[Rameshwar Pooniya]

[b]Is it allowed to connect FF flange with RF flange in piping design?
[/b]

Case-1
3″ firewater hydrant (End connection- 150# FF) to be installed where concern piping spec. contains RF flanges for 3″ size.

Piping Mat – CS, 150#, Design pressure 16 Bar, Design Temp. 65 Degree C.

Case-2
3″ RO plate (150#, RF) to be installed in firewater line but concern piping spec has FF flanges for 3″ size.

Piping Mat – CS, 150#, Design pressure 16 Bar, Design Temp. 65 Degree C.

If FF to RF connections are not allowed, then we have to raise a request to Client for required flanges addition in respective piping spec.

Discussion

[Anton Dooley]

Generally, no.

For many reasons, including leakage at the gasket, and damage to the flanges etc.

Solutions?

1. Get FF flanges added to your spec.

2. Go “Out of Spec” and use a FF flange.

3. Use a RF flange appropriate to the pressure rating of the FF flange, and machine off the raised face, essentially turning it into a FF flange.

All Subject to project / Client approval, of course.

[SHAY O'CONNOR]

It looks like you have a cast iron 125# flange with it being a fire line tie-in possibly. is it an existing tie-in.

It’s not recommended to mate a RF steel flange to a FF cast iron flange because it can cause it to crack etc when you torque the bolts.

Solution here if you are in a hurry or at a pinch point is to machine down the RF flange and remember to use a full face gasket.

or as Anton says get one added (FF) to the piping spec and order it from your MTO.

[Author]

Replies