Fiberglass-reinforced plastic anti-corrosion steel pipe

Specifications: Φ89mm–Φ1820mm, Wall thickness: 6mm–20mm

I. Definition of Fiberglass Anti-Corrosion

Applying fiberglass to the surfaces of carbon steel, concrete, or other substrates to prevent the substrate from being damaged or deteriorated under the influence of media or environmental factors is referred to as "fiberglass anti-corrosion." Commonly used fiberglass anti-corrosion techniques include: fiberglass lining, glass flake lining, resin mortar brick and tile lining, epoxy self-leveling coatings, epoxy powder spraying, and fiberglass coating applied directly onto the substrate surface.

II. Product Features

The composite material used for fiberglass corrosion resistance is fiberglass itself, which possesses all the advantages of fiberglass. By selecting materials and designing processes and structures in a scientific and rational manner, it is possible to meet the required technical specifications. The characteristics of fiberglass corrosion resistance are as follows:
1) Excellent designability: Due to the differing properties of the matrix material and the reinforcing materials, fiberglass can meet various physicochemical performance requirements by means of rational selection of raw materials, adjustment of the fiberglass composition ratio, modification of the laying pattern of the reinforcing materials, and scientific structural design.
2) Excellent mechanical properties: The tensile strength of fiberglass reinforced plastic is lower than that of steel but higher than that of ductile iron and concrete. Its specific strength, however, is about three times that of steel, ten times that of ductile iron, and twenty-five times that of concrete. It also exhibits outstanding impact resistance—when subjected to a drop hammer weighing 1.5 kg from a height of 1600 mm, it remains undamaged.
3) Chemical corrosion resistance: Through the rational selection of raw materials and scientific thickness design, fiberglass reinforced plastic (FRP) exhibits long-term durability in environments containing acids, alkalis, salts, and organic solvents.
4) Excellent heat and cold resistance: The typical operating temperature range for conventional fiberglass is -40 to 70°C. However, by selecting special resins or adding UV-absorbing additives, the product can be used in environments ranging from -60 to 300°C while also resisting prolonged exposure to sunlight.
5) Excellent thermal insulation performance: Since fiberglass products are composed of polymer materials and reinforcing fibers, they exhibit a low thermal conductivity—typically ranging from 0.3 to 0.4 kW/m·h·℃ at room temperature, which is only 1/100 to 1/1000 of that of metals. As a result, these materials serve as outstanding thermal insulators. Consequently, under small temperature differences (below 50℃), no special insulation measures are required to achieve highly effective thermal insulation.
6) Low thermal expansion coefficient: Thanks to its low thermal expansion coefficient (2.0×10⁻⁵/℃), fiberglass can be reliably used under a wide range of harsh conditions, including surface, underground, overhead, underwater, high-cold, desert, frozen, humid, and acidic or alkaline environments.
7) Lightweight, high-strength, and easy to install: Its specific gravity is only 1/4 to 1/5 of that of steel or cast iron, and 2/3 of that of concrete. Fiberglass containers weigh approximately one-fourth as much as steel containers of the same specifications. Therefore, they are convenient to load and unload and easy to install.
8) Excellent electrical insulation performance: Fiberglass materials are outstanding insulating materials used to manufacture insulators. They maintain excellent dielectric properties even at high frequencies. They exhibit good microwave transmission and are well-suited for use in areas with dense power and telecommunications lines as well as regions prone to frequent lightning strikes.
9) Excellent construction process performance: Before glass fiber reinforced plastic is cured and formed, its resin’s fluidity allows for the use of various molding methods, making it easy to fabricate into desired shapes. This feature is particularly well-suited to the construction requirements of large-scale, monolithic, and structurally complex equipment. Moreover, depending on environmental conditions, on-site construction is possible.

III. Application Fields

Glass-fiber reinforced plastic (GFRP) anti-corrosion coatings are primarily used in environments with corrosive media and are widely applied in the chemical industry—for ground surfaces, acid-alkali tanks, drainage ditches, sewage ponds, and more; in the electroplating industry—for acid-alkali tanks and ground surfaces; in municipal engineering—for sewage ponds and sewage pumping stations; and in other industries—for acid-alkali tanks, ground surfaces, and structures.

