1. Compression type: insert the pipe into the pipe mouth of the pipe fitting, tighten it with a nut, and use spiral force to compress the sleeve of the pipe mouth through the sealing ring to seal and complete the connection of the pipe.
2. Welding type: process the groove at the end of the pipe, and use manual or automatic welding to make annular welding of the pipe.
3. Flange type: perform annular argon arc welding on the flange and tighten it with quick clamps or bolts to make the sealing gasket between the seal of the flange and complete the pipe connection.
4. Pressing type: insert the pipe into the pipe fitting and use a special installation tool to press the pipe wall into a hexagon, and the internal sealing ring is also deformed into a hexagon.
5. Cone thread type: the external thread and the pipe are annularly welded, and the internal thread pipe fittings are connected with a cone thread to seal and complete the pipe connection.

Supplementary explanation
1. The production process of seamless steel pipes can be divided into cold drawing and hot rolling. The production process of cold-rolled seamless steel pipes is generally more complicated than hot-rolling. The tube blank must first be subjected to three continuous rolling, and then a sizing test must be performed after extrusion. If there is no response crack on the surface, the round tube must be cut by a cutting machine and cut into a blank with a length of about one meter.
2. Enter the annealing process. The annealing must be pickled with an acidic liquid. During pickling, pay attention to whether there is a large amount of blistering on the surface. If there is a large amount of blistering, it means that the quality of the steel pipe does not meet the corresponding standards.
3. The delivery state of hot-rolled seamless steel pipes is generally hot-rolled and heat-treated before delivery. After quality inspection, hot-rolled seamless steel pipes must be strictly hand-selected by staff, and the surface must be oiled after quality inspection, followed by multiple cold drawing tests. After hot rolling treatment, perforation tests must be performed. If the perforation diameter is too large, straightening and correction must be performed.
4. The outer diameter of hot-rolled seamless pipes is generally greater than 32mm, with a wall thickness of 2.5-200mm. The outer diameter of cold-rolled seamless steel pipes can reach 6mm, the wall thickness can reach 0.25mm, the outer diameter of thin-walled pipes can reach 5mm, and the wall thickness is less than 0.25mm. Cold rolling has higher dimensional accuracy than hot rolling.
5. Generally, seamless steel pipes are made of 10, 20, 30, 35, and 45 high-quality carbon steels, 16Mn, 5MnV, and other low-alloy structural steels, or 40Cr, 30CrMnSi, 45Mn2, 40MnB and other alloy steels, which are hot-rolled or cold-rolled. Seamless pipes made of low-carbon steels such as 10 and 20 are mainly used for fluid delivery pipelines.
6. There are three ways to connect pipe threads: cylindrical internal threads inserted into cylindrical external threads, cylindrical internal threads inserted into conical external threads, and conical internal threads inserted into conical external threads. Among them, the latter two methods are more tightly connected and are commonly used connection methods.
(1) Flange connection. Flange loose flanges are generally used for pipes of similar materials such as copper pipes, lead pipes, and plastic pipes. Different operation methods are used according to different materials when flanging. The flanging must be smooth and must not have cracks or wrinkles.
(2) Threaded flange connection: a flange with internal threads is connected to a steel pipe with external threads. This type of flange is mostly made of cast iron and can be used to connect low-pressure pipelines.
(3) Welded flange connection: the flange and the steel pipe are welded together. This type of flange connection is widely used. The welding method is: to select a pair of flanges and install them on the two connected pipe ends respectively. If some equipment already has flanges, select flanges of the same specifications and put them on them. First, spot weld one point, correct the verticality, and finally weld the flange to the pipe firmly.