Classification and application scope of hot rolled

2022-07-22
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As the name suggests, hot rolled seamless pipe refers to the seamless pipe made of high-quality carbon structural steel or solid pipe blanks such as No. 10, No. 20, No. 30 and No. 35 through hot rolling process and perforation. Because of its good sealing, high strength and strong pressure resistance, it is generally used for fluid transportation. Due to the high temperature during processing, the deformation of hot-rolled seamless pipe is large, which can withstand large deformation pressure. The requirement for the accuracy of size is relatively low, which can effectively avoid the shape problem

hot rolling seamless pipe, hot rolling is relative to cold rolling, cold rolling is rolling below the recrystallization temperature, and hot rolling is rolling above the recrystallization temperature. According to different uses and materials, hot-rolled seamless tubes are divided into many types, such as alloy tubes, which are mainly used in petroleum, smelting, chemical and other fields; High pressure boiler tubes are mainly used for the manufacture of heating tubes, steam pipelines and other high-pressure boiler related supporting pipelines; High pressure fertilizer pipe, which is used in ultra-low temperature (-40 ℃) or ultra-high temperature (400 ℃) working environment and high pressure environment. There are many categories of hot-rolled seamless pipes, and the corresponding uses of each sub category are different. Therefore, each type also has different specifications and follows different executive standards. Now we list the Executive Standards and specifications of the ten most commonly used steel pipes as follows

classification of hot rolled seamless pipes

hot rolled seamless pipes

hot rolled seamless pipes are divided into general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, geological steel pipes and other steel pipes

cold rolled (rolled) seamless steel pipe

in addition to general steel pipe, low and medium pressure boiler steel pipe, high pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, petroleum cracking pipe and other steel pipes, it also includes carbon thin-walled steel pipe, alloy thin-walled steel pipe, stainless thin-walled steel pipe and special-shaped steel pipe. The outer diameter of hot-rolled seamless pipe is generally greater than 32mm, and the wall thickness is 2.5-75mm. The outer diameter of cold-rolled seamless pipe can reach 6mm, and the wall thickness can reach 0.25mm. The outer diameter of thin-walled pipe can reach 5mm, and the wall thickness is less than 0.25mm. Cold rolling has higher dimensional accuracy than hot rolling

hot rolled seamless pipe features

advantages

can destroy the casting structure of ingot, refine the grain of steel, and eliminate the defects of microstructure, so as to make the steel dense and improve the mechanical properties. This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic to a certain extent; Bubbles, cracks and porosity formed during pouring can also be welded under high temperature and pressure

disadvantages

after hot rolling, the non-metallic inclusions (mainly sulfides, oxides, and silicates) in the steel are pressed into thin sheets, resulting in delamination (interlayer). Delamination greatly deteriorates the tensile properties of steel along the thickness direction, and it is possible to have interlaminar tearing when the weld shrinks. The local strain induced by weld shrinkage often reaches several times of the yield point strain, which is much larger than the strain caused by load; 2. Residual stress caused by uneven cooling. Residual stress is the stress of internal self-equilibrium without external force. Hot rolled sections of various sections have this kind of residual stress. Generally, the larger the section size of the section steel is, the greater the residual stress is. Although the residual stress is self balanced, it still has a certain impact on the performance of steel members under external forces. For example, it may have adverse effects on deformation, stability, fatigue resistance, etc. 3. The thickness and side width of hot rolled steel products are not easy to control. We are familiar with thermal expansion and cold contraction. Even if the length and thickness meet the standard at the beginning of hot rolling, there will be a certain negative difference after cooling. The wider the negative difference is, the thicker the thickness is, the more obvious it is. Therefore, for large-sized steel, there is no way to require too accurate side width, thickness, length, angle, and sideline of steel

Executive Standards and specifications of hot rolled seamless tubes

1 Alloy pipe

executive standard: GB5310-2008, GB6479-2000, GB9948-2006, din17175-79, astmsa335, astmsa213, jisg3467-88, jisg3458-88

specification: ∮ 8-1240*1-200

2 Stainless steel pipe

executive standard: gb/t14975-2002, gb/t14976-2002, gb13296-2007, astma213, astma269, astma312, jisg3459, din17458

specification: ∮ 6-630*0.5-60

3 Cryogenic tube

executive standard: gb/t18984-2003, astma333

specification: ∮ 8-1240*1-200

4 Executive standard of high pressure boiler tube: GB5310-1995, astmsa106, astmsa210, din17175-79, GB6479-2000

specification: ∮ 8-1240*1-200

5 Petroleum cracking pipe

executive standard: gb9948-2013

specification: ∮ 8-630*1-60

6 Low and medium pressure boiler tubes

executive standard: gb3087-2008

specification: ∮ 8-1240*1-200

7 Executive standard of fluid delivery pipe: gb/t8163-2008, astma106, astma53

specification: ∮ 8-1240*1-200

8 General structural pipe

executive standard: gb/t8162-2008, gb/t17396-1998, astma53

specification: ∮ 8-1240*1-200

9 Oil casing

executive standard: apispec5ct, iso11960

specification: ∮ 60.23-508.00*4.24-16.13

10 Straight seam steel pipe

executive standard: gb/t13793-1992, gb3091-2001

specification: ∮ 32-630*1-30

hot rolled seamless pipe preparation

generally used seamless steel pipe: it is made of 10, 20, 30, 35, 45 and other high-quality carbon Bonded Steel 16Mn, 5mnv and other low-alloy structural steel or 40Cr, 30CrMnSi, 45Mn2, 40MnB and other alloy steel hot rolled or cold rolled. 10. Seamless pipes made of 20 and other low carbon steels are mainly used for fluid transmission pipelines. Seamless pipes made of medium carbon steel such as 45 and 40Cr are used to manufacture mechanical parts, such as the stressed parts of automobiles and tractors. Generally, the strength and flattening test of seamless steel pipes should be ensured. Hot rolled steel pipes are delivered in hot rolled state or heat treatment state; Cold rolled products are delivered in heat-treated condition

1. Hot rolled (extruded) seamless steel pipe: round billet → Heating → Perforation → Three roll cross rolling, continuous rolling or extrusion → Off pipe → Sizing (or reducing) → Cooling → Straightening → Hydrostatic test (or flaw detection) → Mark → Warehousing

2 Cold drawn (rolled) seamless steel pipe: round billet → Heating → Perforation → Lead → Annealing → Pickling → Oiling (copper plating) → Multi pass cold drawing (cold rolling) → Blank tube → Heat treatment → Straightening → Hydrostatic test (flaw detection) → Mark → Warehousing

calculation formula

(outer diameter - wall thickness) * wall thickness *0.02466=kg/meter (weight per meter)

editor's summary: hot rolled seamless pipes are mostly used for the transportation of fluids in large-scale construction, which is conducive to the transportation of oil smelters, geological exploration, gas hydraulics, corrosive materials, etc. therefore, the quality requirements for pipes are very high, requiring their materials to have high corrosion resistance and compression resistance, and the manufacturing process needs to be accurate, It is strictly seamless to prevent the leakage of conveying fluid. Because there are many categories of hot-rolled seamless pipes, users need to choose the most suitable pipes according to their actual construction needs

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