Glass Reinforced Plastic (GRP)

Published: | Updated: September 4, 2020;

Definition - What does Glass Reinforced Plastic (GRP) mean?

Glass-reinforced plastic (GRP) is a composite material consisting of plastic reinforced with fine glass fibers. These fibers may be arranged randomly, flattened as a sheet, or woven to make a fabric-like material. A plastic resin is then overlaid onto the glass fibers to create combined uniform material. This resin may include epoxy, vinyl ester, polyester, polyurethane, or polypropylene.

The glass fibers in GRP have mechanical properties roughly comparable to other types of fibers, such as carbon fiber. However, glass fibers are cheaper, more flexible, and lighter than their carbon counterpart, making it an ideal reinforcing agent for many polymer products.

Additionally, glass fibers are also non-magnetic, corrosion-resistant, resistant to electromagnetic radiation, and chemically inert under specific circumstances. These properties make GRP materials an ideal material for structures and components, such as:

  • Aircraft.
  • Boats.
  • Automobiles.
  • Water tanks.
  • Roofing.
  • Oil and gas lift systems.

In the trenchless construction industry, GRP is used in the construction of underground piping, which can then be installed via pipe jacking, microtunneling, horizontal directional drilling. Some pipe liners used in the rehabilitation of damaged pipes may also be manufactured from GRP.

GRP is also known as glass fiber reinforced plastic (GFRP) or fiberglass reinforced plastic (FRP).

Trenchlesspedia explains Glass Reinforced Plastic (GRP)

In the trenchless industry, corrosion in underground piping is a significant concern. Sulfates and chlorides in soils can be particularly aggressive towards metal piping, resulting in corrosion that can compromise the structural integrity of the piping system. Metal piping must, therefore, be supplemented with various corrosion prevention measures, such as cathodic protection and painting, to preserve the integrity of the pipe material.

GRP pipes were first introduced in 1948 as an alternative to steel piping. The lack of metallic ingredients in this material made it immune to the corrosion processes that plague subterranean metal pipes. By the 1970s, GRP pipes gained widespread use, particularly in trunk mains. Several specifications and standards have since emerged to govern the use of GRP piping for different industries, including AWWA C950, BS EN 1796, and BS 8010, among others.

Some industries that use GRP pipes are:

  • Oil and gas.
  • Mining.
  • Metal production.
  • Specialty chemicals.
  • Water and wastewater.


Figure1: Schematic of the filament winding process used in the manufacture of GRP pipes (source)


Figure 2: Roll of glass fiber typically used in the construction of GRP pipes (source)

In addition to being used as overall pipe material, GRP also plays a crucial role in protecting existing metal piping systems. Layers of resin-saturated woven fiberglass are commonly used in the construction of flange isolation gaskets.

In oil and gas industries, where pipes are exposed to aggressive chemicals, corrosion protection is of utmost importance. One of the most common methods used to prevent pipe corrosion in this industry is cathodic protection (CP). However, when pipe flanges are in direct contact with each other, this can strain existing CP protection measures and reduce its effectiveness.

In this case, the flanges of adjacent metal pipes can be separated by GRP gaskets. This process, also known as flange isolation, effectively breaks up the electrical connectivity of connecting pipes, thereby increasing the effectiveness of CP measures.

Figure 3: GRE/GRP flange isolation kit (source)

By interrupting electrical connectivity between pipes, GRP gaskets also prevent galvanic corrosion between dissimilar metallic pipe materials.

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