Basically pipe fitting is defined as a part used in a piping system, to change direction or function, which is mechanically joined to the system.
Probably the simplest way to achieve this would be to bend the pipe in the direction required, but this process will stretch and thin the outer wall whilst thickening and wrinkling the inner wall. This results in flow resistance and accelerated wall erosion.
A second method sometimes used is a mitre joint, where pipes are cut to the correct angle and welded together to achieve the desired change. Whilst the cross-sectional area and wall thickness are maintained, a great deal of efficiency is lost due to friction and turbulence resulting from the severe changes in direction. For example, a single-mitre bend offers about six times the resistance of a swept elbow.
For these reasons swept fittings are preferred on most piping systems, particularly where internal pressure, flow and corrosion are of major consideration.
In these article we will learn about what are the major benefits of Butt welded fittings and also its types .Generally these type of welded fittings in carbon steel and stainless steel offer many advantages compared to threaded and socketweld fittings. The later are only available up to 4-inch nominal size whereas butt weld fittings are available in sizes from ½” to 72”.
Some of the benefits of Buttweld fittings are :-
- Welded connection offers more robust connection
- The continuous metal structure formed between pipe and fitting adds strength to the system
- Continuous metal structure adds to the strength of the piping system
- Welding a fitting to the pipe means it is permanently leak proof
- Smooth inner surface and gradual directional changes reduce pressure losses and turbulence and minimize the action of corrosion and erosion.
- A welded system utilizes a minimum of space.
Types of Butt welded Fitting :-
The function of a 90° elbow is to change direction or flow in a piping system. Elbows are split into three groups which define the distance over which they change direction, expressed as a function of the distance from the center line of one end to the opposite face. This is known as the center to face distance and is equivalent to the radius through which the elbow is bent.
The most common is the long radius (L.R.) elbow where the center to face dimension is always 11⁄2 times the nominal pipe size of the elbow.
SHORT RADIUS ELBOWS :-
In this case the center to face dimension is the same as the nominal pipe size of the elbow.
In this case the center to face dimension is the same as the nominal pipe size of the elbow.
EXTRA LONG RADIUS :-
This is where the center to face dimension is longer than the standard long radius type. The most common of these is where the center to face dimension is three times the nominal size. i.e. 3D.
This is where the center to face dimension is longer than the standard long radius type. The most common of these is where the center to face dimension is three times the nominal size. i.e. 3D.
The function of a 45° elbow is the same as a 90° elbow, but the measurement of dimensions, however, is different to that of the 90° elbow. The radius of a 45° elbow is the same as the radius of the 90° L.R. elbow where ‘R’ equals 11⁄2 D. However, the center to face dimension is not equivalent to the radius as in 90° L.R. elbows.
This is measured from each face to the point of intersection of the center lines perpendicular to each other. This is due to the smaller degree of bend.
The function of a 180° return bend is to change direction of flow through 180° and there are two basic types, long radius and short radius. Both types have a center to center dimension double the matching 90° elbows. The primary application for these fittings is in heater coils and heat exchangers, boilers etc.
The function of both types of reducer is to reduce the line from a larger to a smaller pipe size, this obviously results in an increased flow pressure. With the eccentric reducer the smaller outlet end is off center to the larger end enabling it to line up with one side of the inlet and not with the other.
The concentric reducer is so manufactured that both inlet and outlet ends are on a common center line. The concentric reducer is easier and less expensive to produce but does not allow quite the same versatility as the eccentric reducer. The lengths of both types are fixed by manufacturing standards.
The function of a tee is to permit flow at 90° to the main direction of flow. The main flow passes through the ‘run’ whilst the 90° outlet is known as the ‘branch’. The equal tee is manufactured with all three outlets being the same size.
The reducing tee is manufactured with the branch outlet smaller than the run to obtain the desired flow and pressure through the system
EQUAL AND REDUCING CROSSES :-
The function of a cross is similar to that of a tee with the exception of providing two 90° outlets opposite each other. Equal crosses have all four outlets of equal size. Reducing crosses have branches that are smaller in size to that of the run to obtain the desired flow and pressure through the system.
CAPS :-
The function of an end cap is to block off the end of a line in piping systems. This is achieved by placing the end cap over the open line and welding around the joint.
A lap joint stub end and its associated slip-on flange in a piping system allows quick disconnection of the particular section involved. Stub ends are installed in pairs and mated together with two lap joint flanges. The surface of the stub end has a phonographic serrated gasket surface which prevents leakage at the joint. Using stub ends allows sections of the line to be opened for cleaning, inspection or quick replacement etc., without the need to re-weld.
There are two basic types of stub end, ANSI types A & B long barrel, and M.S.S. types short barrel. Under certain design criteria such as temperature or pressure, etc., it is not acceptable to have the joint between stub end and pipe in close proximity with the flange joint, in these applications ANSI types are used.
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