A buttwelded Elbow is designed to be welded on site at its ends to connect pipes together and allow change in direction or pipe diameter or branching or ending. This fitting then becomes part of a system for transporting fluids (oil, gas, steam, chemicals & etc.) in a safe and efficient manner, over short or long distances. Elbows are split into two groups Long and Short Radius which define the distance over which they change direction; 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. The centre to face distance for a "long" radius elbow, abbreviated LR always is "1½ x Nominal Pipe Size (NPS) (1½D)", while the centre to face distance for a "short" radius elbow, abbreviated SR even is to nominal pipe size.