Overview of GRP Pipes

GRP Pipes or Glass Reinforced Plastics pipes are composite material pipes consisting of a polymer matrix that is reinforced with glass fibers. They have very high corrosion resistance ability and thus used widely for low-temperature corrosion-resistant applications. In recent times, The GRP pipes are slowly replacing the steel in various services like fire water services. At the same time, GRE or GRP pipes can withstand high pressures. In many places, the term FRP is used interchangeably for GRP pipes. In this article, we will explore an overview of GRP Pipes.

GRP Family

  • GRP: Glass – fibre reinforced plastic.
  • GRE: Glass – fibre reinforced epoxy.
  • GRV: Glass – fibre vinyl ester.
  • GRUP: Glass – fibre reinforced unsaturated polyester.

The different types of pipes are selected according to the required properties like chemical resistance, temperature resistance, and mechanical properties.

Overview of GRP Pipes
Typical GRP pipes

Characteristics of GRP Pipe

  • Corrosion resistance: Corrosion resistant to both inside and outside corrosion. As a result, additional linings and exterior coatings are not required.
  • When the ratio of strength per unit of weight is considered, fibreglass composites surpass CS and SS.
  • Lightweight: Fibreglass piping is only one-sixth the weight of steel products and 10% the weight of similar concrete products.
  • Electrical properties: Standard fibreglass pipes are nonconductive. Some manufacturers offer conductive fibreglass piping system for transporting fluids like Jet Fuel.
  • Dimensional stability: Fibreglass material meets the most stringent material stiffness, dimensional tolerance, weight and cost criteria.
  • Low maintenance cost: Fibreglass piping is easy to maintain because it does not rust, is easily cleaned and requires minimal protection from the environment.

What are the advantages of GRP Pipes

GRP Pipes provides various beneficial advantages as listed below:

  • Long life; highly durable.
  • Low maintenance cost.
  • High Corrosion resistance.
  • Low lifecycle cost.
  • No need for cathodic protection.
  • Less transportation and handling cost.
  • Environmental friendly.
  • Wide application range.
  • Economic when compared with DSS pipe (Duplex stainless steel)

Types of Manufacturing of GRP Pipes

Different types of manufacturing methods are applied for GRP pipes like

  • Filament winding.
  • Centrifuge
  • Continuous winding or Drostholm Method.
  • Helical Filament winding (Fig.1)
helical filament welding method
Fig. 1: helical filament welding method

Materials used:

Polyester Resins – (Temperature limit is 70 deg C.)

  • Isophthalic Polyester (Tg is 90 deg C)-Rarely used in for chemical services but can be used in

underground GRP gasoline storage tanks.

  • Bisphenol A Polyester (Tg is 120 deg C)- High temperature, chemically resistant resin extensively used in chemical services.
  • Chlorinated polyester (Tg is 110 deg C)-Properties same as Bisphenol A Polyester, but has an inherent fire retardant characteristics. This property can be enhanced by addition of antimony oxide particles to the resin mix.

Note: Tg is Glass transition temperature, shall be determined by either Differential Scanning Calorimetry according to ISO 11357 or Differential Thermal Mechanical Analyses according to ISO 6721.

Tg shall be greater than 30 deg C above the maximum design temperature.

  • Vinyl ester resins – (Temperature limit is 100 deg C.)-Compared to polyester resins, vinyl ester resins have improved corrosion resistance and high temperature resistant.
  • Epoxy resins – (Temperature limit is 110 deg C.)- Epoxy resins have excellent resistance to a wide range of moderately strong acids and alkalis and most hydrocarbons. Aliphatic amines, Aromatic amines, anhydrides are few examples of base epoxy resins.

Reinforcing materials:

  • Reinforcing material shall be a suitable grade of glass fibre having glass finish compatible with the resin system used.
  • Glass-fibre materials typically used for GRP Pipes and vessels are E-Glass, C-Glass, ECR Glass, Synthetic etc.

