In the first part of this two-part paper we reported on the development of a novel test method to evaluate the performance of inhibitors for underdeposit corrosion under sweet (carbon dioxide [CO2]) conditions for oil and gas applications. The use of a multi-electrode array enables examination of the effect of varying degrees of precorrosion during a single test and highlights statistical variations in corrosion rate that might be missed by other methods. This paper describes the application of the test method to sour (hydrogen sulfide [H2S]) conditions, where autoclave testing is required to deal with the elevated pressure. Tests on two different inhibitors were carried out in an autoclave containing a simulated Forties brine at 60°C with two different CO2/H2S partial pressure ratios. Effective discrimination of inhibitor performance was more readily achieved at lower partial pressures of H2S. At higher partial pressures of H2S, the iron sulfide film formed very readily and was so protective as to render distinction of comparative inhibitor performance unfeasible.

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