ANSI Flange Class LPG Storage Bullet

[YYCgasman]

I have looked at a few LPG storage Bullets in Alberta and notice that while most all of them have an MAWP of 250psig (or less), They almost all have ANSI 300 Flanges on the nozzles (I say almost all, but in reality I can't find one that doesn't have ANSI 300 flanges). Looking site to site, across multiple clients, I see some spec break at the vessel and drop down to ANSI 150, others keep with the higher pipe class.

Can anyone fill me in on why the nozzle flanges have a higher design rating than the vessel MAWP? Why wouldn't ANSI 150 flanges work?

Thanks in advance.

 

[TGS4]

Probably due to nozzle loads.

 

[SnTMan]

Or client / company / industry standards.

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

 

[Ready2go]

The only nozzles that require 300# ANSI are the nozzles used for multi-port pressure relief valves. Maufacturers only supply 3" 300# or 4" 300#
Other connections will be for specific instruments such as liquid pumps or etc
Manways will always use 150# c/w blind
Hope that helps

 

[georgeverghese]

Probably is related to the worst case LPG vapor pressure at the highest summertime temperature at the location. For example, assuming worst case composition is pure propane, and summer temp is say 50degC max daily average (could be higher in the Middle East), then vapor pressure would be 17.2bar abs = 16.2barg.
Keeping a 10% margin to get to MAWP = 1.1 x 16.2 = 17.8barg = 258psig, which is just within the limits for 150lb. If this were to be in the Middle East, you'd clearly be in ANSI 300lb territory.
In some company standards, ANSI 300lb for LPG may be stipulated regardless of location.

 

[mk3223]

IMO, for the pressure vessel to store the hazardous material, the 300# nozzle flanges are tightened with higher bolt torque to prevent the process leaking. It can be the Client preference.