Corrosion Inhibitor Evaluation for Crude Oil Transmission Pipelines

Abstract Localized corrosion can occur in pipelines transporting crude oil in areas of the pipeline where water wets the pipe surface either during operation or shutdowns. This has been attributed to the presence of CO2, and in some cases O2, in the crude oil which dissolves in the water that drops out. It has been reported that the performance of many CO2 corrosion inhibitors decreases when dissolved oxygen is present. A test program was implemented to evaluate a total of 19 corrosion inhibitors (CI) at conditions simulating pipelines transporting crude oil with different levels of CO2 and O2. The program included conducting screening tests, performance tests, and secondary property tests (e.g., partitioning, compatibility). This paper discusses results from screening and performance tests conducted under one of the conditions evaluated, simulating a crude oil pipeline, containing dissolved CO2 and O2 representative of concentrations measured in field samples. The initial screening of CIs was based on electrochemical tests conducted using the rotating cylinder electrode (RCE) technique in 100% synthetic brine. More detailed performance tests were conducted in 50% brine/50% mineral oil using a RCE in the aqueous phase and a mass-loss coupon located across the oil/water interface to evaluate CI efficiency in controlling localized corrosion.