A flange is a method of connecting pipes, valves, pumps and other equipment to form a pipe work system. It also provides easy access for cleaning, inspection or modification. Flanges are usually welded or screwed into such systems and then joined with bolts.
What Are Buttweld Fittings?
Buttweld fittings are a family of fittings used in connecting and creating pipe work systems whereby they are welded into the system using circumferential buttwelds. They are used only in conjunction with ANSI pipe and are available in the same size range. They are used in areas where pipe work is permanent and are designed to provide good flow characteristics.
Weld Neck
This flange is circumferentially welded into the system at its neck, which means that the integrity of the buttwelded area can be easily examined by radiography. The bores of both pipe and flange match, which reduces turbulence and erosion inside the pipeline. The weld neck is therefore favoured in critical applications.
Slip-on
This flange is slipped over the pipe and then fillet welded.
Slip-on flanges are easy to use in fabricated applications.
Blind
This flange is used to blank off pipelines, valves and pumps.
It can also be used as an inspection cover. It is sometimes referred to as a blanking flange.
Socket Weld
This flange is counter bored to accept the pipe before being fillet welded. The bore of the pipe and flange are both the same therefore giving good flow characteristics.
Threaded
This flange is referred to as either threaded or screwed. It is used to connect other threaded components in low pressure, non-critical applications. No welding is required.
Lap Joint
These flanges are always used with either a stub end or taft which is buttwelded to the pipe with the flange loose behind it. This means the stub end or taft always makes the face. The lap joint is favoured in low-pressure applications because it is easily assembled and aligned.
Ring Type Joint
This is a method of ensuring leak proof flange connection at high pressures. A metal ring is compressed into a hexagonal groove on the face of the flange to make the seal. This jointing method can be employed on Weld Neck, Slip-on and Blind Flanges.
For what is each fitting used?
| Fitting Use | Use/Notes | Fitting Use | Use/Notes |
| Long Radius Elbows: 45 and 90 Degree Elbow and 180 Degree Return Bends | Concentric Reducer | ||
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Enables the pipe run to be turned through 45 degree, a right angle or back on itself. Radius is 1.5 times nominal pipe size. |  |
Used to connect two pipes of different dimensions. Designed to have good flow characteristics thus reducing erosion and corrosion. |
| 90 Degree Short Radius Elbows and 180 Degree Return Bends | Eccentric Reducer | ||
 |
Enables the pipe run to be turned through a right angle or back on itself. Radius is 1 times nominal pipe size. |  |
Used to connect two pipes of different dimensions. Designed to have good flow characteristics thus reducing erosion and corrosion. |
| Equal Tee | End Cap | ||
 |
Allows connection of a branch at right angles from main pipe run. Branch has same dimensions as main pipe run. |  |
Used to blank off at the end of pipe work. |
| Reducing Tee | Stub End: Made to MSS SP43 | ||
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Allows connection of a branch at right angles from main pipe run. Branch has same dimensions as main pipe run. When stating the size, the larger dimension always specifies the main pipe run, no matter which order the dimensions are quoted in. |  |
Always used with a lap joint flange as a backing flange. Flange can be made of coated mild steel, as it does not come into contact with the product in the pipe. This is a cheap method of flanging in low-pressure, non- critical applications. |
| CARBON | ALLOY STEEL | STAINLESS STEEL | DUPLEX/ S.DUPLEX | NICKEL ALLOY | ALUMINIUM | TITANIUM |
| A105(N) | A182 F1 | A182 F304/H/L | – A182 F51/UNS S31803 | MONEL 400/UNS N04400 | B381 F2 | |
| A181 | A182 F2 | A182 F310 | – A182 F53/UNS S32750 | INCONEL 600/US N06600 | B381 F5 | |
| A266 | A182 F5/A | A182 F316/H/L | – A182 F55/UNS S32760 | INCONEL 625/UNS N00625 | B381 F7 | |
| A350 LF1/LF2/LF3 | A182 F6/A | A182 F321/H | – A182 F44/UNS S31254 | INCOLOY 800/UNS N08800 | B381 F12 | |
| A694 F42 | A182 F9 | A182 F347/H | – A182 F49/UNS S34565 | INCOLOY 825/UNS N08825 | ||
| A694 F52 | A182 F11 | A182 F348/H | ALLOY C276/UNS N10276 | |||
| A694 F60 | A182 F12 | A182 F10 | ||||
| A694 F65 | A182 F22 | |||||
| A707/3 CL.2/CL.3 | A182 F91 | |||||
| A707/5 CL.3 |