Corrosion resistance of fiberglass reinforced plastic pipes

The main advantage of fiberglass reinforced plastic pipes is their corrosion resistance. Within its temperature tolerance range, it can withstand most acid and alkali media. The specific corrosion resistance varies slightly among products from different manufacturers. However, its disadvantages are also obvious; mainly, it cannot withstand high temperatures, and if used for extended periods, the maximum temperature should not exceed 80 degrees. Of course, the products from different manufacturers are not exactly the same. Furthermore, its strength decreases rapidly as the temperature rises.

Different grades of fiberglass resin are somewhat more resistant to certain corrosive agents, but overall, fiberglass possesses strong corrosion resistance. Not only those mentioned above, but there are also issues related to strong acids, strong bases, and chloride ion corrosion, etc. It’s all fine, except that it can’t withstand high temperatures; above 60 degrees, problems arise after prolonged use. Its pressure resistance is also weaker than that of metal pipes.

Fiberglass reinforced plastic pipes can resist the erosion of acids, alkalis, salts, seawater, untreated sewage, corrosive soil or groundwater, as well as numerous chemical fluids. It has a longer service life than traditional pipes, with a designed service life of generally over 50 years. Sand-laid fiberglass reinforced plastic pipes produced by fiber winding have a specific gravity of 1.65–2.0, which is only 1/4 that of steel. However, their circumferential tensile strength is 180–300 MPa, and their axial tensile strength is 60–150 MPa, making them comparable to alloy steel. The inner wall of glass fiber reinforced plastic pipe is very smooth, with low roughness and friction. The roughness coefficient is 0.0084, while the n value for concrete pipes is 0.014 and that for cast iron pipes is 0.013; therefore, glass fiber pipes can significantly reduce the fluid pressure loss along the pipeline, thereby improving the transportation capacity. Due to its resistance to corrosion, wear, freezing, and contamination, glass fiber reinforced plastic pipes require no measures such as rust prevention, contamination control, insulation, or heat preservation, nor do they need regular maintenance. Underground pipes do not require cathodic protection, which can save more than 70% on maintenance costs.

I see that everything mentioned above sounds good, but I’m not sure if you have ever used FRP pipes. Yes, in theory, FRP pipes are quite resistant to corrosion; of course, this depends a lot on the type of resin used. Ten years ago, when I first started working at the factory, we worked on a project involving ion exchange membranes, designed by a well-known domestic design institute. It involved pipes for brine, with temperatures of just over 60° Celsius – essentially saturated brine. FRP pipes were chosen for these pipes. We also visited several manufacturers, but their products didn’t seem very satisfactory. Some people suggested using steel pipes lined with rubber or plastic, but that was only a suggestion. For some reason, FRP pipes were still used in the end. Since the piping system inside the facility was quite complex, with many fittings, the manufacturers supplied the pipes according to axonometric drawings. Yet, there were still many areas where cuts and welding were necessary on-site. During the testing phase, leaks occurred everywhere, though they were minor. Once the moisture dried up, dry NACL would adhere to the outer surface of the pipes, all over them. At first, there were few leak points, and they were small； Later, the problem spread everywhere; we hired people from the manufacturer to deal with it, but leaks still occurred throughout. After persisting for 2 months, we replaced all the pipes with steel-lined rubber pipes. The direct cost related to just the pipes was around 700,000; it was really heartbreaking at that time! ! ! It’s just my personal experience; there’s no other meaning to it

Non-metallic materials are very sensitive to temperature changes! Large temperature fluctuations can easily lead to leakage issues such as weld cracks

Glass fiber reinforced plastic is widely used in anti-corrosion equipment and pipelines. There are many types of glass fiber reinforced plastic; traditional phenolic resins have good acid resistance, epoxy resins can resist dilute acids and dilute bases, furan resins can resist both acids and bases, while modern epoxy vinyl resins are widely used in desulfurization processes. The temperature resistance of fiberglass-reinforced plastic still needs to be improved; generally, its temperature tolerance does not exceed 100°C. The cost of materials with higher temperature resistance rises sharply. Additionally, there are issues when using this material in the presence of strong solvents such as toluene, etc. Different resins have varying levels of resistance to solvents, and it is necessary to determine this before use.

There are many glass fiber pipes used in fire protection systems; they are used with seawater, and they have good corrosion resistance. Since there is no issue of high temperatures, they work well in fire protection systems. I haven’t seen them used in other types of process systems

The strength is too low, resulting in high maintenance costs. It’s new and still needs improvement.

The guys have already explained it in great detail: fiberglass-reinforced plastic is resistant to acids and alkalis, but not to high temperatures. I remember seeing it once before; it was warm alkaline wastewater, with a temperature of no more than 50°C. The new pipes had been in use for just a few months when they were almost completely corroded, leaving only a network-like structure behind.