Effect of Field Operational Variables on Internal Pitting Corrosion of Oil and Gas Pipelines

• Published in: Corrosion (Houston, Tex.) Vol. 65; no. 11; pp. 741 - 747
• Main Authors: DEMOZ, A, PAPAVINASAM, S, OMOTOSO, O, MICHAELIAN, K, REVIE, R. W
• Format: Journal Article
• Language: English
• Published: Houston, TX NACE International 01.11.2009
• Subjects: Applied sciences; Carbon dioxide; Corrosion; Corrosion effects; Corrosion environments; Corrosion products; Corrosion rate; Covering; Exact sciences and technology; Experiments; Fourier transforms; Gas pipelines; Gas production; Hydrogen sulfide; Iron carbonate; Iron sulfides; Mathematical models; Metals. Metallurgy; Natural gas; Oil and gas production; Petroleum pipelines; Pipelines; Pipes; Pitting (corrosion); Protected species; R&D; Repair & maintenance; Research & development; Sand; Scanning electron microscopy; Siderite; Steel; Submarine pipelines; Sulphides; Surface layers; Gas pipeline; Prediction; Localized corrosion; Gas industry; Corrosion rate; sour; oil and gas pipelines; pitting corrosion rate; internal pitting corrosion; Pipeline; Oil industry; Pitting corrosion; sweet; Application
• DOI: 10.5006/1.3319100
• ISSN: 0010-9312

Internal pitting corrosion, caused by carbon dioxide (CO2) and hydrogen sulfide (H^sub 2^S), is one of the predominant failure mechanisms of these pipelines.1-7 An integrated model to predict internal pitting corrosion of oil and gas pipelines has already been described.8 According to this model, the internal pitting corrosion of oil and gas pipelines occurs in four stages: -the low- or no-corrosion stage when the internal surface of the pipeline is covered by hydrocarbons, i.e., oil-wet conditions; -formation of surface layers on the steel surface due to corrosion reactions once the surface is covered with water, i.e., water-wet conditions; -initiation of pits at localized regions on the steel surface when surface-layer breakdown occurs; and -pit propagation and eventual penetration of the pipe wall. In the absence of any surface layer and other extraneous materials (e.g., sand), the susceptibility to pitting corrosion was low, as found with Pipe B. CONCLUSIONS Based on field experiments conducted over a period of four years in six operating fields, it was found that: * Pitting corrosion rates were similar when the compositions of surface layers were similar. * When a compact layer of a single species formed, the surface was protected from pitting corrosion; the FeS layer was more protective than the FeCO3 layer. * When multiple layers of several species formed, the susceptibility of the surface to pitting corrosion increased.