Elbow in the piping system, the elbow is to change the direction of pipe fittings. According to the angle, there are 45 degrees and 90 degrees, 180 degrees of the most commonly used, in addition, according to the needs of the project also includes 60 degrees and other abnormal angle of elbow, such as three. Elbow materials are cast iron, stainless steel, alloy steel, malleable cast iron, carbon steel, non-ferrous metals and plastics, etc.. Connected with the pipe are: direct welding (the most common way) flange connection, hot melt connection, fused connection, threaded connection and socket connection. According to the production process can be divided into: welding, stamping elbow elbow, push bend, elbow cast, elbow etc.