Fibreglass / GRP (Glass Reinforced Polyester) 

Fibreglass or Glass Reinforced Polyester pipes are made up of the following materials in different % proportions to tailormade for your specific pressure pipe application, hence the reason why it is referred to as composite materials:

  • Glass Fibres - for strenght & stiffness
  • Polyester Resin - for chemical resistance, protect the glass fibres & for load transfering properties
  • Inorganic sand filler material - for variable wall thickness & mechanical resistance  
  • Pigment - for UV stabilisation and reflection

When considering a fibreglass pipe the following design criteria needs to be taken into account:

  • Nominal Pipe Diameter (DN) - directly related % dependant on the hydraulic flow required
  • Pressure Class (PN) - directly related & dependant on the MAOP (Max Alowable Operating Pressure) and Surge allowances
  • Stiffness Class (SN) - directly related & dependant on the burial conditions & vacuum pressures

There is a misconception that the thicker the wall the higher the Pressure Class (PN), this is actually the opposite. The higher the PN Class the more polyester resin is added and less sand filler material, making the wall much thinner but in correlation to a higher Stiffness Class (SN) the more sand filler material is added and less polyester resin, resulting in a thicker wall.  

There is two kinds of pipe designs available to choose from which is direct related to the PN & SN Class that will ultimately determine your correct pipe design for your specific needs:

  • Vectus™ - designed with a bell and spiggot ended pipe. These pipes are individually made on a mandrel.
  • Flowtite™ - designed plain ended pipe with a Reca™ coupling connection or mechanical VJ coupling design. These pipes are manufactured in a continuous process

We have found that there is a misconception that fibreglass is not flexible. GRP pipes is tested under the ASTM 2412 specification, measuring the pipes ability to resist deflection under load. GRP is tested to 30% deflection but can sustain higher deflection values before rapture, as shown in the picture below.

Fibreglass pipes are commonly used in applications such as:

  • Bulk Water Supply pipelines - due to its ability to be manufactured in very large diameters (4000 DN)
  • Underground Water pipelines - due to its light weight and low price
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The main reason why GRP should be considered as a material of choice is for the following properties and characteristics it offers:

  • Long Service Life
  • Chemical resistance, no need for internal or external protection
  • Biofilm bacterial resistance, especially in water pipeline conveyance
  • UV stabilised to install pipelines above ground
  • Light weight for ease of handling
  • Excellent hydraulic low friction properties, resulting in smaller pumps and less energy consumed
  • Excellent waterhammer properties due to flexibility
  • No cathodic protection required
  • Comprehensive fittings list available
  • Low maintenance cost over duration of pipeline life cycle
  • Low installation costs



Please contact us to assist you with your selection of the correct GRP pipe design for your pipeline application.