Elbow is a kind of connecting pipe commonly used in pipeline installation. It connects two pipes with the same or different nominal diameters to make the pipeline turn at a certain angle. In the pipeline system, the elbow is a pipe fitting that changes the direction of the pipeline. Among all the pipe fittings used in the piping system, the proportion is the largest, about 80%. Usually, different forming processes are selected for elbows with different materials or wall thicknesses. At present, the commonly used seamless elbow forming process has hot push , stamping, extrusion, etc. According to the production process, it can be divided into: welding elbow, stamping elbow, pushing elbow, casting elbow, etc. According to the manufacturing standard, it can be divided into electric standard, water standard, American standard, German standard, Japanese standard, Russian standard, etc. Our elbows include German standard elbows, Japanese standard elbows, American standard elbows, etc. The commonly used materials for elbows are cast iron, stainless steel, alloy steel, malleable cast iron, carbon steel, non-ferrous metals and Plastics, etc. The ways of connecting with pipes are: direct welding (the most common way), flange connection, hot melt connection, electrofusion connection, threaded connection and socket connection, etc.