In piping systems, elbows are fittings used to change the direction of pipes. By angle, there are three commonly used types: 45°, 90°, and 180°, as well as other non-standard angles like 60° according to engineering requirements. Elbow materials include cast iron, stainless steel, alloy steel, malleable cast iron, carbon steel, non-ferrous metals, and plastics.

Ways to connect pipes include direct welding (common method), flange connection, hot melt connection, electric melt connection, threaded connection, and socket welding connection, etc. They can be categorized by production process into welded elbows, stamped elbows, expanded elbows, cast elbows, and socket-welded elbows, etc. Other names: 90-degree elbows, right-angle elbows, etc.