慢应变速率作用下P110管材的环境开裂行为及防护措施

Environmental Cracking Behavior and Protection Measures of P110 Pipe under Slow Strain Rate

为有效降低管材P110在含硫油气井服役工况中存在力学性能不确定性以及应力腐蚀开裂的风险,采用慢应变速率拉伸试验(SSRT)方法,实验研究表面电镀Ni-W前后套管钢P110在NACE TM 0177标准A溶液、油田模拟地层水2种环境中的应力腐蚀行为特性,分析测试了管材强度、塑性以及应变能的变化规律。结果表明:慢速率应变拉伸动载条件下P110套管钢在含H_(2)S液相腐蚀介质中的环境开裂敏感性及损伤行为显著,强度及变形能力均低于室温拉伸实验且发生脆性断裂;表面电镀Ni-W合金并进行热处理后,可有效抑制P110套管钢的强度损伤,屈服强度降低幅度仅为1.00%~2.25%,断后延伸率、应变能降低幅度显著减小,且断裂方式恢复为韧性断裂。建议管材服役于含硫且承受高水平外载荷的油气井工况时,适当提升安全系数或降低管柱承受载荷大小,同时表面采用Ni-W合金镀层防护措施,综合降低管材环境开裂敏感性及其脆性断裂的风险。

P110 pipe has uncertain mechanical properties and the risk of stress corrosion cracking when used in oil-gas well containing sulfur.For solving this problem,slow strain rate tensile(SSRT)test was used to research the environmental cracking behavior of P110 pipe with and without Ni-W coating in the A solution specified in NACE TM 0177 and a simulated oilfield formation water,and the change laws of the strength,plasticity and strain energy of the pipe was analyzed and tested.Results showed that P110 pipe had significant environmental cracking sensitivity and damage behavior under dynamic load of slow strain tensile in environment containing liquid corrosion medium of H_(2)S,its strength and deformation properties were both lower than those obtained in the standard tensile test at room temperature,and a brittle fracture occurred.After electroplating Ni-W alloy on the surface and a heat treatment,the strength damage could be effectively restrained,and the yield strength decreased only by 1.00%~2.25%.Meanwhile,the descent of elongation and strain energy decreased significantly,and the fracture mode reverted to ductile fracture.Hence,it was recommended that when the pipe was used in oil and gas wells containing sulfur under a high level of external load,the safety coefficient should be appropriately increased or the load on the pipe string should be reduced.At the same time,the surface of pipe should be protected by Ni-W alloy coating in order to reduce the environmental cracking sensitivity and the risk of brittle fracture of the pipe comprehensively.