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In recent times, GRP and FRP are being extensively used in the process, water, and chemical industries due to their high resistance to corrosion. Also, their service life is usually very high, in the range of 50 years. So, the total cost of GRP/FRP piping for the service life becomes cheaper as compared to metallic pipes. GRP/FRP pipes are increasingly used to transfer water, oil, Fuel, Glycol, wastewater, sewer, etc. Because of this, the demand for GRP/FRP piping is continuously increasing.

Fiberglass reinforced pipes (FRP) are used in trenchless installation of pipelines because it is lightweight, temperature resistant, strong, and highly resistant to chemicals and corrosion. FRP basically consists of fiberglass and thermosetting resins

The full form of FRP is fiberglass reinforced plastic that is a composite material consisting of a polymer matrix reinforced with fibers. So, an FRP pipe is a pipe manufactured of FRP material by contact molding or filament winding method. Various types of resins like thermosetting polyester, epoxy, phenolic resin, etc are used to get specific FRP pipe properties in the final product. The most widely used reinforcement is the glass fiber “E-glass”. As a corrosion-resistant alternative to metallic piping, the FRP piping system has found worldwide application. By selecting FRP as the pipe material, the need for internal lining, external coating, and cathodic protection can easily be eliminated. FRP piping system is available in a wide range of sizes starting from 1 inch to 144 inches.

Applications of FRP Pipes

Due to its high durability, corrosion resistance, and moderate strength, the use of FRP pipes is increasing day by day. FRP piping systems are used in various industries like:

• Potable Water and desalination industries
• Chemical, Petrochemical, Oil & Gas industries
• Ducting and Vent piping
• Irrigation and Sanitary services
• Water distribution and transmission
• Slurry piping
• Power plants, etc.

Properties of FRP Piping

The main properties that make FRP Pipes an ideal selection for various industries worldwide are

• Excellent corrosion resistance
• Excellent strength to weight ratio. Note that, the strength to weight ratio of FRP pipes are higher than steel or other metallic pipes.
• Light weight which makes easy for handling and transportation.
• Dimensional stability
• Non-toxicity
• Low coefficient of friction (>25% better than steel) that ensures excellent flow characteristics.
• Good abrasion resistance
• Suitable for both aboveground and buried piping
• Resistance to biological attacks like bacteria
• Non-conductive to electricity
• Low maintenance cost

Typical mechanical properties of the FRP piping system are provided in the table below:

Mechanical Properties of FRP Pipe	Typical Range
Tensile Strength	14 to 550 Mpa
Tensile Modulus	3.5 to 34.5 Gpa
Flexural Strength	28-480 Mpa
Flexural Modulus	6.9 to 34.5 Gpa
Poisson’s Ratio	0.3
Thermal Co-efficient	14 to 54 mm/mm/0C
Specific gravity	1.2 to 2.3
Compressive Strength	69-275 Mpa

Joining of FRP Pipes

As the FRP pipe lengths are limited by transportation and handling, they are required to be joined. Also, various FRP Pipe fittings need to be joined as per the requirement. The joining system of the FRP pipe should be such that it does not leak for the intended service condition at the operating pressure. Depending on the specific joint configuration and design conditions, the FRP pipe joints may be restrained or unrestrained.

Unrestrained FRP Pipe Joints

Joints that can withstand the internal pressure but cannot withstand the longitudinal tensile loads are known as Unrestrained FRP Pipe joints. Examples of such joints are Coupling joints, bell and spigot joints, mechanical coupling joints with elastomeric seals, flanged joints, butt joints with laminated overlay, etc

Restrained FRP Pipe joints

Such pipe joints are capable of withstanding both the internal pressure and longitudinal tensile loads. For these joints, supplemental restraining elements are added to restrict the longitudinal loads. Threaded joints, bell, and spigot joints with laminated overlay or adhesive bonds are examples of Restrained FRP pipe joints.

Note that FRP pipe joint tightness must be ensured following ASTM D4161.