Abstract
A new high-strength alpha-beta titanium alloy, UNS R55400, developed specifically for HPHT oil/gas production service was laboratory tested in severe sour environments for ANSI/NACE MR0175/ISO 15156 Standard1 sour service qualification. Extruded pipe and forged plate from three heats were tested in both alpha-beta and transformed-beta conditions at yield strengths exceeding 930 MPa and up to 41 HRC via five SSC/SCC test methods: NACE TM01770 (Method A) tensiles, four-point bent beam, C-rings (Method C), slow strain rate tensile (SSRT), and KSCC testing. Iron-coupled and non-coupled tensiles stressed to 100% actual YS resisted cracking in the 30 day NACE TM0177 Solution A exposure. C-rings stressed to 100% actual YS survived 90 day exposure to NACE VII plus conditions involving 25 wt.% NaCl brine with 3.45 MPa H2S and CO2, and elemental sulfur at 2880C; as did bent beam specimens tested at NACE Level VI at 1770C. SSRT testing in the 2880C sour brine revealed no indications of SSC/SCC susceptibility, and KSCC exceeded 62 MPa vm. Based on this database combined with demonstrated crevice corrosion resistance as tested under worst-case, aerated, and acidified saltwater conditions up to 2880C, UNS R55400 alloy is considered qualified for sour service to 41 HRC maximum hardness.
