Localised Corrosion and Inhibitor Selection

Corrosion control of oil and gas production systems is an essential element in the overall asset integrity programme. It is common industrial practice to inject corrosion inhibitor into the produced fluid to provide corrosion protection of the internal of carbon steel structures. In the sour environment, corrosion of carbon steel is typically in the form of localised attack, e.g. pitting. It is recognised that there are limitations in the selection of chemical by simply basing the decision on the results of linear polarisation resistance (LPR) measurements obtained in standard laboratory bubble test set-up and field side stream testing. This is particularly the case in sour environments where the general (or uniform) corrosion rate is at such low value that the evaluation of the performance of candidate inhibitors can be difficult. This paper considers the merits of conducting supplementary laboratory tests to complement the LPR results in the evaluation process. Of particular interest is the data obtained in autoclave tests, from which the localised corrosion behaviour of carbon steel can be characterised and the effectiveness of chemical in controlling localised corrosion qualified. In addition, the use of electrochemical noise monitoring technique in the assessment of the performance of corrosion inhibitor in localised corrosion environment was explored. The overall approach in the laboratory chemical selection process and field assessment are discussed. [This is an unrefereed preprint].