ASME Sec VIII Dic 2 Table 4.4.1

[PVLead]

If a vessel has a Design Temperature of 850°F for internal pressure and 350°F for external pressure, does Table 4.4.1 of Div 2 prohibit the use of low alloy material as material of construction for this pressure vessel? The material in consideration has allowable stresses up to 1000°F in Section II Part D.

 

[TGS4]

Do you have compressive stresses when the temperature is greater than 800°F?

 

[PVLead]

There will be on the leeward side doing the wind analysis. Also in seismic analysis. These conditions never govern, always governing is internal pressure at design temperature.

 

[TGS4]

Are the stresses actually compressive, or are the tensile stresses lower?

If the stresses are actually compressive, then the prohibition stands. The allowable stresses listed in Table 5/5A are allowable tensile stresses. In compressive stresses, the failure mode is buckling. Above the temperature listed in Table 4.4.1, the failure mode becomes creep buckling - which is something that the allowable tensile and compressive stresses do not consider.

You cannot make the determination of whether creep buckling governs unless you actually perform a creep buckling analysis - the calculations provided in Part 4.4 do not consider that failure mode. Therefore, you are unable to make the statement "These conditions never govern...".

 

[PVLead]

Then the path forward is to go to Part 5 Design by Analysis which allows the material in question up to 900°F.

 

[TGS4]

Exactly what material are you dealing with?

You didn't answer my question...