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Anonymous Poster

SORF Flanges

10/31/2008 7:30 AM

What is meant by SORF flange, How many types of Flanges are there? What are the advantages over compared to other type of flanges.

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Engineering Fields - Piping Design Engineering - Retired Piper

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#1

Re: SORF flange

10/31/2008 9:27 AM

SORF means:

S. = Slip

O. = On

R. = Raised

F. = Face

Normally written, SO RF as in Class 150 SO RF

How many types of (Pipe) Flanges are there?

Flange Types:

Weld Neck Flanges:
Weld Neck Flanges are distinguished from other flange types by their long tapered hub and gentle transition of thickness in the region of the butt weld that joins them to pipe or a fitting. A weld-neck flange is attached to a pipe or a fitting with a single full penetration, "V" bevel weld. The long tapered hub provides an important reinforcement of the flange proper from the standpoint of strength and resistance to dishing. The smooth transition from the flange thickness to the pipe wall thickness by the taper is extremely beneficial under conditions of repeated bending caused by line expansion or other variable forces, and produces an endurance strength of welding neck flanged assemblies equivalent to that of a butt-welded joint. This type of flange is preferred for severe service conditions, whether loading conditions are substantially constant or fluctuate between wide limits.

The weld neck flange is used in each of the seven flange ratings and has the advantage of requiring only one weld to attach it to the adjacent pipe or fitting.

The key dimension for a weld neck flange in the length through the hub from the beveled end to the contact face of the flange. This "length" includes the bevel, the tapered hub, and the thickness of the plate part of the flange and the raised face. To obtain the correct dimension you must look at a correctly constructed flange dimension chart (see the "Tools" button on this website) or a flange manufacturers catalog. Electronic piping design software will normally already have the correct dimension built-in.

It is important to understand and remember that the (1/16") raised face on the 150# raised face and on the 300# raised face flanges is normally included in the length dimension. However, the ¼" raised face is not included in the chart or catalog length dimension for the 400# and higher pressure rated flanges. The raised face dimension for 400# flanges (and up) normally must be added to the chart or catalog length to arrive at the true total length of these higher-pressure flanges.

Slip-on Flanges:
Slip-On (SO) Flanges are preferred by some contractors, over the Weld-neck, because of the lower initial cost. However, this may be offset by the added cost of the two fillet welds required for proper installation. The strength of the slip-on flange is ample for it's rating, but its life under fatigue conditions is considered to be only one-third that of the weld-neck flange.

The slip-on flange may be attached to the end of a piece of pipe or to one or more ends of a pipefitting. The slip-on flange is positioned so the inserted end of the pipe or fitting is set back or short of the flange face by the thickness of the pipe wall plus 1/8 of an inch. This allows for a fillet weld inside the SO flange equal to the thickness of the pipe without doing any damage to the flange face. The back or outside of the flange is also welded with a fillet weld.

A variation of the Slip-On flange also exists. This is the Slip-On Reducing Flange. This is simply a larger (say a 14") Slip-On flange blank that, instead of the Center (pipe) hole being cut out (or drilled out) for 14" pipe it is cut out for a 6" pipe. The SO Reducing flange is basically used for reducing the line size where space limitations will not allow the length of a weld neck flange and reducer combination. The use of the Slip-On Reducing Flange should only be used where the flow direction is from the smaller size into the larger size.

Lap Joint Flanges:
A Lap Joint Flange is a two piece device that is much like a weld-neck flange but also like a loose slip-on flange. One piece is a sleeve called a 'Stub-end" and is shaped like a short piece of pipe with a weld bevel on one end and a narrow shoulder on the other end called the hub. The hub is the same outside diameter as the raised face (gasket contact surface) of a weld neck flange. The thickness of the hub is normally about ¼" to 3/8". The back face of the hub has a rounded transition (or inside fillet) that joins the hub to the sleeve.

The other piece of a Lap Joint Flange is the backing flange. This flange has all the same common dimensions (O.D., bolt circle, bolt hole size, etc.) as any other flange however it does not have a raised face. One side, the backside, has a slight shoulder that is square cut at the center or pipe hole. The front side has flat face and at the center hole an outside fillet to match the fillet of the "Stub-end" piece. The flange part of the Lap-joint flange assembly is slipped on to the stub-end prior to the sleeve being welded to the adjoining pipe or fitting. The flange itself is not welded or fixed in any way. It is free to spin for proper alignment with what ever it is joining to.

The "Stub-end" can normally be purchased in two lengths. There is a short version, about 3" long and a long version of about 6" long. It is prudent for the piping designer to know which version is in the piping specification.

Because of it's two piece configuration, the Lap Joint Flange offers a way to cut cost or simplify work. The cost saving comes when the piping system requires a high cost alloy for all "wetted" parts to reduce corrosion. The sleeve or Stub-end can be the required higher cost alloy but the flange can be the lower cost forged carbon steel.

