Effect of Strain Rate on Stress Corrosion Cracking of Titanium Alloy Ti425 for Oil and Gas Pipes

The corrosion behavior and the effect of strain rate on stress corrosion cracking of titanium alloy Ti425 in simulated environment of oil and gas well were studied by electrochemical measurement, immersion test and slow strain rate test. The results show that Ti425 titanium alloy had repassivation property, low corrosion current density (in magnitude of 10^-7 A/cm²) and high impedance (in magnitude of 10⁵ Ω·cm²). Meanwhile, slight pitting corrosion was found on the surface of Ti425 titanium alloy, and the longer the immersion time held, the more serious the pitting corrosion was. When the strain rate was changed from 10^-6 s^-1 to 10^-3 s^-1, the yield strength and tensile strength, percentage elongation after fracture and percentage reduction of area increased, the dimple feature of fracture was more evident, meanwhile the secondary crack and the stress corrosion sensitivity index were all reduced.