Thick-walled seamless carbon steel pipe

What is a thick-walled seamless carbon steel pipe?

Thick-walled seamless carbon steel pipe refers to a carbon steel pipe produced by seamless processes (such as hot rolling, cold drawing or extrusion), with a large wall thickness to pipe diameter ratio (usually wall thickness/outer diameter ≥ 0.05). Since there is no weld, its structure is more uniform and its strength is higher, suitable for high pressure, high load or harsh environment.

Production process:
Hot rolling method: used for large-diameter thick-walled pipes (such as Φ≥50mm), high-temperature forming and cooling.
Cold drawing method: produces small-diameter high-precision thick-walled pipes with high surface finish.

Extrusion method: suitable for special alloys or special-shaped thick-walled pipes.

Manufacturing and processing technology of thick-walled seamless carbon steel pipes:

The manufacturing of thick-walled seamless carbon steel pipes is a complex and delicate process, mainly including raw material preparation, perforation, rolling, heat treatment, finishing and inspection. The raw materials are mostly high-quality carbon steel, which can enter the production process only after strict chemical composition analysis and mechanical property testing.

1. Raw material preparation
The production of thick-walled seamless pipes begins with the preparation of raw materials. Usually, steel billets or ingots are used as raw materials, which are heated to a certain temperature through a heating furnace to make them soft and processable. The heating process is usually carried out at around 1500℃ to ensure that the steel has sufficient plasticity.

2. Perforation
The perforation process is the first and most critical step in the manufacture of thick-walled seamless carbon steel pipes. Solid round steel billets are perforated into hollow rough tubes through hot perforation or cold perforation processes. Hot perforation uses high temperature to soften the metal and reduce deformation resistance, while cold perforation relies on strong pressure to perforate the billet directly at room temperature. Both have their advantages and disadvantages, and they are selected according to product requirements and material characteristics.

Extrusion process: The heated billet passes through an extruder or rolling mill for initial deformation. During the extrusion process, the billet is strongly extruded through a die to form a rough tube billet. Rolling passes the billet through a series of rollers to gradually reduce its cross-section to form a tubular semi-finished product. The purpose of this stage is to transform the billet into the approximate shape of the required outer diameter and wall thickness.

3. Rolling
The rolling process is a key link in improving the uniformity of the wall thickness and dimensional accuracy of the steel pipe. The perforated pipe enters the sizing mill and continuously adjusts the inner and outer diameters and wall thickness of the steel pipe through multiple rolling passes until the design requirements are met. In this process, temperature control, roll design and precise adjustment of rolling process parameters are essential to achieve the required mechanical properties and dimensional requirements.

4. Heat treatment
The pipe undergoes a heat treatment process to improve its mechanical properties. Common heat treatment methods for carbon steel seamless pipes include annealing and normalizing. Annealing helps eliminate internal stress in the pipe and improve its toughness and plasticity. Normalizing increases the strength and hardness of the pipe to ensure its stable performance in use. The specific selection depends on the material and final use of the steel pipe.

5. Finishing and inspection
Finally, the thick-walled seamless pipe is finished, inspected and processed. This includes dimensional inspection, non-destructive testing (such as ultrasonic testing or radiographic testing) to ensure that there are no internal defects, as well as visual inspection and pressure testing. After passing the inspection, the pipe undergoes final surface treatment, such as anti-corrosion coating or cleaning, to improve its durability and protective performance.

Main application areas of thick-walled carbon steel pipes:

Oil and gas: drill pipes, casing, oil pipelines.
Chemical equipment: high-pressure reactors, heat exchanger pipelines.
Power energy: boiler tubes, steam transmission pipes.
Mechanical manufacturing: hydraulic cylinders, bearing sleeves, heavy equipment brackets.
Military and aerospace: pressure-resistant components, missile shells.

Selection recommendations:

High-pressure/high-load environments (such as oil and chemicals): seamless thick-walled steel pipes are preferred.
Limited budget and low pressure: welded thick-walled steel pipes can be considered (weld quality needs to be tested).
Anti-corrosion requirements: choose galvanized, plastic-coated or stainless steel composite pipes.

Thick-walled seamless carbon steel pipes have become the preferred pipe material in key industrial fields due to their high strength, pressure resistance, and long life.

Read more: Thick-walled Mechanical Tubing vs. Structural Tubing