Codes and Standards for GRP Pipes

  • BS EN ISO 14692: Petroleum and natural gas industries – Glass-reinforced plastics (GRP) piping.
  • AWWA M45:Fibreglass Pipe Design.
  • SHELL DEP 31.40.10.19:GRP Pipelines and Piping Systems (Supplements to ISO 14692)
  • UKOOA: United Kingdom Offshore Operator Association.

GRP Pipes and Fittings

Refer to Fig. 2 which shows some typical GRP pipes and fittings.

GRP Fittings
Fig. 2: GRP Fittings

GRP Pipe Joining methods

  • Adhesive Joint (Fig. 3)
  • Flange Joint (Fig. 5)
  • Lamination Joint (Fig. 5)
  • Rubber Seal Lock Joint (Fig. 4)
Adhesive joints
Fig. 3: Adhesive joints
Rubber Seal Lock Joint
Fig. 4: Rubber Seal Lock Joint
Flanged and lamination joint
Fig. 5: Flanged and lamination joint

Applications of GRP and GRE Pipes

GRP Pipes are widely used in the following plants:

  • Chemical process.
  • Desalination.
  • Industrial effluents.
  • Mining.
  • Oil fields.
  • Potable water.
  • Power plant cooling and raw water.
  • Seawater intake and outfalls.
  • Metal Production
  • Slurry piping.
  • Water distribution.
  • Pulp and Paper Mills.
  • Sewerage & Drainage
  • Transportation of oils, alcohols, fats, disposal, and solutions for food industries.

GRP Pipe Failures

Fig. 6 shows a typical failed GRP pipe.

GRP pipe failures
Fig. 6: GRP pipe failures

Metallic-GRP Piping interface

  • In order to have reliable flange sealing, generally, steel ring elastomer gaskets are used.
  • Gasket material should match with pressure, temperature, chemical resistance requirements
  • PTFE-envelope type gaskets should be avoided for large size and high pressure.
  • Refer to Fig. 7 which clearly shows the GRP-Metallic interface in a piping system.
Metallic GRP Interface
Fig. 7: Metallic GRP Interface

GRP/GRE pipe Supporting

Refer to Fig. 8 to Fig. 10 for typical GRP piping supports.

Clamped shoe support on GRP Pipes
Fig. 8: Clamped shoe support on GRP Pipes
  • Standard CS support may not match GRP as pipe Outer Diameter may be different.
  • Use of Saddles & Elastomeric pads may allow the use of standard support.
  • The support design should be as per the vendor catalog.
  • GRE pipes are generally rested with clamp & shoe for all supports.
  • Heavy in-line items like valves, strainers should be independently supported.
  • Parasite support (pipe to pipe) is not allowed.
  • Supports on fittings to be avoided.
  • Excessive clamping forces can cause pipe crushing.
  • GRP spans are much less than the CS spans, in absence of vendor data ISO 14692 can be used.
  • Piping should be supported for shock loadings
  • Special care to be taken in a freezing environment.
Flange Support on GRE Pipe
Fig. 9: Flange Support on GRE Pipe
GRE Pipe support with Guide and Line Stop
Fig. 10: GRE Pipe support with Guide and Line Stop

Few more related articles to give you more insights into the subject.

An Article on HYDROSTATIC FIELD TEST of GRP / GRE lines
Stress Analysis of GRP / GRE / FRP piping system using Caesar II
Basic Principles for an aboveground GRP piping system
Buried GRP/FRP pipe Laying and Installation Procedure
Stress Analysis of GRP / GRE / FRP Piping using START-PROF
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Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

3 thoughts on “Overview of GRP Pipes

  1. Sir please guide on lamination joint,
    Also the thickness of lamination joint.
    How much will be its thickness ? How much will be its temperature at time of jointing etc.
    Please also mention standard of iso or astm for lamination joint.
    Thanking you in anticipation.

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