B16.5 Flange Pressure Rating
B16.5 Flange Pressure Rating
(OP)
Hi,
I have two questions regarding B16.5 flange rating
1. If, for example, at 950F the maximum flange rating is 35psi, does it mean that piping is accepatble at 35psi? What about the margin for bending moment on flange due to piping?
If piping is at a pressure near to pressure rating of flange, the flanges would fail at very small moment as equivalent pressure is already equal to pressure rating
2. I have to rerate a line at 950F which was previoulsy at 800F. It was built in 1971. The pressure rating for 150# A105 flange in B16.5 1966 is 55 psi, in 1973 it is 40psi and in all later codes it is 35psi. Which rating should I use for rerate?
In my opinion, the rating was reduced based on experience and more insight in creep at elevated temperature and new values should be used. Please let me know your opinion.
Thanks
I have two questions regarding B16.5 flange rating
1. If, for example, at 950F the maximum flange rating is 35psi, does it mean that piping is accepatble at 35psi? What about the margin for bending moment on flange due to piping?
If piping is at a pressure near to pressure rating of flange, the flanges would fail at very small moment as equivalent pressure is already equal to pressure rating
2. I have to rerate a line at 950F which was previoulsy at 800F. It was built in 1971. The pressure rating for 150# A105 flange in B16.5 1966 is 55 psi, in 1973 it is 40psi and in all later codes it is 35psi. Which rating should I use for rerate?
In my opinion, the rating was reduced based on experience and more insight in creep at elevated temperature and new values should be used. Please let me know your opinion.
Thanks





RE: B16.5 Flange Pressure Rating
The CL150 A105 flange would be marginal at 800 deg F.
Service at 950 deg F would be a long term problem for CL150 A105, and I would prefer to use a welded joint at 950 deg F. as well as use an upgrade of material for the piping.
What is the fluid? What is the flange size? Is the 950 deg F. constant, or an excursion from much lower temperature?
RE: B16.5 Flange Pressure Rating
Consider converting your forces and/or moments at the flange into an equivalent internal pressure for use with SecVII method or B16.5 tables. See the "Kellogg equation."
RE: B16.5 Flange Pressure Rating
RE: B16.5 Flange Pressure Rating
RE: B16.5 Flange Pressure Rating
Check with your primary piping code (B31.x). The way I read B31.3-2008, the Div2 method is not acceptable for B31.3 piping.
RE: B16.5 Flange Pressure Rating
The 950F is not excursion but constant temperature and fluid is steam. The pipe sizes are 10" to 4".
I still have confusion over "pressure rating" to be same as line design pressure. Suppose pressure rating for flange is 260psi. Is it acceptable for a line with design pressure 260psi? If we convert bending moment and axial force on flanges into pressure and add it to design pressure to calculate equivalent pressure as reccommended by experienced people such as from COADE, the flange will fail at very small loading.
What margin we should have between flange rating pressure and design pressure?
RE: B16.5 Flange Pressure Rating
I guess it looks like that in the Code ... but I don't believe it's intended that way. Much work went into the new method for flange design in Div. 2, and I think that B31.3 is currently out of step.
Either way, it's ultimately the owner's responsibility to allow or not, the use of Div 2 rules.
RE: B16.5 Flange Pressure Rating
RE: B16.5 Flange Pressure Rating
Stanweld is correct....your A105 carbon steel simply cannot be used or "rerated" at 950F. It will fail...
Regardless of the code, standard or rule set selected, a process known as "graphitization" occurs when carbon steel is exposed to temperatures above 800F for long periods of time.
http://www.hghouston.com/x/37_carbon.html
h
ht
This phenomena is the reason why alloy steel pipe was developed !
Tell your MBA boss that the existing system will have to be ripped out and replaced with one that meets the current piping codes and material requirements therein. (he will not be happy)
-MJC
RE: B16.5 Flange Pressure Rating
we now use this .