Corrosivity Assessment of Three New Gas Transmission Lines

The purpose of this study was to perform lab analysis to assess the corrosivity of fluids transported through three transmission lines from Gas Compression Plants (GCPs) to Gas Plants (GPs), where CO₂ varies from 44 to 55 mol%, and H₂S varies from 9 to 40 mol%. The study consisted of four parts: 1) corrosion rate prediction using corrosion modeling; 2) uniform corrosion measurements in liquid and gas phases; 3) pitting corrosion measurements in liquid and gas phases; and 4) gas phase corrosion measurements. The highest corrosion rate measured under simulated field conditions was 144 mpy which is much less than the 1500 mpy obtained by running corrosion prediction modeling (CPM). The highest water film average wall shear stress estimated by CPM for the three lines was 14 Pa. The highest corrosion rate value, i.e. 144 mpy, was measured at a wall shear stress of 29 Pa assuming a worst-case scenario. Pitting attacks were observed under one test conditions in the tests left running for a period of 14 days. The results show that sweet corrosion rates in the liquid phase are comparable or higher than sour corrosion rates, while in the gas phase sour corrosion rates are higher than their sweet counterparts. Unlike CO₂, the presence of H₂S appears to facilitate wetting of the steel surface in the gas phase. Gas phase corrosion was studied at low velocities to avoid any water splashing. The highest measured corrosion rate value in the gas phase was 52 mpy.