How to detect plastic-coated steel pipes?

Plastic-coated steel pipes are composite materials that integrate the strength of steel with the corrosion resistance of plastic. These pipes consist of a steel base coated with a protective plastic layer on either the inner surface or both inner and outer surfaces. This coating is applied using processes such as spraying, rolling, dipping, or suction. Below is an overview of key testing methods and properties of plastic-coated steel pipes.

1. Appearance Inspection

Inspect the surface of the plastic-coated steel pipe for any visible defects to ensure the coating is uniform and free from imperfections.

2. Coating Thickness Measurement

Select two cross-sections from different lengths at each end of the pipe. Measure the coating thickness at four orthogonal points on the circumference of each section using an electromagnetic thickness gauge.

3. Pinhole Detection Test

• Specimen Preparation: Cut a pipe section approximately 1000 mm in length.

• Test Method: Use an electric spark leak detector with a specified test voltage.

• For coatings≤0.4 mm, the test voltage is 1500 V.

• For coatings > 0.4 mm, the test voltage is 2000 V.

• Objective: Detect any electric sparks indicating coating defects.

4. Adhesion Test

Perform the adhesion test according to section 7.4.2 of CJ/T 120-2008. The results must comply with the specifications outlined in section 5.6 of the standard.

5. Bending Test (For Pipes with DN≤50 mm)

• Specimen: Cut a pipe section of (1200±100) mm in length.

• Test Conditions:

• Perform the test at a temperature of (20±5)°C.

• Bend the pipe to a radius 8 times its nominal diameter with a bending angle of 30°.

• Method: Use a pipe bending machine or mold. Ensure the weld is on the side of the bending surface and avoid using fillers inside the pipe.

• Assessment: After bending, cut the specimen at the arc’s midpoint to inspect the inner coating. Results must meet section 5.7 requirements.

6. Flattening Test (For Pipes with DN > 50 mm)

• Specimen: Cut a pipe section of (50±10) mm in length.

• Test Conditions:

• Perform the test at a temperature of (20±5)°C.

• Gradually compress the pipe between two plates until the gap is four-fifths of its outer diameter.

• Method: Position the pipe weld perpendicular to the load direction.

• Assessment: Inspect the inner coating after flattening, ensuring compliance with section 5.8.

7. Impact Test

• Specimen: Cut a 100 mm section from the pipe.

• Test Conditions: Perform the test at (20±5)°C with the weld positioned opposite the impact surface.

• Objective: Verify the coating’s integrity as per section 5.9 requirements.

Key Features of Plastic-Coated Steel Pipes

• Corrosion Resistance: Offers excellent protection against environmental and chemical corrosion.

• Low Friction: Reduces flow resistance for efficient transport.

• Material Versatility:

• Epoxy-Coated Pipes: Suitable for water supply, drainage, seawater, warm water, oil, and gas transport.

• PVC-Coated Pipes: Ideal for drainage, seawater, oil, and gas transport.

• Structural Advantages: Combines the strength and durability of steel with the corrosion resistance of plastic.

• Enhanced Lifespan: Reduces issues like scaling, corrosion, and pollution. Provides a design life of up to 50 years.

Plastic-coated steel pipes are widely used in industries where durability, corrosion resistance, and high performance are critical, making them a reliable choice for various transportation needs.