Abstract: The Φ9 800 mm large-scale coke drum of a refinery appeared corrosion after commission. The corrosion was mainly shown as pitting corrosion of cone section inner wall and cracks in the girth weld. Through sampling and analysis of the corrosion area, and combining with the characteristics of production process, it was considered that the causes of pitting included: Under the high temperature, the high temperature resistance of coke tower was decreased. Under the action of alternating load and impact load, hot-cold fatigue and creep cracking were occurred on the parent material. The etch pits were formed while the part of the cracks cross was spalled. Also, the single-side feeding of cone section and short coking cycle accelerated the formation of the pitting. The main cause of cracks in girth weld was thermal mechanical fatigue which caused by an 18 hour coking cycle. The protection measures were put forward for corrosion reasons from the aspects of process operation and material upgrading etc. The measures included upgrading the material of the cone section, prolonging the coking period and steam blowing time, increasing final preheating temperature of coke drum and changing the feed mode, etc. After the implementation of above measures, the corrosion of the coke drum was obviously alleviated.