Cause analysis of corrosion leakage in convection section of ethylene cracking furnace

Abstract

Convection tubes of an ethylene cracking furnace at a petrochemical plant had multiple leaking points along longitudinal directions after a fraction of the anticipated tube life span. To study the cause of the failure, the failed tubes were investigated with macro inspections, chemical composition analysis, metallographic microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Through analysis of the failed tube samples, we found no evidence of scaling corrosion caused by S and Cl and no significant corrosion contributed by carburisation of the inner wall. By combining cavitation characteristics observed from the leaking tube inner wall and the feed composition changed by the plant recently, we highly suspected that cavitation was the main reason causing the tube to leak. A simulation model was built to illustrate the possibility of liquid cavitation at the leaking region of the tube. After the plant controlled the heavy component in the light hydrocarbon suspected of causing the liquid cavitation, the investigated tube section did not show any similar leaking problem.