Weld Neck RF Flange vs. Weld Neck FF Flange

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MANNU Active Contributor Join Date: Apr 2008 Posts: 12	Weld Neck RF Flange vs. Weld Neck FF Flange 05/01/2008 11:29 PM
	IS THERE ANY DIFFERNCE IN DIMENSIONS (LENGHT THROUGH HUB) OF WELD NECK RF & WELD NECK FF FLANGE.
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Zaphod2Headed Power-User Join Date: Nov 2007 Location: Alberta Canada Posts: 182 Good Answers: 9	#1 Re: Weld Neck RF Flange vs. Weld Neck FF Flange 05/02/2008 2:50 PM
	Yes. The flat face flange is shorter through the neck by the thickness of the raised face which has been removed to make it into a flat face. The thickness of the face removed depends upon the pressure class of the flange, as different pressure classes have different face thicknesses. __________________ Vote for something useful this time, vote to repeal the second law of thermodynamics!
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PennPiper Guru Join Date: Feb 2007 Location: Bayonet Point, Florida Posts: 635 Good Answers: 61	#2 Re: Weld Neck RF Flange vs. Weld Neck FF Flange 05/02/2008 6:22 PM
	The previous commenter is correct but in only some cases. This happens on Valves as well as Weld-Neck (and other) Flanges and it all depends on how the Flat Face surface on the object was created. If the Flat Face Weld-Neck Flange (or Valve) was created by modifing an existing Raised Face item then he is correct. However some items (Weld-Neck Flanges and Valves) are created as "Flat Face" in the factory during original manufacturing. When this is done then the Face-to-Face dimension for Raised Face Valves and Flat Face Valves is the same. This is because the creation of the raised face part of the flange face is a second operation (not a primary operation). If the dimensioning is critical then to be safe you may wantd to check with your flange (or Valve) supplier to confirm the actual dimensions. __________________ Do it once and do it right
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Abdel Halim Galala Guru Join Date: Feb 2007 Location: Cairo, Egypt Posts: 1733 Good Answers: 248	#3 In reply to #2 Re: Weld Neck RF Flange vs. Weld Neck FF Flange 05/03/2008 2:13 AM
	Yes PennPiper, you are wright. Where from ASME B16.5, we find that: 1. The flat face is only available for lapped flanges, and not available for welding neck flanges. 2. The thickness t_f of flange for any type (threaded, SO, SW, lapped, blind & WN) is the same for the same rating or class. 3. When you need to change any flange from RF to FF, only you have to remove the raised face height, and that will not reduce the effective thickness t_f of the flange to resist the pressure and temp. Note. Also, I'd like to add that for nonstandard flanges or tubesheets like those designed for heat exchangers, the raised face/or recessed thickness (if needed) have to be added to the calculated thickness of flange or tubesheet. __________________ It is better to be defeated on principles, than to win on lies!
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pipewelder Guru Join Date: Apr 2007 Location: North Georgia, USA Posts: 671 Good Answers: 33	#4 Re: Weld Neck RF Flange vs. Weld Neck FF Flange 05/05/2008 8:46 AM
	In a bind I have turned down a raised face on the lathe to fit a flat face valve or another flat face flange. I think all flanges are forged to be flat and then machined into what ever they will be.(as been stated already)The difference in dimensions are so small that it can easily be made up by a little wider root gap on the next few fits. On allot of burner management pipe skids we make in the shop have the flat face cast iron FM rated valves so we have to be careful to not get the flanges welded to the wrong end of a spool piece. There is nothing worse to find out when it is time to bolt everything together after it has been to the paint shop that we did this. They make a spacer ring for raised face flanges so they will fit up to flat face flanges. If you use a raised face on a flat face cast iron valve you run the risk of cracking it when tightening the bolts. Same thing if you don't use a full face gasket with the flat face flanges. pipewelder __________________ pipewelder
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skofitting Member Join Date: Dec 2011 Posts: 8	#5 In reply to #4 Re: Weld Neck RF Flange vs. Weld Neck FF Flange 12/23/2011 2:04 AM
	CR4 ADMIN: Deleted Post Spam: This post was deleted because it contained advertising outside the Commercial Space forum. Please review Section 14 of the CR4 Site FAQ about advertising.
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