The sulphide stress cracking (SSC) resistance of 32 casing and drill pipe materials corresponding to API 5D/5CT grades C-95 to S-135 has been evaluated using NACE TM0177 tensile testing. The standard method has been extended to include a range of temperatures from ambient to 107°C, and H2S contents in the gas phase in the range 100 to 0.1 mol. By defining an acceptable material as one that can bear a minimum load corresponding to 80% specified minimum yield strength for 720 hours in the given combination of H2S content and temperature, the results so derived have been used as the basis for defining operational limits for each material grade. In most cases these limits extend the useful application of the casing materials compared to NACE MR0175, particularly in marginally sour environments. The results showed that materials of the same API grade sourced from different manufacturers had variable performance, particularly when the aggressivity of the environment was increased. It was also found that the SSC resistance of specially modified C-steels that are marketed as “sulphide resistant” was poorer than anticipated. These inconsistencies emphasise that some kind of qualification testing and qualilty control is necessary when selecting such materials. A thorough analysis of the mechanical properties, chemical composition, and metallography of the materials facilitated correlation with the SSC results and hence derivation of guidelines for procurement/specification of materials for use in H2S containing environments. These are intended as a procedural guide for the selection of casing and drill pipe materials for H2S-service in formation waters of pH 3.5 or higher.
Keywords: corrosion, hydrogen sufphide, testing, carbon steel, casing, drill-pipe, materials selection