Piping Elbows and Bends are very important pipe fitting which are used very frequently for changing direction in piping system. Piping Elbow and Piping bend are not the same, even though sometimes these two terms are interchangeably used.A BEND is simply a generic term in piping for an “offset” – a change in direction of the piping. It signifies that there is a “bend” i.e, a change in direction of the piping (usually for some specific reason) – but it lacks specific, engineering definition as to direction and degree. Bends are usually made by using a bending machine (hot bending and cold bending) on site and suited for a specific need. Use of bends are economic as it reduces number of expensive fittings.An ELBOW, on the other hand, is a specific, standard, engineered bend pre-fabricated as a spool piece (based on ASME B 16.9) and designed to either be screwed, flanged, or welded to the piping it is associated with. An elbow can be 45 degree or 90 degree. There can also be custom-designed elbows, although most are catagorized as either “short radius” or long radius”.
In short “All bends are elbows but all elbows are not bend”
Whenever the term elbow is used, it must also carry the qualifiers of type (45 or 90 degree) and radius (short or long) – besides the nominal size.
Elbows can change direction to any angle as per requirement. An elbow angle can be defined as the angle by which the flow direction deviates from its original flowing direction (See Fig.1 below).Even though An elbow angle can be anything greater than 0 but less or equal to 90°But still a change in direction greater than 90° at a single point is not desirable. Normally, a 45° and a 90° elbow combinedly used while making piping layouts for such situations.
Elbow angle can be easily calculated using simple geometrical technique of mathematics. Lets give an example for you. Refer to Fig.2. Pipe direction is changing at point A with the help of an elbow and again the direction is changing at the point G using another elbow.
In order to find out the elbow angle at A, it is necessary to consider a plane which contains the arms of the elbow. If there had been no change in direction at point A, the pipe would have moved along line AD but pipe is moving along line AG. Plane AFGD contains lines AD and AG and elbow angle (phi) is marked which denotes the angle by which the flow is deviating from its original direction.
No comments:
Post a Comment