Inhibitor protection and corrosion monitoring in Benfield installation to purify gas for synthesis

Abstract

The aggressive media in the Benfield processfor preparing gasfor use in synthesis by means of ‘potassium purification’ consist of KHCO₃ + K₂CO₃ solutions having total contents and molar ratios that vary over a very wide range which also contain diethanoloamine. Operating temperatures are typically 70–120°C. Despite the use of inhibitors, intensive corrosion of mild steel walls has been observed in several installations. In laboratory tests performed in simulated Benfield solutions, a relationship has been established between the inhibitor content necessary to suppress active dissolution and pitting corrosion and the total content and molar ratio of the carbonates. These results have been checked and verified in an industrial installation. The corrosion monitoring system applied to critical parts of the equipment allowed the solution composition to be controlled and an inhibitor content appropriate to the composition of the aggressive medium to be maintained. As a result, substantial decreases in corrosion have been achieved, as was confirmed by microscopic examination of disposable electrodes and by the observation of the inner surface of an installation during routine maintenance.