Temporary "Upset" Temperature Design

[UWMech]

Fellow Members,
I have been trying to find if there is a similar rule for Section VIII-1 pressure vessels to allow temporary increases in pressure and temperature avove the design conditions as is allowed in B31.3 for process piping.

I don't know if that would be considered as "abnormal pressures" under UG-22(i), where you can use a higher maximum allowable stress value per UG-23(d). (My instinct says "No".)

I can't seem to find any special rules, but if there are some, any help would be appreciated.

I have been charged to specify an air cooler for normal temperatures around 300 deg.F, but having an PSV relief case bringing the expected temp up to around 800 deg.F. The cooler will be in Coker Blowdown Condensing service.

Thank you again.
UWMech

 

[flaka]

Hi,

Don't think there is an exemption in the code but iven if there's one, you are pushing it beyond the limit.
You are increasing your temperature (for how long?)with a factor 2?
What kind of materials are you using, and how do you verify if the material will handle the temperature? Indeed by designing the cooler at 800°F.

Only my personal suggestion/opinion.

 

[prex]

The condition you describe is not really abnormal IMO, as it appears to be part of your process and it is expected under certain conditions (it is deterministic). ASME VIII has nothing similar to the allowances for pressure and temperature variations of B31.3, so you should take this condition as part of the normal operation of the vessel as intended by UG-21.
However consider that the temperature to be taken as the design temeperature is always the average wall temperature. If your transient condition is sufficiently fast so that wall temperatures will not be substantially the same as fluid temperatures, you could calculate wall temperatures and use them as design values (but of course the AI could have something to say about).

prex

http://www.xcalcs.com

: Online tools for structural design

http://www.megamag.it

: Magnetic brakes for fun rides

http://www.levitans.com

: Air bearing pads

 

[jte]

As prex sagely pointed out, you are planning to operate at some time with a high process fluid temperature. A relief scenario is one of several reasonable operating scenarios. If you use reasonably conservative boundary conditions, a transient heat transfer analysis is not an unreasonable approach. Not typical by a long shot, but with substantial potential savings, worth investigating. Get the AI on board early, run your numbers, and see what happens. All of this is explicit in UG-20:

Maximum. Except as required in UW-2(d)(3), the maximum temperature used in design shall be not less than the mean metal temperature (through the thickness) expected under operating conditions for the part considered (see 3-2). If necessary, the metal temperature shall be determined by computation or by measurement from equipment in service under equivalent operating conditions.

jt

 

[UWMech]

Thank you all for your replies. You've confirmed my belief that there are no "easy outs" to this one. I appreciate your input. Because of people like you, this forum has become an immeasurably useful reference tool to me. Usually my questions have already been answered in one way or another.

UWMech

 

[moltenmetal]

There is one exception I can imagine: if the pressure conditions of your 2nd case render the "vessel" no longer a vessel. If it's an atmospheric steam-out condition, say, or an atmospheric burn-out condition with the vessel essentially open to the atmosphere, it's not really a design case for the vessel. The process design would need to ensure that the vessel could not be overpressured (i.e. beyond 15 psig) during this case.

 

[jte]

molten-

An interesting perspective. I can definitely see you point and might make the same argument from a plant operations point of view.

I would, however, caution the owner/user to verify (in writing) with the local jurisdiction that such a scheme is acceptable. I know based on experience with a similar issue that I would have a very difficult time selling this case to my jurisdiction though I might ultimately prevail. Different jurisdictions have different definitions of what is and is not a vessel. Generally similar to, but not exactly, as stated in the Scope part of VIII-1.

One point to consider is whether a refinery vacuum column is a code vessel? If under normal operating conditions it is under a vacuum condition, and 15 psig (or roughly -0.3 psia depending on altitude) is a physically impossible loading condition (refineries on the Gulf Coast operating under flood waters might be an exception...), then why bother stamping a vacuum column?

jt