The purpose of the study was to assess the relative degree of severity of the test methods that are available to determine the Sulfide Stress Cracking (SSC) resistance of oilfield tubulars. Three different steel grades were used: a Sour Service Line Pipe grade (X65), a Sour Service OCTG grade (T95) and a non sour service OCTG grade (P110). The SSC threshold stresses of these steels were obtained in the NACE TM0177 solution A through Tensile Tests, C-Ring Tests, and Four Point Bent Beam Tests. The two Sour Service grades exhibited high threshold stress values ( >= 90% YS) whatever the test method that was used. Not unsurprisingly the non-Sour Service grade P110 gave much lower values ( < 40%YS). The exact threshold stress values depended on the test method, the tensile test being the most conservative of all with a threshold stress below 10% YS. This first part of the study allowed us to rank the test methods in terms of severity. However, for a non Sour service grade the exact value of the threshold stress itself is of little
interest for the user. It is not practical nor even possible to reduce the stress level in service, and therefore the only conclusion that can be drawn from the P110 test results is that the material is not fit for service in the conditions of NACE TM0177 solution A (PH2S 1bar, pH 2.7). More meaningful is the information regarding under which PH2S -pH conditions the P110 grade becomes fully resistant to SSC (threshold stress >= 90% YS). The remaining part of the study was devoted to obtaining this information through the use of the EFC 16 guidelines.
Keywords: Sulfide Stress Cracking, Carbon Steel, Test Methods.