Elbows are connecting pipe fittings used in piping systems to change the direction of pipelines. They are widely used in basic engineering projects such as chemical, construction, petroleum, plumbing, and power. These fittings are available in three common models based on their angle: 45°, 90°, and 180°. Elbow materials include cast iron, malleable cast iron, stainless steel, alloy steel, carbon steel, non-ferrous metals, and plastics. Connection methods include direct welding, flange connection, hot melt connection, electrofusion connection, threaded connection, socket connection, and clamp connection.