What is a seamless carbon steel pipe?
Seamless carbon steel pipe is a weld-free metal pipe made of carbon steel (carbon content 0.02%~2.11%) through hot rolling, cold rolling or cold drawing. Its core feature is that the overall structure is continuous, and its pressure bearing capacity is better than that of welded steel pipe, which is suitable for scenes with high pressure, high temperature or high precision requirements.
Characteristics of seamless carbon steel pipe:
1. No weld defects: avoid strength weaknesses and leakage risks caused by welding.
2. High pressure bearing capacity: The bursting pressure can reach 1.5 times that of welded pipes of the same specification.
3. Temperature range: carbon steel pipe: -20~350℃; alloy steel pipe (such as 15CrMo): -40~550℃.
4. Processing flexibility: heat treatment (quenching, tempering), bending, and flaring are possible.
Types of seamless carbon steel pipes:
1. Classification by carbon content
Seamless carbon steel pipes can be divided into low carbon steel, medium carbon steel and high carbon steel according to carbon content. Low carbon steel has good toughness and weldability, and is suitable for manufacturing general structures and fluid delivery pipelines; medium carbon steel has high strength and wear resistance, and is often used to manufacture mechanical parts and bearings; high carbon steel is often used to manufacture knives and cutting tools due to its high hardness and wear resistance.
2. Classification by use
a. Seamless carbon steel pipe for structure: used for structural support in the fields of construction, machinery manufacturing (mechanical pipes), etc. It has high strength and rigidity and can withstand large loads.
b. Seamless carbon steel pipe for fluid transportation: mainly used to transport various fluid media, such as oil, natural gas, tap water, etc. This type of steel pipe requires good pressure resistance, sealing and corrosion resistance.
c. Seamless carbon steel pipe for high-pressure boiler pipe: used for power station boilers, industrial boilers and other equipment, and withstands the effects of high-temperature and high-pressure steam. It is required to have good heat resistance, pressure resistance and oxidation resistance.
d. Seamless carbon steel pipe for hydraulic use: used for hydraulic systems such as hydraulic cylinders and oil cylinders, and belongs to the type of cold-drawn or cold-rolled precision seamless steel pipe.
d. Seamless carbon steel pipe for petroleum cracking: used in cracking devices in the petrochemical industry, and withstands high temperature, high pressure and corrosive media. It has good corrosion resistance and high temperature strength.
3. Classification by production process
Seamless carbon steel pipes can be divided into the following three main types according to the production process:
1) Hot-rolled seamless steel pipes
Hot-rolled seamless steel pipes are a large category of seamless steel pipes, which are divided according to the production method. Hot rolling is relative to cold rolling, which is rolling at room temperature, while hot rolling is rolling above the recrystallization temperature. Seamless steel pipes are relative to welded steel pipes. Seamless steel pipes are usually made by perforating round steel and then processing, and welded steel pipes are usually made by welding steel plates in different ways.
Hot-rolled seamless steel pipes are generally produced on automatic pipe rolling units. The solid tube billet is inspected and surface defects are removed, cut into the required length, centered on the end face of the perforated end of the tube billet, and then sent to the heating furnace for heating and perforated on the perforator. While piercing, it rotates and moves forward continuously. Under the action of the rollers and the head, a cavity is gradually formed inside the tube billet, which is called a rough tube. Then it is sent to the automatic tube rolling machine for further rolling. Finally, the wall thickness is leveled by the leveling machine, and the diameter is determined by the sizing machine to meet the specification requirements. The use of a continuous tube rolling unit to produce hot-rolled seamless steel pipes is a more advanced method.
Process flow:
Hot-rolled seamless steel pipe: round tube billet → heating to 1200℃ → piercing → three-roller oblique rolling, continuous rolling or extrusion → tube removal → sizing (or reducing diameter) → cooling → billet tube → straightening → hydrostatic test (or flaw detection) → marking → storage.
Hot-rolled seamless pipes are usually used in large projects involving higher pressures and temperatures. Typical standard: ASTM A106
Features:
Advantages: The heat treatment process makes it extremely hard and tough, and can withstand high temperatures and high pressures. Compared with cold rolling, it has high production efficiency and cost-effectiveness, and can produce large-diameter and thick-walled steel pipes.
Disadvantages: Rough surface (with oxide scale), low dimensional accuracy (tolerance ±1%), heavy weight, and may be difficult to transport and install.
Application scenarios:
Oil casing (API 5CT J55/N80)
Building structure support (such as plant columns)
Ordinary fluid delivery pipeline (low-pressure water, gas)
Boiler pipe for high temperature and high pressure.
2) Cold-rolled/cold-drawn seamless steel pipe
Cold-rolled precision seamless steel pipe is a seamless steel pipe with high dimensional accuracy and good surface finish for precision mechanical structures, hydraulic equipment or steel sleeves.
