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Recommended temperature rate during startup or shutdown

Recommended temperature rate during startup or shutdown

Recommended temperature rate during startup or shutdown

(OP)
I am in search of some reference document or method to evaluate the recommended temperature rate during startup or shutdown, for a carbon steel or low-alloy pressure vessel.

Thanks in advance,
Yann

RE: Recommended temperature rate during startup or shutdown

It all depends on the vessel (especially wall thickness and differences in wall thickness between shell and nozzles). Using high heat-up and cool-down rates can cause high secondary and peak stresses, which will exacerbate fatigue.

The best example is coke drums - they are susceptible to very low cycle fatigue because the heat-up and cool-down are severe. That's not to say that this is bad - just that you need to understand it and incorporate it into your vessel integrity management plan.

RE: Recommended temperature rate during startup or shutdown

(OP)
Thank you for your reply TGS4.
Maybe the term "rate" was not the accurate one in my question.
I will take an example : For a reactor in start-up the recommendations are: raise the temperature to 300°C at a rate of 55°C per hour. How to determine the value of 55°C without performing a fatigue analysis ? My purpose is to understand how the general recommendations for start-up are made.

RE: Recommended temperature rate during startup or shutdown

The method I recommend is to the use the simplified calculation procedure of the EU normative method specified in EN 12952-3, which was borrowed from the older german boiler code TRD 301 annex 1. The allowable ramp rate is inversely proportional to the square of teh wall thickness, once you have ascertained tha llowable fatigue damage permitted for each cycle.

"Nobody expects the Spanish Inquisition! "

RE: Recommended temperature rate during startup or shutdown

(OP)
I'm just reading Annex C3 of EN 12952-3. It looks like I was searching for.
Thank you very much davefitz for the valuable tip !

RE: Recommended temperature rate during startup or shutdown

After seeing many different recommendations across various different vessels in a number of different services, it is my firm belief that most values are withdrawn from some rand engineer's rectal cavity.

Without performing some sort of calculation, it is impossible to know the magnitude of the stresses involved with a slow vs fast thermal and pressure transient. I've done the evaluation in some - and they've been very conservative. Others have been way off and lead to premature failure...

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