H_2S,CO_2酸性环境中110ksi钢P110,C110套管的应力腐蚀速率

Determination of Stress-Corrosion Rate of 110 ksi SteelCasings PI 10 and C110 under Acidic Oilfield Environment Containing Hydrogen Sulfide and Carbon Dioxide

110 ksi钢级C110,P110套管在酸性油气田环境服役过程中受到应力和腐蚀的双重作用,其腐蚀速率与静态的结果不同。如何利用室内试验结果为现场选材提供依据,目前研究尚不充分。采用挂片法、高温高压恒载荷应力腐蚀试验装置和高温高压三点弯曲应力腐蚀试验装置测试了60℃,10MPa,10%(体积分数,下同)H_2S,20%CO_2酸性环境中,P110,C110套管钢分别在自由状态、拉应力以及剪应力状态下的腐蚀速率。结果表明:在酸性环境中,套管钢承受应力作用时会发生应变老化,腐蚀速率显著增大;腐蚀作用在缺口敏感和应力集中部位尤为明显,这些特殊结构部位将形成微裂纹并持续扩展,造成套管钢力学性能和使用寿命降低。本方法适合受应力和腐蚀双重作用下管材腐蚀速率的测试。

A high tempera-ture-high pressure-constant load stress-corrosion test rig and a hightemperature-high pressure-three spot bending stress-corrosion test rig were separately performed to determine the corrosion rates of Pi 10 and CI 10 casing steels under undisturbed state as well as in the presence of tensile stress and shearing stress,with which the stress-corrosion tests were conducted at 60 X. and 10 MPa in the presence of 10% H2 S(volume fraction; the same hereafter) and20% C02. Results showed that the stress associated with the acidic environment led to strain aging of the tested casing steels and significantly accelerated their corrosion. Particularly, the stress-corrosion of the casing steels was more severe at the notch-sensitive locations and stress concentration zones, where micro-cracks were preferentially initiated and expanded thereby reducing the mechanical properties ^ service life of the casing steels. In one word, the present approach is suitable for the determination of the corrosion rate of tubing materials under dual attacks by stress and corrosion,