Compatibility of Flat Face vs.Raised Face flanges

[DavidCR]

In a technical paper of DIPRA they say that ASME B16.1 flat face class 125 flanges are compatible with ASME B16.5 raised face class 150 flanges if the raise is 0.06inches.

Previously, I was told that steel raised face flanges are not recomended with cast iron flat face flanges, since there is a risk of breaking the iron flange.

Does somebody know more about the subject?.
I want to use flat face cast iron flanges conected with raised face steel flanges for a fire protection system and want to know if there is an important consideration I should take on account (about the bolt torques, tipe of gaskets, etc) or if I can follow the same requirements as if I were using steel flanges).

Thanks.

 

[TBP]

What service is this in, and what is the applicable code? If it's B31.1 Power Piping Code, then the raised face on the Class 150 must be removed. I'd use a full face gasket so there's no gap for the thin & brittle Class 125 to spring into, when the flange bolts get tightened. There are other considerations for ring gaskets, like low-strength bolts with a specified maximum tensile strength. The idea being that if over-torquing occurs, the bolts will simply twist-off rather than break the cast iron flange.

I really don't like 125 CI, and my experience is that by the time you fool around getting the raised face machined off the 150 flange, and rounding up the correct grade of nuts & bolts (and ensuring that they get used), you've probably incurred pretty much the same cost as if you'd just bought the more expensive 150 mating flange to begin with. And with a pair of 150's, you're left with a MUCH stronger joint.

 

[DavidCR]

The application is water fire protection system, the standards is NFPA 24, but I´not sure if they include a specific consideration on this matter. Most fire protection valves are UL-FM and made of cast iron. Thanks for the point. I´ve been recomended to buy B16.5 flanges and ask them to be delivered with the raising face removed, but I donñt know if it is an extra cost.

 

[IVNJ]

Most carbon steel flanges (ASTM/ASME B16.5) are available with a flat face from the manufacturers - usually at the same cost of the raised face. Contact your local supply house.

 

[jcfoley]

I have seen several threads on this subject. I have seen documented approvals and I have also seen many industries that oppose this practice. In short, I have used this fit up on 100 psig Helium applications without problems with the flanges or leaks (yes helium is a real pain!). You just need to be careful to torque the studs carefully. If it works with Helium, water is no problem!

Chris Foley
Midland, TX

 

[MJCronin]

DavidCR,

Based on my experience:

- The "Pump Handbook" (Karassik et al) contains a cautionary statement about never configuring the piping system with cast iron flat-faced flanges mated with raised-face piping flanges

- Several in-house process chemical compay guidelines I have read state that pumps shall always be purchased with raised face flanges. ( They seem to agree with the point made above that FF flanges are not worth the trouble)

MJC

MJC

 

[StressGuy]

How would getting your pump supplied with raised face flanges keep the iron from cracking if the bolts are overtorqued?

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[MJCronin]

ed,

Sorry.... I should be more specific..

I purchase most of my pumps with cast steel casings and RF flange faces.

If a cast iron pump was a client or practical requirement, I would ensure that there were FF Flanges on both the pump casing and the piping.....This is as much insurance as reasonably could be expected to prevent cracked flanges.....

However, there may be some big gorrila fitter out there that could crack these also

My opinion only

MJC

 

[IVNJ]

All good replies, but I think you guys are over thinking the original question. Steel flanges are compatible to Cast Iron flanges in their bolting dimensions. Flat face steel flanges are readily available from any good manufacturer or local supply house. The variable in the make up of this joint the size, the gasket selection, and the bolts. The bolt issues have been discussed on thread929-112403. A good explaination on the gaskets can be found at

http://www.durlon.com/installtorque.htm

. The bolt torque proceedure is pretty basic stuff, but you may want to refer to a manufacturer or pipefitter for specifics.

 

[MartinSr00]

I work for a large water district. We have a few CI flanges in our system, but most are steel. Virtually all our flanges, CI and steel are purchased flat-faced. This is allowable under ANSI B16.5.

If there's a chance that your flanges will be bolted up to CI flanges, a mating steel flange should be purchased flat-faced.

For steel flanges, you can order them to ANSI B16.1 (CI) dimensions. Or, if they are 24 inches in size or less, ANSI B16.5 flanges will bolt right up. On sizes greater than 24, ANSI B16.47 governs for steel flanges, and one of the types there will bolt up to CI flanges, but they are thicker.