Analysis of Corrosion Failure of Weld Seam on Furnace Tube of Ethylene Cracking Apparatus

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.