Failure Analysis on Furnace Tube of Cycle Ethane Pyrolysis Furnace

Failure causes of the cycle ethane ethane pyrolysis furnace tube with material of 35Cr45Ni high nickel-chrome austenitic heat resistance steel which cracked in the shutdown process were presented based on theory calculation and a series of test including macro and micro morphological observation, metallographic examination, chemical compositions analysis and mechanical properties test. The corresponding protective measures were also put forward. The results show that long-term working at high temperatures resulted in the formation of a thick layer of coke inside the tube surface and the decrease of strength, plasticity and toughness of the furnace tube. Large difference of thermal expansion coefficient between the coke and the furnace tube led to the hoop stress exceeding the furnace tube strength in the shutdown process and the longitudinal cracking of the whole furnace tube.