Weld Neck Flanges are drilled(machined) with the wall thickness of the flange having the same dimensions of the matching pipe, the lighter the pipe is, the larger the bore, conversely, the heavier the pipe, the small the bore, they are normally used for high pressure, cold or hot temperature

The slip-on flange has a low hub because the pipe slips into the flange prior to welding. It iswelded both inside and out to provide sufficient strength and prevent leakage.They are ideal forlow pressure applications.

The socket welding flange is similar to a slip-on flange except it has a bore and a counter bore dimension. The counter bore is slightly lager than the outer diameter of the matching pipe, allowing the pipe to be inserted into the flange similar to a slip-on flange. The diameter of the smaller bore is the same as the inner diameter of the matching pipe. A restriction is built into the bottom of the bore which sets as a shoulder for the pipe to rest on. This eliminates any restriction in flow when using a socket welding flange.

THREADED FLANGES are confined to special applications. Their chief merit lies in the fact that they can be assembled without welding this explains their use in extremely high pressure services, particularly at or near atmospheric temperature, where alloy steel is essential for strength and where the necessary post weld heat treatment is impractical. Threaded flanges are unsuited for conditions involving temperature or bending stresses of any magnitude, particularly under cyclic conditions, where leakage through the threads may occur in relatively few cycles of heating or stress; sea welding is sometimes employed to overcome this, but cannot be considered as entirely satisfactory.