材料期刊网

目的：考察有机盐钻井液对S135钻杆材料腐蚀及疲劳性能的影响。方法首先利用高温高压釜模拟有机盐钻井液井筒的工况环境,对疲劳试样进行预腐蚀,通过点蚀仪测定试样表面的腐蚀状况；然后利用旋转弯曲疲劳试验机在不同弯曲应力条件下对预腐蚀试样和未腐蚀试样的疲劳性能进行测试,算得不同存活率下的疲劳强度,并绘制不同存活率下的S-N曲线。用体视显微镜和扫描电镜观察预腐蚀试样和未腐蚀试样的疲劳断口形貌,进而得出S135钻杆材料表面腐蚀对其疲劳寿命的影响程度和影响机制。结果经过腐蚀的试样表面有较多腐蚀坑,腐蚀坑深度在0.4~0.7 mm之间。未腐蚀试样的疲劳强度为553 MPa,其疲劳断口只观察到单个疲劳裂纹源；腐蚀试样的疲劳强度为409 MPa,其疲劳断口观察到多个疲劳裂纹源。 S135钻杆材料腐蚀疲劳开裂敏感性指数为26%。结论经过高温高压有机盐钻井液环境腐蚀后,试样表面点蚀严重,腐蚀坑底部存在应力集中并导致裂纹源的形成,多个裂纹源的同时生长加快了裂纹的扩展,最终降低S135钻杆钢的疲劳强度。

ABSTRACT:Objective To study the impact of organic salt drilling fluid on corrosion and fatigue properties of S135 drill pipe. Methods The organic salt drilling fluid corrosive condition was simulated by using autoclave and the fatigue samples were pre-corro-ded. The corrosion status of sample surface was measured by pitting instrument. The fatigue test with pre-corrosion samples and normal samples was conducted by using PQ-6 bending fatigue test machine under different stress conditions. The fatigue strength under different reliability was calculated and the S-N curves were drawn. The fatigue fracture morphologies of corroded and normal samples were observed by stereomicroscope and scanning electron microscopy ( SEM) . Then the influence of surface corrosion of S135 drill pipe material on its fatigue life as well as the influencing mechanism was obtained. Results The surface of the corroded sample had many pits and the depth of corrosion pits was in range of 0. 4~0. 7 mm. The fatigue strength of normal samples was 553 MPa, and the fatigue fracture surface had a single crack source, while the fatigue strength of pre-corroded samples was 409 MPa, and the fatigue fracture surface had several crack sources. The fatigue corrosion cracking sensitivity index of S135 drill pipe material was 26%. Conclusion The sample surface was pitted seriously after corrosion in high-temperature and pressure environ-ment of organic salt drilling fluid. The existence of stress concentration at the bottom of corrosion pits led to formation of crack sources, and the simultaneous growth of multiple crack sources accelerated crack propagation and finally reduced the fatigue strength of S135 drill pipe steel.