Metallurgical characterization of a failed A106 Gr-B carbon steel welded condensate pipeline in a petroleum refinery

A condensate pipeline made of carbon steel alloy with grade A106-Gr.B, had a leakage in the form of a pinhole at the girth weld after 16 years of operation. Visual examination, optical and scanning electron microscopy (SEM), coupled with energy-dispersive X-ray spectroscopy (EDS), chemical analysis, and hardness measurements were performed on the failed pipeline samples. Visual examination of the inner surface of the circumferential weld line showed many types of welding defects, as well as severe localized corrosion pits in the weld zone at the bottom of the pipe surface. The microscopic analysis shows that the localized corrosion attack is the root cause of the pipe failure. XRD patterns of the inner surface of the failed pipe emphasizes a formation of corrosion products of iron oxyhydroxides such as Lepiodocrocite (Fe + 3O(OH)), and Goethite (FeO(OH)). Additionally, the foreign ele-ments of aluminum, and chlorine, detected by the EDS analytical results promote under-deposit corrosion, particularly in regions with stagnant water, i.e., at 6 O'clock pipe position.