Div 2, Table 4.4.1 temperature limit for compressive stress

[jtseng123]

Dear all,
Div 2, Table 4.4.1 sets the 800 F limit for many commonly used materials for compressive stress, that means I can not use the materials that I used to use if temp is exceeding 800F unless I switch to Div 1.

The compressive stress will occur at design temperature from weight, wind, seismic or vacuum, and not always below 800F. I have a hydrocracker reactor at 2500 psig and 850 F with 2 1/4Cr-1Mo or 2 1/4Cr-1Mo-1/4V. Years ago we built many from Div 2. But due to the temp limit, forcing us to use Div 1, more expensive with thicker wall.

Questions:
Why Div. 1 has no temperature limit ?

Why can't Div 1 and Div 2 come up with the same rules on compressive stress? Metal can not tell it is Div 1 or 2. People was talking about creep or rupture stress, but apparently Div 1 has no concern to set temp limit.

Any code case or interpretation that Div 2 is allowed to be used above 800 F for my reactor ?

Thanks for any of your opinion.

 

[Geoff13]

Div 1 does have temperature limits on compression stresses. These are found in the appropriate figure in Section II Part D Subpart 3.

The materials you list are covered by Figure CS-2, and thus would be limited to 900°F for Div 1 compressive stresses.

It looks like Table 4.4.1 appeared in Div 2 in the 2007 edition, which is perhaps why you could go hotter (same temp limits as Div 1 though) years ago.

 

[TGS4]

The failure mode for compressive stresses is bucking. At and above those temperatures, you're dealing with creep buckling, which is a much more complex failure mechanism.

For thick-walled hydrotreater vessels, the minimal compressive stresses at temperature can likely be neglected using engineering judgement. But you need to be very cognizant of creep bucking nevertheless.