4. Product Construction Method

1. Raw Material Preparation

Select appropriate raw materials based on the type of storage medium and the medium’s temperature. Cut the required reinforcing materials according to the dimensions of the structure that needs FRP corrosion protection. Prepare all necessary construction equipment and tools, protective gear, ventilation facilities, and other related equipment.

2. Substrate Surface Treatment

Select different treatment processes based on the type of substrate. For metal substrates, perform degreasing, deoiling, rust removal, dust removal, passivation, or phosphating treatments to eliminate surface protrusions, burrs, and other imperfections, repair surface defects, ensure a smooth surface, and maintain an appropriate degree of roughness. For concrete substrates, apply mortar for leveling and smoothing; the surface should be free from honeycombing, roughness, dusting, or sanding. After the concrete reaches its curing strength, conduct a water-pressure test for waterproofing and leak-proofing. Once the test is passed, remove any surface dust and repair any remaining surface defects. Use 500# silicate cement for the cement. For new concrete with higher alkalinity, apply a coating of 15–20% zinc sulfate or zinc chloride 2–4 times, allowing 12–24 hours between each application, then rinse off any residue with clean water. No further alkali removal is required for at least six months. For old concrete, remove any corroded or loose concrete, repeatedly rinse the remaining sound and firmly bonded concrete with clean water, and allow it to air-dry naturally for 12–24 hours. Repair damaged areas with fresh concrete, ensuring that the surface remains free from honeycombing, roughness, dusting, or sanding. After the concrete reaches its curing strength, use sandpaper or a trowel to remove any loose sand, debris, or dust from the concrete surface, and grind the surface to achieve an appropriate degree of roughness suitable for fiberglass anti-corrosion coating. If the moisture content of the concrete surface exceeds 6%, dry it at 50–60°C for three days to ensure that the surface moisture content is reduced below 6%.

3. Fabrication of the transition bonding layer

After the substrate is prepared, apply a transition adhesive material onto its surface to facilitate bonding between the fiberglass and the substrate. Epoxy resin is typically used as the transition adhesive layer. The number of primer coats can range from 2 to 4, depending on the specific requirements. The viscosity of the primer resin solution must be carefully controlled, and the application rate should be maintained at 200–250 g/m². For concrete or porous wood substrates, the curing time for the first primer coat should be appropriately extended to allow the resin solution to fully penetrate the substrate and enhance the strength of the bonded surface. The primer must be allowed to cure for at least 24 hours before proceeding to the next step; in colder temperatures, the curing time should be further extended accordingly. Once curing is complete, use putty to smooth out any defects, weld seams, or sharp corners on the substrate surface. Corners must be smoothly rounded for a seamless transition.

4. Reinforcement Layer Fabrication

For laminates with fewer plies, the continuous lay-up method is used; for laminates with more plies, the discontinuous lay-up method is employed. The staggered overlap method can also be adopted. The plies are laid according to a pre-defined process, and when preparing the resin adhesive, its curing time should be controlled within 0.5 hours to prevent the resin adhesive from flowing. The pre-cut reinforcing materials are laid sequentially, ensuring that they are completely impregnated by the adhesive and that there are no dry fibers or white spots on the surface.

5. Construction of the impermeable layer and the surface layer

After the structural layer has cured to a certain strength, an anti-seepage layer can be applied on the surface (or omitted entirely, depending on requirements); this layer typically consists of short-chopped mat. Once the lamination design requirements are met and the anti-seepage layer has cured to a sufficient strength, apply a resin gel coat to the surface of the anti-seepage layer, repeating the application 2 to 3 times, with each application controlled at 300 to 400 g/m². The product can be delivered for use after curing for 24 hours at temperatures above 25°C; when ambient temperatures are lower, the curing time should be extended. Extending the curing time can enhance both the mechanical properties and the corrosion resistance of the fiberglass material.

6. Instructions for Epoxy Self-Leveling and Acid-Resistant Brick Corrosion Protection

The epoxy self-leveling reinforcement layer typically consists of a quartz sand layer, with the surface finished using a resin-based self-leveling coating. For acid-resistant brick corrosion protection, acid-resistant bricks are used as the reinforcement layer; the key is to carefully control the width of the joints between the acid-resistant bricks. Otherwise, the procedure is identical to that for fiberglass corrosion protection.