Flanges

the only place i have ever used RF is on high pressure piping. the mating flange being sized to just barely fit inside the raised portion in the case where the raised portion is on the perimeter. the other style i've used has the raised portion on the inner edge of the flange. not sure what the purpose of that was.

FF i've used for muni water supplies etc on relatively low pressure systems.

both normally use a flat composite gasket for sealing.

hope this helped.

To Summarize:

FF :is for low pressure-Cast iron or thin flange -cannot tighten bolts too much-might break/bend/leak.

RF : Go ahead ,tighten all bolts hard --flange edges will go to elastic bending mode right up to Yield point-- and no leaks.

And if you need to go to extreme prestress--avoid a flat fibre/composite gasket. Instead have a "SOFT IRON" ring in trapezoidal groove in both Raised Face Flanges.

Pressure. Pressure point (sealing) greater on RF since the bolt torque is concentrated on the smaller ring. Gaskets are greatly different for a RF also and that is where some sealing technology plays in as well.

FF Flanges are used only for Class 150 flanges (and occasionally for Class 300) - particularly when Cast Iron or other brittle items are present in the piping. Gaskets need to be full-face and made up of soft materials.

RF Flanges are normally used for Class 150, 300 and 600. Flat ring gaskets are used for Class 150 and spiral wound gaskets for 150, 300 & 600.

To add for the completion of knowledge....,for Class 900 and above RTJ flanges are specified.

Flanges on pumps are usually made of Cast Iron which would crack/break when the bolts are tightened because of moment due to the raised face. Normal Piping is made from forged steel which is much stronger and will not break upon tightening the bolts.

Also note that Cast Iron and Forged Steel flanges are slightly different dimensionally.

I think.

Reference ANSI-B16.5 for raised face flange use, and specifications. See ANSI-B16.24 for flat face flange data.

The Flange face type should not be confused with flange "finish".which indiactes the surface contact finish applied to the actual face of the flange. The major types are

1. smmoth finish

2. serrated finish.

The grooves are 1.6 mm deep with 24 to 40 grooves per one inch ( 25.40 mm) Other finishes may be furnished as determined by the user.

a. serrated concentric groove

b. serrated spiral groove

1.0 Raised Face:

Used in majaority of Flange applications for pressure up to 900 psi. ( 6400 Kpa) Face height of 1.60 mm ( 1/16" ) are used for Flange classes 150, 250, and 300.

Higher number Flange classes use 6.40 mm ( 1/4" ) raised face for classes 400, 600, 900, 1500, and 2500.

1.1 Large male & female: The face design provides ample gasket sealing area while still giving good gasket support.

1.2 Large Toungue & Groove: The small contact sealing area in the design contributes to good gasket compresion under low bolt loading. The grooved slot also provides excellent gasket containment under high pressure service.

2.0 Flat Face :

Used commonly on Cast Iron Flanges and as mating Flanges to pumps and valves in low pressure applications.

3.0 Lap joint ( Van Stone Flange) and Ring Joint type face types:

They are the other two types.

Lap Joint: Similar face face area design to that of Raised Face Flange, but differs in that the stub end makes up the seating face.

Ring Joint: The flange face design consists of a grooved slot in which a metal ring gasket is used for sealing.The metal ring sealing face makes it ideal for corrosive and high pressure / temparature applications.

Most of the standard steel and alloy flannges are covered under ASME / ANSI specifications B 16.5 for flange pressures from 150 to 2500.

Cast iron flanges are covered under ASME / ANSI B16.1 for classes 25, 125, 250 and 800. Cast iron flanges are usually threaded connections, with 25 & 125 having FLAT Face and class 250 & 800 having Raised Face of 1.60 and 6.35 mm respectively.

SRIDHAR- Advance Institute of Welding Technology, Chennai -India,

Go to this web site and read the article about flanges. http://www.pipingdesigners.com/Training%20-%20section%201d.htm

No differences, but .......

If you have two flanges rated 150#, one with raised face and other with flat face, all dimensions must be the same, the only difference is the socket of raised face. This is logic for low working pressure. For high pressure, it is not logic to tight two flat face flanges, such a raised face is required to allow good tighten.

But from my experience, you can assemble two flanges working at high pressure, one flange RF and other FF, taking into consideration that the RF height must be twice the standard to allow enough gab to tight the stud bolts.

At this case, all dimensions of both flanges must be the same, especially, flange thickness, no. of holes, BCD, ID, OD, ... etc., except the raised face.

For special applications, we have to design a Non Standard Flanges with special dimensions to suit pressure vessels and heat exchangers. Most of shell and tube heat exchangers designed in accordance with TEMA code can be furnished with one flange with raised face and other with inner groove.

Here is an address to a very good article about Raised Face and Flat Face flanges. http://www.gouldspumps.com/pom_0007.html All readers should be aware that some of the responses that have been posted to this thread (and others) are way off base, full of wrong and misleading information. Let me give you all some flange rules. 1. Flange faces must be matched: Raised face against raised face, flat face against flat face, Ring joint against ring joint, etc. NO EXCEPTIONS. 2. Flange ratings must be matched: 150# against 150#, 300# against 300#, 400# against 400#, etc.

Glad you posted this. I was reading two of these posts and the hair raised on my neck !!!!!!!!! I think the question has been answered but others have offered more than the answer that may pose safety risks.

May be the question has been answered and enough for normal users, but there are a lot -at least from my point of view- to say for deeper specialists related to design of standard and nonstandard flanges.

I am sorry, but with all due respect to the honorable gentleman from Cairo, I feel that he should recuse himself from ferther comments until he has had proper training in the basics of piping materials, piping engineering and piping design. Curently the information he is posting is sadly misleading and will only confuse young piping students and may lead to costly mistakes in their work.

That is right. Thank you & Welcome.