How often does industry replace coke drums?

[calvin gao]

How often does industry replace coke drums? Normally how many cycles do you put on a coke drum before considering replacing it? When each shutdown requires extensive drum repairs that outweigh the economics of replacing drums? I understand it depends a lot on operational severity etc. but is there a rule of thumb value? Is 7000 cycles a good number?

[evan]

7000 cycles is a typical number before the first crack IF, big IF…you do everything right. Most sites do not. So experience varies from cracks after 3 years to barely any after 30+ years. Tons of factors at play here….material, fabrication, operator/process, etc. Also coke drums can be repaired indefinitely for a price of course with automated, engineered weld overlay. Some operators will replace drums after 15~ years while others are still going strong after 30-40 years with repairs….it is an engineering desicison and a economic one. No simple answer…but 7000 cycles is a good rule of thumb to start to expect cracking.

[evan]

7000 cycles is a typical number before the first crack IF, big IF…you do everything right. Most sites do not. So experience varies from cracks after 3 years to barely any after 30+ years. Tons of factors at play here….material, fabrication, operator/process, etc. Also coke drums can be repaired indefinitely for a price of course with automated, engineered weld overlay. Some operators will replace drums after 15~ years while others are still going strong after 30-40 years with repairs….it is an engineering desicison and a economic one. No simple answer…but 7000 cycles is a good rule of thumb to start to expect cracking.

[calvin gao]

Thanks Evan for your perspective. We should conduct a study of extensive repair vs replace the drum every so often. The labour cost here in Fort Mcmurray is so high and the production impact is high for upgraders too. It will be interesting to know what the study will tell us.

[Mike Kimbrell]

Coke drums will last as long as you work on them. The amount of work that they require increases with time. If you are trying to prevent a through wall crack while the drum is in service, the amount of inspection and repair increases dramatically as the drum age.

For coke drums making shot coke or bonded shot coke, the number of cycles to the first through wall crack has ranged from a low of about 2000 cycles to a high of 5000 cycles. Normally, the first through wall crack occurs when the drums have accumulated approximately 70% of the maximum number of cycles for the material. Drums in shot coke service will normally be replaced by about 8000 cycles. Replacing the damaged material or performing weld overlay will change the number of cycles the drum has left before it is economic to replace.

Cokers producing sponge coke normally have lower peak stresses during the cycle so drums on those units normally experience between 5000 and 7000 cycles before the first through wall crack with a maximum of approximately 10,000 cycles before the drum is replaced.

In the late stage of coke drum life, there can be a large number of cracks that have to be repaired before the drum or drum section is replace. The number of cracks that occur is exponential with time, so even a slight delay in doing the repairs or replacement can result in a lot of through wall cracks. Mostly, these cracks are identified during the water quench phase, still some are not identified until the drum is in the coking phase and there is a release of hydrocarbons that has caught fire in some of those instances.

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