Mitigation of Under-Deposit and Weldment Corrosion with an Environmentally Acceptable Corrosion Inhibitor

The subsea flow lines of an oilfield located offshore Norway were at risk of corrosion due to several factors. First, the flow lines contained high levels of CO₂ that resulted in general and pitting corrosion problems. In addition, the oil wells produced significant amount of solids and, in areas where these solids accumulated, there was the potential for under-deposit corrosion to occur. Finally, there was evidence that the welds within the pipeline were corroding preferentially. Therefore, a corrosion inhibitor was required that could mitigate all the forms of corrosion present in the flow lines. To qualify an inhibitor for this application, several environmentally acceptable corrosion inhibitors were developed. This paper details the test work performed to qualify a new corrosion inhibitor for this field. The inhibitors were evaluated in numerous tests including kettle tests, rotating cylinder electrode test, high pressure autoclaves, under-deposit corrosion tests and weldment corrosion tests.