Coke drum design is heavily constrained by the severe thermo-mechanical loading required to pyrolyze heavy crude oil residuum. Given the susceptibility of skirt-to-vessel attachment welds to fatigue damage, most contemporary coke drums incorporate keyholes into skirt designs to relieve stress at the attachment weld. As such, multiple fatigue-prone locations—namely, the “skirt” and “vessel” sides of the attachment weld, and the keyhole itself—must be considered. Skirt design aimed at optimizing fatigue life at these three locations is not without its challenges, as keyhole sizing efforts are often constrained by inverse stress relationships between these regions of interest(e.g. stress reduction at the skirt side of the attachment weld may deprive the keyhole of fatigue resistance). A recent study proposed a linear regression model to optimize fatigue life on the skirt side of the attachment weld without the need for numerical simulations. The present study aims to extend this modeling approach to fatigue assessment of the vessel side of attachment welds and the top keyhole, to provide a more comprehensive estimate of fatigue performance. The proposed models together provide a methodology to quickly optimize skirt design, while significantly reducing the upfront computational effort involved.
