材料期刊网

目的：研究有机涂层在天然气井高温、高压环境下的失效特征和失效原因,为天然气井井筒有机涂层应用提供建议。方法模拟含CO2,H2 S等介质的气井井下环境,通过9轮次、1914 h的长周期浸泡试验,对比测试某种有机涂层试样的厚度、冲击韧性等物理、机械性能参数,分析涂层宏、微观形貌变化。结果经过反复升、降压的苛刻室内浸泡实验后,有机涂层逐步老化。耐磨值由最初的3.28 L/μm下降到2 L/μm左右；硬度值由最初的125下降到95左右；冲击韧性值由最初的37.6 J下降到浸泡890 h时的23.5 J左右,之后趋于平稳。1914 h后,涂层与碳钢基体界面结合性能变差,表面出现明显的局部腐蚀坑点。结论室内涂层试验与气井油管涂层现场生产中发生的失效特征类似,存在失重、减薄—鼓泡—膜下腐蚀、脱落的失效过程。为避免油管内涂层失效,提高防腐效果,建议：在油管生产加工过程中控制固化度,避免因固化度不足导致涂层缺陷；在工程作业中应避免钢丝作业、快速泄压等对涂层的潜在损伤；定期进行缓蚀剂加注,减轻腐蚀。

Objective To conduct failure analysis of organic coating under high temperature, high pressure condition of natural gas well, so as to provide suggestions for the selection of the organic coating used in the natural gas well pipes. Methods In this paper, the downhole condition of natural gas well containing media such as CO2 and H2 S was simulated and the long-term immer-sion experiment of 9 rounds lasting 1914 h was conducted to compare and test the thickness, impact toughness and other mechanic parameters of organic coatings. Macroscopic and microcosmic changes of immersion surface were observed and analyzed. Results Organic coatings aged slowly after repeated pressure increasing and decompression in the rigorous indoor test. The wear resistant value decreased from the initial 3. 28 L/μm down to around 2 L/μm. The hardness value decreased from the initial 125 to about 95. The impact toughness dropped from the initial 37. 6 J to about 23. 5 J at 890 hours of immersion, then tended to be stable. Af-ter 1914 hours, the connect property between coating and carbon steel matrix turned worse, and obvious local pitting corrosion was found on the coating surface. Conclusion Failure characters which occurred in the indoor coating test were similar with those in the field production of pipe coating in gas well field. The failure process was weight loss, less thickness—blister—corrosion under pol-ymer layer, and then peeling off. In order to avoid the failure of internal coating of oil pipe and to improve the corrosion protection effect, it is recommended to control the degree of cure in oil production and processing process so as to reduce the coating defects caused by low degree of cure, avoid potential damage of coating which is due to wire operation and rapid pressure releasing in engi-neering operation, and inject corrosion inhibitor regularly to reduce corrosion.