ASME Section 2 part D Extrapolation

[bryansonnier]

I've done the design study for standard temperature. My part has a max psi of 3000 at standard temp. using a material with an allowable stress of 24ksi. Can i extrapolate the max pressure to 300 psi using the listed allowable stress of 21.2? so 21.2/24*3000 giving a max pressure of 2650 psi. I know there is a linear relationship but is this form of extrapolation allowed or am i required to run the study at the higher temperature.

 

[SnTMan]

Allowed by who?

Regards

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[bryansonnier]

ASME code 16.34 or section 8 div 2 and allowable stresses given by section 2 part D, which now that i'm re-reading my e-mail i didn't stipulate. I think i answered my own question, though as i was looking at the pressure temperature tables for the flanges in ASME 16.5 and it looks like a direct interpolation. going from standard temperature at (-20F to 100F) the 900 class flange in WCB material has a rating of 2220 psi and at a temp of 300 it has a rating of 1960 psi which coincides directly using the allowable stress of 24ksi at standard temp and 21.2 ksi at 300F.

Calculation: 21.2/24*2220 = 1960 which matches the 1965 in the spec. The same is for the class 1500 range as well 21.2/24*3705 = 3273 which matches the 3270 in the spec.

So if my valve has a maximum operating pressure of 3000 psi at standard temp then 21.2/24*3000 = 2650 psi maximum operating pressure at 300F, where 24ksi = allowable stress at standard temp and 21.2 = allowable stress at 300F

 

[Christine74]

I'm not seeing a direct correlation between the rate that the allowable stress of a material drops off with increasing temperature in ASME Section II Part D and the rate at which the Pressure-Temperature Rating for the same material drops with temperature in ASME B16.5. In fact different flange rating categories (150#, 300#, etc.) in ASME B16.5 drop at different rates for the same material class.


-Christine