Specifications of small diameter seamless steel pipes

Small-diameter seamless steel pipes refer to seamless steel pipes with relatively small outer diameters. They are often categorized into two types: seamless small-diameter steel pipes and straight-seam (welded) small-diameter steel pipes.

While standard seamless pipes are widely used in daily applications, small-diameter seamless steel pipes are designed for more specific or precision-based uses. Typically, pipes with an outer diameter below 89 mm and above 4 mm are classified as small-diameter seamless steel pipes.

Features and Applications of Small-Diameter Seamless Steel Pipes

Compared with solid steel bars such as round steel, small-diameter seamless pipes are lighter in weight while maintaining high bending and torsional strength. This makes them a cost-effective and efficient material for engineering and manufacturing applications.

They are commonly used in:

Oil drilling and energy equipment

Automotive drive shafts and bicycle frames

Mechanical parts and precision components

Construction scaffolding and structural supports

In fluid transport systems, small-diameter seamless pipes are often preferred for their smooth internal walls, high pressure resistance, and long service life.

Specifications and Dimensions of Small-Diameter Seamless Steel Pipes

Small-diameter seamless steel pipes generally have:

Outer diameter: 6–89 mm

Wall thickness: 1–12 mm

Depending on wall thickness, they can be further divided into:

Small-diameter thick-walled seamless pipes

Small-diameter thin-walled seamless pipes

Weight calculation formula:
(OuterDiameter−WallThickness)×WallThickness×0.02466=Weight(kg/m)(Outer Diameter − Wall Thickness) × Wall Thickness × 0.02466 = Weight (kg/m)(OuterDiameter−WallThickness)×WallThickness×0.02466=Weight(kg/m)

Hot-Rolled vs. Cold-Rolled Small-Diameter Seamless Pipes

Hot-rolled seamless steel pipes:

Outer diameter: > 32 mm

Wall thickness: 2.5–75 mm

Commonly used when the diameter exceeds 57 mm

Cold-rolled seamless steel pipes:

Outer diameter: ≥ 6 mm

Wall thickness: ≥ 0.25 mm

Known for high dimensional accuracy and smooth surface finish

Often used when the diameter is below 57 mm

Thin-walled seamless pipes can have diameters as small as 5 mm and wall thicknesses less than 0.25 mm, making them ideal for precision instruments and high-performance systems.

The specifications for small-diameter seamless steel pipes are approximately as follows:
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.