Development of a 110 Ksi Yield Strength Grade OCTG Product for Shale Applications in Mildly Sour Environments

API 5CT Grade P110 casing is widely used in Shale Gas applications to stand high pressures during hydraulic fracture. The presence of H₂S have been reported in many of these applications, which is a risk for such material as is clear from NACE MR0175/ISO 15156 part 2. In fact, failures said to be related to hydrogen embrittlement have been reported even when no H₂S presence was identified. These problems were mainly observed in high yield strength (YS) P110 materials, in the connection area (due to resultant high stresses); the presence of H₂S will undoubtedly make the material more susceptible to cracking. For these and other similar applications the development of materials able to cover the mechanical requirements of API 5CT P110 and have acceptable resistance to SSC in very mild sour environments (Region 1, ISO 15156 part 2) is needed. On this basis a 110 ksi yield strength material that covers the requirements for P110 and is adequate for service in severity Region 1 has been developed. Steel design criteria is presented in this paper as well as the obtained performance. It was successfully qualified for Region 1 as per ISO 15156 Part 2 and a material K-limit (minimum stress intensity factor that produces crack growth initiation) of 35 MPa m^1/2 (32 Ksi.in^1/2) was obtained at room temperature, in an API 5CT test solution with pH 3,5 and 0,07 bar H₂S with a Nitrogen balance.