Understanding the structure of FRP (Fiberglass Reinforced Plastic) pipes

Fiberglass Reinforced Plastic (FRP) pipes are known for their outstanding corrosion resistance, high strength-to-weight ratio, and long service life. These impressive properties stem from their carefully engineered layered structure, where each layer plays a distinct and vital role in ensuring the overall performance and durability of the pipe. Let’s take a closer look at the key structural layers that make up an FRP pipe.

The Four Major Layers of an FRP Pipe

FRP Pipes and Pipe Fittings

1.Inner Surface Layer (Liner Surface)

Also referred to as part of the inner liner, the inner surface layer is composed of liner resin reinforced with glass fiber surface mat. This layer contains more than 90% resin, ensuring excellent airtightness and a smooth surface finish.

Its primary functions are:

• Providing strong corrosion resistance
• Preventing leakage
• Ensuring a clean internal surface for fluid transport

2.Inner Reinforcement Layer (Sub-Liner)

Also part of the inner liner, the sub-liner is made from liner resin combined with chopped strand mat (short glass fibers). This layer typically contains more than 80% resin.

Its main purposes are:

• Protecting the inner surface layer
• Improving the internal pressure resistance of the liner
• Preventing crack propagation from the inner to outer layers

FRP Fittings

3.Structural Layer

The structural layer is the core strength layer of the FRP pipe. It is formed by cross-winding continuous strand roving impregnated with structural resin, often with added ribs for reinforcement during the winding process.

The resin content in this layer is around 45%, and it provides the pipe with:

• High tensile and compressive strength
• The ability to withstand external loads
• Structural integrity under high-pressure or heavy-duty conditions

4.Outer Protective Layer

The outer protection layer is composed of high-resin-content (≥80%) surface coating, reinforced with additives such as UV-9 ultraviolet absorbers.

This layer plays a vital role in:

• Preventing photo-oxidation and aging caused by UV exposure
• Enhancing the pipe’s weather resistance and durability in outdoor environments

Each layer in an FRP pipe is engineered to perform a specific function—from corrosion protection to structural support and environmental shielding. This multi-layered composite design allows FRP pipes to outperform many traditional piping materials in terms of durability, versatility, and lifecycle cost.

Whether used in municipal water systems, chemical processing plants, or offshore oil platforms, the internal and external structure of FRP pipes makes them an ideal solution for modern, high-performance piping needs. Email:sales@haihaogroup.com

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