Assessment of a coke drum for seismic stability is generally a well-documented load case, with ample examples and historical design experience. However, the long-term effects of non-uniform temperature distributions have in many cases led to a phenomenon in coke drums commonly referred to as the “banana effect”. The banana effect leads to out-of-plumb, and local weakening of the shell due to bulging, and creates a more vulnerable structure where the contributions of tilting angle and effective seismic loads vary with each stage of the coking cycle. This paper outlines one practical approach to this challenging problem, along with the derivations and analytical techniques necessary to support the resulting conclusions. The framework developed was able to compare the influences of tilting and seismic accelerations independently, even when acting simultaneously. Using this technique, the analysis was able to efficiently predict a relationship between an expected seismic load and the critical drum tilt angle, with only minor adjustments needed to account for non-linear vertical distribution of the shear force.

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