Buttweld Fitting
Buttweld pipe fittings, abbreviated as BWF, can be split up into different categories depending on what it's function is. These categories are:
 Elbows are used whenever there is a direction change required
 Branch Connections are used when a piece of pipe or tubing is joining to another piece of pipe or tubing.
 Reducers are used when the nominal diameter of the pipe changes.
 Caps are used when the pipe run ends.
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Nomenclature & Symbols 

Buttweld Fitting Branch Connection Types
Straight Cross  A straight cross has the same branch size as the pipe. These are used for making 90 degree branching from the main run of pipe.
Straight Tee  A straight tee has the same branch size as the pipe. These are used for making 90 degree branching from the main run of pipe.
Reducing Cross  Reducing crosses have two 90 degree branches from the main run of pipe. The branch is smaller than the main run.
Reducing Tee  Reducing tees have a single 90 degree branch from the main run of pipe. The branch is smaller than the main run.
Reinforcing Saddle  These saddles are split in two pieces that fully encircle the branch connection. They come in two types. One slides over the branch and the other fits around the branch. The saddle is split along the length of the pipe. Reinforcing saddles come both in full and reducing branches.
Saddle  A saddle or tapping saddle is used when you do not want to shut down a pipeline, but want to add a branch. This allows a branch to be added for hot tapping an existing system. Saddles come in both full and reducing branches.
Split Tee
Stubin  It is the term for a branch of pipe welded directly into the side of a main pipe run. It is not a fitting. This is the most common and least expensive method of welding a full size or reducing branch for pipe. A stub in can be reinforced. It is very important to verify the stub in connection against whatever applicable piping code you are designing to. For example, B31.3 allows for stub in connections only if calculations are performed to ensure the connection is strong enough to withstand whatever forces are expected on the weld.
Buttweld Fitting Cap Types
Dished Head Cap  These have a straight tangent with a rounded head.
Flat Closure Cap  These are flat plates normally cut for pipe at the site.
Buttweld Fitting Elbow Types
45 Elbow Long Radius  A 45 degree elbow "long radius" has a centerline curvature equal to 11/2 times the nominal pipe size (NPS) for 3/4 inch and larger sizes.
45 Elbow Long Radius Long Tangent  A 45 degree elbow "long radius, long tangent" is a long radius with the centerline curvature equal to 11/2 times the nominal pipe size (NPS) and a straight extension at both ends (long tangent) for 2 inch and larger sizes. Tangent elbows provide a straight length at the end to accept a Slipon Flange. The tangent end for the flange is not beveled.
45 Elbow Three Radius  A 45 degree elbow "three radius" is a long radius elbow with the centerline curvature equal to 3 times the nominal pipe size (NPS).
90 Elbow Long Radius  A 90 degree elbow "long radius" has a centerline curvature equal to 11/2 times the nominal pipe size (NPS) for 3/4 inch and larger sizes.
90 Elbow Long Radius Long Tangent  A 90 degree elbow "long radius, long tangent" is a long radius with the centerline curvature equal to 11/2 times the nominal pipe size (NPS) and a straight extension at both ends (long tangent) for 2 inch and larger sizes. Tangent elbows provide a straight length at the end to accept a Slipon Flange. The tangent end for the flange is not beveled.
90 Elbow Short Radius  A 90 degree elbow "short radius" has a centerline curvature equal to 1 times the nominal pipe size (NPS) for 1 inch and larger sizes.
90 Elbow Short Radius Long Tangent  A 90 degree elbow "short radius, long tangent" is a short radius with the centerline curvature equal to 1 times the nominal pipe size (NPS) and a straight extension at both ends (long tangent) for 8 inch and larger sizes. Tangent elbows provide a straight length at the end to accept a Slipon Flange. The tangent end for the flange is not beveled.
90 Elbow Three Radius
 A 90 degree elbow "three radius" is a long radius with the centerline curvature equal to 3 times the nominal pipe size (NPS).180 Return Long Radius  A 180 degree return "long radius" has a centerline curvature equal to 11/2 times the nominal pipe size (NPS) for 3/4 inch and larger sizes.
180 Return Short Radius  A 180 degree return "short radius" has a centerline curvature equal to 1 times the nominal pipe size (NPS) for 1 inch and larger sizes.
Mitered Elbow  A mitered elbow is fabricated from pipe and is not a fitting. A miter is used for larger pipes, where pressure drop is not important and cost is a factor. A 2 piece 90 degree miter has 4 to 6 times hydraulic resistance of the corresponding long radius elbow. A 3 piece, 90 degree miter has about double the resistance. The normal number of miter pieces used are 3, 4, or 5.
Bend  A bend is made from a straight piece of pipe. The most common bends are 3 or 5 times the nominal pipe size (NPS) radius.
Buttweld Fitting Reducer Types
Concentric Reducer  The concentric reducer centerline of the inlet and outlet is at the same level.
Eccentric Reducer  The eccentric reducer (abbreviated as offset is equals 1/2 times the larger ID minus the smaller ID. The eccentric reducer is used to keep either the top or bottom of the pipe level. It is used with the flat side up (flat on top FOT) or flat side down (flat on bottom FOB). In wet gas such as casing gas applications, an eccentric reducer should be used that is flat on bottom to prevent condensing liquids from pocketing. It is common practice to install eccentric reducers on a liquid line that might have a little gas in it with the flat side of the reducer is put on the top. That ensures that any bubbles that come along the top pass immediately through the pump and not accumulate. If they accumulate, they may collect and enter the pump in bulk causing it to intermittently cavitate.
Swage  There are three types  concentric (CONC SWG), eccentric (ECC SWG) and ventury. A swage is used to connect buttwelded and screwed fittings/pipe to smaller or larger buttweld or screwed fittings/pipe.

Concentric swage  centerline of the inlet and outlet is at the same level.

Eccentric swage  is offset either on the top or bottom of the line level.

Venturi swage  creates a smooth flow
Buttweld Fitting Standards
ASME Standards
 ASME B16.9  FactoryMade Wrought Buttwelding Fittings
Buttweld Fitting Datasheets
Tags: Pipe Fitting