1.How harsh is the environment in highly polluted areas?
High concentrations of chemical pollutants:
Acid gases: SO₂ (sulfur dioxide), NOx (nitrogen oxides), HCl (hydrogen chloride), etc., are easily soluble in water to form acid rain and acid mist, which directly corrode coatings and metal substrates.
Alkaline substances: such as ammonia (NH₃).
Salt: Chloride ions (Cl⁻) in coastal or chemical plant areas are extremely corrosive and can penetrate the coating and destroy the metal passivation layer, which is the culprit of pitting corrosion.
Particulate matter: smoke and dust adhere to the surface, absorb moisture and pollutants, and form local corrosion of the battery.
Moist heat and condensation:
Industrial areas are often accompanied by high temperature, high humidity or temperature fluctuations, which can easily produce condensation on the surface of materials. The condensate concentrates the pollutants in the air to form a highly concentrated corrosive liquid, which continuously penetrates and soaks the coating.
2.What is the failure mechanism and performance of color-coated rolls in this environment?
Rapid aging of coating:
Chalking and fading: The synergistic effect of ultraviolet rays, chemicals and moisture causes the coating resin to degrade, the pigment to powder and fall off, and the appearance to deteriorate rapidly.
Blistering and peeling: The corrosive medium penetrates into the interface between the coating and the substrate, or penetrates into the galvanized layer, producing corrosion products. The volume expansion causes the coating to bulge and peel off.
Accelerated consumption of galvanized layer:
In a clean atmosphere, the galvanized layer is slowly consumed as a "sacrificial anode" to protect the iron base. However, in highly polluted areas, substances such as acids and salts directly accelerate the corrosion of zinc. The consumption rate of the zinc coating may increase several to dozens of times, and the protection period is greatly shortened.
Rapid corrosion of substrate:
Once the coating develops even tiny pinholes, scratches (see the previous discussion on scratches and cracks), or the galvanized layer is consumed, corrosive media will directly attack the steel substrate, causing rapid rust and punctures.
3.Why is it not recommended to use standard color coated rolls?
Even ordinary color-coated rolls with PE or SMP coating may only have a lifespan of 1-3 years in this environment, resulting in frequent maintenance and replacement, high overall costs and potential safety hazards.
4.If you insist on using a color coating system, what are the precautions?
Substrate: Choose aluminized zinc (AZ) substrate (corrosion resistance is better than pure galvanized) or galvanized sheet with high zinc layer content (such as Z275).
Coating: PVDF (fluorocarbon) coating must be used. Its excellent chemical and weather resistance is the only option likely to last for an extended period of time in this environment.
Coating thickness: Choose products with front coating thickness > 25μm or even higher.
Even so, this is only an "improvement", not a "cure", and you still need to expect shorter maintenance intervals than in a normal environment.
5.What are the more reliable, mainstream alternatives?
Glass fiber reinforced plastic (FRP): preferred recommendation. It has excellent corrosion resistance to acid, alkali and salt spray, and is integrally formed without seams. It is especially suitable for use as shells, pipes, scrubbers, etc. in chemical environments.
Stainless steel:
316/316L stainless steel: Contains molybdenum, and its resistance to chloride ion pitting corrosion is significantly better than that of 304.
Duplex stainless steel: higher strength and better corrosion resistance.
Galvanized sheet/carbon steel + heavy anti-corrosion coating system:
Using professional heavy-duty anti-corrosion coatings (such as epoxy zinc-rich primer + epoxy mica intermediate paint + fluorocarbon/polysiloxane topcoat), professional and controllable coating construction is carried out in the factory, and the coating quality far exceeds on-site coating.