Hello Fellow Stressers!!

We have 3 sets of coke drums (2 coke drums per set). The coking time for each set is 15 hrs & decoking time is 2 hrs.

Please correct if my understanding of the coking & decoking process is correct:

1) Coking & Decoking ----> Line is pressurized & hot (Total 17 hrs)

2) Calculation of thermal/pressure cycles for 25 years:

First Case:

1 year = 365 x 24 = 8760 hrs
25 years = 219000 hrs

No. of Cycles = 219000/17 =12882 cycles

Second Case:

Set 1 Coke Drum is coking & decoking for 17 hrs then stop

Set 2 Coke Drum is coking & Decoking after 17 hrs (after Set 1 stop Decoking)

Set 3 Coke Drum is coking & Decoking after 34 hrs (after Set 2 stop Decoking)

Then cycle repeats:

In this case, the line is hot & pressurized for 17 hrs then cold/non pressurized for 34 hrs, therefore 1 cycle = 51 hrs

Cycle for 25 years = 219000/51 =4294 cycles which is less than 7000 cycles.

Please share your experience for this coking/decoking fatigue analysis. Are you considering both temperature/pressure is cycling or thermal alone. Normally, the expansion stress already considers 7000 cycles by default but this is for cyclic temperature only.

Your opinion is highly appreciated.

Just correct any wrong statement I've made.

Warm Regards,