Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
(OP)
Although mechanically I know that this is okay, it is my understanding that connecting a raised face flange to flat face flange is a poor piping practice and should be avoided regardless of what material the flanges are.
Am I correct?
Am I correct?





RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
You also did not give us any detail on the:
- Commodity
- Operating Pressure
- Operating Temperature
Sometimes its possible to do all the right things and still get bad results
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
My other thought is that, why would someone deliberately bolt two different flange facings together when they don't need to?
Op. Temp = 80 deg. F
Op. Press = 20 PSIG
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
As I stated, I understand that it CAN be done, I'm just curious if it is a bad practice and why anyone would deliberately select a raised face flange over a flat face flange if they are tying into a flat face flange. Seems much simpler to avoid any potential confusion with gasket selection, surface finishes, and relaying the message 10 years from now when maintenance has to disconnect the flanges and sees two different flange facings.
All can be avoided by just mating FF to FF regardless of material. It's just my opinion but I still appreciate any opinions telling me why otherwise.
Thanks again for the reference thread.
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
When both are ductile materials, it's really not a problem unless the people doing your fitting are incompetent.
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
Availability? Price? Necessity, or at least perceived necessity (e.g. they can get the item quickly, or off the shelf with raised face, but have to wait for flat)?? A raised face flange after all requires less facing/machining than a full/flat-faced flange.
While flat-face to raised face has been used for decades for such reasons, it can be argued a bad practice for sure when too strong bolting may result in breakage of a very strong flange material bolted to a weaker or less tough material. It is harder to argue against a practice that works.
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
The poor practice is simply that the uneducated look at it and either condemn it as not being allowed or think that if it's ok in that location then it's ok in other situations where the material is different ( but looks the same) and where you can overstress the flange (classically class 125 cast or ductile Iron FF flanges).
It's difficult to show in the field that both materials are C Steel and it's Ok so will / could cause confusion and alarm in 10 years time when everyone has gone away and then a check or breaking of the flange shows up this apparent anomaly.
So is it poor practice? Weellll no, but I would try and avoid it if possible simply for the long term consequences. It also looks better.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
You said it is CS FF flange. As all people pointed out, it is usually cast iron pump or other equipment which comes with FF flange. You have to buy RF flange and cut off RF in order to get matching FF flange. So it cost more money.
Do you know why other side of tie in is FF?
This simple doesn't make sense to me...
Curtis
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
It is a vendor supplied fire water pump house with single stage horizontal split case pump and all vendor supplied suction, discharge, relief, and drain piping inside the pump house is galvanized carbon steel. All vendor tie-point flanges are also FF galvanized carbon steel flanges.
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
Can't you just ask the package vendor to supply a loose FF flange to fit?
I'm not surprised the pump vendor just uses FF flanges regardless of material because then he doesn't have this issue.
I would suggest you join him.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
What it ultimately boils down to is lack of knowledge on the everyday issues involved with certain design practices. Some people only focus on if it CAN be done instead of focusing on if it SHOULD be done and what implications come along with designing something a certain way. I prefer to take the route that makes more sense and avoids more confusion.
And luckily, I get very valuable tips and advice through eng-tips that continue to aid me in areas that I may need second opinions.
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
LI
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
You would be surprised how often I have to talk coworkers out of poor designs or practices.
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
Do we have a mass-production mentality applied to process plant design even though almost all are custom designs?
I'll now go back to my cave, mumble to myself and wait for lawn trespassers.
RE: Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice?
FF to RF is permissible, sometimes, without meaningful negative consequences. Permitting FF to RF when both flanges are ductile is NOT bad practice. In some cases is unavoidable, i.e. when one of the flanges isn't in fact raised face, but rather is a LAP JOINT.