Small-diameter seamless steel pipes refer to seamless steel tubes with relatively small outer diameters. They can be categorized into seamless small-diameter pipes and straight-seam (welded) small-diameter pipes. In general, pipes with an outer diameter between 4 mm and 89 mm fall into the small-diameter range.
Although widely used, many users have limited familiarity with their specifications. These pipes are produced and inspected in accordance with standards such as ASTM A106, ASTM A53, EN 10216, and GB/T 8163, which define their chemical composition, mechanical properties, and dimensional tolerances.
Standard Specifications of Small-Diameter Seamless Steel Pipes
1. Diameter (OD) and Wall Thickness (WT)
Outer diameter typically ranges from 4 mm to 89 mm.
Common sizes for industrial and hydraulic systems fall between Φ6 mm and Φ89 mm.
Standard wall thickness is usually 1.0 mm to 5.0 mm.
Precision tubes may have wall thicknesses down to 0.5 mm.
For high-pressure or thick-wall applications, WT can increase to 10 mm.
2. Manufacturing Process
Small-diameter seamless steel pipes are mainly produced using cold drawing or cold rolling, which provides:
High dimensional accuracy
Smooth inner and outer surfaces
Tight tolerance control
This makes them ideal for applications requiring high precision and reliable mechanical performance.
Specifications of Small Diameter Seamless Steel Pipes
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6*1
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18*5
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25*6
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8*1
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18*6
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25*7
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8*1.5
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19*1.5
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25*8
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8*2
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19*2
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27*2
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10*1
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19*2.5
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27*2.5
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10*1.5
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19*3
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27*3
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10*2
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19*4
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27*4
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10*2.5
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19*5
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27*5
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12*1
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20*1.5
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27*6
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12*1.5
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20*2
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27*7
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12*2
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20*2.5
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28*2
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12*2.5
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20*3
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28*2.5
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12*3
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20*4
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28*3
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14*1.5
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20*5
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28*3.5
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14*2
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20*6
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28*4
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14*2.5
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22*1.5
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28*5
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14*3
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22*2
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28*6
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14*4
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22*2.5
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28*7
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16*1.5
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22*3
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30*2
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16*2
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22*4
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30*3
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16*2.5
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22*5
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30*4
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16*3
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22*6
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30*5
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16*4
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25*1.5
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30*6
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16*5
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25*2
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30*7
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18*1.5
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25*2.5
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30*8
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18*2
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25*3
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41*2
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18*2.5
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25*3.5
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18*3
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25*4
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18*4
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25*5
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How to Choose the Right Small-Diameter Seamless Steel Pipe
Identify the Application
Determine whether the pipe will be used for hydraulic systems, precision instruments, medical equipment, high-pressure pipelines, or structural installations.
Select Proper Size and Wall Thickness
Choose the appropriate outer diameter (OD) and wall thickness (WT) based on operating pressure, structural load requirements, and installation space limitations.
Choose Suitable Material and Standards
For environments requiring corrosion resistance, hygiene, or high-temperature performance, consider stainless steel or alloy steel. Ensure the pipe complies with standards such as GB/T, ASTM, API, or EN.
Evaluate Precision and Surface Quality
Pipes manufactured via cold drawing or cold rolling offer high dimensional accuracy, smooth surfaces, and tight tolerance control—ideal for precision or high-efficiency systems.
Check Certification and Quality Assurance
Opt for products with complete documentation, including Material Test Certificates (MTC), non-destructive testing reports, and quality guarantees from reputable manufacturers.
FAQ — Small-Diameter Seamless Steel Pipes
1. What is considered a small-diameter seamless steel pipe?
Small-diameter seamless pipes generally refer to pipes with an outer diameter between 4 mm and 89 mm.
2. What standards are commonly used for small-diameter seamless steel pipes?
Typical standards include ASTM A106, ASTM A53, EN 10216, and GB/T 8163, covering chemical composition, mechanical properties, and dimensional tolerances.
3. What is the typical wall thickness range?
Most small-diameter pipes have a wall thickness of 1.0–5.0 mm, while precision tubes may be as thin as 0.5 mm. For high-pressure use, wall thickness can reach up to 10 mm.
4. What manufacturing methods are used?
Small-diameter seamless pipes are mainly produced through cold drawing or cold rolling, ensuring high dimensional accuracy and a smooth internal/external surface.
5. What are the common applications?
They are widely used in hydraulic systems, automotive parts, machinery, boilers, heat exchangers, medical devices, and precision instruments.
6. How is dimensional accuracy controlled?
High-precision tubes follow strict tolerance requirements defined in standards and are processed using cold finishing techniques.
7. Do small-diameter seamless pipes require testing?
Yes. Typical inspections include hydrostatic testing, eddy current testing, ultrasonic testing, chemical composition analysis, and dimensional checks.
8. Can small-diameter seamless pipes be customized?
Yes, reputable manufacturers can customize OD, wall thickness, length, tolerances, and surface treatment according to project needs.
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