Analysis on welding quality problems and causes of crack formation of girth welds in high grade steel pipeline

Physical and chemical inspection and defect analysis were carried out on twelve girth welds with cracks of high grade steel pipeline. and the forming mechanism of cracks caused by welding quality problems were studied. The reuts showed that the overhead welding area ol girth welds was the high occurrence area of crack initiation, which accounted for 83.33%6 in this paper. The tensile strength and Vickers hard ness of girth welds met the standard requirements. However, the Charpy impact energy of some girth welds was lower than the standard require ments, and the number of unqualified samples acounted for about 19.449 of the total samples. The main reason for unqualified impact tough ness was the insulficient number of welding layers and pases. The main welding quality problems leading to girth weld cracking included fou categories, such as inner surace defects of root welding, groove and root incomplete fusion, sulfur segregation in root welding and copper pollu tion in filling welding groove. The insuficient number of welding layers and passes, the excessive amount of weld misalignment and the super position of the above defects promoted the formation of cracks.