Qualifications of Ti-6%Al-4%V-Ru Alloy Production Tubulars for Aggressive Fluoride-Containing Mobile Bay Well Service

Ti-6%Al-4%V-Ru alloy (102-mm [4-in.] outer diameter [OD]) seamless pipe was evaluated as candidate production string tubulars for a specific Mobile Bay field producing corrosive sodium chloride (NaCl)- and calcium fluoride (CaF₂)-saturated sour brines at 210°C (410°F). The extensive qualification test program, which was mandated by a major Mobile Bay gas producer, included assessment of long-term pipe property and metallurgical stability at well temperature, long-term corrosion resistance in this sour production brine, injected organic acidizing solutions, liquid scale inhibitor, and methanol (CH₃OH) solvent for hydrate control; in addition to resistance to sodium bromide (NaBr) brine completion/packer fluids when coupled to steel casings under sour conditions. Test results, documented herein, revealed that this Ti-6%Al-4%V-Ru pipe exhibited good long-term thermal stability in metallurgy and mechanical properties consistent with all specification requirements and acceptable, exceptional resistance to all forms of corrosion and embrittlement in all specific well environments tested. The only exception was the expected susceptibility of the Ti alloy pipe to stress corrosion cracking (SCC) in water-lean methanol solutions, which is addressed by ensuring that the methanol contains at least 7 wt% to 10 wt% water prior to well injection. Based on this relevant property and corrosion performance database, Ti-6%Al-4%V-Ru alloy pipe is considered to be a viable, suitable, and attractive alternative for production tubing strings in sour, fluoride-containing Mobile Bay gas wells.