In the pipeline system, the elbow is a pipe fitting that changes the direction of the pipeline. According to the angle, there are three most commonly used ones: 45° and 90°180°. In addition, according to engineering needs, it also includes other abnormal angle elbows such as 60°. The elbow materials are cast iron, stainless steel, alloy steel, malleable cast iron, carbon steel, non-ferrous metals and plastics.