Welding Neck Flanges
The welding neck flange is normally referred to as the "high hub" flange. It
is designed to transfers tresses to the pipe, there by reducing high stress
concentrations at the base of the flange. The welding neck flange is the
best designed but-welded flange of those currently available because of
its inherent structural value. It is expensive because of the design.
Threaded (Screwed) Flanges
The threaded flange is similar to the slip-on flange, but the bore is threaded.
Its chief merit is that it can be assembled without welding, explaining its use
in low pressure service at ordinary atmospheric temperatures, and in highly
explosive areas where welding create a hazard.
Slip-on Flanges
The slip-on flange has a low hub because the pipe slips into the flange
prior to welding. It is welded both inside and out to provide sufficient
strength and prevent leakage. Slip-on flanges are all bored slightly larger
than the O.D. of the matching pipe, They are preferred over welding neck
flanges by many users due to their lower initial cost, but final installation
cost is probably not much less than that of the welding neck flange
because of the additional welding involved.
Lap Joint Flanges
The lap joint flange is practically identical to the slip-on flange except it
has a radius at the intersection of the bore and flange face. This radius is
necessary to have the flange accommodate a lap joint stub end.
Normally, a lap joint flange and the lap joint stub end are mated together
in an assembly system.
Socket Welding Flanges
The socked welding flange if similar to a slip-on flange except it has a
bore and a counterbore dimension. the counterbore is slightly larger than
the O.D. 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 I.D. 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.
Blind Flanges
The blind flange is a flange without a bore. It is used to close off the
ends of a piping system and/or a pressure vessel opening. It also
permits easy access to the interior of a line of vessel once it has been
sealed and must be reopened.
Orifice Flanges
Orifice Flanges are intended for use instead of standard pipe flanges
when an orifice plate or flow nozzle must be installed. Pairs of pressure
"Tappings", mostly on 2 sides, directly opposite each other, are machined
into the orifice flange. This makes separate orifice carriers or tappings in
the pipe wall unnecessary.
