Hydraulic tube vs Mechanical tube

Difference between hydraulic tubes and mechanical tubes:

Although both hydraulic tubes and mechanical tubes are industrial steel tubes, they have different focuses in industrial applications due to different application scenarios and performance requirements. They have significant differences in materials, manufacturing processes, performance, standards, etc., but they may be cross-used in some scenarios. The following is a detailed comparison:

Hydraulic Tube: 

Designed for hydraulic systems, used to transmit high-pressure liquids (such as hydraulic oil, emulsions), and withstand periodic pressure fluctuations.

Typical scenarios: construction machinery (excavators, cranes), injection molding machines, hydraulic cylinders, hydraulic stations, etc.

Core requirements: high pressure resistance, fatigue resistance, and sealing.

Mechanical Tube: 

A broad-based mechanical structure tube used for non-fluid transmission scenarios such as support, transmission, frame, and protection.

Typical scenarios: machine tool guide rails, conveyor rollers, steel structure frames, etc.

Core requirements: strength, stiffness, and dimensional accuracy.

1. Material and Manufacturing Process

Steel pipe material:
Hydraulic pipes are usually made of high-strength carbon steel (ST52, A106) and stainless steel (304/316), while mechanical pipes are usually made of ordinary carbon steel (Q235, 20#), low-alloy steel, and aluminum pipes.

Processing:
Hydraulic pipes: Hydraulic pipes are often made of cold-drawn/precision-rolled seamless pipes, which are suitable for high-pressure scenarios.
Mechanical pipe: seamless or welded (depending on the purpose)

Inner wall treatment:
Hydraulic pipe: honing, polishing (reducing fluid resistance and preventing corrosion)
Mechanical pipe: generally no special treatment is done (unless rust prevention is required)

Surface treatment:
Hydraulic pipe: inner wall honing, galvanizing/chrome plating, phosphating (corrosion prevention)
Mechanical pipe: painting, blackening, galvanizing (rust prevention)

Defect tolerance:
Hydraulic pipe: micro cracks and pores are not allowed
Mechanical pipe: minor defects may be acceptable (non-pressure bearing)

2. Performance requirements

Hydraulic tube: high pressure resistance, usually ≥20MPa, up to 70MPa. Extremely high requirements for dimensional accuracy (inner diameter ±0.05mm, wall thickness ±5%), high corrosion resistance requirements, rust prevention, and hydraulic oil corrosion resistance. Excellent fatigue resistance.

Mechanical tube: low pressure or zero pressure, mainly bears mechanical loads. Ordinary rust prevention is sufficient, and the dimensional accuracy depends on the purpose. Fatigue resistance is average.

3. Implementation standards

Common standards for seamless hydraulic pipes
International standards: ISO 3304, DIN 2391, ASTM A106
Chinese standards: GB/T 3639 (precision hydraulic seamless pipes)

Common standards for seamless mechanical pipes
International standards: ASTM A519, EN 10297, JIS G3445
Chinese standards: GB/T 8162 (structural seamless pipes)

Can hydraulic tubes and mechanical tubes be interchangeable (replaceable)?

Hydraulic tubes can be used as mechanical tubes:
Hydraulic pipes can be used for high-load mechanical structures (such as precision instrument brackets) due to their high precision and high strength, but the cost is relatively high. Generally, they are only used when there are special needs (such as high-precision guide rails).

Limitations of mechanical tubes replacing hydraulic tubes:
Ordinary mechanical pipes cannot be used in high-pressure hydraulic systems if they have not been tested for pressure resistance or the inner wall has not been treated. There is a risk of leakage (rough inner wall, poor sealing) or bursting (insufficient pressure bearing), and the life is shortened (insufficient fatigue resistance).

Exception: Low-pressure hydraulic systems (such as agricultural equipment) may use thick-walled welded mechanical pipes.

Selection suggestions:

Prioritize the use:
When it involves fluid transmission and the pressure is ≥10MPa, hydraulic pipes must be used.
Mechanical tubes can be used in pure structural support scenarios to reduce costs.

Inspection report:
Hydraulic tubes need to provide a water pressure test report (such as ISO 10763 requirements) and check the inner wall finish (Ra≤0.8μm);
Mechanical tubes need to pay attention to bending strength and dimensional tolerance, and choose anti-rust treatment (galvanizing, painting) according to the use environment.

Conclusion:

Hydraulic tubes are "high-end special versions" of mechanical tubes. The basic materials of the two may be similar, but hydraulic tubes have stricter process and testing standards due to strict working conditions. When selecting, it is necessary to avoid mixing to reduce costs, especially prohibiting the use of ordinary mechanical tubes instead of high-pressure hydraulic tubes.

Read more: Cold Drawn Seamless Tube for Mechanical & Hydraulic