Fatigue Property Considerations for Coke Drum Girth Seams

Coke drums experience one of the most severe cyclic services of any common pressure vessel type in the process or heavy industries. While the severe loading is thermal in nature, with an inherently random and statistical aspect to it, the end results are very predictable. Namely that cracking adjacent to the girth (or circumferential) weld seams, initiating overwhelmingly from the inside surface, tends to set the economic life of the drums. The concept of calibrating loading to known cracking can be leveraged, but to do so requires meaningful fatigue initiation and crack growth data for typical coke drum welded joints. Such data is reviewed and analyzed, and property recommendations made for both the inside (with clad restoration) and outside (simple matching weld joint) including appropriate test-based fatigue strength reduction factors. Focus is given to the common coke drum material SA-387 Grade 11 Cl. 2 (1.25Cr-0.5Mo) due to the volume of data available for it, and typical coke drum welded joints. Coke drum thermal loading is reviewed to develop realistic load ranges for use with the property recommendations to validate that they are capable of giving meaningful life predictions.