Coke drums are large pressure equipment critical to the delayed coking unit (DCU) of refineries, which are used for the carbonization reaction involving dehydrogenation, rearrangement and polymerization. Due to the complexity of the internal process medium, the variability of structure and severe operation loads, many potential damage mechanisms may occur in the in-service coke drums. Failures such as corrosion, bulging and local thinning of the drum body; cracking at the connection between outlet nozzle and drum body and the fillet weld in skirt-to-conical head joints have been frequently found. Therefore, it is very important for a pressure vessel inspector to identify the exact potential damage mechanisms at a specific place of the coke drum. In this article, typical damage mechanisms of coke drum in delayed coking unit are identified according to the component content of internal process medium, the construction materials of the coke drums, and the structure features of the vessel. The main characterizations, the crucial influencing factors, and the control measures are put forward as well. Based on some inspection examples of coke drums, the causes of typical failures and the corresponding inspection and detection methods are given to provide reference for pressure vessel inspectors and periodic inspection of coke drums.

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