Characteristics of longitudinal seam welds of carbon steel pipe for room and moderate temperature service

Carbon steel pipes for room and moderate temperature service cause easily the solidification cracking and the liquation cracking in the seam welds because of the high carbon content. The effects of chemical compositions and welding conditions on such cracking were studied experimentally. The solidification cracking in the weld metal depends largely on the contents of C, P and S in weld metal and can be estimated well by UCS value proposed by Bailey, et. al. The solidification cracking depends, in addition to the chemical compositions, on the welding conditions such as heat input and welding speed as well as the shape of penetration. The liquation cracking in the heat affected zone depends on the chemical compositions of steel, paticularly on the C content, and also on the heat input. Based on these results, carbon steel pipe for room and moderate temperature service was manufactured for trial. In consequence, a sound weld free from hot cracking was obtained. This steel pipe proved to be excellent in tensile strength at elevated temperatures and creep strength both for base metal and welds, and satisfied the specification, ASTM A672, C70. (author)