Raised Face Flange nd Flate fFace Valve 4

Flat Face (FF) - The Flat Face is primarily used on Cast Iron flanges. With this face the whole contact face of the flange is machined flat.

Raised Face (RF) - The Raised Face is most common of all flange faces. The flange has a raised area machined on the flange face equal to the contact area of a gasket.

Flat face flanges are never to be bolted to a raised face flange. If you need to bolt a Forged steel flange to cast iron then you must call for the forged steel flange to be machined off to a flat face.

For more information on flanges, flange faces, gaskets and bolting see
pipingdesigner

Piping designer,
Please clarify, If macnining of the raiced face will enable him bolt FF to RF what is wrong with using a spacer same material as the RF flange as he suggested?
I feel if the sapacer can be machined to fit well it is ok.
If this violates any pining code please let us know.
Thanks

Abba.

On this specific subject, Gasprocess should check out this site.


He and others should also listen to what Piping Designer has to say.

PennPiper

abba7114:

I'm frankly very surprised. As an ME you should know better than to hope that you can obtain the required facing finish on a shim or spacer that you have suggested for a raised face flange. As a Chem E who has the mechanical hands-on experience and the lathe abilities (still!) I don't think any engineer can machine the washer you're proposing (or defending) to the true thickness (1/16") face finish that will match the sealing and torque requirements of the flanged joint - and do it economically. Besides that, the proposal is just plain foolish and hazardous. I see no way that you can ensure that the washer face will line up true with the raised face to ensure that the compression forces on each flange will be evenly distributed.

The advice that pipingdesigner and pennpiper are giving is not only sound and logical - it's the safest manner to carry out a necessary procedure that comes up mainly when flanging up cast iron equipment to carbon steel piping. Otherwise, it should be avoided.

This subject has come up many times on the Forums (even with FRP & GRP pipe flanges) - and the logical answer is always the same.

There is another reason the spacer won't work. Simply sandwiching a spacer between the flat flange face and the gasket will leave a leak path between the flange and spacer. The best course is difinately to machine off the rased face. With that said. We run into this regularly in our refinery. Equipment manufacturers regulary make oil line connections as machined flat surfaces directly on the bearing housing or casing of a machine. Our piping is almost always raised face to meet our piping spec. This is also commonly how skid mounted systems come from the manufacturer. We use Garlock rings as gaskets in this situation. But since I am referring to lube oil at perhaps 20 psi, we have not had any problems. I have never liked this situation.

I think if you do an "advanced search" on all forums you will get about SIX PAGES of "hits" on the keywords "raised face" -- it appears this subject is discussed quite frequently! (see e.g. earlier this year at

I have followed a few of these RF to FF threads.

How come the use of a spool piece is not more frequently recommended, if at all?

We often use spool pieces to joing different size pipes (rather than a reducer) and different ANSI rated pipes (900# to 300#).

I don't see why a spool piece with FF on one end and RF on the other won't work?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

Ashereng's spool piece is a good suggestion, especially for new construction, but could be expensive and difficult for an existing installation. There might not be enough room without extensive piping mods. Another issue we often run into is the face-to-face dimension of new valves compared to older valves, which requires piping changes regardless of facings.

A good solution to the existing raised face flanges is to contact a company such as In-Place Machining, Inc. Look at A company such as this can machine the flange faces without removing any piping.

Larry

The question I have is what is the material of the Class 125 FF valves?

The assumption is that they are cast iron but since class 150 RF flanged valves were the intent, they wouldn't have been cast iron, so how bad did the valve order get botched?

If the valves a carbon steel, just use a suitable ring-cut sheet gasket, bolt it up and forget the spacer.

My 2¢

NozzleTwister
Houston, Texas

NozzleTwister has a good point. Look at the Goulds pump page suggested by pennpiper for a good explanation. The flange facing itself is not a problem, it's the cast iron FF to steel RF bolting that is an issue. You can bolt steel FF flanges to steel RF flanges.

Larry

Montemayor,
Sorry for not giving it much thought, I have never encountred such a problem practically, I was only considering the low pressure service.
Thanks for pointing it out, I will quickly add that you are too hash in your response.
Abba

well, one reason the washer/spacer is a bad idea is maintaining the stupid things.

what mechanic in a hurry is not going to drop, misplace or just ignore such a device. or worse yet, not center it properly?

we are trying to get rid of cast iron flanges in our storehouse since there have been instances where they have been mis-applied and later broken due to stresses when tightening the bolting.

not sure anyone has addressed if these valves are actually cast iron or not, but i am with Montemayor on this one. it is a bad practice. and bad practices lead to bad games.

with regards to harshness, i too am beginning to lose patience with bad ideas. everyone seems to think that having a special procedure for every installation is something that will be remembered down the road.

well, we can do thus and so if we only torque this combination to some number of pound feet or use special low strength bolts (there are some special ones for cast iron, btw) and we should be okay.

well, when Bubba comes along to tighten a flange and you ask him how much torque he is going to use, he'll likely say he's going to torque it till its tight.

maintainability in many cases comes down to repeatability and not special procedures tucked away in page 38 of volume 7 of some project notes.

ben, a ChemE with a lathe and an end mill in his garage.