Standards and Specifications for Acceptance of Hydraulic Tubes

Hydraulic tube is an essential material in industry and machinery manufacturing, primarily used to carry and transmit high-pressure liquid media. Due to its excellent pressure resistance, corrosion resistance, and reliable sealing, it is widely used in various machinery, automobiles, and industrial equipment.

However, since the quality of hydraulic tube is invisible and intangible, it is important to adhere to certain acceptance standards and specifications (such as GB/T 3639, DIN 2391, EN 10305, and ASTM A519) during the selection and use of hydraulic tubes.

Appearance Quality Inspection of Hydraulic Tube

The appearance quality of hydraulic tubes directly affects their service life and safety. Therefore, during acceptance, the appearance of hydraulic tubes must be carefully inspected to ensure that they meet the following standards and specifications:

1. Surface Requirements

The tube wall must be smooth and flat, free of unevenness, wear, or deformation. The hose surface must be free of defects such as cracks, scratches, ripples, or scars.

2. End Face Requirements

The end faces must be smooth and even, with the cut perpendicular to the pipe axis. The cut or sawed edges must be free of burrs, cracks, or other defects.

3. Protection Requirements

Before delivery, the pipe body must be clean and free of oil, water stains, and scale. In some demanding applications, plastic caps may be added to seal the pipe to prevent dust ingress.

Mechanical Property Inspection of Hydraulic Tube

Hydraulic tubes are subject to various pressures during use. Therefore, their mechanical properties must be inspected during acceptance. The following are standard specifications for the mechanical properties of hydraulic tubes:

1. Pressure Test

Place the hydraulic piping on a testing machine and apply a certain pressure. No leakage or bursting should occur within a certain period of time.

For example, apply 1.5 times the working pressure on the hydraulic testing machine for at least 5 seconds. No leakage or bursting should occur.

Common hydraulic tubes can operate at pressures of 20–40 MPa, and high-pressure hydraulic tubes can even reach 70 MPa.

2. Tensile Test

Test the hydraulic steel tube's tensile strength and elongation, among other performance indicators. The pipe must meet the specified tensile strength and yield strength.

For example, the tensile strength of 20# precision seamless steel pipe must be ≥ 490 MPa, and the elongation must be ≥ 20%.

3. Hardness Test

Hydraulic tube hardness is tested. Brinell hardness (HBW) or Rockwell hardness (HRB/HRC) are commonly used.

Hydraulic tube hardness is generally required to be ≤ 90 HRB to ensure good cold bending and fatigue resistance.

Chemical Composition Test of Hydraulic Tube

The chemical composition of hydraulic steel tube is a key factor affecting its performance. The following are standard specifications for chemical composition analysis of hydraulic steel tube:

1. Chemical Composition and Material Quality

Use spectroscopic or chemical analysis methods to test the content of elements such as carbon (C), sulfur (S), phosphorus (P), manganese (Mn), and silicon (Si).

For example, the typical chemical composition of 20# steel pipe is C 0.17–0.23%, Mn 0.35–0.65%, Si 0.17–0.37%, S ≤ 0.035%, and P ≤ 0.035%.

2. Process Requirements

Inspect the pipe manufacturing process, including the longitudinal weld seam and removal of black scale. For welded pipes, inspect the weld seam quality to ensure there are no defects such as slag inclusions, pores, and incomplete fusion.

3. Material Uniformity

Analyze the quality of the hydraulic tube. Avoid segregation or hard spots to ensure the pipe's stability under high pressure.

Heat Transfer Performance Testing of Hydraulic Tube

The heat transfer performance of hydraulic steel tubes directly affects the operating efficiency and energy consumption of the hydraulic system. The following are standard specifications for testing the heat transfer performance of hydraulic tubes:

1. Testing High-Temperature Stability

The operating temperature range of common hydraulic tubes is -40°C to +120°C, while special alloy steel pipes can reach +400°C.

2. Testing Thermal Conductivity

Ensure that the pipe does not leak due to excessive thermal expansion in high-temperature environments.

3. Testing Thermal Expansion Coefficient

The thermal expansion coefficient for steel hydraulic tubes is generally 11.5 × 10⁻⁶/°C. Allowance for expansion and contraction must be made during installation.

FAQ

1. What is the Most Important Inspection Item During Hydraulic Tube Acceptance?

Hydraulic tube acceptance typically focuses on inspections of appearance, mechanical properties, chemical composition, and cleanliness.

The most critical of these is the pressure test, as it directly impacts whether the pipe can safely withstand operating pressure.

2. What is the Purpose of Chemical Composition Testing for Hydraulic Tubes?

The purpose is to confirm whether the material of the hydraulic tube meets standard requirements, for example, whether the carbon, manganese, silicon, sulfur, and phosphorus contents are within specified ranges.

Chemical composition directly affects the strength, toughness, and corrosion resistance of the hydraulic steel tube.

3. What are Some Common Failures During Hydraulic Tube Acceptance?

Surface scratches, cracks, or rust;

Wall thickness deviation exceeds the standard;

Leakage during the pressure test;

Inner wall cleanliness does not meet standards, such as the presence of iron filings and oil stains.

Summary

The above are the standard specifications for hydraulic tube acceptance. Correct acceptance standards and specifications are crucial for ensuring the safety of machines and personnel. We encourage you to strictly adhere to them when handling hydraulic tubes.