Analysis of Corrosion Failure of Weld Seam on Furnace Tube of Ethylene Cracking Apparatus
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摘要: 针对发生失效的乙烯裂解装置炉管焊缝，采用材料化学成分分析、宏观形貌观察、金相检查、扫描电镜和能谱分析等手段进行了失效分析，同时测量了原料油的终馏点，模拟了含焊接缺陷的炉管内的流场。结果表明：焊缝腐蚀区存在大量硫及低熔点共晶物；失效炉管段的介质温度处于加氢尾油的终馏点附近；活性硫在镍基焊缝偏聚，镍与硫形成的低熔点共晶物在高温下熔化，并被介质冲走，导致炉管快速腐蚀。Abstract: An ethylene cracking furnace tube weld seam failed because of corrosion.Chemical composition analysis,macro morphology observation,metallographic inspection,scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to analyze the failure reasons.The final distillation temperature of raw material oil was measured,and simulation of fluid flow in the tube containing welding flaws was carried out.The results reveal that there was a large amount of sulfur and eutectic compounds with low melting point in the corrosion area of weld seam.The temperature of medium in the failed furnace tube was around final distillation temperature of heavy vacuum gas oil (HVGO).Sulfur was enriched near the nickel based weld seam.Eutectic compounds with low melting point forming in the reaction of nickel and sulfur were washed away by the medium,which resulted in fast corrosion of furnace tube.
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