C2024-20609 Sour Service Qualification of Carbon Steels (SMYS 450 MPa) and Their Welds Considering Field H2S Fugacity / Dissolved H2S Concentration - Qualification at Design and Atmospheric Pressure

Hugh Zhang - A facility’s design-case off-spec sour gas contains 22 mol% CO2 and 6,700 ppm H2S at a total pressure of 332 bara. These highly sour conditions could cause SSC of a susceptible carbon steel material in a relatively short exposure period. A sour service qualification program of girth welded carbon steel spools involving multiple heats of X65 piping, WPHY65 fittings, and F65 flanges was developed involving Part I and Part II.Prior to the SSC qualification testing, an H2S solubility study was performed to predict the H2S in aqueous phase (CH2S) and the H2S fugacity (fH2S) as well as to compare the sour severity of a methane-rich “production” environment to a nitrogen-rich “lab” environment. This information was later used to optimize the SSC qualification tests.Part I involved testing at 332 bara using batch-loaded high-pressure autoclaves based on fH2S.Part II involved testing at atmospheric pressure using two approaches; Approach #1 was designed to match the predict