The work simplification comes into the picture where there are cases that require frequent and rapid disassembly and assembly during the operation of a plant. The ability to spin that backing flange compensates for misalignment of the boltholes during reassembly.

Screwed (or Threaded) Flanges:
Screwed flanges look very much like a Slip-On flange in some ways. The main difference is the Screwed flange was bored out initially to match a specific pipe inside diameter. The backside of this center opening is then threaded with the proper sized tapered pipe thread. This flange is primarily used to make flanged joints where required in small sizes in threaded pipe specs

Socket Weld Flanges:
Socket Weld flanges also look very much like a Slip-On flange. Here the main difference is the Socket Weld flange was also bored out initially to match a specific pipe inside diameter. Here however, the backside of this center opening is then counter bored to form the proper size socket to take the pipe O.D. This flange is primarily used to make flanged joints where required in small sizes in socket welded pipe specs

Blind Flanges:
Blind flanges are a round plate with all the proper boltholes but no center hold. This flange is used to provide positive closer on the ends of pipes, valves or equipment nozzles.

For more about Flangefaces, Flange Rating, etc. go to
http://www.pipingdesigners.com/Training%20-%20section%201d.htm

PennPiper (aka: Jop)

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Engineering Fields - Piping Design Engineering - New Member Egypt - Member - Member since 02/18/2007

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#2
In reply to #1

Re: SORF flange

10/31/2008 3:33 PM

Good answer PennPiper, but only I'd like to add two additional types of flanges:

LWN Flanges (LWN = Long Welded Neck): characterized by its long neck as a solid extension which can be selected to be welded directly into a pipe or a vessel without adding a nozzle from a pipe. The thickness of neck is in accordance with the flange schedule, where the length of neck can be selected by the purchaser.

Integral Flanges: is a special type furnished with a built in neck (solid extension at the back of the flange called tapered hub) with thickness of end of tapered hub (usually selected by purchaser) greater than the hub thickness adjacent to the flange (which represents the flange schedule). That bigger thickness compensates for loss of strength occurred by nozzle opening in shell of vessel or pipe, where no need to add any reinforcing pad. This type of flanges are used in vessels and piping works where a relatively higher pressure is required.

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Anonymous Poster
#6
In reply to #1

Re: SORF flange

12/18/2008 10:17 AM

PennPiper,

If we use a socket weld flange is critical to specify schedule since there is a 1/16" gap inside between the pipe and the inside of the flange.

Seems the suppliers never request for wall thickness or schedule on the socket weld flange description unless of course they are buttweld.

Thanks

Peter Piper

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Participant

Join Date: Dec 2008
Location: Calgary, Alberta, Canada
Posts: 1
#7
In reply to #1

Re: SORF flange

12/18/2008 3:54 PM

PennPiper,

Very good description of the socket weld flanges.

Would you or anyone else know if the socket weld flanges generally come off the shelf with a standard bore equal to the inside pipe diameter of a standard pipe?

If so and someone requires other than standard bore for a socket weld flange to match other pipe schedule would this then increase cost or are they all off the shelf items.

Thanks

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Join Date: Mar 2010
Posts: 26
#9
In reply to #1

Re: SORF flange

03/18/2010 10:53 PM

Thanks, I enjoyed your answer

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Carbon steel pipes, fittings, flanges manufacturer from China
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#10
In reply to #1

Re: SORF flange

05/20/2010 7:18 AM

PennPiper, while using PVElite software to analyze FFS of a damaged flange I have come accross a drop-down menu where I have to choose the flange type. For SORF flanges there are two choices: Loose Slip on and Integral Slip on. Any idea what the difference is? As I understand it, the integral flange definition applies to a flange whose hub is sufficiently thick to provide opening compensation...then how can this apply to a slip on flange?

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Commentator

Join Date: Feb 2008
Posts: 77
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#3

Re: SORF Flanges

11/01/2008 10:31 AM

See my comment in this posting under Thickness and Pressure Rating of Blind Flanges.

You can get a good sense for what is available in the Taylor Web site.

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Engineering Fields - Piping Design Engineering - New Member Egypt - Member - Member since 02/18/2007

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#4
In reply to #3

Re: SORF Flanges

11/01/2008 12:27 PM
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#5
In reply to #4

Re: SORF Flanges

11/02/2008 9:42 AM

Thanks for adding the link!

GCF

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Anonymous Poster
#8
In reply to #5

Re: SORF Flanges

06/12/2009 2:02 AM

Good information wrt Flanges

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Anonymous Poster
#11

Re: SORF Flanges

06/16/2010 4:48 AM

slip on raised face flange, we can use this in low pr. line , there ll be two socket weldin in each face ........

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Engineering Fields - Piping Design Engineering - Retired Piper

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#12
In reply to #11

Re: SORF Flanges

06/16/2010 12:46 PM

A Raised Face Slip-On Flange is NOT attached with "socket-welds" on each face.

A Slip-On Flange is attached with two "Fillet" welds. One on the inside (or front) of the flange and one on the outside (or back) of the flange.

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