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Flat face and Raised face flanges.

Flat face and Raised face flanges.

Flat face and Raised face flanges.

Dear flange experts.

I´d like to know if it´s possible to mate ANSI B16.5 raised face flanges with ANSI B16.1 flat face flanges.

I have carbon steel pipes with ANSI B16.5 A105, class 150 and 300 raised face  flanges, and want to install betwen them OS&Y cast iron valves (ASTM A126 class B) with ANSI B16.1 flat face flanges (Which I suppose are the most common flanges for cast iron accesories).

So my questions would be:

1. Is it OK to mate flat face with raised face?. If not, what is the correct way to specify flat faced cast steel valve companions?

2. Is there an equivalency of ANSI B16.5 (class 150 and 300) and ANSI B16.1. flange dimensions?

Thanks a lot.

RE: Flat face and Raised face flanges.

ASME B31.1 says that when connecting 125 flat face cast iron flanges to 150 steel flanges, the raised face on the steel flange must be removed, and that a full face gasket is required. This is to keep the thin, bittle cast iron flange from being sprung into the gap caused by the raised face of the 150 flange, and/or a ring gasket. 250 CI has a raised face, and it can be bolted to a 300 steel flange without removing either, and a ring gasket can be used.

What's in your pipe, and what kind of plant is it? That'll determine what code applies. There are a great many steam systems with boiler safety valves that lift at 150 PSIG, but operate to maintain a header pressure of 125 PSIG. A huge number of these systems are just FULL of 125 CI components that, of course, don't meet code. The 150 flanges have their raised faces intact, they often use ring gaskets, and the fasteners are usually SAE Gr 5. (It's like "Can you spot all 75 mistakes in this picture?") There are some really "intersting" installations out there.

RE: Flat face and Raised face flanges.

Thanks a lot for your comment.

The application...

The case is a power plant, located in Costa Rica. We are adding some lines to an existing fire water protection system. The pipe: A53 B (NPSs from 2 to 12), exposed, the valves: OS&Y gate valves for fire protection, we are not obligated to, but we try to follow NFPA criteria. We are used to B31.1 so it influenced too.

In the purchase specification we asked for the valves (like NIBCO OS&Y gate valves, 125lbs, including companion flanges ANSI B16.5 SO-RF with gasket and accesories. So with your comment, "looks" like we made the mistake of including the RF indication with no aclaration.

Reading your lines, we will try to ask the contractor to remove de RF (or we will have to remove ourselves), and of course, you may guess that I´m wondering how critical would it be to leave it RF.

Reading the NIBCO catalog for 125lbs valves they don´t say information about the flanges. We didnt ask for a specific class of flanges, just the ANSI B16.5 mate flanges.

Any aditional comment..?

RE: Flat face and Raised face flanges.

You're into fire protection stuff, and that's not my long suit. Whatever the governing code is may (should?) reference this situation.

I don't think I know of any equipment manufacturers that stray very far away from their particular product, regarding code requirements. They usually list the various approvals they have from code bodies, and whatever standards their bit meets, but that's all. They're basically vendors, and leave it to the designer to ensure that the correct component is being selected for whatever the service is.

RE: Flat face and Raised face flanges.


The "Piping Handbook" also contains cautions about using RF steel flanges with cast iron flanges.

Usually the mistake is made with a cast iron pump face and steel piping flanges.....When the flanges are tightened, th casing cracks. I would remove the RF from the flanges......an experienced piping contractor should be able to do this.

If your boss is putting pressure on you, have him take responsibility if there are any cracks.

My opinion only....


RE: Flat face and Raised face flanges.

Good one on the "boss thing", MJC. They ALWAYS step up to "take the bullet" for some stupid cost saving thing that they insisted on :)

RE: Flat face and Raised face flanges.

I've played with this one before. NO you normally can't or shouldn't use a RF flange with a FF flange. You could if they were both steel construction, but not a with a cast iron flange. The reasons for this has been noted already, it can lead to cracking of the cast iron flange when you torque the bolts. You can machine the RF portion off a steel flange and then this connection is good IF you use a FF gasket.
 BUT if your in a pinch, and don't have time to remove the RF of the steel flange, you can make a spacer that fits around the outside of the RF section. This spacer will need holes cut for the stud-bolts and the spacer has to be the same thickness as the height of the RF section (1/16" approx.). Essentially your making a FF adaptor for a RF flange. The one I had to make was out of brass, so easy to fabricate. Hope this helps! ...Mark

RE: Flat face and Raised face flanges.

  If you are in a PINCH and the piping system is not deemed critical if failure ocurred, take TEMPORARY procedural or physical precations to not damage your equipment.  TEMPORARY means you have documented the situation and will return at a planned date to correct the situation.  If your are NOT in a pinch or the system is deemed critical, change out the one flange so they mate properly.

Regards dugal

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