Large-diameter steel pipes are also called large-diameter galvanized steel pipes, which refer to welded steel pipes with hot-dip plating or electro-galvanized layers on the surface of large-diameter steel pipes. Galvanizing can increase the corrosion resistance of steel pipes and extend their service life. Galvanized pipes are widely used. In addition to being used as pipeline pipes for general low-pressure fluids such as water, gas, and oil, they are also used as oil well pipes and oil pipelines in the petroleum industry, especially offshore oil fields, and as oil heaters and condensation in chemical coking equipment. Pipes for coolers, coal distillate wash oil exchangers, pipes for trestle pipe piles, support frames for mine tunnels, etc.

Large diameter steel pipe forming method:
1. Hot push expansion method: The push expansion equipment is simple, low cost, easy to maintain, economical, and durable, and the product specifications can be changed flexibly. If you need to prepare large-diameter steel pipes and other similar products, you only need to add some accessories. It is suitable for producing medium and thin-walled large-diameter steel pipes, and can also produce thick-walled pipes that do not exceed the equipment’s capacity.
2. Hot extrusion method: The blank needs to be machined and pre-processed before extrusion. When extruding pipe fittings with a diameter of less than 100mm, the equipment investment is small, the material waste is less, and the technology is relatively mature. However, once the diameter of the pipe increases, the hot extrusion method requires large-tonnage and high-power equipment, and the corresponding control system must also be upgraded.
3. Hot piercing rolling method: Hot piercing rolling is mainly based on longitudinal rolling extension and cross-rolling extension. Longitudinal rolling and extension rolling mainly include continuous tube rolling with limited moving mandrel, continuous tube rolling with limited-stand mandrel, three-roll continuous tube rolling with limited mandrel, and continuous tube rolling with the floating mandrel. These methods have high production efficiency, low metal consumption, good products, and control systems, and are increasingly widely used.

At present, the main production processes for large-diameter steel pipes in my country are hot-rolled large-diameter steel pipes and heat-expanded diameter steel pipes. The largest specifications of heat-expanded seamless steel pipes are 325 mm-1220 mm and the thickness is 120mm. Thermal-expanded seamless steel pipes can produce non-national standard sizes. Seamless pipe is what we often call thermal expansion. It is a rough pipe finishing process in which steel pipes with relatively low density but strong shrinkage are enlarged by cross-rolling or drawing methods. Thickening steel pipes in a short period can produce non-standard and special types of seamless pipes with low cost and high production efficiency. This is the current development trend in the field of pipe rolling.

Large diameter steel pipes are annealed and heat-treated before leaving the factory. This delivery state is called the annealed state. The purpose of annealing is mainly to eliminate the structural defects and internal stress left over from the previous process and to prepare the structure and performance for the subsequent process, such as alloy structural steel, structural steel with guaranteed hardenability, cold heading steel, and bearing steel. Steels such as tool steel, steam turbine blade steel, and cable-type stainless heat-resistant steel are usually delivered in an annealed state.

Large diameter steel pipe processing method:
1. Rolling; a pressure processing method in which large-diameter steel pipe metal blanks are passed through the gap (of various shapes) between a pair of rotating rollers. Due to the compression of the rollers, the cross-section of the material is reduced and the length is increased. This is a commonly used method for producing large-diameter steel pipes. The production method is mainly used to produce large-diameter steel pipe profiles, plates, and pipes. Divided into cold rolling and hot rolling.
2. Forging; a pressure processing method that uses the reciprocating impact of a forging hammer or the pressure of a press to change the blank into the shape and size we require. Generally divided into free forging and die forging, they are often used to produce large materials, blanks, and other materials with larger cross-sections and larger diameters.
3. Drawing: It is a processing method that draws the rolled metal blank (shaped, tube, product, etc.) through the die hole into a reduced cross-section and an increased length. Most of them are used for cold working.
4. Extrusion; it is a processing method in which large-diameter steel pipes place metal in a closed extrusion cylinder and apply pressure on one end to extrude the metal from a prescribed die hole to obtain finished products of the same shape and size. It is mostly used in production. Non-ferrous metal large-diameter steel pipe.