This dual-layer epoxy powder coating system is carefully formulated using special epoxy resins and functional curing agents. The base layer, like other epoxy anti-corrosion powder coatings, offers excellent anti-corrosion properties. The outer layer, while maintaining anti-corrosion properties, enhances protective performance. Compared to a three-layer PE structure, it offers a lower comprehensive anti-corrosion cost.
Suitable for complex anti-corrosion environments, especially pipelines crossing through mountainous, river, and hilly areas.
Powder Coating Performance Parameters
| Test Item | Technical Specification | Remarks |
|---|---|---|
| Appearance | Uniform color, no lumps | Visual inspection |
| Particle Size Distribution | Residuals ≤4.0 at 150um, ≤0.2 at 250um | Q/CNPC 38-2002 Appendix C |
| Volatile Content (%) | ≤0.6 | Q/CNPC 38-2002 Appendix B |
| Gellation Time at 205±3°C (s) | ≥12 | Q/CNPC 38-2002 Appendix A |
| Curing Time at 230°C (min) | ≤3 | SY/T 0315-2005 |
| Magnetic Substance Content (%) | ≤0.002 | GB/T 6570 |
| Test Item | Technical Specification | Remarks |
|---|---|---|
| Appearance | Smooth, uniform color, no bubbles, no cracks, allows slight orange peel | Visual inspection |
| Adhesion (Grade) | 1-2 | SY/T 0315-2005 |
| Negative Electrode剥离 at 24h (mm) | ≤6.5 | SY/T 0315-2005 |
| Negative Electrode剥离 at 28d (mm) | ≤8 | SY/T 0315-2005 |
| Cross-sectional Crack Rate | 1-4 | SY/T 0315-2005 |
| Coating Surface Porosity Rate | 1-4 | SY/T 0315-2005 |
| Bending Resistance (3°) | No cracks | SY/T 0315-2005 |
| Volume Resistivity | ≤1*10¹³ | GB/T 1410 |
| Electric Strength (MV/m) | ≥30 | GB/T 1408.1 |
| Impact Resistance (1.5J at -30°) | No leakage points | SY/T 0315-2005 |
| Chemical Resistance | Qualified | SY/T 0315-2005 |
| Wear Resistance (Abrasion Method) | ≤3 | SY/T 0315-2005 |
| Salt Spray Test (1000h) | Coating shows no change | GB/T 1771-1991 |
Q/CNPC 38-2002 “Technical Specification for Double Layer Fusion Bonded Epoxy Powder Coating on Steel Pipes”
| Property | Specification | Remarks |
|---|---|---|
| Temperature | 200-230°C for 3-1.5 minutes | Medium-frequency heating recommended |
| Parameter | Specification | Notes |
|---|---|---|
| Applicable Equipment | Frictional charging spray, corona electrostatic spray | |
| Film Thickness | 250-500um | Adjustable according to workpiece requirements |
Dual‑layer epoxy anti‑corrosion powder coating is a multi‑layer protective system that uses two distinct epoxy layers applied sequentially to a substrate. Typically, the base layer provides foundational corrosion resistance and adhesion, while the outer layer enhances barrier properties and mechanical durability. This layered approach significantly outperforms single‑layer systems in aggressive environments such as buried pipelines, marine infrastructure, and industrial steel structures.
The core advantage of dual‑layer coatings lies in their complementary protective mechanisms:
Base layer (primer): Highly adherent epoxy network that bonds to the steel substrate, forming a strong foundation against corrosion.
Outer layer: Often formulated with denser resin, hard particles, or additional functional additives to resist permeation, scratching, and environmental stress.
This multi‑barrier structure dramatically increases resistance to moisture, salts, and corrosive agents compared with a single coating application.
Typical technical characteristics of dual‑layer systems include:
Strong adhesion between layers: Ensures integrity and reduces delamination risk under thermal or mechanical stress.
Cathodic disbondment resistance: Many dual‑layer epoxies are engineered to withstand electrochemical stress that can weaken coatings in buried or marine environments.
Scratch and impact resistance: The outer layer often has higher hardness and density to protect the base layer from mechanical damage.
Layer synergy: Performance metrics such as impact resistance, flexibility, and adhesion are often improved due to synergistic interaction between primer and top layer.
Epoxy powder coatings—especially dual‑layer systems—protect metal through multiple mechanisms:
Barrier Protection: The cured epoxy forms a dense, impermeable film that blocks corrosive agents (moisture, oxygen, salts) from reaching the substrate.
