Control of Corrosion Inhibitor Fouling in a Highly Sour System

Black tar-like fouling material was driving frequent shut-downs and increasing corrosion in the inlet area of a gas plant that processes lean gas with high acid gas content (68%CH₄, 20%CO₂ and 12%H₂S). Analytical work indicated that the nitrogen containing corrosion inhibitor (CI) polymerized with sulfur compounds (polysulfides, elemental sulfur and/or H₂S) in a type of a vulcanization process resulting in a hard-to-clean insoluble fouling product. Corrosion testing confirmed the role of the CI in creating this fouling. A customized autoclave testing was designed to include powdered elemental sulfur circulating in the bulk fluid. This allowed for a recreation of the condition in the plant where solid elemental sulfur comes out of solution and fouling occurs. The tests reproduced the tar-like fouling substance in the presence of the incumbent corrosion inhibitor. The data showed that a surfactant (wetting agent) used to keep elemental sulfur from depositing would also protect the steel from elemental sulfur corrosion. Other CIs were tested, but none provided protection at an acceptable dosage level without forming this foulant material.