First, the connection methods for seamless steel pipes:
1. Compression type: The pipe is inserted into the pipe end of the steel fitting and tightened with a nut. The screw force compresses the sleeve at the pipe end of the seamless steel pipe through the sealing ring, achieving a seal and completing the pipe connection.
2. Welding type: The ends of the pipe are beveled and then circumferentially welded together manually or automatically.
3. Flange type: The flange is circumferentially argon-arc welded to the pipe and tightened with quick clamps or bolts. The sealing gasket between the flanges provides a seal, completing the pipe connection.
4. Press-fit type: The pipe is inserted into the fitting, and the seamless steel pipe wall is pressed into a hexagon using a special installation tool. The internal sealing ring also deforms into a hexagon.
5. Tapered thread type: The external thread is circumferentially argon-arc welded to the pipe, and the internal threaded fitting is connected with a tapered thread for sealing, completing the pipe connection.
Second, Detailed Processing of Seamless Steel Pipes
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 complex than that of hot-rolled pipes. The billet first undergoes three-roll continuous rolling, followed by sizing testing. If no cracks are found on the surface, the round pipe is cut into billets approximately one meter in length.
2. The pipe then enters the annealing process. Annealing involves pickling with an acidic liquid. During pickling, it is important to check for excessive blistering on the surface of the seamless steel pipe. Excessive blistering indicates that the quality of the seamless steel pipe does not meet the corresponding standards.
3. Hot-rolled seamless steel pipes are generally delivered in their hot-rolled state after heat treatment. After quality inspection, hot-rolled seamless steel pipes undergo rigorous manual selection by staff. Following quality inspection, the surface is oiled, followed by multiple cold drawing tests. After hot rolling, a piercing test is performed. If the piercing diameter is too large, straightening and correction are necessary.
4. Hot-rolled seamless steel pipes generally have an outer diameter greater than 32mm and a wall thickness of 2.5-200mm. Cold-rolled seamless steel pipes can have an outer diameter down to 6mm and a wall thickness down to 0.25mm. Thin-walled pipes can have an outer diameter down to 5mm and a wall thickness less than 0.25mm. Cold-rolled pipes have higher dimensional accuracy than hot-rolled pipes.
5. Commonly used seamless steel pipes are made from high-quality carbon structural steels such as 10, 20, 30, 35, and 45, low-alloy structural steels such as 16Mn and 5MnV, or alloy structural steels such as 40Cr, 30CrMnSi, 45Mn2, and 40MnB, through hot rolling or cold rolling. Seamless steel pipes made from low-carbon steels such as 10 and 20 are mainly used for fluid transportation pipelines.
6. Seamless steel pipe thread connections include three methods: cylindrical internal threads fitted into cylindrical external threads, cylindrical internal threads fitted into conical external threads, and conical internal threads fitted into conical external threads. The latter two methods provide a tighter connection and are commonly used.
(1) Flange Connection. Flange connection is generally used for pipes made of similar materials, such as copper, lead, and plastic. Different methods are used depending on the material being flanged. The flange must be flat and free of cracks and 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 for low-pressure pipe connections.
(3) Welded Flange Connection. The flange and steel pipe are connected by welding. This type of flange connection is widely used. The welding method is as follows: Select a pair of flanges and install them on the two pipe ends. If the equipment already has flanges, select flanges of the same specification and fit them on the pipe. First, spot-weld a small area to correct the verticality, and finally, weld the flange to the pipe securely.
Post time: Dec-11-2025