Tubing Definition and Knowledge
Tubing is a hollow section with no welds from end to end. Steel pipes, which have hollow sections, are extensively used for conveying fluids such as oil, natural gas, gas, water, and certain solid materials. Compared to solid steel bars like round steel, steel pipes with the same bending and torsional strength are lighter in weight, making them an economical choice of material. They are widely used in manufacturing structural parts and mechanical components, like drill pipes for oil wells, drive shafts for automobiles, frames for bicycles, and steel scaffolding used in construction. Using steel pipes to manufacture ring-shaped parts can increase material utilization rate, simplify manufacturing processes, save materials, and reduce processing time. Examples include raceways for rolling bearings and cylinders for jacks, which are now commonly made using steel pipes. Steel pipes are also indispensable materials for various conventional weapons, including barrels and cannon tubes. Depending on the shape of their cross-sections, steel pipes can be classified into round pipes and special-shaped pipes. Since a circle has the largest area among shapes with equal perimeters, round pipes can convey more fluid. Additionally, when subjected to internal or external radial pressure, circular cross-sections distribute stress evenly; therefore, most steel pipes are round.

Manufacturing Methods:
① Generally, boiler pipes are used at temperatures below 450°C and are primarily manufactured using hot-rolled or cold-drawn pipes made from carbon structural steels with grades 10 and 20.
② High-pressure boiler pipes often operate under high temperature and pressure conditions. The pipes may oxidize and corrode under the influence of high-temperature flue gases and steam. Therefore, they require high sustained strength, excellent resistance to oxidation and corrosion, and good organizational stability.

Uses:
① General boiler pipes are mainly used for manufacturing water-cooled wall pipes, boiling pipes, overheated steam pipes, and small smoke pipes used in locomotive boilers.
② High-pressure boiler pipes are primarily used for making superheater pipes, reheater pipes, guide pipes, and main steam pipes for high-pressure and ultra-high-pressure boilers.

However, round pipes have limitations too. For example, under conditions of plane bending, square or rectangular pipes have greater bending strength than round pipes. Therefore, square or rectangular pipes are commonly used in the frames of agricultural machinery and steel furniture. Depending on the application, other types of special-shaped steel pipes with different cross-sectional shapes are also needed.

1. Structural seamless steel pipes (GB/T8162-1999) are used for general structural and mechanical components.
2. Seamless steel pipes for fluid transportation (GB/T8163-1999) are used for conveying fluids like water, oil, and gas.
3. Low and medium-pressure boiler seamless steel pipes (GB3087-1999) are used for manufacturing low and medium-pressure boiler superheater pipes, boiling pipes, locomotive boiler superheater pipes, large smoke pipes, small smoke pipes, and arch brick pipes.
4. High-pressure boiler seamless steel pipes (GB5310-1995) are used for manufacturing high-pressure and above water-tube boiler heating surfaces using high-quality carbon steel, alloy steel, and heat-resistant stainless steel seamless pipes.
5. High-pressure seamless steel pipes for fertilizer equipment (GB6479-2000) are suitable for chemical equipment and pipelines operating between -40°C and 400°C under pressures of 10 to 30 MPa.
6. Seamless steel pipes for petroleum refining (GB9948-88) are suitable for furnace tubes, heat exchangers, and pipelines in petroleum refineries.
7. Geologic drilling steel pipes (YB235-70) are used by geological departments for core drilling and can be divided into drill rods, collars, core tubes, casing tubes, and settling tubes based on their usage.
8. Seamless steel pipes for diamond core drilling (GB3423-82) are used for drill rods, core rods, and casing tubes in diamond core drilling.
9. Oil drilling pipes (YB528-65) are seamless steel pipes with thickened ends used for oil drilling. These pipes come either threaded or unthreaded. Threaded pipes are connected with couplings, while unthreaded pipes are joined using welding.
10. Carbon steel seamless steel pipes for ships (GB5213-85) are used to manufacture ship-grade pressure pipes and boilers.
11. Seamless steel pipes for automobile semi-shaft sleeves (GB3088-82) are used for manufacturing high-quality carbon structural steel and alloy structural steel hot-rolled seamless steel pipes for automobile semi-shaft sleeves and drive bridge housings.
12. High-pressure oil pipes for diesel engines (GB3093-86) are cold-drawn seamless steel pipes used for manufacturing high-pressure oil lines in diesel engine injection systems.
13. Precision inner diameter seamless steel pipes for hydraulic and pneumatic cylinders (GB8713-88) are cold-drawn or cold-rolled precision seamless steel pipes with precise inner diameters used for hydraulic and pneumatic cylinders.
14. Cold-drawn or cold-rolled precision seamless steel pipes (GB3639-83) are used for mechanical structures and hydraulic equipment due to their high dimensional accuracy and good surface finish. Selecting precision seamless steel pipes can significantly reduce machining time, improve material utilization rates, and enhance product quality.
15. Stainless steel seamless steel pipes for structural purposes (GB/T14975-1994) are widely used in corrosive environments across industries like chemicals, petrochemicals, textiles, medical devices, food processing, and machinery, and are made of stainless steel through hot-rolling (extrusion, expansion) or cold-drawing.
16. Stainless steel seamless steel pipes for fluid transportation (GB/T14976-1994) are used for conveying fluids and are made of stainless steel through hot-rolling (extrusion, expansion) or cold-drawing.
17. Special-shaped seamless steel pipes refer to all seamless steel pipes with cross-sectional shapes other than round. According to the shape and size of the pipe’s cross-section, they can be further divided into equi-thickness special-shaped seamless steel pipes (code D), variable thickness special-shaped seamless steel pipes (code BD), and variable diameter special-shaped seamless steel pipes (code BJ). Special-shaped seamless steel pipes are widely used in structural components, tools, and mechanical parts. Compared to round pipes, they generally have larger moments of inertia and sectional modulus, offering higher resistance to bending and twisting, thereby significantly reducing structure weight and saving steel.

Generally, seamless steel pipes are made from high-quality carbon structural steels such as grades 10, 20, 30, 35, 45, low-alloy structural steels like 16Mn, 5MnV, or alloy structural steels like 40Cr, 30CrMnSi, 45Mn2, 40MnB through hot-rolling or cold-rolling. Low-carbon steels such as grades 10 and 20 are used to make seamless pipes primarily for fluid transportation pipelines, whereas medium-carbon steels like grades 45 and 40Cr are used to manufacture mechanical parts, such as stressed parts in automobiles and tractors. Typically, seamless steel pipes must pass strength and flattening tests. Hot-rolled steel pipes are delivered in a hot-rolled state or after heat treatment; cold-rolled pipes are delivered after heat treatment. Low and medium-pressure boiler seamless steel pipes are used for manufacturing various low and medium-pressure boilers, superheated steam pipes, boiling pipes, water-cooled wall pipes, locomotive boiler superheater pipes, large smoke pipes, small smoke pipes, and arch brick pipes.

High-quality carbon structural steel hot-rolled or cold-drawn (rolled) seamless steel pipes are used. Mainly made from grades 10 and 20 steels, these pipes must undergo hydrostatic testing, flaring, expanding, and flattening tests. Hot-rolled steel pipes are delivered in a hot-rolled state, and cold-rolled (drawn) pipes are delivered after heat treatment.

18. GB18248-2000 (Seamless steel pipes for gas cylinders) is primarily used for manufacturing various gas and hydraulic cylinders. Typical materials include 37Mn alloy steel tubes, 34Mn2V, 35CrMo steel tubes, J55 oil casing tubes, etc.