Large-diameter steel pipes are also called large-diameter galvanized steel pipes, which refer to welded steel pipes with hot-dip or electro-galvanized layers on the surface of large-diameter steel pipes. Galvanizing can increase the corrosion resistance of steel pipes and prolong 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 oil heaters and condensation pipes for chemical coking equipment. Pipes for coolers, coal distillation washing oil exchangers, trestle piles, support pipes for mine tunnels, etc.
The forming method of large-diameter steel pipe:
1. Hot push expansion method: The push expansion equipment is simple, low in cost, easy to maintain, economical, and durable, and the product specification 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 the production of medium and thin-wall thick large-diameter steel pipes, and can also produce thick-wall pipes that do not exceed the capacity of the equipment.
2. Hot extrusion method: Before extrusion, the billet needs to be machined and pretreated. 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 be upgraded.
3. Hot piercing and rolling method: Hot piercing and rolling are mainly longitudinal rolling and cross rolling. Longitudinal rolling and extension rolling are mainly limited-moving mandrel tube rolling, few-stand limited-moving mandrel tube rolling, three-roller limited-moving mandrel tube rolling, and floating mandrel tube rolling. These methods have high production efficiency, low metal consumption, good product, and control system, and are increasingly widely used.
At present, the main production processes of large-diameter steel pipes in my country are hot-rolled large-diameter steel pipes and heat-expanded steel pipes. Seamless pipe is what we often call thermal expansion pipe. A steel pipe with a relatively low density but strong shrinkage is used to expand the diameter of the pipe by cross-rolling or drawing. A rough pipe finishes the rolling process. In a short period, the steel pipe can be thickened to produce non-standard and special-type seamless pipes with low cost and high production efficiency, which 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 for the structure and performance of the subsequent process. Alloy structural steel, structural steel with guaranteed hardenability, cold heading steel, bearing steel, tool steel, steel for steam turbine blades, and stainless heat-resistant steel with cable bodies are usually delivered in an annealed state.
Large-diameter steel pipe processing method:
1. Rolling: The metal billet of large-diameter steel pipes passes through the gap between a pair of rotating rolls (various shapes), and the material cross-section is reduced due to the compression of the rolls, and the length is increased. The pressure processing method is commonly used in the production of 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 force of the forging hammer or the pressure of the press to change the blank into the shape and size we need. It is generally divided into free forging and die forging and is often used to produce materials with large cross-sectional dimensions such as large-scale steel pipes and billets.
3. Pulling; it is a processing method in which the rolled metal blank (type, pipe, product, etc.) is pulled through the die hole to reduce the cross-section and increase the length. Most of them are used for cold work.
4. Extrusion: It is a processing method in which a large-diameter steel pipe puts the metal in a closed extrusion box, and one end applies pressure to extrude the metal from the specified die-hole to obtain a finished product with the same shape and size. It is mostly used in the production of Large-diameter steel pipes made of non-ferrous metals.