Cyclic Plasticity Analysis Of The Coke Drum Circumferential Weld Connection Region Under Moving Axial Temperature Difference

Coke drum is the key equipment in the delayed coking process. However it is prone tobulging and cracking due to its complex temperature and pressure load，which endanger thesafe operation of the equipment. Cyclic plasticity analysis of coke drum may contribute tothe prediction of the deformation and failure and ensure the safety of the equipment.Monotonic tensile and ratcheting experiments were carried out under20℃,200℃,300℃, and400℃. The ratcheting strain of both parent material and weld were predictedby OW-II model, which predicts ratcheting strain rate well for stable segments.The transient temperature field under oil-feeding and water quenching werenumerically simulated with the help of dynamic coordinate system method, which yieldedthe axial temperature difference and its characteristic value for the simplified characteristicload to be used in the cyclic plastic analysis of coke drum.Cyclic plastic analysis was done for the coke drum cycled between oil-feeding andwater quenching with OW-II constitutive model parameters of the coke drum parentmaterial. It is founded that the bottom alignment of temperature difference ranges producesmuch ratchet strain rate. In addition, the co-existence of cyclic internal pressure wouldincrease the ratcheting strain of the structure. The ratchet boundary was determined for thetemperature gradient under oil-feeding and water quenching. It indicates that, whentemperature difference range of water quenching Hw is smaller, the ratchet boundarieswould be influenced much more by the cyclic internal pressure.According to the comparison of the ratcheting strain between the parent metal and weldunder the axial temperature difference load, ratcheting strain rate of weld area material islower than parent metal under the same loading, it causes the coke drum bulging near theweld. Cyclic plastic analysis of the coke drum circumferential weld connecting regionunder moving axial temperature difference indicates the bulging position is about10mmabove the weld. The co-existence of cyclic internal pressure would increase the ratchetingstrain of the structure. The ratcheting strain rate of structures increases with the cyclicinternal pressure range.