1.What damage does fire do to the galvanized layer?
The core of rust prevention of galvanized metal (such as galvanized pipes and galvanized sheets) is the surface zinc layer. The melting point of zinc is about 419℃ and the boiling point is about 907℃:
If the flame temperature exceeds 419℃ but does not reach the boiling point, the zinc layer will melt and flow, causing the local zinc layer to become thinner or fall off, destroying the uniform protective layer. The zinc layer in the unfallen area may also become loose due to high-temperature oxidation, and the rust prevention ability will be greatly reduced.
If the temperature exceeds 907℃, the zinc layer will evaporate to form zinc vapor, completely losing its protective function, and the exposed base steel will be directly exposed to the risk of rust.
2.What damage does fire do to ordinary iron pipes?
Ungalvanized iron pipes have no anti-rust layer themselves. After being burned, a scale (iron oxide) will form on the surface. However, this scale has a loose texture and cannot prevent the penetration of moisture and oxygen. On the contrary, it may accelerate the change of the internal lattice of the steel due to high temperature, causing subsequent corrosion to occur faster.
3.How should we treat burned metal to regain its rust-proof properties?
Cleaning up the burn residue
Use a wire brush, sandpaper or high-pressure water gun to thoroughly remove the charred material, oxide scale, and molten zinc slag (if it is a galvanized part) on the surface to expose the original color of the metal and avoid residual impurities that affect the subsequent anti-rust layer adhesion.
Rebuild the protective layer
Apply anti-rust paint: Apply anti-rust paint or zinc repair agent on the cleaned surface to form a physical barrier to isolate water and oxygen.
Note: The paint needs to cover all exposed areas, especially the parts where the zinc layer has fallen off after the fire.
Local galvanizing (only suitable for small area damage): Re-galvanize the area where the zinc layer has fallen off through electrogalvanizing or hot spraying zinc technology, but the cost is high and it is suitable for key parts.
Apply grease or vaseline: For short-term temporary rust prevention, a layer of grease can be applied to block moisture, but regular maintenance is required (such as re-coating every 1-3 months).
4.What is the rust resistance after fire without treatment?
Fire will destroy the original anti-rust layer (such as zinc layer) or cause loose oxide scale to form on the surface, which will not only lose its anti-rust ability but may also accelerate rust.
5.How are things handled in accordance with regulations after a fire?
By cleaning the burning residue and reapplying the anti-rust layer (paint, repair plating, etc.), a certain degree of rust prevention ability can be restored, but the effect is usually not as good as the original state without fire (especially when the high temperature causes damage to the metal surface structure).