The cold processing methods of steel pipes mainly include cold drawing and cold rolling. The raw materials of cold-processed steel pipes can be hot-rolled seamless steel pipes or welded pipes. The common characteristics of the cold processing method of steel pipes are high dimensional accuracy and good surface roughness. It can produce thin-walled pipes with extremely thin diameters of 0.05~0.01mm and capillaries with extremely thin diameters of 0.3~0.1 mm.
Cold-rolled seamless steel pipe:
Cold-rolled seamless pipe is cold-rolled on the basis of hot-rolled steel pipe, which can achieve higher dimensional accuracy and surface quality, and is suitable for manufacturing high-precision, small-diameter steel pipes. Unlike hot-rolled steel pipes, cold-rolled steel pipes are harder and more brittle. Cold-rolled steel pipes have higher processing and forming accuracy and are very suitable for precision equipment.
In appearance, cold-rolled seamless steel pipes are shorter than hot-rolled seamless steel pipes. The wall thickness of cold-rolled seamless steel pipes is generally smaller than that of hot-rolled seamless steel pipes, but the surface looks brighter than thick-walled seamless steel pipes, with less surface roughness and fewer burrs on the diameter. The maximum nominal diameter of cold-rolled pipes is 200 mm, and the maximum nominal diameter of hot-rolled pipes is 600 mm.
Cold-drawn seamless steel pipes:
Cold-drawn seamless pipes & tubes are made by forcing hot-rolled pipes through one or more dies, which can further improve the dimensional accuracy and surface quality of the steel pipes, while improving the strength of the steel pipes. They are suitable for manufacturing high-precision, high-strength steel pipes. This forces the material to become denser, thereby increasing its strength. They are ideal for applications where strength and pressure resistance are critical.
Process:
Hot rolled tube blank → pickling → cold rolling/cold drawing → annealing → finishing
Cold rolled tube production uses a cyclic cold rolling mill. The working characteristics of the cyclic cold rolling mill are that the steel tube and mandrel are stationary, and the rolling mill is driven by the reciprocating motion of the frame to reciprocate the rolling of the steel tube, and the rolled piece is compressed by a variable cross-section hole to achieve the purpose of reducing the diameter and wall.
Features:
Advantages: high dimensional accuracy (tolerance ±0.05mm), smooth surface (Ra≤1.6μm), and 20%~30% increase in strength.
Disadvantages: low production efficiency, high cost, limited specifications (usually Φ≤250mm), and limited customization.
Differences between cold rolling and cold drawing:
Cold rolling is radial compression forming, and cold drawing is axial stretching forming. Cold rolling with multiple passes can better control dimensional accuracy, while cold drawing with unidirectional stretching can easily lead to micro-ovality. Cold-rolled tubes have uniform work hardening and fatigue life 30% to 50% higher than cold-drawn tubes. For key pressure-bearing components (such as hydraulic systems), cold-rolled tubes should be used first even if the cost increases by 30%, which can greatly reduce the risk of tube explosion.
Cold-rolled tubes: used for high precision, high fatigue strength, and harsh environments (hydraulics, bearings, energy). Typical standard: ASTM A519.
Cold-drawn tubes: suitable for general structures, low costs, and medium and low load scenarios (construction, general machinery).
Application scenarios:
Hydraulic cylinders, bearing sleeves (such as 45# precision cold-drawn tubes)
Automobile transmission shafts, precision instrument components
High-precision fluid control systems (such as chemical metering pump tubes)
3) Extruded seamless steel pipes
Extruded seamless steel pipes are weld-free steel pipes produced by hot extrusion processes, which are particularly suitable for the manufacture of high-alloy steels, difficult-to-deform metals, and large-diameter thick-walled pipes. It has core characteristics such as high strength, high temperature resistance, corrosion resistance, wear resistance, and aging resistance. Its production process ensures strength uniformity and dimensional stability through precision processing.
Process:
Steel billet → heating → glass lubrication → extruder forming → straightening
Features:
Advantages: can produce complex cross-sections (such as special-shaped tubes) and high-alloy steel tubes (such as P91).
Disadvantages: large equipment investment, only suitable for small batches of special tubes.
Typical standard: ASTM A213
Application scenarios:
Nuclear power steam generator pipelines
Supercritical power plant boiler tubes (such as 12Cr1MoVG)
Selection suggestions:
Select hot-rolled tubes: low cost, large diameter requirements (such as water pipes above DN400).
Select cold-drawn tubes: high precision, high strength scenarios (such as hydraulic systems).
Select alloy steel tubes: high temperature/low temperature/corrosive environment (such as 15CrMo heat resistance, 09MnD low temperature resistance).
Conclusion:
Seamless carbon steel pipes meet different needs through three processes: hot rolling, cold rolling/cold drawing, and extrusion. Its weld-free and high-strength characteristics make it a core material in energy, machinery and other fields. When selecting a model, you need to consider the four major factors of pressure, temperature, accuracy, and cost, and strictly follow relevant industry standards (such as API, ASTM, GB).
Read more: Schedule 80 Carbon Steel Pipe or Carbon Steel vs Black Steel
