FRP Laminate structure for pipe and fittings

Two standard manufacturing methods are used in FRP laminate construction as an overwrap for thermoplastic piping systems: Filament Winding and Contact Molding (hand lay-up).

Pipes and fittings of Type D, as per DIN 16965 / 966 standards, consist of a Chemical Barrier Layer (CBL) with a minimum thickness of 2.5 mm and a structural layer filament-wound from woven roving, Chopped Strand glass mats, and unidirectional woven roving. Additionally, there is a bonding layer that connects the thermoplastic liner to the FRP structure. The top layer serves as exterior protection and includes a resin layer with paraffin wax and UV protection.

Below figure shows CBL, Structural layer, top layer.

For Chemical barrier layer (CBL):  Chemical barrier layer consists of Resin-rich layer with a gelcoat veil and chopped strand mats. It is having resin content 75 ± 5% and Glass content 25 ± 5%.

Structure layer: This layer is the primary structural portion of the laminate and is designed to withstand the loads caused by pressure, wind, seismic and other conditions. It consists of alternating layers of chopped strand.

Structured layer for pipes: Filament winded from roving, Chopped strand mats and woven roving. It will have resin content 40 ± 5% and Glass content 60 ± 5%.

Structured layer for fittings: Laminated from Chopped Strand mats and woven roving. It is having resin content 45 - 65% and Glass content 35 - 55%.

Top layer / Outer Surface Layer: The top veil is used for protection against all weather conditions, UV radiation, and chemical reactions. If the outer surface of a laminate is to be exposed to a corrosive environment, a veil layer or a chopped strand layer may be added over the structural layer for additional protection. The outer surface can also be pigmented for color designation if necessary.

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Laminate Construction of FRP Pipe

 Dear Readers,

This is continuation of my previous post of “Introduction of FRP Pipe.”

Fiberglass reinforced plastic (FRP) laminates are manufactured with thermosetting polyester or Vinyl ester resins and various types of fibrous glass reinforcing. The fiberglass reinforcement is thoroughly saturated with catalysed resin to form a dense laminate with the required physical and chemical resistant properties.

In general, the glass reinforcing provides the strength to the laminate and the resin binder provides the shape and chemical resistance. To achieve optimum chemical and abrasion resistance, all laminates are composed of an Inner surface, an Interior layer, a Structural layer, and an Outer Surface layer.

The combination of inner surface and interior layer is often referred to as the Liner or Corrosion Barrier and is generally considered to contribute structural strength as well as corrosion resistance to the laminate.

Summary of Laminate Structure as follows.

Liner / CBL (Corrosion Barrier Layer or Chemical Barrier Layer)

Structural Layer

Top Layer or Surface Layer

Inner Surface - This surface is exposed to the cursive environment and is composed of resin reinforced glass veil or a synthetic veil.

Interior Layer - This portion of the laminate is composed of multiple layers of chopped strand fiberglass reinforcement.

Structural Layer - This layer is primary structural portion of the laminate and is designated to withstand the loads caused by pressure, wind, seismic and other conditions. It consists of alternating layers of chopped strand and Woven Roving to the required thickness.

Outer Surface Layer - This surface is a resin coating formulated to be non-air inhibited and fully cured. When exposed to the environment, this coating contains ultraviolet absorbers or pigments to minimise ultraviolet degradation.

Introduction of FRP Pipe

Dear Readers,

The Expansion of FRP is fiberglass-reinforced plastic which is a composite material consisting of thermoset resin and fibre reinforcement. FRP is principally made up of thermoset resin and glass Fibers. Resins can be divided into two broad classes: thermosetting and thermoplastic. Thermosetting resins cure to produce an infusible solid material that does not melt when heated. They soften when heated above their glass transition temperature, but do not reach a liquid state. Thermosetting resins used for FRP are typically purchased in liquid form and are reacted to a solid with chemical additives.

FRP is a reliable material of construction for piping and equipment in acid and base chemical services, such as hydrochloric acid (HCI), sulfuric acid (H₂SO₄), Chlorine dioxide (ClO₂), sodium hypochlorite (NaOCI) and caustic (NaOH) solutions.

Compared to most metals, FRP is generally considered a non-ductile material. FRP has a long elastic zone and markedly lower modulus of elasticity as compared to carbon and stainless steel. It should be noted that since FRP is a composite material, its material properties are orthotropic in nature, meaning that the properties are different in the hoop and axial directions.

Pipes can be manufactured by contact moulding (Hand lay-up) or hand lay up in combination with filament winding.

Types of glass fibre reinforcements

1. Chopped Stand Mat (CSM)

2. Rovings

3. Woven glass fabrics

4. Surface Veil

They are manufactured from glass or synthetic fibres such as polyester.  

A wide range of process equipment is constructed from FRP to meet the service conditions including Chlorine dioxide generators and storage tanks, bleach towers, Effluent Piping, Process Piping, Sump, and trough linings. FRP piping system is available in a wide range of sizes starting from 1 inch to 144 inches.

FRP Pipes are light Weight and Non-Corrosive and easily constructed, it is up to 75% less than Steel weight but it is equally strong. Density of FRP composite is 1800 Kg/Cum, Where as Carbon Steel is 7860 Kg/Cum.