Causes for Weld Seam Performance Nonconformance and Spot Defect of SAWL Pipe

Addressing the nonconformance concerning low temperature impact toughness and guided bending,and the near surface spot defects as developed in the weld seam of the SAWL pipe,the blank steel plate chemical composition,and the macro-morphology and metallographic structure of the metal where the said defects present are analyzed. Based on the analysis,actions as follows should be taken:adjusting the chemical composition of the L485M base metal to get the base metal of the batches as following free of the alloy element Mo,so as to reduce the cost;determining well-matched weld wire by the pipe maker to adjust the chemical element contents of the weld seam so as to ensure the impact toughness thereof;and under the condition that the weld seam penetration is assured,trying as far as possible to use small weldingheat input amount to make the cooled down and solidified weld pool metal have ideal after-welding microstructure and grain structure as well.