Assessment, Mitigation, Management and Extension of Coke Drum Life Through Equipment Health Monitoring Systems and On Line Inspection

The reliability of coke drums has become a central theme to many refineries worldwide as high value products are recovered from refinery residuum. The severe thermal gradients inherent in the coking process have led to ever more frequent failures from cracks in bulges, skirts and cones, which reduce productivity and jeopardize the safe and reliable operation of coke drums. An intrinsically-safe coke drum health monitoring system rated for operation in hazardous environments, consisting of high temperature strain gauges and thermocouples was installed on a coke drum at a refinery in the United States. Specific locations identified as high risk areas through a combination of engineering analyses, inspections and historical repairs were targeted for monitoring. The health monitoring system calculates the cumulative damage and damage rates at critical locations through the quantification of thermal transient gradients and measured strains, and analyzes the trends over time. Of particular interest are two high damage events recorded with the health monitoring system that closely preceded the propagation of a through wall crack, approximately one week after the events. This paper performed a post-mortem analysis of the event, and shows how the data obtained via health monitoring systems can be used for prioritizing inspections and the potential for anticipation of failures. By analyzing damage accumulation trends from specific operational practices, the impacts of process changes on the expected life of the coke drum can be assessed. Finally, a detailed review of the maintenance and inspection records, results of the on-line Non-Destructive Examination (NDE), laser mapping, and bulged severity assessment were used to prepare a detailed inspection and repair plan for a forthcoming turnaround. The damage accumulation trends captured with an Equipment Health Monitoring System (EHMS) were used to optimize operating parameters of the coke drums referred to in this paper. This together with the execution of detailed inspection plan and comprehensive repairs are allowing a safe and reliable operation of these drums.