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.
Pipelines have primarily been developed for the oil and gas business as well as building domestic water networks. To ensure the quality and longstanding pipelines, inspection and quality during design, construction and operations are of prime importance. During construction, pipe manufacturing and field fabrication represent the major cornerstone of a construction quality program. In fact, many international publications, including codes, standards, procedures and technical reports, have laid the rules of such a cornerstone [1-6]. During fabrication, welding inspection through Nondestructive Testing (NDT) is imperative and regularly performed [6-7]. The type and extent of NDT is determined based on the design rules set and criticality of pipeline to customers and operators [1, 2, 6].
To mitigate corrosion during service, internal coating systems are typically applied to form a physical barrier capable of isolating the corrosive medium from the substrate to be protected. In the international domain, significant amount of financial losses were reported as a result of premature failure of coatings. Zamanzadeh et al. collected several case studies of such failures. In their evaluation, the significant premature failure causes were attributed to improper surface preparation, coating application, coating system selection, and handling and transportation of coated pipes [10]. Such failures could have been prevented through devising and implementing proper quality models that capture failure lessons learned and prevent such premature failures.
