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Forged Flanges
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Weld Fittings
   
   
WELDING NECK FLANGES are attached by butt welding to the pipe or shell. They are preferred when radiography is required, and provide optimum stress distribution. The long tapered hub provides an important reinforcement of the flange proper from the standpoint of strength and resistance to dishing.
Welding Neck Flange

Slip-On Flange
SLIP-ON FLANGES slide over the pipe and are attached by two fillet welds. They are prefered by many users over welding necks on account of their initially lower cost and ease of alignment. Their calculated strength under internal pressure is of the order of two-thirds that of welding neck flanges.

LAP JOINT FLANGES also slide over the pipe and are most frequently used with Lap Joint Stub Ends. In some cases the lap is formed on the pipe end. Since they are free to rotate or swivel, there is no problem of bolt hole alignment. This type of connection is easy to maintain. The chief use of lap joint flanges in carbon or low alloy steel piping systems is in services necessitating frequent dismantling for inspection and cleaning.
Lap Joint Flange

Threaded Flange
THREADED FLANGES are turned firmly onto matching pipe and are used where welding is not feasible. They are not recommended for severe cyclic service conditions. Their chief merit lies in the fact that they can be assembled without welding, often used when alloy steel is essential for strength and where the necessary post-weld heat treatment is impractical.

SOCKET WELDING FLANGES are attached by inserting the pipe into the flange socket and applying a fillet weld at the top of the hub. They are usually specified for small diameter pipe applications.
Socket Welding Flange