In piping systems, elbows are fittings used to change the direction of the pipeline. By angle, there are three commonly used types: 45°, 90°, and 180°, with additional non-standard angles like 60° included based on 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-weld connection, etc. They can be categorized by production process into: welded elbows, stamped elbows, expansion elbows, cast elbows, and socket-weld elbows, etc. Other names: 90-degree elbows, right-angle elbows, etc.