Hot rolled seamless steel tube

What is Hot-rolled Seamless Steel Tubes

Hot rolling is relative to cold rolling, cold rolling is rolling below the recrystallization temperature, and hot rolling is rolling above the recrystallization temperature.

Hot-rolled seamless steel tubes are made from carbon or alloy steel through high-temperature rolling and perforation. They typically have an outer diameter of 32mm or greater and a wall thickness ranging from 2.5mm to 75mm. The production process includes ingot perforation, hot rolling, and quality inspection. This process refines the grain size and improves mechanical properties, making it suitable for applications in construction, machining, petrochemicals, and fluid transportation.

Hot-rolled seamless steel tubes are divided into general steel tubes, low- and medium-pressure boiler steel tubes, high-pressure boiler steel tubes, alloy steel tubes, stainless steel tubes, petroleum cracking tubes, geological steel tubes and other steel tubes.

Hot-Rolled Seamless Steel Tube Production Process

Hot-rolled seamless steel tubes: Round billet → Heating → Perforation → Three-roller cross-rolling, continuous rolling, or extrusion → Tube stripping → Sizing (or reducing) → Cooling → Billet tube → Straightening → Hydrostatic testing (or flaw detection) → Marking → Storage.

Materials of Hot-Rolled Seamless Steel Tubes

Hot-rolled seamless steel tubes are typically made of carbon steel, alloy steel, and stainless steel.

Carbon steel grades include 20#, 45#, and Q345B.

Alloy steel grades include 16Mn, 12CrMo, and 15CrMo.

Stainless steel grades include 304 and 316.

Specifications And Wall Thicknesses of Hot-Rolled Seamless Steel Tubes

Hot-rolled seamless steel tubes come in a wide variety of specifications and wall thicknesses, generally classified by outer diameter and wall thickness.

Common outer diameters range from φ6 to φ720 mm, and wall thicknesses range from 0.5 to 60 mm.

Hot-rolled seamless steel tubes of varying specifications and wall thicknesses are suitable for different applications.

Hot-Rolled Seamless Steel Tube Advantage

1. Uniform Wall Thickness

Due to the high temperature and pressure experienced during the hot rolling process, the steel pipe achieves a more uniform wall thickness.

2. Smooth Internal and External Surfaces

The smooth internal and external surfaces of hot-rolled seamless steel tubes reduce fluid resistance in the pipe.

3. Precise Dimensions

The precise dimensions of hot-rolled seamless steel tubes meet the requirements of various industrial applications.

4. High-Temperature and Pressure Resistance

Hot-rolled seamless steel tubes offer excellent high-temperature and pressure resistance, making them suitable for use in high-temperature and high-pressure environments.

Hot-Rolled Seamless Steel Tube Disadvantage

1. Delamination Occurs

After hot rolling, the non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, and delamination (interlayer) occurs.

Delamination greatly deteriorates the tensile properties of the steel in the thickness direction, and it is possible that interlayer tearing may occur when the weld shrinks.

2. Residual Stress Caused by Uneven Cooling

Residual stress is the internal self-balanced stress without external force. Hot-rolled steel sections of various cross-sections have such residual stresses.

Generally, the larger the section size of the steel section, the larger the residual stress. Although the residual stress is self-balanced, it still has a certain influence on the performance of the steel member under the action of external force.

For example, it may have adverse effects on deformation, stability, fatigue resistance, etc.

3. Not Easy to Control in Terms of Thickness and Edge Width

Since at the beginning, even if the length and thickness are up to the standard, there will be a certain negative difference after the final cooling.

The wider the negative difference, the thicker the thickness, the more obvious the performance.

Therefore, for large-sized steel, the side width, thickness, length, angle, and sideline of the steel cannot be too precise.

Quality Control of Hot-Rolled Seamless Steel Tubes

Ensuring the quality of hot-rolled seamless steel tubes requires strict control in multiple areas:

1. Raw material control

The chemical composition of the steel billet must be diverse and meet standard requirements, and the content of harmful elements must be strictly controlled. Surface quality and internal defects in the steel billet must also be monitored through testing.

2. Process parameter control

Parameters such as heating temperature, rolling temperature, deformation, and rolling speed all require precise control. Any deviation can result in substandard product performance. Modern production lines typically utilize automated control systems to ensure process stability.

3. Finished product inspection

Hot-rolled seamless steel tubes undergo multiple tests before leaving the factory, including dimensional measurement, surface inspection, ultrasonic testing, hydrostatic testing, and mechanical property testing. Only products that pass all inspections are released.

In addition to routine testing, some seamless steel pipes for special applications require additional testing, such as low-temperature impact testing, intergranular corrosion testing, and non-destructive testing, to meet the requirements of specific operating environments.

The Difference Between Hot-Rolled and Cold-Rolled Seamless Tubes

Many may wonder what the difference is between hot-rolled and cold-rolled seamless tubes. In reality, the primary difference lies in the production process and final performance:

1. Production Process

Hot rolling is performed at high temperatures, while cold rolling is performed at room temperature or lower.

2. Surface Quality

Cold-rolled tubes have a smoother surface and higher dimensional accuracy, but hot-rolled pipes have greater toughness.

3. Cost

The hot-rolling process is relatively simple, resulting in lower production costs and suitable for large-scale production.

How to Choose the Right Hot-rolled Seamless Tube?

In actual purchasing, consumers may face the dilemma of how to choose. The following factors are worth considering:

1. Material

Different steel pipe materials, such as ordinary carbon steel, alloy steel, or stainless steel, are suitable for different environments, and the choice should be based on specific needs.

2. Dimensional Accuracy

If you have strict requirements for pipe diameter and wall thickness, you should prioritize manufacturers with strong quality control.

3. Price

The price of hot-rolled seamless tube is affected by raw materials, processing technology, and market supply and demand. We recommend choosing products with the best value for money within your budget.

Read more: Hot-rolled vs Cold-drawn or Infolding of hot rolled seamless steel pipes