Galvanized Aluminum & Aluminized Pipes

1. Brand and Chemical Composition
The brand and chemical composition of steel used for galvanized aluminum pipes and aluminized pipes must comply with the specifications for black pipes as outlined in GB/T 3092. These standards also apply to aluminized pipe products.

2. Manufacturing Method
Manufacturers may choose either furnace welding or electric welding for producing black pipes, galvanized aluminum pipes, or aluminized pipes. The hot-dip method is consistently used for both galvanized and aluminized pipe production.

3. Threads and Pipe Joints

• Threads: For steel pipes, including galvanized aluminum pipes and aluminized pipes, with threads, they must be machined after the specified time. The threads must meet the requirements of YB 822.
• Pipe Joints: Steel pipe joints, whether for galvanized aluminum, aluminized, or black pipes, must comply with YB 238 standards. Forgeable cast iron joints should meet YB 230.

4. Mechanical Properties
The mechanical properties of steel pipes, including galvanized aluminum pipes and aluminized pipes, before resetting must meet the standards in Chapter 3092 of the national specification.

5. Uniformity of Coating
Galvanized aluminum pipes and aluminized pipes must undergo testing to ensure uniformity of the coating. After five consecutive electroplating cycles in copper sulfate solution, the steel pipe should not show any red or copper-plated coloration.

6. Cold Bending Test
Symmetrical steel pipes, including galvanized aluminum and aluminized pipes, with a nominal diameter of 50mm or less must undergo a cold bending test. The pipe is bent at a 90° angle with a radius eight times the outer diameter. No filler should be used during the test, and the weld must be positioned locally or at the upper part of the pipe. After the test, there should be no cracks or zinc peeling on the specimen.

7. Water Pressure Test
A water pressure test should be conducted on the black tube, galvanized aluminum pipe, or aluminized pipe. Eddy current flaw detection can also be used as an alternative. The test ensures that the steel pipe meets the size and mechanical property requirements specified in GB/T 3092.

Mechanical Properties of Steel:

• Tensile Strength (σb): The maximum force a specimen can bear before breaking, divided by the strain absorbed by the original tension area. It is expressed in N/mm² (MPa) and indicates the material’s ability to resist tension-induced damage.

  • Fb: Maximum force at break (N)
  • So: Original cross-sectional area (mm²)

• Yield Point (σs): The stress at which the material begins to deform without increasing force. If the material has distinct yield points, both upper and lower yield points should be noted.

  • Upper Yield Point (σsu): The maximum stress before the material begins to yield.
  • Lower Yield Point (σsl): The stress at which yielding continues with no further increase in force.

• Elongation after Fracture (σ): The percentage increase in gauge length after fracture compared to the original length.

  • L1: Gauge length after fracture (mm)
  • L0: Original gauge length (mm)

• Section Shrinkage (ψ): The percentage reduction in cross-sectional area at the point of fracture.

  • S0: Minimum area at the shrinkage point (mm²)

• Hardness: The ability of the material to resist deformation or indentation. Common hardness tests for steel pipes, including galvanized aluminum and aluminized pipes, include:

  • Brinell: Hardness measured using a steel ball under a set force, expressed as HBS (N/mm² or MPa).
  • Rockwell and Vickers: Other methods for measuring hardness.

Material Properties:

• Carbon: High carbon content increases hardness but reduces plasticity and tensile strength.
• Sulfur: Excess sulfur can cause hot brittleness, making steel prone to cracking at high temperatures.
• Phosphorus: Reduces toughness, especially in low temperatures, causing cold brittleness.
• Manganese: Increases strength, reduces sulfur’s negative effects, and improves wear resistance in high-alloy steels.
• Silicon: Improves hardness but decreases plasticity and flame retardancy. Electrical steels often contain silicon to improve magnetic properties.
• Tungsten: Enhances red hardness, heat strength, and wear resistance.
• Chromium: Improves hardenability, wear resistance, and corrosion/oxidation resistance.

Corrosion Resistance:

To improve corrosion resistance, steel pipes, including galvanized aluminum pipes and aluminized pipes, are often treated. They may undergo thermal reduction or electric zinc coating. Thermal reduction results in a thicker coating, while electric zinc coating is more cost-effective but thinner. As a leading aluminized supplier, we ensure that our aluminized pipes offer superior protection against corrosion.