Abstract
In recent times, the increase in pressure, depth and diameter of wells has required Oil Country Tubular Goods (OCTG) with higher yield strength. Because Sulphide Stress Cracking (SSC) can occur when high strength steel is exposed to wet sour gas, SSC characterization of such materials must be addressed to avoid failures in sour wells. A test program was designed, using NACE TM0177 Method A, C (C-Ring) and Four Point Bent Beam (FPBB) tests according to EFC publication N°17, in order to assess the high s trength carbon steel alloys grades P-110, Q-125, 140 and 150. This was in order to determine the risk in the use of such steel grades for production casing in H2S containing well environment. The results from this test program revealed that the well known relation between yield and SSC resistance (the higher the yield strength the lower the SSC performance) was confirmed also for these steel grades. Steel grade P-110, in fact, has the largest window of applicability compared to steel grades Q-125, 140 and 150. Fit for purpose tests performed on steel grade Q-125, with 1 bar of ppH2S and NACE solution A, using NACE TM0177 Method A, at test temperature of 80°C p roduced no SSC failure. A threshold temperature was determined by means of NACE TM0177 Method C for steel grade 140 (90 °C).
