A pipe flange is a mechanical device to join pipes. Flanges are available in multiple shapes, as welding neck (the pipe is welded to the collar of the flange), threaded (the pipe is screwed on the flange), socket weld (fillet welds connections), lap joint (for connections using stub ends), slip on, etc. The ASME B16.5 and ASME B16.47 specifications cover US standard pipe flanges, the EN 1092-1 specification covers European steel flanges.
Pipe flanges are available in dimensions between 1/8 and 80 inches and in multiple (forged) material grades as:
- ASTM A105 (carbon steel flanges for high-temperature service),
- ASTM A350 (CS flanges for low temperature),
- ASTM A694 (high yield carbon steel flanges for line pipes),
- ASTM A182 F304, F316, F321 (stainless steel flanges),
- ASTM A182 F51 (duplex steel flanges), ASTM A182 F53/55 (super duplex flanges), and higher grades (Inconel, Hastelloy, Monel flanges).
Non-ferrous pipe flanges (copper, cupronickel, and aluminum) are used in marine and aeronautical applications. The pipe and the flange material shall, of course, match.
For specific applications, flanges may be coated, painted or internally lined (with Teflon, for example) to enhance the resistance of the metal to the aggression of corrosive or erosive fluids.
The key specifications covering flanges for petrochemical applications are the ASME B16.5 (flanges below 24 inches) and the ASME B16.47 (flanges above 24 inches in diameter). Upstream oil & gas flanges are covered by the API 6A specification.
Flange insulation kits are available to protect the flanged joint from the corrosion from static currents.
A flanged joint is the connection of two lengths of pipes by using:
- two mating flanges (the “main” and the “companion” flange). The key dimensional parameters of a flange are the nominal pipe size (NPS), i.e. the diameter of the flange bore to match the pipe and the flange rating class
- one set of stud bolts (the dimension and the number of needed stud bolts and nuts are outlined by the stud bolts charts)
- two gaskets (which can be either metallic, as spiral wound, ring joint, jacketed and Camprofile types, or non-metallic, i.e. made of soft non-asbestos materials, depending on the flange face type, RF, FF or RTJ).
To prevent dangerous leakages in the pipeline, flanged joints shall be executed by trained personnel only (the standard TSE – TS EN 1591 Part 1-4, “Flanges and their joints” is the reference norm).
Steel pipes can be connected to flanges by welding the pipe with the flange (welded connection, made with weld neck, socket weld, slip on and lap joint flanges) or by screwing the flange onto the pipe (threaded connection, made using threaded flanges).
Welded connections are used for pipelines and piping systems featuring high pressures and temperatures, and diameters above 2 inches. Threaded connections are used for small diameter piping systems that are not subject to mechanical forces as expansion, vibration, contraction, oscillation (conditions that would crack the threaded joints). Let’s take a close look at the welded connections types.
WELD NECK CONNECTION (WELD NECK FLANGES)
Weld-neck flanges have a tapered hub with a butt weld end that can be welded to a butt weld pipe. The quality of the welded joint may be examined visually or using radiography and/or ultrasounds (UT).
The welded connection between a weld neck flange and a pipe features a good fatigue and mechanical stress performance.
SOCKET WELD CONNECTION (SOCKET WELD FLANGES)
SLIP-ON CONNECTION (SLIP ON FLANGES)
Slip-on flanges are generally preferred to weld-neck flanges due to their lower cost and installation speed (and ease). The downside of slip-on flanges vs. a weld neck flanges is that their strength is about 1/3 lower. For this reasons, slip-on flanges are typically used for low-pressure, non-critical services such as fire water, cooling water, and similar nonchallenging pipeworks. The pipe is welded to both the hub and the bore of the flange and MP, PT, or a simple visual examination are the approaches used to check the integrity of a slip-on connection. Slip-on flanges are used, generally, for pipe sizes greater than NPS 2¹⁄₂ (DN 65).
LAP JOINT CONNECTION (LAP JOINT FLANGES AND STUB ENDS)
This type of connection is sometimes used for pipelines in high-cost materials (as stainless steel and nickel alloys) as it helps to reduce the overall cost of the required flanged connections.
A lap joint connection is made by the combination of a stub end (which is the part welded to the pipe) and a backing flange, or lapped flange.
A stainless steel stub end can be for instance used in combination with a carbon steel lap joint flange to have a reliable welded connection at a cheaper cost than a full stainless steel connection (less stainless steel is required, hence the cost is lower). Lap joint flanges have generally a raised face and are sealed with flat ring gasket.
1. Lap Joint flange 2. Stub End 3. Butt weld 4. Pipe or Fitting
HOW TO ORDER FLANGES
The following parameters have to specify to order (or request estimates) for flanges:
- Flange type (welding neck, slip-on, threaded, lap joint flange)
- Flange specification (example ASME B16.5, ASME B16.47 type A, EN 1092-1, JIS, UNI, DIN, etc.)
- Nominal pipe size (NPS)
- Flange rating (or class): flanges’ rating can range from 150 to 2500 for ASME flanges, from 5k to 30k for JIS B2220 flanges and KS1503 flanges; from PN 6 to PN 100 for European and Russian-standard flanges (DIN, UNI, EN 1092-1, GOST 12820 / 12821-80); Class 600/3, 1000/3, 1600/3, 2500/3, 4000/3 for SANS/SABS flanges (South African standard for flanges)
- Pipe schedule (for welding neck and socket weld flanges)
- Flange facing type (FF; RF, RTJ): according to ASME B16.5, the raised face is the standard facing for flanges (different facings, like RTJ or flat face FF, have to be ordered specifically)
- Flange surface finish (smooth, stock, concentric serrated, etc)
- Material grade (forged carbon, stainless, duplex, nickel-alloy steels or, non-ferrous materials as cupronickel, copper, aluminum, and bronze)
Looking for the price of flanges? Click on the image and check our online flanges price estimation tool!
The tool estimates the price for flanges manufactured in Europe and Asia.
Even if our price estimates are reliable, prices shall always be double checked with flange manufacturers and distributors.
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