Localized pitting corrosion of API 5L grade A pipe used in industrial fire water piping applications

In this present paper, failure analysis is conducted for a pipe used in fire water applications. In petroleum industries many failures were observed in API 5 L grade steel pipes. The past inspection history records were observed, which reveals that failed pipeline is poorly maintained since construction. Visual inspection, macroscopic and microscopic examinations were conducted for the failed pipe. The microscopic analysis reveals that the pitting corrosion is a root cause of failure which perforates the wall thickness at 6′o′ clock pipe position. The mechanism of pitting corrosion is correlated with ferrite matrix dissolution. The Cu, Co & Zn ions were detected in scale deposits reveals that the fire water is severely contaminated by various makeup water sources which results in under deposit corrosion. The various sources of foreign elements are discussed in detail. The copper deposits identified at suspected location attributed to galvanic corrosion. Moreover, the severity of pitting is aggravated by grain boundary attack which acts as an anode during corrosion process. Based on various experimental evidences, the conclusions were drawn and further recommendations are discussed to mitigate the corrosion failure.