Al Taie Building (1st floor), Al Qurum, Sultanate of Oman
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GRE pipes are manufactured by the filament winding process on precision steel mandrels in a helical pattern. Composite Pipes Industry with its Engineering department capability and experience can provide customize Engineering solution to customer starting at the early stage of the project. CPI has a big advantage of having in-house design capability along with manufacturing unit of GRP piping System. Production difficulties encountered along with effective quality system provides necessary input to design so as to take into account and make necessary changes to the GRP product design to provide economical and reliable product which meet the customer requirement up to highest level of customer satisfaction. Moreover, Having the design facility as an own design consultation along with field service work force which monitors complete process include from offloading of material , bonding, installation, and commissioning of GRP piping system. We provide the feedback needed to improve the design and incorporate the difficulties face by customer so as continuous improvement in design. With past track experience of more than 23 years we have achieved more than 3000 km of pipe and over 300,000 fittings globally.

GRP Pipes Wall Description


It is in direct contact with the conveyed fluid and guarantees the maximum resistance to the chemical attack from the fluid itself. Moreover, the liner presents an internal surface particularly smooth, without defects, cracks or delaminated zones. The liner is composed of one glass veil and one glass mat tape resin impregnated

Filament or mechanical resistant layer

Its function is to render the pipe wall resistant to the stresses due to the design conditions (stresses due to the internal and/or external pressure, flexural strength due to the external loads etc.) and generated by transport and laying operations. The thickness of the filament depend, then, upon the design conditions. The mechanical layer is composed of winded glass filament roving glass, glass mat reinforcement, all resin impregnated.

External layer (Top Coat)

It has a thickness of about 0.3 mm and consist of resin with Top coat veil glass. It guarantees the complete impregnation of the peripheral fibers, thus yielding the external pipe surface completely free of protruding fibers and well finished. The main intention of Top coat is to provide protection against ultraviolet rays in order to prevent the nearly negligible weathering effects.

Fabrication Process

GRE pipes are manufactured by the filament winding process on precision steel mandrels in a helical pattern.
The basic GRE pipe is constructed of the following:

The resin rich inner liner is reinforced to provide good resistance to aggressive and abrasive environments. The resin used in the liner shall be an aromatic or cyclo-aliphatic amine cured epoxy resin. . The structural wall of the pipe consists of filament winding glass roving’s impregnated with resin. After impregnation, the roving’s are wound around a steel mandrel in precisely set helical winding angle and with a uniform tension. The helical winding process allows the manufacture of pipe with plain ends, Bell and Spigots for adhesive joints and Bell and Spigots for Rubber Seal Lock Joints.


In the preparation stage, the correct mandrel size required is cleaned, and placed in the liner forming station of the pipe production line.

The liner is manufactured as follows:

One or more layers of ‘C’ glass veil are wound with a preset overlap around the rotating steel mandrel and impregnated with resin.

The correct computer program to wind the pipe to the proper design parameters is selected from the control panel.   The computer program selected sets and controls the rotation speed of the mandrel and the speed at which the carriage which transports the impregnated filament windings travel across the mandrel.  The winding angle is also controlled along with the number of layers in the pipe.     Typical helical winding angles vary from 55 to 73 degrees.

A rack containing the filament winding glass spools is set facing the rotating mandrels at a distance and the proper ends of each spool is drawn through a ceramic ‘eye’ to the impregnation unit on the carriage.   An Automatic dozing machine produces the exact mix of resin and curing agent.

The catalyzed resin for the structural wall is poured into the receiving trough, where the glass filaments are impregnated by passing in the trough and from there onto a steel roller and a ‘comb’ where excess resin is drained back into the trough before winding.   As the winding starts, the carriage travels horizontally back and forth across the rotating mandrel resulting in the helical winding pattern of the pipe.   The comb also controls the tension of the glass filaments being wound and gives a slight prestressing effect.

After completing filament winding the mandrel is transported to the oven for curing by overhead cranes.

Curing of the pipe takes place in a large oven whose capacity matches the output of the filament winding station.   The actual heating is done by infrared ray heaters.  Inside the oven the pipe and mandrel rotate slowly during the curing process to insure a uniform the even curing temperature.  The oven has two doors, one for feeding the fresh pipes and mandrels and one for getting out the cured pipes.  Epoxy pipes are also post cured.

Pipes are manufactured on solid mandrels having a length of slightly over 9.8 / 12 meters.  A separate demolding station removes the steel mandrel using an electric winch with a steel ring retaining the pipe while the pipe is pulled. The mandrel are slightly conical, to eases this operation.  The finished pipe has a laying length of 9 /12 meters.

The unit is equipped with Diamond tipped cutting and calibrating tool.  Socket x spigots of the pipes calibrated as per requirements.

After cutting and calibration, Pipes are moved to the hydrotest machine to be tested at 1.5*Design Pressure.

Tests made on individual pipes and tests made per lot production are described in the Inspection and Testing Plan (ITP)

Raw materials

The mechanical strength of GRP pipes depends on the amount, type and arrangement of glass reinforcement. The common glass types used in the GRP pipes are:

Designation​ General Application
E Good electrical resistance​
ECR Good Acid resistance​
C Good Chemical resistance​


are available in different forms

consisting of bundled, untwisted, strand. It provides excellent mechanical properties.

consisting of chopped strands held together with binder. It is used to provide multidirectional reinforcement in pipes as well as fittings

are of light weight that allow high resin content layers, that helps in improving the environmental resistance of pipes and fittings, in addition to smooth surface.


Only thermosetting resins are used in the production of GRP pipes. There mainly 3 types

Epoxy resins are resistant to a wide range of moderately strong acids and alkalis, and most Hydrocarbons. There are several types of base epoxy resins and associated curing agents.

Curing agents typically used for epoxy resin are:

  • Aliphatic amine;
  • Cyclo aliphatic amine (IPD);
  • Aromatic Amine (MDA);
  • Anhydride

For water services, e.g. sea-water cooling, Isophthalic polyester resin is typically used.

Isophthalic polyester is a relatively low cost resin, with limited chemical resistance.

For water services, e.g. sea-water cooling, Isophthalic polyester resin is typically used.

Isophthalic polyester is a relatively low cost resin, with limited chemical resistance.

Product Feature and Benefits

CPI GRP pipes and fittings are bringing the product which provide low cost, long term piping corrosion solution, light weight to the customer around the world.

Features Benefits
Corrosion resistant materials. . Long effective Design Life.
. No need for cathodic protection.
. No need for extra cost for pipe coating, wrapping, lining, painting.
. Low maintenance cost.
. Hydraulic characteristics remain unchanged over period of time.
Light weight: 1/4th weight of ductile iron and 1/10th of concrete pipe. . Easy to install. No need for expansive handling and installation equipment.
. Low delivery cost.
Extremely smooth bore . Less friction loss means less pumping energy needed.
. Minimum slime build up can help lower cleaning costs.
Dimensional stability . Pipe can maintain the critical tolerances required of the most demanding structural and piping applications.
. The material meets the most stringent material stiffness, dimensional tolerance and weight.
Pipe specifications meet or exceed worldwide standards . Assure high quality product specification.
High technology pipe manufacturing system . Help ensure consistent product quality.