In situ electrochemical evaluation of pitting corrosion of carbon steel pipelines exposed to slightly sour seawater service

2017 by NACE International. Pitting corrosion susceptibility was studied in a slightly sour seawater transport piping system using electrochemical methods deployed in situ. By establishing a benchmark testing environment based on the operating conditions of the seawater treatment plant, the objective of the study is to identify the root cause and to evaluate mitigation strategies for the pitting attack observed on the pipeline network. The study of pitting susceptibility of carbon steel exposed to slightly sour service environment is conducted by using direct current and electrochemical impedance (IES). The test matrix is designed considering the oxidizing potential of the seawater as the independent variable, and the stable pitting likelihood as the dependent parameter to assess pitting susceptibility. The results show that the oxidation of the sulfides in the environment to sulfur are the main cause for the presence of pitting of carbon steel; hence the pitting resistance is increased by reducing the concentration of excess oxidizing species. The IES results suggest that the iron oxide/sulfide layer formed on the steel surface contributes to the reduction of pitting susceptibility. The use of corrosion inhibition is found to decrease the pitting propagation rate in both the highly oxidizing and reducing types of slightly sour seawater service conditions.

In situ electrochemical evaluation of pitting corrosion of carbon steel pipelines exposed to slightly sour seawater service Conference Paper