The function of the Buttweld Elbow / Bends is to change direction of flow in a piping system
Butt Weld Elbows are split into 3 groups, which define the distance over which they change direction, which is expressed as a function of the distance from the centre line of one end to the opposite face. this is known as the centre to face distance and is equivalent to the radius through which the elbow is Bent..

• Long Radius Elbow : The most common is the long radius (L.R.) elbow where the center to face dimension is always 1.5 times the nominal pipe size of the elbow.
• Short Radius Elbow : In this case the centre dimension is the same as the nominal pipe size of the elbow.
• Extra Long Radius : This is where the centre to face dimension is longer than the standard long radius type. The most common of these is where the centre to face dimension is three times, five times, ten times the nominal size, i.e. 3D, 5D, 10D etc.

Technical Points :
Most of the people do not know where to measure the thickness of this Elbows & Bends they check the thickness at the bevelled ends which is not the correct way .......... Engineers working under Oil & Gas sector and under third party inspection agency like EIL, DNV, BV etc have the correct knowledge of measuring the wall thickness which is measured at the back of the elbows/bends by ultrasonic thickness gauge instrument. The People buying the quality products and less concerned about the prices will definitely go with the measuring at the back of the elbow and others who are very much price conscious will not understand this part.
Most Traders and other traders who represent themselves as manufacturer of fittings & flanges will not know this .......... Secondly as per ASME/ANSI B16.9 the Radius of an elbow from 15NB - 25NB is 38mm, But they will supply 15NB Elbow Radius 19mm & 20NB Elbow Radius 29mm which is not as per standard. 
As on today we try to make our customer know about such thing and try to convince them but if he is willing to accept less thickness at the back then we take such types of orders.

The function of the Buttweld Elbow / Bends is to change direction of flow in a piping system
Butt Weld Elbows are split into 3 groups, which define the distance over which they change direction, which is expressed as a function of the distance from the centre line of one end to the opposite face. this is known as the centre to face distance and is equivalent to the radius through which the elbow is Bent..

• Long Radius Elbow : The most common is the long radius (L.R.) elbow where the center to face dimension is always 1.5 times the nominal pipe size of the elbow.
• Short Radius Elbow : In this case the centre dimension is the same as the nominal pipe size of the elbow.
• Extra Long Radius : This is where the centre to face dimension is longer than the standard long radius type. The most common of these is where the centre to face dimension is three times, five times, ten times the nominal size, i.e. 3D, 5D, 10D etc.

Technical Points :
Most of the people do not know where to measure the thickness of this Elbows & Bends they check the thickness at the bevelled ends which is not the correct way .......... Engineers working under Oil & Gas sector and under third party inspection agency like EIL, DNV, BV etc have the correct knowledge of measuring the wall thickness which is measured at the back of the elbows/bends by ultrasonic thickness gauge instrument. The People buying the quality products and less concerned about the prices will definitely go with the measuring at the back of the elbow and others who are very much price conscious will not understand this part.
Most Traders and other traders who represent themselves as manufacturer of fittings & flanges will not know this .......... Secondly as per ASME/ANSI B16.9 the Radius of an elbow from 15NB - 25NB is 38mm, But they will supply 15NB Elbow Radius 19mm & 20NB Elbow Radius 29mm which is not as per standard. 
As on today we try to make our customer know about such thing and try to convince them but if he is willing to accept less thickness at the back then we take such types of orders.