ASME Section VIII Div. 2 - CS/Low Alloy Material use for design temperature over 800 deg. F

[rambalu80]

I am trying to design a vertical pressure vessel with a design pressure of 2500 psi @ a design temperature of 810 deg. F. The specified material of construction is 2.25 Cr - 1 Mo and for my design I'm using SA-336-F22 Cl.3 forged shell courses & SA-387 Gr.22 Cl. 2 hemi heads.

Per ASME Sec. II, Part D, Table 5A, SA-336-F22 Cl.3 is good for temperatures up to 1200 deg. F, but per ASME Sec. VIII Div. 2,table 4.4.1, the maximum temperature for Compressive Stress rules is 800 deg. F for Carbon and Low Alloy Steels that fall under Table 3-A.1 and all of my pressure boundary materials including SA-336-F22 Cl.3 fall under this table. Moreover, since the shell will be in compression, I get a warning on my design software output that the design temperature is greater than the maximum of 800 deg. F.

Even though Section II Pard D has allowables for higher temperatures, based on Sec. VIII Div. 2, Table 4.4.1, it appears that it would be impossible to fabricate a CS or Low Alloy or even High Alloy Div. 2 pressure vessel with a design temperature over 800 deg. F, but I am confused because I am of several Low Alloy vessels that have been fabricated per Div. 2 with design temperatures greater than 800 deg. F that are currently in operation.

I am unable to locate any related Interpretations or Code Cases that would allow for the higher design temperatures and would truly appreciate if someone could please shed some light on this or guide me in the right direction?

Thanks in advance.

 

[TGS4]

First question is whether or not you will indeed have compressive stresses at the design temperature? Typically, vacuum conditions will occur at lower temperatures.

A little bit of background: beyond 800°F, the allowable stresses are generally based on creep properties. However, the Code does not have creep-buckling rules (yet). Therefore, the buckling rules (i.e. compressive stress rules) are based on time-independent properties.

You are allowed to have different coincident temperatures with different pressures (internal and external pressures).

 

[rambalu80]

TGS4, thank you for the response.

The vessel is designed for FV @ 350 deg. F and the material falls within the CS-2 chart for external pressure.