Max. Working Temp. (MWT)

[shamrock138]

Hello all, I was wondering if anyone is familiar with the terms "maximum working temperature" and "upper design temperature"? They are stated in a spec I am reviewing and I never seen those terms used before. Any help would be greatly appreciated.

 

[doct9960]

Here's my take on MWT & UDT in terms of ASME VIII-1 nomenclature...

Maximum Working Temperature = Maximum Operating Temperature

Upper Design Temperature = Design Temperature (i.e. maximum temperature used in design per UG-20(a))

Lower Design Temperature = Minimum Design Metal Temperature (MDMT) per UG-20(b)

 

[TomBarsh]

This may be related: I have seen the question asked for existing vessels, "what is highest temperature the vessel can be operated at?". For example, say a vessel was designed for 100 psi at 400° F and has an MAWP (at design temp) of 137 psi. As part of a process redesign, the owner might want to operate with same design pressure but at a higher temperature. The materials will have lower allowable stresses at the higher temperature; the task is to find the highest possible temperature for each component based on the design pressure. In some cases this is a simple exercise, other times it is not so simple.

Or perhaps you were given several sets of design pressures and temperatures for the new vessel? In such a case the design pressure would likely be lower with each increase in temperature. The highest temperature would be the "maximum working temperature" of the sets.

 

[SnTMan]

I would agree with both opinions and add that when only carbon steel materials are involved it may be possible to up the design temperature without reducing the allowable stresses as these do not begin to fall off till about 450 - 500 deg F, dependng on the exact product. If stainless or non-ferrous materials are involved a temperature uprate may not be possible, as many of these fall off from ambient up.

Regards,

Mike

 

[vesselfab]

there are really a lot of chances on everyone guessing incorrectly

when in doubt, ask the writer of the spec.

 

[SnTMan]

Can't argue w/ that!