Large diameter square pipe, with hollow section, is widely used as a pipe for conveying fluid Such as pipelines for transporting oil, natural gas, gas, water and some solid materials. Compared with solid steel such as round steel, steel pipe has the same bending and torsional strength and light weight. It is an economic section steel. It is widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipe, automobile transmission shaft, bicycle frame and steel scaffold used in construction. Manufacturing ring parts with steel pipes can improve material utilization, simplify manufacturing processes, and save materials and processing hours, such as rolling bearing rings, Jack sleeves, etc. steel pipes have been widely used for manufacturing. Steel pipe is also an indispensable material for all kinds of conventional weapons. Gun barrel and barrel should be made of steel pipe. Steel pipe can be divided into round pipe and special-shaped pipe according to different cross-sectional area and shape. Because the circular area is the largest under the condition of equal circumference, more fluid can be transported by circular pipe. In addition, when the ring section is subjected to internal or external radial pressure, the force is more uniform. Therefore, most steel pipes are round pipes. However, the circular pipe also has certain limitations. For example, under the condition of plane bending, the bending strength of the circular pipe is not as strong as that of the square and rectangular pipe. Square and rectangular pipes are commonly used in the framework of some agricultural machines and tools and steel and wood furniture. Special shaped steel pipes with other section shapes are also required according to different purposes. 1. Large diameter square tube for structure (GB / T8162-1999) is a large diameter square tube for general structure and mechanical structure. 2. Large diameter square tube for fluid transportation (GB / t8163-1999) is a general large diameter square tube used to transport water, oil, gas and other fluids. 3. Large diameter square tubes for low and medium pressure boilers (GB3087-1999) are high-quality carbon structural steel hot-rolled and cold drawn (rolled) large diameter square tubes for manufacturing superheated steam tubes, boiling water tubes for low and medium pressure boilers of various structures and superheated steam tubes, large smoke tubes, small smoke tubes and arch brick tubes for locomotive boilers. 4. Large diameter square tubes for high-pressure boilers (GB5310-1995) are high-quality carbon steel, alloy steel and stainless heat-resistant steel large-diameter square tubes used to manufacture the heating surface of water tube boilers with high pressure and above. 5. High pressure large diameter square pipe (GB6479-2000) for chemical fertilizer equipment is a high-quality carbon structural steel and alloy steel large diameter square pipe suitable for chemical equipment and pipeline with working temperature of - 40 ~ 400 ℃ and working pressure of 10 ~ 30mA. 6. Large diameter square tubes for petroleum cracking (gb9948-88) are large diameter square tubes suitable for furnace tubes, heat exchangers and pipelines in petroleum refineries. 7. The steel pipe for geological drilling (yb235-70) is the steel pipe used by the geological department for core drilling. According to the purpose, it can be divided into drill pipe, drill collar, core pipe, casing and sedimentation pipe. 8. Large diameter square tube (gb3423-82) for diamond core drilling is a large diameter square tube for drill pipe, core rod and casing used for diamond core drilling. 9. Oil drilling pipe (yb528-65) is a large-diameter square pipe used for internal or external thickening at both ends of oil drilling. The steel pipe is divided into turning wire and non turning wire. The turning wire pipe is connected with the joint, and the non turning wire pipe is connected with the tool joint by butt welding. 10. Marine carbon steel large-diameter square pipe (gb5213-85) is a carbon steel large-diameter square pipe for manufacturing class I pressure pipe system, class II pressure pipe system, boiler and superheater. The working temperature of carbon steel large-diameter square tube wall shall not exceed 450 ℃, and the working temperature of alloy steel large-diameter square tube wall shall exceed 450 ℃. 11. Large diameter square tube for automobile half axle sleeve (gb3088-82) is a hot-rolled large diameter square tube made of high-quality carbon structural steel and alloy structural steel for automobile half axle sleeve and drive axle housing. 12. High pressure oil pipe for diesel engine (gb3093-2002) is a cold drawn large-diameter square pipe for manufacturing high-pressure pipe of diesel engine injection system. 13. Precision inner diameter large diameter square tube for hydraulic and pneumatic cylinder barrel (GB8713-88) is a cold drawn or cold rolled precision large diameter square tube with precision inner diameter for manufacturing hydraulic and pneumatic cylinder barrel. 14. Cold drawn or cold rolled precision large diameter square tube (GB3639-2000) is a cold drawn or cold rolled precision large diameter square tube with high dimensional accuracy and good surface finish for mechanical structure and hydraulic equipment. Selecting precision large-diameter square tube to manufacture mechanical structure or hydraulic equipment can greatly save machining hours, improve material utilization and improve product quality. 15. Stainless steel large-diameter square pipe for structure (GB / T14975-2002) is a hot-rolled (extruded, expanded) and cold drawn (rolled) large-diameter square pipe made of stainless steel for corrosion-resistant pipes, structural parts and parts widely used in chemical, petroleum, light textile, medical, food, machinery and other industries. 16. Stainless steel large diameter square tube for fluid transportation (GB / T14976-2002) is a hot-rolled (extruded, expanded) and cold drawn (rolled) large diameter square tube made of stainless steel for fluid transportation. 17. Special shaped large-diameter square tube is the general name of large-diameter square tube with other section shapes except circular tube. According to the different shape and size of steel pipe section, it can be divided into special-shaped large-diameter square pipe with equal wall thickness (code D), special-shaped large-diameter square pipe with different wall thickness (code BD) and special-shaped seamless steel pipe with variable diameter (code BJ). Special shaped large-diameter rectangular tubes are widely used in various structural parts, tools and mechanical parts. Compared with circular pipe, special-shaped pipe generally has larger moment of inertia and section modulus, and has greater bending and torsion resistance, which can greatly reduce the structural weight and save steel. Many defects of square tube are caused in perforation, so the power transmission process of square tube blank is the key procedure for producing square tube. The main difficulty of perforation of high alloy lies in the low perforation performance. In order to ensure the quality, it is necessary to rationally select the deformation parameters of perforation. Small compression will cause instability in the perforation process, so when the critical compression is small, the plug should be in the front, and the compression is generally set at about 7%, otherwise it will not bite, or even increase the movement or get stuck in the front. The increase of the compression in front of the plug will also form the hole cavity and sink the defects in the sound. Therefore, if you want to solve the customer service problem, the pipe blank should be centered, and the empty depth of centering should be compared according to other steel grades. Therefore, the heating system is the outlet temperature and the requirements for heating quality. The quality of heating depends largely on heating operation and heating system. A small ellipticity coefficient will generally improve the quality of the capillary and limit the transverse deformation. However, the ellipse coefficient is too small, which will cause the difficulty of rolling piece rotation, and even lead to the wear of guide plate, which is easy to cause defects on the surface. Therefore, the wear of the guide plate should be generally checked when the ship is binding the square pipe. Once it is found, it should be replaced immediately. The degree of ellipse should be controlled within the range of 1.07-1.08. It affects the normal operation of subsequent processes, as well as the key process of heating square tube blank, which also has a great impact on the quality of finished products.