In what kind of environment is it not suitable to use the Ductile iron manhole square covers

Ductile gratings, with the full name of Ductile iron manhole square covers (abbreviated as FRP), is a composite material with synthetic resin as the matrix and glass fiber and its products as the reinforcing material. It has the following characteristics:

1. Lightweight and high strength: The density of FRP is about 1.5 - 2.0 g/cm³, only 1/4 to 1/5 of that of carbon steel, but its strength can reach or even exceed the level of some alloy steels.

2. Corrosion resistance (subject to the actual report): FRP has good resistance to the atmosphere, water, and common concentrations of acids, alkalis, salts, and various oils and solvents, and is suitable for the chemical anti-corrosion (subject to the actual report) industry.

3. Good electrical properties: It is a good insulating material and can be used to make the shells of electrical products.

4. Good thermal properties: The thermal conductivity of FRP is low, and it is an excellent thermal insulation material.

5. Strong designability: According to needs, its physical and chemical properties can be adjusted by changing the resin system, reinforcing materials, and processing techniques to make various products.

6. Excellent processability: FRP can adopt a variety of molding processes, such as hand lay-up, spraying, winding, molding, injection, etc., which is convenient to manufacture products of various shapes.

Due to the above advantages, FRP is widely used in industries such as ships, automobiles, chemical industry, architecture, transportation, and environmental protection. However, FRP also has some disadvantages, such as aging when exposed to ultraviolet rays and the atmosphere for a long time, and easy delamination between layers under the action of shear force.