Development of a Multi-Pass Weld Transverse Cracking Test

Transverse weld metal cracking has been occasionally observed in girth welds on large diameter thick wall pipelines that utilize high strength steels. The cracks are typically in the last one or two layers of the weld, and are not necessarily surface-breaking cracks. These cracks are a serious concern as they are parallel to the pipe axis, an orientation that is perpendicular to the hoop stress due to pipeline operation. Weldability tests have been developed or modified in recent years that were intended to specifically examine the tendency for cracking in multipass welds. Test methods are somewhat similar in that a multilayer full-thickness weld is deposited in a restrained (or self-restrained) weld joint, followed by examination to determine the occurrence of cracking after a specified delay period. The primary objective of this study has been to develop a test method that can then be used to compare the incidence of cracking to hydrogen-induced cracking prediction methods (for example delay time), also allowing one to develop welding conditions that would avoid cracking of field welds during pipeline construction. This could be achieved in two ways; a) determining delayed cracking time, and b) assessing the effects of pre-heat and interpass temperature. The test has been successful in producing transverse cracks in the top layers of the fill passes, similar to the cracking that has been observed on thick weldments in high strength steels. The test has been instrumented to assess the restraint level and also to attempt to detect cracking. The cracking has also been detected by UT and subsequent sectioning.