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Fatigue and Materials Deterioration




Coke Drum Fatigue and Remaining Life Analysis


Fatigue for a coke drum occurs primarily from differential thermal strains that occur during the heatup
and cool down portions of the coking cycle. Fatigue is a crack initiation and growth process caused by cyclic loading. Welds are typically weaker than plate material in fatigue because of notches and minute flaws at the weld to plate junction.

Fatigue in the skirt occurs from thermal gradients when the coke drum is hot, and from differences in temperature between the skirt and shell during heatup and cool down. Fatigue in the shell occurs during cool down as the cooling steam and water contact the shell in irregular patterns.

Local wrinkling of the shell and cladding disbonding are two additional problems related to high thermal stresses from heatup and cool down.


Skirt to Shell Weld
1. Crack growth will be estimated at the root and toe of the skirt to shell weld.
2. Eight initial cycles will be measured, with additional monitoring optional
3. Prediction of significant cracking within 3 to 6 years will be provided.
4. Recommendations will be calculated that increase the life time of the coke drum.

Shell Fatigue
1. Determination of effects of process variable on shell fatigue
2. Prediction of life time of shell with high accuracy.
3. Recommendations will be calculated that increase the life of the shell.

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