Qualification of corrosion inhibitors for field deployment involves performance testing in the laboratory. Especially for sour service, a common set of test methods and associated protocols or guidelines used across the oil and gas industry, chemical companies and laboratories does, however, not exist. Development and testing of robust methodology were at the core of a Joint Industry Project (JIP) carried out at the Institute for Energy Technology (IFE). This contribution presents a selection of findings related to precorrosion, one of the aspects addressed in the JIP.
A series of benchmark experiments assessing the performance characteristics of various inhibitor
chemistries mitigating corrosion of carbon steel under sweet (CO2) and sour (CO2:H2S 1:1) conditions at 25 °C and 60 °C without any precorrosion raised concerns related to uneven attack and risk for developing undesirable experimental artifacts, e.g. localized corrosion. Subsequent study of several precorrosion methods, including natural and electrochemically accelerated (anodic polarization) corrosion either in the absence or presence of H2S provided valuable insight into advantages and shortcomings of each approach.
From a methodology viewpoint the precorrosion approach and the selected conditions make it possible to generate corroding carbon steel surface either free of protective corrosion products, covered by nonprotective FeS, pre-load the test solution with suspended FeS particles etc., which could be useful for tuning the inhibitor tests to various scenarios relevant to sour corrosion.