| 摘要: |
| 目的 明确四川某高含硫气井井口法兰盘连接螺栓断裂失效的原因。方法 采用宏观观察、材质理化检测、断口形貌分析、微观腐蚀形貌和产物分析等方法，结合服役环境特征，对失效过程和原因进行分析。结果 螺栓材质理化指标中洛氏硬度高于35 HRC，且拉伸断后伸长率低于16%，断面收缩率低于50%，具有较高的应力腐蚀开裂敏感性；螺栓断口为脆性断口，断面上S元素质量分数高达9.67%，属于硫化物应力腐蚀开裂；螺栓腐蚀最严重部分集中在中间螺纹区，螺纹腐蚀路径向上下两侧拓展，腐蚀产物主要为Fe3O4，发生了严重的氧腐蚀。结论 螺栓在长期大气氧腐蚀和缝隙加速腐蚀的作用下，由中部至两端的螺纹逐渐被腐蚀破坏，法兰密封性能减弱，微渗漏的含硫气沿着腐蚀路径扩散聚集，叠加螺栓预紧力作用，最终导致螺栓发生硫化物应力腐蚀开裂失效。 |
| 关键词: 螺栓 H2S 硫化物应力腐蚀开裂 氧腐蚀 失效分析 |
| DOI：10.3969/j.issn.1007-3426.2024.06.015 |
| 分类号: |
| 基金项目:中国石油天然气集团有限公司攻关应用性科技专项“海相碳酸盐岩油气规模增储上产与勘探开发技术研究”子课题“复杂碳酸盐岩气藏效益上产与提高采收率技术研究”（2023ZZ16-03） |
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| Failure cause analysis of flange bolt fracture at the wellhead of a high sulfur gas well |
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YU Zhiming1, ZHANG Shibo2, YUAN Xi1, LIU Fujun3, MAO Ting1
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1.Research Institute of Natural Gas Technology, PetroChina Southwest Oil & Gasfield Company, Chengdu, Sichuan, China;2.Chengdu Tianfu New Area Huatian Xingneng Gas Co., Ltd. of Sichuan Huayou Group, Chengdu, Sichuan, China;3.Chongqing Gas District, PetroChina Southwest Oil & Gasfield Company, Chongqing, China
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| Abstract: |
| Objective Clarify the failure cause of the flange bolt fracture at the wellhead of a high sulfur gas well in Sichuan. Methods The failure process and causes were analyzed by the methods of macroscopic observation, physical and chemical testing of materials, fracture morphology analysis, microscopic corrosion morphology and corrosion product analysis, combined with the characteristics of the service environment. Results The bolt material exhibits hardness exceeding 35 HRC, elongation after tensile fracture of less than 16% and percentage reduction of area of less than 50%, indicating a high susceptibility to stress corrosion cracking. The bolt displays brittle fracture, with the fracture surface showing a high S element mass fraction of 9.67%, indicative of sulfide stress corrosion cracking. The most severely corroded areas of the bolt are concentrated in the middle thread region, with corrosion paths of the thread extending to the upper and lower sides. The main corrosion product is Fe3O4, and severe oxygen corrosion occurs. Conclusions Due to long-term atmospheric oxygen corrosion and accelerated crevice corrosion, the threads from the middle to the both ends of the bolt are progressively corroded and damaged, weakening the flange's sealing capabilities. Microleakage sulfur gas diffuses and accumulates along the corrosion paths, and the combined effect with the bolt's pre-tightening force ultimately leads to sulfide stress corrosion cracking, resulting in bolt failure. |
| Key words: bolt H2S sulfide stress corrosion cracking(SSCC) oxygen corrosion failure analysis |
