Seamless steel pipes with small outer diameters are called small-diameter seamless steel pipes. Small-diameter seamless steel pipes can be further divided into: seamless small-diameter steel pipes and straight-seam (also called welded) small-diameter seamless steel pipes. Generally, pipes with an outer diameter of 4mm or less than 89mm can be collectively referred to as small-diameter seamless steel pipes.
Standard Specifications of Seamless Steel Pipes— Common Sizes
Diameter (OD) and Wall Thickness (WT)
Small-diameter seamless steel pipes generally range from 4 mm to 89 mm in outer diameter.
Common industrial and hydraulic applications often use Φ6 mm to Φ89 mm.
Wall thickness usually ranges from 1.0 mm to 5.0 mm, but precision tubes may have wall thicknesses as low as 0.5 mm.
For high-strength or thick-walled applications, wall thickness may go up to 10 mm.
Small-diameter seamless pipes are typically manufactured using cold drawing or cold rolling processes, ensuring high dimensional accuracy, smooth surfaces, and tight tolerance control.
Specifications of Small Diameter Seamless Steel Pipes
| Specification | Specification | Specification |
| 6*1 | 18*5 | 25*6 |
| 8*1 | 18*6 | 25*7 |
| 8*1.5 | 19*1.5 | 25*8 |
| 8*2 | 19*2 | 27*2 |
| 10*1 | 19*2.5 | 27*2.5 |
| 10*1.5 | 19*3 | 27*3 |
| 10*2 | 19*4 | 27*4 |
| 10*2.5 | 19*5 | 27*5 |
| 12*1 | 20*1.5 | 27*6 |
| 12*1.5 | 20*2 | 27*7 |
| 12*2 | 20*2.5 | 28*2 |
| 12*2.5 | 20*3 | 28*2.5 |
| 12*3 | 20*4 | 28*3 |
| 14*1.5 | 20*5 | 28*3.5 |
| 14*2 | 20*6 | 28*4 |
| 14*2.5 | 22*1.5 | 28*5 |
| 14*3 | 22*2 | 28*6 |
| 14*4 | 22*2.5 | 28*7 |
| 16*1.5 | 22*3 | 30*2 |
| 16*2 | 22*4 | 30*3 |
| 16*2.5 | 22*5 | 30*4 |
| 16*3 | 22*6 | 30*5 |
| 16*4 | 25*1.5 | 30*6 |
| 16*5 | 25*2 | 30*7 |
| 18*1.5 | 25*2.5 | 30*8 |
| 18*2 | 25*3 | 41*2 |
| 18*2.5 | 25*3.5 | |
| 18*3 | 25*4 | |
| 18*4 | 25*5 |
How to Choose the Right Small-Diameter Seamless Steel Pipe？
1.Use Case – Determine if it’s for hydraulic, precision instruments, medical, high-pressure, or structural applications.
2.Size & Wall Thickness – Choose appropriate OD and WT based on fluid pressure, structural load, and spatial constraints.
3.Material & Standards – For corrosion resistance, hygiene, or high temperature, select stainless or alloy steel and ensure compliance with relevant standards (GB/T, ASTM, API, EN).
4.Precision & Surface Finish – Cold drawing/rolling ensures tight tolerances and smooth surfaces for precision applications.
5.Certification & Quality Assurance – Prefer pipes with inspection certificates (MTC), non-destructive testing, and guaranteed quality from reputable manufacturers.
Small-diameter seamless steel pipes are manufactured and tested according to standards like ASTM A106, ASTM A53, EN 10216, and GB/T 8163, which specify their chemical composition, mechanical properties, and dimensional tolerances Email : pipe@stpipefitting.cn
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