Hydrogen Induced Crack Development in Submerged Arc Welded Steel Pipes

Abstract

The current work examines hydrogen sensitivity in different pipeline steels (X65, X70 and X80 HSLA grades) from four productions. Hydrogen Induced Cracking (HIC) experiments were performed and then the welds were characterized via optical and scanning electron microscopy techniques. The optical micrographs revealed cracks only in one of the four welds. Transverse cracks were found along bainitic-ferrite/carbide islands within the heat affected zone and the base metal of production B. Found inclusions e.g. MnS inside the cracks acted as initiation points for the HIC. However, the weld zones in all productions consisting of acicular ferrite and grain boundary ferrite were found to be resistant in hydrogen embrittlement. Therefore, the presence of bainitic ferrite with carbides at the grain boundaries in the microstructures and the intense presence of MnS inclusions caused HIC in pipeline steel from production B. The manufacturing process, the forming and welding conditions in the examined case seem not to have negatively influenced the pipeline steel in terms of HIC.