On the Influence of Acetate-Based Buffers on the Reliability of SSC Qualification Tests

Abstract Sulfide Stress Cracking (SSC) and Hydrogen-Induced Cracking (HIC) are common failure mechanisms affecting carbon and low alloy steels in the oil and gas industry. For SSC, ISO 15156-2 defines different severity regions based on pH and the partial pressure of H2S, which are considered the primary parameters influencing the risk of cracking in carbon steels and are key inputs for material selection. To control pH during testing, various buffer systems can be employed, most of which are based on the acetic acid/acetate pair. But in recent years, concerns have been raised within the industry regarding the potential impact of high-acetate buffer systems on qualification test outcomes. Acetates are reported to increase the corrosion rate of carbon steels and to alter the protectiveness of corrosion scales formed during sour service testing. To investigate these concerns, a test program was carried out on C125 casing steel as per API 5CT / ISO 11960. The experiments were designed to assess SSC resistance (pass/fail criteria), measure corrosion rates, and monitor hydrogen uptake in loaded specimens. Solutions with varying acetate concentrations were evaluated across different pH–pH2S conditions to generate data supporting the discussion on how buffer system selection may influence qualification test results