Butt Weld fitting Elbow Elbows 45° – 90° – 180° LR/SR The function of a elbow is to change direction or flow in a piping system. By default, there are 5 opportunities, the 45°, 90° and 180° elbows, all three in the long radius version, and in addition the 90° and 180° elbows both in the short radius version. Long and Short Radius Elbows are split into two groups which define the distance over which they change direction; 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 center to face distance for a long radius elbow, abbreviated LR always is 1.1/2 x Nominal Pipe Size (NPS) (1.1/2D), while the center to face distance for a short radius elbow, abbreviated SR even is to nominal pipe size.