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"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.\n\n\n\nGRP Family\n\n\n\nGRP: Glass – fibre reinforced plastic.GRE: Glass – fibre reinforced epoxy.GRV: Glass – fibre vinyl ester.GRUP: Glass – fibre reinforced unsaturated polyester.\n\n\n\nThe different types of pipes are selected according to the required properties like chemical resistance, temperature resistance, and mechanical properties.\n\n\n\nTypical GRP pipes\n\n\n\nCharacteristics of GRP Pipe\n\n\n\nCorrosion 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.\n\n\n\nWhat are the advantages of GRP Pipes\n\n\n\nGRP Pipes provides various beneficial advantages as listed below:\n\n\n\nLong 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)\n\n\n\nTypes of Manufacturing of GRP Pipes\n\n\n\nDifferent types of manufacturing methods are applied for GRP pipes like\n\n\n\nFilament winding.CentrifugeContinuous winding or Drostholm Method.Helical Filament winding (Fig.1)\n\n\n\nFig. 1: helical filament welding method\n\n\n\nMaterials used:\n\n\n\nPolyester Resins – (Temperature limit is 70 deg C.)\n\n\n\nIsophthalic Polyester (Tg is 90 deg C)-Rarely used in for chemical services but can be used in\n\n\n\nunderground GRP gasoline storage tanks.\n\n\n\nBisphenol 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.\n\n\n\nNote: 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.\n\n\n\nTg shall be greater than 30 deg C above the maximum design temperature.\n\n\n\nVinyl 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.\n\n\n\nReinforcing materials:\n\n\n\nReinforcing 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.\n\n\n\nCodes and Standards for GRP Pipes\n\n\n\nBS 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.\n\n\n\nGRP Pipes and Fittings \n\n\n\nRefer to Fig. 2 which shows some typical GRP pipes and fittings.\n\n\n\nFig. 2: GRP Fittings\n\n\n\nGRP Pipe Joining methods\n\n\n\nAdhesive Joint (Fig. 3)Flange Joint (Fig. 5)Lamination Joint (Fig. 5)Rubber Seal Lock Joint (Fig. 4)\n\n\n\nFig. 3: Adhesive joints\n\n\n\nFig. 4: Rubber Seal Lock Joint\n\n\n\nFig. 5: Flanged and lamination joint\n\n\n\nApplications of GRP and GRE Pipes\n\n\n\nGRP Pipes are widely used in the following plants:\n\n\n\nChemical process.Desalination.Industrial effluents.Mining.Oil fields.Potable water.Power plant cooling and raw water.Seawater intake and outfalls.Metal ProductionSlurry piping.Water distribution.Pulp and Paper Mills.Sewerage &amp; DrainageTransportation of oils, alcohols, fats, disposal, and solutions for food industries.\n\n\n\nGRP Pipe Failures \n\n\n\nFig. 6 shows a typical failed GRP pipe.\n\n\n\nFig. 6: GRP pipe failures\n\n\n\nMetallic-GRP Piping interface\n\n\n\nIn order to have reliable flange sealing, generally, steel ring elastomer gaskets are used.Gasket material should match with pressure, temperature, chemical resistance requirementsPTFE-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.\n\n\n\nFig. 7: Metallic GRP Interface\n\n\n\nGRP/GRE pipe Supporting\n\n\n\nRefer to Fig. 8 to Fig. 10 for typical GRP piping supports. \n\n\n\nFig. 8: Clamped shoe support on GRP Pipes\n\n\n\nStandard CS support may not match GRP as pipe Outer Diameter may be different.Use of Saddles &amp; 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 &amp; 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 loadingsSpecial care to be taken in a freezing environment.\n\n\n\nFig. 9: Flange Support on GRE Pipe\n\n\n\nFig. 10: GRE Pipe support with Guide and Line Stop\n\n\n\nFew more related articles to give you more insights into the subject.An Article on HYDROSTATIC FIELD TEST of GRP / GRE linesStress Analysis of GRP / GRE / FRP piping system using Caesar IIBasic Principles for an aboveground GRP piping systemBuried GRP/FRP pipe Laying and Installation ProcedureStress Analysis of GRP / GRE / FRP Piping using START-PROF"
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