high frequency resistance welding (HFW) pipe were measured, and the effects of microstructure and surface defects on the properties of the welded joint were discussed. The results show that there is a weakening zone at the welded joint of X70 HFW pipeline. However, all mechanical properties, including strength and impact energy, are better than those specified in API Specification for X70 pipeline pipe. The decrease of strength, toughness and S-N fatigue resistance of welded joints leads to the coarsening of microstructure at the welded jointsion zone. However, for the specimens without surface finishing, the resistance to S-N fatigue for the weld joint was further reduced. This phenomenon was mainly attributed to the burring defects and microstructural coarsening at the heat-affected zone (HAZ). Therefore, to improve the quality of the X70 HFW pipe, refining the microstructure of weld joint and reducing the deburring defects by optimizing the postweld heat treatment (PWHT) and deburring processes should be firstly considered in the future research works.

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