Small Diameter Seamless Steel Pipe

Generally, seamless steel pipes with outer diameters less than 89 mm and greater than 4 mm can be collectively referred to as small-diameter seamless pipes. Small-diameter seamless pipes are mainly used for mechanical structures, hydraulic equipment and various mechanical parts, etc. They have high dimensional accuracy and good surface finish. The use of precision seamless pipes to manufacture mechanical structures or hydraulic equipment can greatly save machining time, improve material utilization, and help improve product quality.

Small-diameter seamless pipes are a kind of seamless steel pipes with a wide range of uses. Their specifications and uses vary in different fields. This article will introduce the specifications and uses of small-diameter seamless steel pipes in detail to help readers better understand their application range.

Specifications of small-diameter seamless steel pipes:

The specifications of small-diameter seamless pipes usually refer to the outer diameter and wall thickness. The outer diameter range is generally 4mm-89mm, and the wall thickness range is generally 2mm-10mm. 

1. Outside Diameter Range (OD)
Hot-rolled tubes: Typically cover medium diameters, but are less common in the small diameter segment.
Cold-drawn tubes/cold-rolled tubes: This is the primary production method for small diameter seamless tubes, offering a wide range of specifications.

Common range: Φ6mm to Φ89mm (even smaller, as small as Φ3mm, and larger, as large as Φ114mm and above).
Most commonly used range: Φ10mm to Φ50mm (e.g., Φ18mm, Φ25mm, and Φ38mm commonly used in hydraulic systems).

2. Wall Thickness Range (WT)
Wall thickness is related to the "Schedule" (e.g., Sch40, Sch80), but for small diameter tubes, it's more common to look directly at the wall thickness value.
Extremely thin wall: Up to 0.5mm (used in precision instruments). 

Common wall thicknesses: 1.0mm to 5.0mm (for example, a 25mm diameter pipe can have wall thicknesses of 1.5mm, 2.0mm, 2.5mm, 3.0mm, etc.).
Thick-wall/ultra-thick-wall: We can offer specifications with wall thicknesses significantly greater than welded pipe. For example, "thick-wall seamless pipe" for small-diameter hydraulic cylinders can have wall thicknesses of 10mm or even greater.

The specific specifications and uses are as follows:

1. Water pipes

Small-diameter seamless pipes are often used to make water pipes. Their outer diameter and wall thickness vary according to different usage occasions. For example, household water pipes generally use small-diameter seamless steel pipes with an outer diameter of 20mm-30mm and a wall thickness of 2mm-3mm, while industrial water pipes may use small-diameter seamless steel pipes with an outer diameter of 50mm-100mm and a wall thickness of 3mm-5mm.

2. Oil pipes
Small-diameter seamless pipes can also be used to make oil pipes, and their outer diameters and wall thicknesses also vary according to different usage occasions. For example, hydraulic oil pipes generally use small-diameter seamless steel pipes with an outer diameter of 12mm-38mm and a wall thickness of 1mm-2mm, while aviation oil pipes may use small-diameter seamless steel pipes with an outer diameter of 20mm-60mm and a wall thickness of 2mm-4mm.

3. Air pipes
Small-diameter seamless pipes can also be used to make air pipes, and their outer diameters and wall thicknesses are mainly determined by the pressure and flow of the gas. Generally speaking, the outer diameter of small-diameter seamless steel pipes ranges from 12mm-50mm and the wall thickness ranges from 1mm-3mm.

4. Electricity pipes
Small-diameter seamless steel pipes can also be used to make electricity pipes, and their outer diameter and wall thickness are generally determined by the size of the cable and the operating voltage. Generally speaking, the outer diameter of the electricity pipe of small-diameter seamless steel pipes ranges from 15mm to 40mm, and the wall thickness ranges from 2mm to 4mm.

Uses of small-diameter seamless steel pipes:

Small-diameter seamless steel pipes have a wide range of applications, and their uses mainly depend on different materials and specifications. The following are several common uses of small-diameter seamless pipes:

1. Construction field
In the construction field, small-diameter seamless pipes can be used to manufacture structural components such as brackets, supports, and hangers, and can also be used to make facilities such as pipelines and lines. For example, in high-rise buildings, small-diameter seamless pipes can be used to support structural components such as elevator rails and stair handrails.

2. Machinery manufacturing field
In the machinery manufacturing field, small-diameter seamless pipes can be used to manufacture various mechanical parts and components. For example, small-diameter seamless steel pipes are often used in automobile manufacturing to manufacture automobile bodies, chassis and other components. In addition, in the field of aerospace, small-diameter seamless steel pipes are also often used to manufacture aircraft fuselages, wings and other parts.

3. Petrochemical field
In the field of petrochemicals, small-diameter seamless pipes can be used to manufacture various pipes, containers, reactors and other equipment. For example, in oil extraction, small-diameter seamless steel pipes can be used to manufacture oil well casing pipes, oil drill pipes, oil pipelines and other equipment; in chemical production, small-diameter seamless steel pipes can be used to manufacture various chemical reaction equipment, storage containers and other equipment.

4. Power field

In the field of power, small-diameter seamless pipes can be used to manufacture various cable pipes, brackets and other facilities. For example, in urban power grid construction, small-diameter seamless steel pipes can be used to manufacture cable brackets, pipelines and other facilities; in thermal power plants, small-diameter seamless steel pipes can be used to manufacture boiler pipes, heat exchangers and other equipment.

Representative standards for small-diameter seamless pipes:

ASTM A106: Seamless carbon steel pipe for high-temperature service.
ASTM A179: Seamless cold-drawn low-carbon steel pipe for heat exchangers and condensers.
DIN 2391: Precision seamless steel pipe (St series, extremely high dimensional accuracy).
GB/T 3639: China's national standard for "Cold-drawn or cold-rolled precision seamless steel pipes."

In short, small-diameter seamless steel pipes are widely used in various fields, and their specifications and uses vary depending on the occasion of use. Understanding the specifications and uses of small-diameter seamless pipes will help you better select and use this material.

Read more: Schedule 40 Steel Pipe or Cold Drawn Seamless Tube for Mechanical & Hydraulic