GRP Pipes – Do You Know Everything About Them?


Selling GRP pipes is a lot like dating. What most companies do is: they go out into the marketplace, push offers to prospects and ask complete strangers to marry them!

If you think about it in this way, it becomes quite difficult to convince technical offices to change the tenders, or investors to choose your GRP pipes. You need to have a clear approach and build the trust in the product, but…

How can you do this properly with GRP pipes?

This article will provide you with information on GRP pipes. You probably already know some of the details, but the rest will be new to you. Read the article carefully and think about it from the perspective of the end-users, so you can understand their concerns and fears, making it easier for you to hit the target.

There are several reasons why GRP pipes solutions have been replacing conventional pipes in many countries, so this relatively new product should be kept in mind when evaluating a new pipe project or planning on revamping one.

In parallel, engineers involved in specifying GRP pipes should have a clear understanding of pipe’s nature and properties.

You probably already know the main advantages of the GRP pipes, but let’s just quickly mention them anyway:

  • compared to the cast iron and carbon steel pipes, GRP pipes have an elevated corrosion resistance, because of the inert nature of the materials they are composed of. It is not unusual to design a GRP pipe for a working life of 50-60 years. Nowadays, some producers are even estimating a lifetime of over 100 years. GRP pipes can be designed to resist corrosion on the inside and outside. In fact, with the aid of an internal-external barrier, and the use of the correct resin barriers, the pipe can
    withstand varied corrosion environments;
  • another major benefit is lightweight construction. Typically, a GRP pipe’s weight is 35% of a comparable carbon steel pipe’s weight, and 10% of a comparable concrete pipe’s weight. This means the costs of handling, shipping, long-haul transport and site installation are significantly lower;
  • ordinary GRP pipes don’t conduct electricity and consequently have much better electrical properties than their steel counterparts. However, if electrical conductivity is required, it is possible to add conductive reinforced fiber or fillers during the fabrication process;
  • due to their composite structure, the GRP pipes can be designed to exactly match the project requirements, leading to cost savings;
  • an additional advantage of GRP pipes is the pressure absorption: they are designed to absorb 40% of the surge pressure, without the need to increase the pressure class;
  • GRP pipes also possess a natural damping property. The fatigue endurance and strength to weight ratio are the key attributes associated with the replacement cost and the ability to design lightweight pipes;
  • thanks to their smooth inner surface, there is minimum friction loss, and they keep this characteristic throughout their entire service life;
  • last but not least feature of the GRP pipes is low maintenance, which comes from the fact that they don’t undergo the corrosive attack that the metallic counterparts have.

They have many advantages, right?

The Decision makers must also consider the particular characteristics of the GRP pipes

In spite of these advantages, the decision makers must also consider the particular characteristics of the GRP pipes, which means:

  • to calculate the total investment costs correctly, the investor must also consider the installation, erection and maintenance costs, in order to be able to compare these with other materials. If only the initial cost is evaluated, the project’s figures will not be realistic;
  • the market of composites is, compared to many traditional materials, not as big, so you can’t consider GRP a commodity. It is a customized product, which must be prepared individually for every single project, and thus the delivery times may be longer than of the traditional materials;
  • the design of the GRP pipes, as I mentioned before, is performance-based. In other words, the investor must take care when identifying the project requirements and true operating conditions and only then share the information with the pipe supplier;
  • the composite pipe manufacture should require that the investor adheres to specific instructions in order to ensure the long-term performance of the pipeline.

It is also very important that the Engineers understand the limitations of the GRP pipes, which depend on the technology used to manufacture them. During recent years I have noticed, that some projects have been influenced by strong marketing and miraculous promises from some pipe manufactures, leading to the incorrect use of the product.

For example, the performance of a Continuous Filament Winding pipe is very high on certain applications and lower on other applications, the same is true of the Discontinuous Filament Wound pipe or the Centrifugally Cast GRP pipe.

Which pipe is the right one for your application and needs?

Well, as I mentioned before, it depends on your specific project, from the design to the installation method.

As indicated in one of my previous articles, we can generally say that the marine, industrial and oil & gas markets demand small quantities of pipe of medium to high pressures and with particular technical characteristics, so generally, the pipes need to be produced with the discontinuous filament winding system. This concept is also applicable to the civil infrastructure market but is related to very small quantities and medium to high pressures.

If extensive lengths of pipelines are needed for the civil infrastructure projects (over 1000 km), a CFW production line is recommended, also because the cost of a produced pipe is 15-30% lower compared to the pipes produced with a discontinuous or centrifugally cast line.

If small quantities and low pressures are needed by a particular market (for example sewer pipes for small works), a centrifugally cast line can be chosen, even though this system does not offer the flexibility of a continuous or discontinuous system.

