Demand for high strength casing has increased to develop high pressure and/or deep wells. In order to cope with H2S contained in produced fluid, the high strength casings are often required to be resistant to SSC (Sulfide Stress Cracking). Effects of environmental
factors such as H2S partial pressure and pH on SSC resistance of C125 grade OCTG were made clear using some types of SSC tests (tensile, V-notched 4-point bent beam, DC13. compact, tension, SSRT) and a hydrogen permeation test. For hydrogen entry into steel, one unit of pH decline is equivalent to a tenfold rise of H2S partial pressure although the effect of pH becomes lower after long time. SSC resistance of C125 decreases with increasing ppH2S and decreasing pH and is very high at H2S partial pressure of 0.001 MPa or lower and high at 0.01 MPa in case of bigher PH.
Keywords : sulfide stress cracking, sour gas OCTG, casing, high strength steel. hydrogen embrittlernent