Qualified standard of 3PE coated pipe

The 3PE (Three-Layer Polyethylene) coating is a widely used anti-corrosion coating for steel pipes, particularly in the oil and gas, water, and chemical industries. The 3PE coating consists of three layers: an epoxy primer layer, a adhesive layer, and a polyethylene outer layer. These layers provide excellent corrosion resistance, mechanical protection, and resistance to external environmental factors.

Here are the key qualified standards and requirements for 3PE coated pipes:

1. Material Composition

Epoxy Layer (Primer): The epoxy resin should have high adhesion properties to the steel pipe, ensuring that it provides a strong bond with the pipe surface. It also provides anti-corrosion protection.

Adhesive Layer: The adhesive layer is usually a copolymer, which helps bond the epoxy layer to the polyethylene outer layer. The adhesive should be compatible with both the epoxy and polyethylene materials.

Polyethylene Outer Layer: The outer layer should be high-density polyethylene (HDPE) that provides mechanical protection against physical damage, environmental exposure, and abrasion.

2. Thickness of Coating Layers

Epoxy Layer: Typically, the epoxy layer should have a thickness of around 100 to 200 microns.

Adhesive Layer: The adhesive layer is usually thinner, with a recommended thickness of around 50 to 100 microns.

Polyethylene Layer: The polyethylene layer should have a thickness of 2.0 to 3.0 mm, depending on the specific application and environmental factors.

3. Adhesion Strength

The adhesion strength between the epoxy primer and steel pipe, as well as between the adhesive and polyethylene layer, should meet specific standards, typically exceeding 12 MPa.

The adhesion strength is critical to ensuring the coating remains intact under various mechanical stresses and environmental conditions.

4. Corrosion Resistance

The 3PE coating should demonstrate excellent resistance to corrosion, especially in aggressive environments such as soils with high moisture content or areas prone to chemical exposure.

The coating should pass salt spray tests (ASTM B117 or similar) with no signs of rust or coating failure after a certain period, typically 1,000 to 2,000 hours.

5. Impact Resistance

The outer polyethylene layer should be resistant to mechanical impact, as it provides the primary protection against physical damage such as abrasion, scraping, and other mechanical stresses.

Impact testing is generally performed according to standards such as ISO 21809-1 or EN 10290, with a required impact resistance of at least 2 Joules at temperatures down to -30°C.

6. Chemical Resistance

The 3PE coating must show resistance to a range of chemicals, including acids, alkalis, and salts. The outer polyethylene layer should provide a barrier to chemical attack, while the epoxy layer offers additional protection against aggressive substances.

7. Thermal Stability

The coating should have good thermal stability, maintaining its integrity and properties at temperatures between -30°C to 80°C (some applications may require higher temperature resistance).

The material should not degrade, soften, or lose adhesion when exposed to high temperatures or UV light.

8. Flexibility and Stress Resistance

The coating should maintain flexibility under low temperatures and should not crack or peel under mechanical stress or bending.

The coating should also be capable of withstanding the stresses that occur during pipeline installation, such as bending or crushing.

9. External Surface Quality

The outer surface of the 3PE coated pipe should be smooth and free of defects such as bubbles, pinholes, or cracks. These defects can compromise the pipe's protective properties and may allow for moisture ingress.

Visual inspection and high-voltage spark testing are typically performed to ensure the integrity of the coating.

10. Standard Compliance

3PE coated pipes should comply with international standards, such as:

ISO 21809-1: This standard specifies the requirements for coating materials and application methods for the corrosion protection of pipeline systems.

EN 10290: This standard defines the specifications for coating materials for pipes used in the gas and oil industries.

API 5L: For pipes used in oil and gas pipelines, the 3PE coating process should meet API 5L requirements for pipe coating.

GB/T 23257: This Chinese standard provides guidelines for the 3PE coating of steel pipes used in various industries.

11. Testing and Inspection

Thickness Measurement: Coating thickness is typically measured using a micrometer or ultrasonic thickness gauge.

Adhesion Tests: Standard tests like the cross-cut adhesion test and pull-off adhesion test are conducted to ensure strong bonding between layers.

Electrical Resistance: High-voltage spark testing or holiday detection is used to identify pinholes or defects in the coating.

By adhering to these standards and testing protocols, 3PE coated pipes can offer long-lasting protection against corrosion, physical damage, and environmental degradation, ensuring reliable performance in demanding applications.