FF FLANGE VS RF FLANGE DIMS

I am setting up cadworx specs and we have gotten into a discussion on the flange thickness dimension of FF vs RF.
On 300lb and below flanges the 1/16 RF is included in the flange thickness, on 400 & above the 1/4" has to be added. The question is - do all FF flanges start as RF then the RF is machined off (which would be 1/16 or 1/4 shorter than RF flanges), or is the FF created to match the dimension of the RF which includes the 1/16"-1/4".

I believe all steel flanges start out as raise-face connections, I'd hazard to guess manufactures sell 50/100 flanges before they'd need a single flat-face flange, and if a flat-face is required the raised face is machined off (an easy operation). One thing I need to point out, and this is "written between the lines" here, flat-face connections are usually for a cast iron flange connection(or other "soft" metal flanges) ...on pumps, strainers, & etc. The two ratings in cast iron service are 125# & 250# ...and they are dealt with 150# & 300# steel piping systems. SO you won't run across any 600# flat-flanges (or higher), where you'll need to machine off the 1/4" (0.25") raised face on a flange. SO on the flanges(150# & 300#) you do machine, your only loosing 1/16" (0.062") ...which can be maked-up in the weld gaps .

Hi,

We are one of the flange manufacturer's based in India, www.kalpindustries.com/ . Yes, FF flanges start as RF then RF is machined off.

FF flanges start as RF flanges and yes FF created to match the dimension of the RF for more detail dimension of flanges www.summitsteel.co.in

The CADWorx install data tables include the raised face in the overall flange dimensions. One has to add tables for flat face flanges. Weld neck flanges (as an example) are forged into a dimensional shape based on the required class/standard and then holes, welding bevel and facing are machined.