In piping systems, elbows are pipe fittings used to change the direction of the pipeline. By angle, there are three commonly used types: 45°, 90°, and 180° elbows. Additionally, according to engineering requirements, other non-standard angle elbows such as 60° are also included. 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, mandrel-formed elbows, cast elbows, and double-welded elbows, etc. Other names: 90-degree elbows, right-angle bends, etc.