Volatile Fatty Acid-Enhanced Carbon Dioxide Corrosion of a Multiphase Well of a Multiphase Well Fluid Pipeline

摘要

A multiphase well fluid pipeline extending from an unmanned platform to a process platform in India's Western offshore field was commissioned in 1984-85. Owned by Oil and Natural Gas Corp. Ltd. (ONGC), the 12-in. (305-mm) diameter, API 5L Grade X-52, 5.2-mile (8.4-km) long pipeline was cathodically protected by sacrificial anodes. The partial pressure of carbon dioxide (CO2) and hydrogen sulfide (H,S) in the flowing gas were 5 and 0.062 psi (34 and 0.43 kPa), respectively. In May 2000, the pipeline ruptured along 3.25 m (10.7 ft) in the 6-0'clock position and at its widest point was 0.59-ni (1.9-ft) wide (Figure 1). The average wall-thickness reduction at the 6 o'clock position was 50 to 60 percent. There was a channel consisting of a maximum width of 14 mm (0.6 in.) and a wall thickness as low as 1 mm (0.04 in.) at the center of the channel (Figure 2). Laboratory investigations were carried out to identify the cause of premature failure. The details of the studies are presented in this article.