B16.5 Flange Surpasses App. 2 1

[loilfan]

Hello everyone,

Has anyone checked a B16.5 RFWN flange against VIII-1 App. 2 and had it pass at a pressure much higher than what B16.5 permits?

We have an NPS 6, Sch 80, A105, RFWN with A193 B7 bolts and a gasket with m=3 and y=9,000. Per B16.5, this is rated for up to 285 psig. Using App. 2, we can get it to pass at ~570 psig!!

It is well known that many B16.5 flanges fail the App. 2 formulas. We were expecting this to fail or marginally pass, not double the pressure rating. We have combed over the inputs and calculations but don't see any mistakes. Just curious if this is something abnormal, but acceptable. Or if we are missing something.

Thanks,
loilfan

 

[SnTMan]

I doubt I've seen one make by such a large margin, but really, I don't run 'em that often. You don't give enough data for anyone to check it...

Regards,

Mike

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

 

[MJCronin]

Hasn't this been discussed a couple of times on this forum ???

MJCronin
Sr. Process Engineer

 

[SnTMan]

Usually, the discussion is about them failing under Apx 2.

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

 

[loilfan]

SnTMan, agreed, I couldn't find any discussion about people passing B16.5 flanges by such a margin in App. 2, just discussions about failing them.

I used a standard A105 B16.5 150# RFWN with the additional info:
Bore 5.761" for Sch 80
Gasket OD 8.25"
Gasket ID 7.1875"
Raised face 0.06"
Hub thickness h=0.8054"
Length e=3.44"
CA=0"
Bolts 8 - A193 B7 3/4" UNC
m=3
y=9,000

This is a B31.3 application, so B31.3 allowables were used. Sh, St, and Sr were all low enough to stay below the allowables.

This passed at 500 psig at 100F. We used Codeware COMPRESS to do the calculations.

 

[SnTMan]

loilfan, Codecalc is giving me over 600 psi @ 100 F for this flange.

Regards,

Mike

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

 

[loilfan]

Thanks SnTMan. The result is still quite surprising to me, but it was a good exercise! Did your calculations use the Bolt spacing factor Bsc?

 

[SnTMan]

Yes, 1.206

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