温度对镍基合金718在高含H_2S/CO_2环境下应力腐蚀行为的影响

Effect of Temperature on Stress Corrosion Behavior of Nickel-Based Alloy 718 in High H_2S/CO_2-Containing Environment

镍基合金718是一种高酸性油气井中常用的金属材料,但对其应力腐蚀开裂敏感性及其影响因素的研究较少。利用高温高压反应釜进行应力腐蚀开裂模拟试验,结合扫描电子显微镜(SEM)和能谱仪(EDS)等分析手段研究了温度对718镍基合金在高含H_2S/CO_2环境下应力腐蚀行为的影响。结果表明:在CO_2分压3.5 MPa、H_2S分压3.5 MPa、Cl^-含量150 000 mg/L的模拟环境下,镍基合金718在150,175,205℃下均未发现点蚀和裂纹,应力腐蚀开裂敏感性较低;但随温度升高,镍基合金718的C环应力腐蚀试样表面的钝化膜出现明显的硫化和颗粒状的腐蚀产物,并逐步团聚形成点蚀源。

718 nickel-based alloy as one of metal materials of downhole tools and equipment is commonly used in high acid oil and gas wells. However, stress corrosion cracking sensitivity and impact factors have not been widely researched. In this paper, with simulating the stress cor- rosion cracking test by high temperature and high pressure reactor, the effect of temperature on the stress corrosion behaviors of 718 alloy in H2S/CO2-containing environment was studied by scanning electron microscopy （SEM） and X-ray energy spectmum analysis （EDS）. Results showed that under the simulating environment of 3.5 MPa C02 partial pressure, 3.5 MPa H2S partial pressure and 150 000 mg/L Cl- concentration, no obvious corrosion pits or cracks were observed on the surface of 718 alloy at 150, 175, 505℃, presenting that the stress corrosion cracking sensitivity of alloy was low. However, with the increase of temperature, the passivating film on the surface of the C-ring stress corrosion specimen of 718 alloy showed obvious sulfidation, and some granular corrosion products existed, which gradually agglomerated to form a pitting corrosion source.