110ksi级钛合金油管耐蚀性能研究

Study on Corrosion Performance of 110ksi Grade Titanium Alloy Tubing

针对钛合金在油气井环境下面临的腐蚀问题,通过开展模拟油田腐蚀工况下应力腐蚀及不同温度条件下酸化液中失重试验,同时开展与镍基合金管材的缝隙腐蚀和电偶腐蚀等系列试验,采用扫描电子显微镜、XRD等方法观察试样形貌和腐蚀产物,评价钛合金油管的耐腐蚀性能。结果表明,在苛刻腐蚀工况(溶液介质:5 MPa H_(2)S+11 MPa CO_(2)+10%Cl^(-))及NACE TM 0177标准A溶液下,采用四点弯曲的试验方法,加载应力为758 MPa,经720 h后试样未发生断裂且无应力腐蚀裂纹,表明该钛合金管材应力腐蚀敏感性较低。在两种浓度为0.1 mol/L的酸化液中,随着试验温度从室温升至160℃,钛合金管材腐蚀速率均逐渐增大,且腐蚀速率在胶凝酸中低于在转向酸中;与镍基合金管材对比,钛合金管材具有更优异的抗点蚀和抗缝隙腐蚀;在模拟苛刻腐蚀工况下,钛合金管材分别与625和825镍基合金偶接后均未出现明显的电偶腐蚀效应导致加速腐蚀现象。

In term of corrosion of titanium alloys in oil and gas well environments,by conducting stress corrosion tests under simulated oilfield corrosion conditions and weight loss tests in acidic fluids under different temperature conditions,as well as conducting a series of tests on crevice corrosion and galvanic corrosion with nickel based alloy pipes,the morphology of the sample and corrosion products are observed by using tools such as Scanning Electron Microscopy and X-ray diffraction etc.The results showed that under harsh corrosion conditions(solution medium:5 MPa H_(2)S+11 MPa CO_(2)+10%Cl^(-))and the NACE TM 0177 standard A solution,the four point bending test method was used,and the loading stress was 758 MPa.After 720 hours,the sample did not fracture and there were no stress corrosion cracks,indicating that the stress corrosion sensitivity of the titanium alloy pipe was low.The corrosion rate of titanium alloy pipes gradually increased with the rise of temperature from room to 160℃in two acidic solutions with a concentration of 0.1 mol/L and the corrosion rate in gelled acid was significantly lower than that in turning acid.Titanium alloy has excellent pitting corrosion resistance and crevice corrosion resistance superior to 625 and 825 nickel⁃based alloys under crevice conditions.No obvious accelerated corrosion phenomenon of titanium alloy in the simulated harsh corrosion conditions was observed due to galvanic corrosion effect after coupling titanium alloy with 625 and 825 nickel based alloys,respectively.