I hope everything is clear so far?

Raw Materials and their properties in GRP Pipes

Let’s talk some more about the Raw Materials because you need to understand their properties if you would like to understand the GRP pipes better.

The resins used in the filament winding process are mostly polyester, vinyl ester and epoxy resins. What is resin’s role in a pipe? It serves as the glue that binds the fibers in the pipe together after the curing (when the resin sets). The pipe liner resin also provides the most definitive corrosion resistance to the transported fluids. Its chemical and physical properties play a key role in the pipe design.

Firstly, let us look at the polyester resins used in the manufacturing of the composite materials. They are classified as orthophthalic, isophthalic or terephthalic resins. The orthophthalic resins are general-purpose resins, for water conveyance and sewerage applications. They are used for manufacturing laminates, which are not subjected to strong chemical attacks or weathering. From a thermal point of view, these resins are employed at ambient or medium-to-low temperatures. It has to be mentioned, that the orthophthalic resins should not be used for constructing the internal liner of a fiberglass pipe. Isophthalic resins have their most suitable end-use in the manufacture of pipes conveying waste liquids, drinking water and seawater, above or below ground. In fact, they are more resistant to corrosive substances present in the ground; to most salts; and to mildly oxidizing acids at medium concentrations. This type of resin is always used for the internal liner of the pipe.

Secondly, we have vinylester resins. They combine a greater resistance to chemicals with a high mechanical strength, which is true at high temperatures as well. Of course, they are more expensive than polyester resins.

Last ones are epoxy resins, which are normally used for smaller diameters and for higher pressures, compared to other resins.

Besides the quality of the resin, two decisive factors for obtaining an excellent final result are the types of glass employed and its use in the most appropriate manner for fully exploiting its structural properties.

Glass fibers are obtained with the silica glass-based melting mixtures of inorganic materials, at temperatures varying between 1300°C and 1600°C. Under these conditions, the cross-linked structure of the silica is destroyed; its continuity is interrupted; and its structure is modified by the introduction of other oxides.

The form of the fiber reinforcements varies considerably, depending on the pipe manufacturing process and the design load requirements. The major examples include directional fibers (roving), chopped fibers and fabric reinforcement forms (mat, woven roving, etc.).

The actual fiber content in a composite depends on the end use design. The fiber orientation, the layup sequence of the laminate, and the number of reinforcements determine the actual pipe stiffness, strength, and mechanical properties.

The reinforcements used in the manufacturing of the industrial products, such as vessels, silos and pipes, are made from three different types of glass compositions:
– “C” glass, which displays very good properties of chemical inertness to corrosive environment;
– “E” glass, which is not so resistant to corrosion, but displays a very high mechanical strength;
– “ECR” glass, which is similar to E-glass but without boron and fluorine. Due to the absence of these components, the chemical resistance (including water-resistance, acid-resistance and alkali-resistance) is greatly improved. When compared to the E-glass fibers, the ECR-glass shows higher temperature resistance, better dielectric strength, lower electrical leakage, and higher surface resistance.

In many cases, design and manufacturing of the GRP pipes incorporate additional components. Many of these, including catalyst and hardeners, are the processing aids for the resins and are necessary for the completion of the chemical process and curing of the laminate. The filler may be used to enhance the appearance, economy or performance of the pipe. Another role of the fillers is to increase the stiffness of the pipe structure.

Get the most out of your raw materials

If your intention is to maximize your return on investment in the composites market, utilizing a filament winding technology, it is important for you to know that you will need to get the maximum capacities out of your raw materials. Unfortunately, less than half of the existing manufacturing plants are optimizing their design in such a way, that they are using the same pipe design regardless of the type of materials involved in the production.

This happens because many investors who, in good faith, followed the incorrect advice offered by the technology and machine suppliers, now realize, that they are the ones who have to face the wrath of the competitive market.

We have spent more than 16 years traveling, installing CFW plants (more than 35) and helping companies to penetrate the market with the GRP pipes. We have developed and successfully applied our EFFECTIVE FILAMENT WINDING method, which is the first-ever to guarantee profit-making.

What is our secret?

Our secrets are in-depth knowledge on the Filament Winding Process; hard work; and taking effective steps with the use of an analytical method. If you have a project and you are looking for a company that can guarantee the reliability of the pipeline that your end customer deserves, without unpleasant surprises occurring during the installation even if the project is located in remote or complicated locations, thus ensuring you get maximum profits, then you seriously need to consider contacting me and my team.

Contact us by sending an email to Me and my staff at TOPFIBRA will contact you, and together we will evaluate your project to see if and how we can help.

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