In piping systems, elbows are pipe fittings used to change the direction of the pipeline. They come in three commonly used angles: 45°, 90°, and 180°. Additionally, other non-standard angles, such as 60°, are 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 (the most common method), flange connection, hot melt connection, electric melt connection, threaded connection, and socket welding connection, among others. According to production processes, they can be categorized into welded elbows, stamped elbows, expanded elbows, cast elbows, and socket-welded elbows, etc. Other names include 90-degree elbows, right-angle elbows, etc.