Interlayer Adhesion: Strong interlayer bonds prevent microcrack propagation that can cause corrosion under film defects.
Cathodic Protection (in some systems): When combined with zinc‑rich primers, the system offers electrochemical protection that helps protect scratched or damaged areas.
Mechanical Shielding: The outer layer often enhances resistance to abrasion and physical impact, maintaining barrier integrity over service life.
A typical dual‑layer epoxy powder coating system uses:
Primer Layer: Usually a standard or functionalized epoxy resin that ensures adhesion and initial corrosion resistance.
Outer Protection Layer: A modified epoxy or blended resin designed for increased hardness, impermeability, and weather resistance.
Hybrid designs may incorporate additives (e.g., fillers, corrosion inhibitors) to tune performance for specific applications.
Dual‑layer systems are widely adopted where long‑term corrosion resistance is critical:
Pipelines & Oil/Gas Networks: Protect steel pipes against soil and moisture corrosion in buried or exposed environments.
Infrastructure Steel: Bridges, guardrails, and structural components in high‑corrosion zones.
Marine & Offshore Structures: Submerged or splash‑zone steel parts where saltwater and humidity accelerate corrosion.
Industrial Fabrications: Machinery, storage tanks, and equipment frames exposed to harsh chemicals or weather.
Applying dual‑layer powder coatings involves:
Substrate preparation: Thorough cleaning, degreasing, and abrasive blasting to achieve proper surface roughness and remove contaminants.
First layer application: Electrostatic spraying of the primer powder, then curing to a gelled or fully cross‑linked state.
Second layer application: After primer cure, spraying the outer layer powder, typically without reheating the substrate (if using cold spray variants) or immediately following primer application in a continuous oven.
Curing: Controlled oven curing ensures full cross‑linking and layer integration.
Powder coatings can be categorized by resin system (epoxy, polyester, hybrid, polyurethane), appearance (smooth, texture, hammer, metallic, pearlescent), or performance level (anti-corrosion, heat-resistant, UV-resistant, architectural grade, automotive grade).
Powder coatings offer thousands of colors in gloss, matte, satin, metallic, candy, texture, wrinkle, hammer tone, wood grain, fluorescent, and other custom effects. Special powders can create soft-touch, anti-scratch, anti-fingerprint, or anti-graffiti surfaces.
The process generally includes surface pretreatment (degreasing, phosphating, chromating, sandblasting), drying, electrostatic spraying, curing in an oven, and cooling. A well-controlled pretreatment and curing process ensures strong adhesion and long service life.
Powder coatings are environmentally friendly, solvent-free, and produce minimal waste. They offer excellent corrosion resistance, weather durability, mechanical strength, and uniform film appearance. The coating is tough, impact-resistant, scratch-resistant, and has a long lifespan.
Powder coatings are widely used in appliances, aluminum profiles, architectural components, automotive parts, bicycles, furniture, outdoor equipment, machinery, electrical cabinets, pipeline systems, and general industrial and consumer goods.
Powder coating is a dry finishing technology where finely ground powder is electrostatically sprayed onto a metal or non-metal surface and then cured at high temperature. After curing, the powder melts into a continuous, durable, and decorative coating layer.
Powder coating protects the substrate from corrosion, weathering, chemical attack, and mechanical wear. It also provides decorative appearance with rich colors, gloss levels, textures, and special effects.
In many industrial applications, powder coating outperforms liquid paint. It forms a thicker and tougher coating, resists corrosion and chemicals better, and does not contain VOCs. It also provides excellent consistency and cost-effective mass production.
It is called powder coating because the coating material is a solid powder instead of a liquid paint. The coating is formed by melting and curing powder particles under heat.
Powder coatings include several families depending on resin chemistry:
• Epoxy powders
• Polyester powders
• Epoxy-polyester hybrid powders
• Polyurethane powders
• Acrylic powders
• Fluorocarbon (PVDF) powders
Each type has its own performance features such as corrosion resistance, UV resistance, chemical resistance, outdoor durability, or decorative properties.
Powder coatings are based on thermoset or thermoplastic resins combined with pigments, curing agents, fillers, additives, and in some cases metallic or effect particles. Common substrates include steel, aluminum, galvanized metal, MDF, and certain heat-resistant plastics.
The lifespan depends on powder type, film thickness, application method, pretreatment, and service environment. Indoor coatings can last more than 10–20 years. High-grade outdoor polyester or fluorocarbon powders can last 15–25 years or longer under UV exposure.
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