Introduction to Actual Field Repair for Skirt Attachment Portion in Coke Drum

Cracks on skirt attachment welds in coke drum fabricated in 1979 installed in a coker plant in Japan were completely repaired by the team of authors in 2016. Coke drums undergo cyclic operations typically in the temperature range from ambient temperature to about 500°C (930°F). Consequently, repetitive large thermal stress which leads to cracks is developed in skirt attachment portion of coke drum. Usually, the existence of serious cracks that need to be repaired extensively is recognized by the regular inspections such as plant turnarounds, whereas the overall schedule of turnarounds from shutdown to start-up is planned carefully in advance with consideration in terms of production loss as well. Accordingly, time constraint becomes a critical problem to consider when an appropriate countermeasure is expected. Although the authors have faced this kind of problem due to serious cracks detected at turnaround, weld repair for entire circumferential seam of skirt attachment and post weld heat treatment for the repaired area have completed satisfactorily. This paper summarizes the actual repair and inspection methods including the work flow from the planning stage in order to accomplish the repair work within the limited turnaround period and achieve the expected quality for further use.