Socket welding and threaded union are two common pipe connection methods. They are different in application scenarios, structural features and usage effects. Socket welding is to insert the pipe into the end position of the other end for welding. After forming, the shape is similar to the internal thread connection. This connection method uses fillet welds, which are mainly used for pipes extending into the valve body for welding. The advantages of socket welding include firm connection, good sealing, and is suitable for high-pressure and high-temperature environments. Threaded union is connected by screwing the steel pipe into the screw hole, so it is called "threaded union". This connection method is easy to operate and is suitable for pipes of various diameters, especially in situations where frequent disassembly and replacement are required.