Influence of length / diameter ratio and post weld heat treatment on collapse resistance of welded pipes

Three steel pipes longitudinally welded by a high-frequency induction process are developed. A post weld heat treatment is performed, and its effect on the microstructure, mechanical properties, and collapse resistance is analysed. The influence of the length/diameter ratios on the collapse resistance, and a method to improve the metallographic analysis of the weld lines are studied. The post weld heat treatment resulted in a homogeneous microstructure and uniform mechanical properties, and the etchant for the weld line analysis revealed the flowlines and the localised decarburisation with excellent contrast. An increase in the length/diameter ratio leads to a decrease in the collapse resistance; however, the tensile strength proved to be a significant influence on this phenomenon. Collapse resistance is a characteristic of the component itself in which several aspects such as manufacturing, mechanical properties, and dimensions shall be considered, and it is not an intrinsic property of the alloy.