天然气管道环焊缝缺陷部位的腐蚀沉淀机理

Corrosion and deposition mechanism at position of defect in circumferential weld of gas pipeline

为了深入分析天然气管道的"梗阻"现象,采用金相法和能谱仪对靖边某气田典型的有大量沉积物管道进行了焊缝和沉积物结构及成分分析.结果表明,焊缝缺陷处的腐蚀和沉淀机理为管内发生CO2腐蚀、缝隙腐蚀和H2S腐蚀,产生了氧化物、氯化物和硫化物等腐蚀产物.随着腐蚀产物的逐渐堆积,其阻隔了管子材料与腐蚀性介质,使得腐蚀速率减慢,沉积物转为以粉尘为主.沉积物堆积到一定高度时,天然气的流向改变,管道顶部的腐蚀变为冲刷腐蚀,腐蚀速率加快,管道壁厚严重减薄,危害管道的正常安全运行.

Metallographic microscope and EDS(energy dispersive spectrometer)were used to investigate the reason which caused the pipe blockage of the gas field in Jingbian.Results showthat there are CO2corrosion,H2S corrosion and crevice corrosion in the natural gas pipeline.The deposits are mainly corrosion products such as iron oxides,iron chlorides and iron sulfides at this stage.As the corrosion continues,the pipe and the fluid inside the pipe are separated by the compact corrosion products.The type of deposits transforms from corrosion products to dust as the corrosion rate drops.When the height of deposits reaches a certain value,the top of the pipe suffers from erosion corrosion because the flow direction of fluid inside the pipe changes.And the corrosion rate accelerates.The thickness of pipe is so thin that it endangers the safety operation of the pipeline.