Design temperature of pressure vessels

[flob]

Hello everybody,

I have same problems to define the "right" design temperature for a new pressure vessel and i need help.
Operating temperature for this equipement is -190° C and the material is stainless steel, so i calculated this vessel with a design temperature at 20°C (because of test).
The ambient temperature of the plant is 50° and my customer says that is the design temperature because during start-up and shutdown cycle of pressure vessel, we have to take into account the couple ambient temp-design pressure.
What do you think about this? Somebody has already done this kind of calculations?
Thanks for your help.

 

[JoeTank]

If you are using the ASME VIII Code, the Design Temperature is normally taken as the highest temperature of operation with due consideration to start-up and shutdown events. This is used to set the allowable stresses for design. The Minimum Design Metal Temp (MDMT) is used to determine the toughness requirements of the materials. The hydrotest temps are accounted for in the Code in the process of setting the test pressures.

Joe Tank

 

[gr2vessels]

Hi flob,
The design temperature you mentioned makes no difference for the mechanical design, the allowable stresses will remain the same for 20 or 50 deg C, so you may extend the design condition to 50 deg C. However, you have not mentioned anything of the process fluid, where the 20 or 50 deg C might make difference (any chlorides around?).

Regards,
gr2vessels

 

[metengr]

Operating temperature for this equipment is -190° C and the material is stainless steel, so i calculated this vessel with a design temperature at 20°C (because of test).

Please review ASME Boiler and Pressure Vessel Code, Section VIII, Div 1 UG-20. The minimum design metal temperature (MDMT) is all you need to be concerned with, not the maximum because the maximum design temperature is not under operation of the vessel.

 

[flob]

Thanks for your advices,
The fluid is a liquid mixture oxygen-nitrogen , this pressure vessel works into a cold box and he's protected
from ambient temperature by a special insulation.
I know i can used the same allowable stress until 150° for my material(according ASME DIV.II),but i don't want to do it.The design life of this equipement is 20-25 years and maintenance every 3-4 years.
I don't think we should take into account occasionals cycles like start-up or shutdown to define design temperature for pressure vessel.

Regards,
Flob