Abstract
During the construction of a 56km long 16 in. carbon steel sour gas pipeline, repetitive surface preparation failures were detected during visual inspection of pipeline girth weld internal surface prior to coating application. Such failures represented 67% of the total pipeline girth welds and was manifested by excessive sharp-edges at the root pass. To identify the failure causes, an investigation was performed through reviewing the pipeline, fabrication and coating application specifications and procedures, quality control records and performing an extensive visual inspection through an advanced video robotic crawler on all pipeline girth welds made. Upon investigation analysis, the failures were caused by sharp-edges in the root pass which were attributed to improper practices during manufacturing, field fabrication and pre-coating quality control. The failure analysis indicated that the mechanized Gas Metal Arc Welding process, with the parameters used, is not suitable for internal girth weld coating application. In addition, a more stringent requirement should be applied to the acceptable pipe-end diameter tolerance and pre-coating quality control to ensure absence of similar premature coating failures. The pre-coating quality control can be improved through utilization of robotic laser contour mapping crawler for precise detection and sizing of unsatisfactory surface weldment defects.
