Hydraulic tubes vs mechanical tubes

Although hydraulic tubes and mechanical tubes are both industrial steel tubes, they serve different roles in various industrial applications due to their distinct performance requirements and application scenarios. Despite having notable differences in materials, manufacturing processes, performance standards, and usage, they can sometimes be used interchangeably depending on the specific needs. Below is a detailed comparison between the two:

Hydraulic Tube:

Hydraulic tubes are specifically designed for hydraulic systems to transmit high-pressure liquids, such as hydraulic oil and emulsions, and are built to withstand periodic pressure fluctuations.

Typical Applications:
Construction machinery (e.g., excavators, cranes), injection molding machines, hydraulic cylinders, hydraulic stations, etc.

Core Requirements:
High pressure resistance, fatigue resistance, and excellent sealing capabilities.

Mechanical Tube:

Mechanical tubes are versatile structural tubes used in non-fluid transmission applications, such as for support, transmission, framing, and protection.

Typical Applications:
Machine tool guide rails, conveyor rollers, steel structural frames, etc.

Core Requirements:
Strength, stiffness, and dimensional accuracy.

1. Material and Manufacturing Process

Steel Pipe Material:

Hydraulic Pipes: Often made from high-strength carbon steels (e.g., ST52, A106) or stainless steels (e.g., 304/316).

Mechanical Pipes: Typically made from ordinary carbon steels (e.g., Q235, 20#), low-alloy steels, or aluminum.

Processing:

Hydraulic Pipes: Usually produced via cold-drawing or precision rolling to meet the high-pressure demands.

Mechanical Pipes: Can be either seamless or welded, depending on the application.

Inner Wall Treatment:

Hydraulic Pipes: Often honed or polished to reduce fluid resistance and prevent corrosion.

Mechanical Pipes: Generally, no special treatment unless rust prevention is needed.

Surface Treatment:

Hydraulic Pipes: May undergo inner wall honing, galvanizing, chrome plating, or phosphating for corrosion protection.

Mechanical Pipes: Typically treated with painting, blackening, or galvanizing for rust prevention.

Defect Tolerance:

Hydraulic Pipes: Must not have micro-cracks or pores.

Mechanical Pipes: Minor defects may be acceptable as they do not bear pressure.

2. Performance Requirements

Hydraulic Tube:

Pressure Resistance: Typically ≥20MPa, can go up to 70MPa.

Dimensional Accuracy: Requires high precision (inner diameter ±0.05mm, wall thickness ±5%).

Corrosion Resistance: High demands for rust prevention and resistance to hydraulic fluid corrosion.

Fatigue Resistance: Excellent fatigue resistance to handle pressure fluctuations.

Mechanical Tube:

Pressure Resistance: Designed for low or zero pressure applications; primarily handles mechanical loads.

Rust Prevention: Regular rust prevention is sufficient for most applications.

Dimensional Accuracy: Accuracy varies depending on the application needs.

Fatigue Resistance: Average fatigue resistance, typically not designed to withstand high pressure.

3. Implementation Standards

Seamless Hydraulic Pipe Standards:

International Standards: ISO 3304, DIN 2391, ASTM A106.

Chinese Standards: GB/T 3639 (precision hydraulic seamless pipes).

Seamless Mechanical Pipe Standards:

International Standards: ASTM A519, EN 10297, JIS G3445.

Chinese Standards: GB/T 8162 (structural seamless pipes).

4. Can Hydraulic Tubes and Mechanical Tubes Be Interchanged?

Hydraulic Tubes Used as Mechanical Tubes:
Hydraulic tubes, due to their high precision and strength, can be used for high-load mechanical structures (e.g., precision instrument brackets). However, they come at a higher cost and are typically only used in specialized scenarios that demand precision, such as high-precision guide rails.

Limitations of Using Mechanical Tubes as Hydraulic Tubes:
Ordinary mechanical pipes cannot be used in high-pressure hydraulic systems unless they have been specifically tested for pressure resistance and their inner walls have been treated. Without these considerations, there is a significant risk of leakage (due to rough inner walls, poor sealing) or pipe failure (insufficient pressure tolerance), which would reduce the lifespan of the system.

Exception: For low-pressure hydraulic systems (such as agricultural equipment), thick-walled welded mechanical pipes might be used.

5. Selection Recommendations:

Priority Usage:

For fluid transmission with pressure ≥10MPa, hydraulic tubes must be used.

Mechanical tubes are suitable for structural support applications where fluid transmission is not required, and cost reduction is a priority.

Inspection Reports:

Hydraulic Tubes: Must provide a water pressure test report (e.g., according to ISO 10763) and ensure the inner wall finish (Ra ≤ 0.8μm).

Mechanical Tubes: Should focus on bending strength, dimensional tolerance, and rust prevention treatments (e.g., galvanizing or painting) depending on the operating environment.

Conclusion:

Hydraulic tubes are essentially "high-performance versions" of mechanical tubes. While both types may share similar base materials, hydraulic tubes have stricter manufacturing, processing, and testing standards due to the demanding conditions they face. It's crucial to avoid using regular mechanical tubes as substitutes for high-pressure hydraulic tubes to ensure the safety, durability, and efficiency of the system.