Corrosion Inhibition of Carbon Steel in Extreme Sour Application Conditions

Corrosion inhibition of carbon steel in sour oil and gas production at elevated temperatures (>100°C) and under high shear stress presents a major challenge for operators, especially when compared to inhibition under sweet conditions. The formation of insoluble iron sulfide scales such as pyrrhotite which are less dense and easily break under high shear presents a major challenge with localized corrosion in extreme sour applications. The main objective of this project was to develop a novel sour corrosion inhibitor solution, which would provide both general and localised corrosion inhibition under such extreme conditions. This paper presents key findings from a laboratory protocol designed to select a candidate sour corrosion inhibitor for a sour application. The laboratory tests were carried out in Hastelloy™ C 276 autoclave test rigs designed specifically for high temperature, high pressure, and high shear conditions in a sour environment. The test conditions were 135°C, with a shear stress of 92 Pascal, CO2 and H2S partial pressures of 3.1 and 6.2 bara respectively. White light interferometry was used for surface analysis of the carbon steel coupons after the tests to compliment the corrosion rate data. Results from the project showed the performance of a novel sour corrosion inhibitor specifically designed for high temperature sour gas applications. The corrosion inhibitor showed significant improvement in general and localised corrosion inhibition against carbon steel material compared to the traditional corrosion inhibitors typically used in sour environments. The product identified from the project has shown to provide better protection for carbon steel pipelines under extreme sour production conditions. Cost analysis confirmed that the chemical application could offer a more cost effective solution than the option of using corrosion resistant alloys.