The connection of the pipe fittings is based on the required performance of the pipe connection. The connection types between the pipe fittings and between the pipe fittings and the pipe are butt welding connection, socket welding connection, pipe thread connection, and flange connection.
1) Butt-welding connections are mostly used for the connection of DN50 and above pipes of the same material. Both ends of the pipe fittings are provided with welding grooves. Compared with several other connection methods, due to its good sealing performance, strength, quality, corrosion resistance, and low price, it is widely used in high-pressure and high-temperature piping systems.
2) Socket welding connection is often used for the connection of small diameter pipes (below DN50). When small-diameter steel pipes are connected by butt welding, the internal cross-sectional area of the pipe may be reduced due to the dripping of the solder. Socket welding uses a fillet weld connection, so there is no problem of reducing the internal section of the pipe due to solder dripping, and the cost is low. However, due to the existence of gaps in the socket welding structure, it should be avoided when the conveyed fluid medium may produce crevice corrosion or severe erosion or when there is a smooth transition requirement for the connection part. Pipe fittings connected by socket welding are divided into socket pipe fittings and socket pipe fittings, which are generally determined by the types of pipe fittings and pipe fitting standards, and attention should be paid when selecting them.
3) Pipe thread connection is mostly used below DN50, which requires a detachable pipe connection. Compared with the same detachable flange connection, its connection structure is small in size. However, the flange connection is more reliable, because the thread processing accuracy is difficult to ensure a complete seal, and the strength is lower than that of the welded connection. Therefore, pipe threaded connections are usually used to transport water, air, and other fluid media that is less harmful even if they leak, or pipe welding may cause the coating to peel off in the pipeline. Working conditions that may produce crevice corrosion, severe erosion, or cyclic loading, pipe threaded joints should be avoided.
4) Flange connections are mostly used for pipes on special occasions, such as cast iron pipes, lined pipes, and equipment. Our country's flange connection pipe fitting standard has GB/T 17185, which adopts ANSIB16.5 non-equivalently.