900# FF flanges ?

[jonesey]

We have a compressor that is fitted with 6" 900# FF flanged outlets. We are replacing some knockout drums that sit directly on the compressor outlets. On the new drums we are considering specifying 900# RF flanges for mating to the compressor. I know that you can easily bolt together 150/300# RF flanges up against FF flanges without leakage problems, you just have to be careful not to over stress the RF flange when tightening so that it doesn't bend.
Anybody have any suggestions ??

 

[aditya707]

Can you pls tell why you are using FF Flanges in such high pressure application?
Also, pls do not use RF flanges for tightening against FF flange of this high rating(900#)since this will increase the chance of leakage.

 

[hacksaw]

what pressures are you dealing with and is the equipment flange cast or forged?

 

[unclesyd]

A quick out is to use a flange facer and make the full face flange on air compressors (275 psig) a raised face. This is what we were able to do in a similar situation on some large air compressors. You should have more than have enough thickness based on the tables to remove 1/16". If not you can do a flange calculation to verify the required thickness.

I ask a manufacturers’ rep about the full face and red rubber gaskets, after checking his answer was when they increased the pressure ratings on some models coupled with experience they saw no need to change the flanges or gaskets within certain operating parameters.

 

[Scipio]

Are you talking about flanges on discharge piping or flange on the compressor cylinder itself?

 

[jonesey]

The 900# FF (flat face) flange is the discharge flange on the compressor cylinder itself. The flange is cast as part of the compressor. The joint itself has been in service for many years without leakage.

 

[hacksaw]

Common practice is to use an adapter spool to connect to the ajacent piping. Be sure to check the loads on the nozzle.

 

[unclesyd]

My reference to machining a raised face on a full face flange was correct. The problem was my memory dropped out because the machining was on the down stream flanges of spool pieces that bolt to a boss on the compressor housing. This boss is still a acting as a FF flange (900) with set-in studs. I called and checked this morning to find out the about the gaskets and flanges. All the flanges bolted to the compressor, with exception of two, are FF with most of the gaskets being a Grafoil gasket with a wire insert. The two remaining are RF and have a spacer at the bolt circle to limit travel. All of the downstream flanges have been changed to a RF.

Having eaten crow its time to try to help you resolve your problem. As mention above it can be done. I wouldn’t recommend this method though.. There are several companies that make gaskets that will seal and have means to prevent to much travel, similar to a spiral wound but not requiring the gasket seating stress required for the spiral wound gasket.
There are other methods that could be used but I can not mention them on an engineering forum.

Two companies that you might discuss your problem with are.

http://www.selcoseal.com

http://www.helicoflex.com

My reference to machining a raised face on a full face flange was correct. The problem was my memory dropped out because the machining was on the down stream flanges of spool pieces that bolt to a boss on the compressor housing. This boss is still a acting as a FF flange (900) with set-in studs. I called and checked this morning to find out the about the gaskets and flanges. All the flanges bolted to the compressor, with exception of two, are FF with most of the gaskets being a Grafoil gasket with a wire insert. The two remaining are RF and have a spacer at the bolt circle to limit travel. All of the downstream flanges have been changed to a RF.

Having eaten crow its time to try to help you resolve your problem. As mention above it can be done. I wouldn’t recommend this method though.. There are several companies that make gaskets that will seal and have means to prevent to much travel, similar to a spiral wound but not requiring the gasket seating stress required for the spiral wound gasket.
There are other methods that could be used but I can not mention them on an engineering forum.

Two companies that you might discuss your problem with are.

http://www.selcoseal.com

http://www.helicoflex.com

After you checkout their websites give them a call. I have used both with great success on very difficult sealing jobs. My reference to machining a raised face on a full face flange was correct. The problem was my memory dropped out because the machining was on the down stream flanges of spool pieces that bolt to a boss on the compressor housing. This boss is still a acting as a FF flange (900) with set-in studs. I called and checked this morning to find out the about the gaskets and flanges. All the flanges bolted to the compressor, with exception of two, are FF with most of the gaskets being a Grafoil gasket with a wire insert. The two remaining are RF with a spacer at the bolt circle to limit travel. All of the downstream flanges have been changed to a RF.

Having eaten crow its time to try to help you resolve your problem. As mention above it can be done, though I wouldn’t recommend this method though.. There are several companies that make gaskets that will seal and have means to prevent to much travel, similar to a spiral wound but not requiring the gasket seating stress required for the spiral wound gasket.
There are other methods that could be used but I can not mention them on an engineering forum.

Two companies that you might discuss your problem with are.

http://www.selcoseal.com

http://www.helicoflex.com

After you checkout their websites give them a call. I have used both with great success on very difficult sealing jobs.

 

[unclesyd]

Got all kinds of error messages. Please ingore the repeate.
This time it really wasn't the operator.

 

[Scipio]

Alright, flat face or even large female face flanges with tapped studholes are pretty much the norm in recip cylinder flanges, I've seen them operating at up to 1500#, and a number of them not even ANSI bolting patterns. In every installation I've seen (mind you, I'm limited in size up to 1800 hp machines, largest cylinder I've dealt with was about 16&quot, the compressor cylinders were either piped directly into, or had volume bottles bolted directly onto the cylinders, either way they're always installed with raised face flanges bolted against full faced cylinder flanges.

So far as I know, there's no much difference in bolting torques if you're bolting a RF to a FF flange (unless you're talking a softer material, like ductile iron or bronze). Just because you've only got one half of the RF joint, you're still looking at the same compressive area on your gasket. You're also still looking at the same bending moment around the raised face of the mating flange as if it was bolted to another raised face. I'm actually looking at a drawing right now of a sour service Worthington compressor in which volume bottles are bolted directly to the cylinder. Cylinder flange is 4"-1500# FF, bottle is 4"-1500# RF. As for gasket material, that'll depend on your service, we normally use composite non-asbestos type gaskets. Best bet is check with the compressor manufacturer for a recommended material and bolt torque.