Hello,

Given a vertical vessel do be steamed out at 300°F. The overhead vapor piping will also be steamed out together with the vessel.

Based on your experience,
Will it be necessary to consider a case where in the vessel is hot at 300°F, while the overhead piping is at 70°F (ambient) ?

The vessel will expand first followed by the piping because of the fact that steam will hit the vessel first. Based on your experience, is the difference in the initial time of exposure to steam significant in this particular case ? The steamout nozzle & the vapor outlet nozzle is about 113 ft apart.

Thanks,

As a general rule it would be prudent to consider a transient case of vessel hot and pipe cold. You might argue for higher than normal nozzle loads if needed, since pressure (and maybe temperature) are likely to be much be less than during operation.

Actually one other (real world) transient case to consider would be: the pipe would be 300 deg at one end (the upper nozzzle) and 70 at the other end (the downstream nozzle or vent.)

The tank, at this intermediate point, probably would not be completely heated up unless you'd been venting the steam continuously for a while. Depends whether the outlet (condensate of the cooled steam) was dumped out of some bottom drain, or out up through the top vent.

How thick walled is the tank? How much mass of steel in the walls and head?

Thanks Moverz & Robert, I got your idea.
As a follow-up question, how do you deal with these thermal transient loads ?
For nozzles, will you have an increased allowable ? (by how much?)
For supports, do you transmit these to Structural as a separate load ?
Can you also give me an idea how long is this transient load ?

Thanks,

You should tabulate normal operating cases and environmental loads and clearly identify steam-out or other transient cases. You need to highlight the background conditions for these, e.g., higher temp, no pressure, duration = x hours. That should allow a sensible judgement to be made.

Allowable loads on vessel nozzles are specific to either the engineering concern or the owner / operator, so there are no Code values or recognised increased values for short term conditions that I'm aware of. It's down to negotiation with vessels and civil engineers. Stress engineers have to be diplomats sometimes .... Aim for a 50 to 100% increase in normal loads.

Duration of the load due to differing vessel / pipe temperatures will as Mr Cooke has pointed out, depend on many factors including the heat capacity (mass, heat conduction etc.) of the vessel and piping. Your process engineers may be able to help.

Moverz,

Thank you very much for your inputs.