1.Why do cracks spread?
Stress persists:
Cracks usually occur when the internal stress of the coating exceeds its endurance limit. This stress may come from substrate deformation, temperature difference expansion and contraction, coating aging and brittleness, etc.
As long as the source of stress (such as day and night temperature difference, structural vibration) continues to exist, the tip of the crack will become a new stress concentration point, causing the crack to continue to lengthen and expand.
The "Breakthrough" of Environmental Erosion:
Once a crack occurs, it provides a direct channel for moisture, oxygen, ultraviolet rays, and corrosive media (acid, alkali, salt spray) in the chemical environment to reach the substrate.
Moisture intrusion: It will cause the underlying metal to rust, and the corrosion product will expand in volume, which will "stretch" the surrounding coating, causing the cracks to widen and branch, forming a more complex network of cracks.
Ultraviolet intrusion: It will accelerate the powdering and aging of the coating on both sides of the crack, further reducing the strength of the coating.
Intrusion of chemical media: It will corrode the substrate and destroy the adhesion between the coating and the substrate, causing the coating to "peel off" starting from cracks.
2.What is the process of spread?
Initial local cracks → Cracks propagate and connect into a network → The coating becomes powdery and loses its luster → The coating partially peels off → The substrate is corroded → The rust spreads and the substrate is perforated
3.How to deal with cracking problem?
Assessment and Diagnosis:
Mild cracks (fine hair-like, only topcoat, not exposed): It may only affect the appearance, but it is a sign of aging.
Moderate to severe cracks (cracks are wide and deep, primer or substrate visible, accompanied by rust): This indicates that the protective function has been seriously damaged and must be dealt with immediately.
Treatment measures:
For mild cracking and in a non-critical, non-corrosive environment:
After cleaning the surface, consider applying a layer of specialized outdoor high-elastic anti-corrosion topcoat to seal and strengthen it. But this can only delay, not cure.
4.How to deal with cracks that have caused corrosion on the substrate?
Thorough Treatment: All loose, peeling coating must be sanded or scraped away to a solid base layer.
Strict rust removal: Polish the exposed metal substrate to St2 or St3 level cleanliness, and immediately apply a special anti-rust primer.
Layered repair: Repair according to the system of "primer-intermediate paint-topcoat", and choose paint with good toughness and strong weather resistance.
Fundamental solution: If the crack area is large, the corrosion is severe, or it is located in a key structural part, the safest solution is to replace the entire color-coated board.
5.What to do if cracks appear on color-coated rolls used in chemical waste gas treatment equipment
Stop production immediately for inspection: Cracks mean corrosive exhaust gas may have contacted the substrate and the equipment is at risk of leakage.
Assessing non-repairability: In chemical environments, local repairs offer little long-term resistance to media penetration and corrosion. The life of the patched area will be short.
It is highly recommended to change the material: this is the most fundamental solution. Cracked color-coated panels should be replaced with truly corrosion-resistant materials, such as fiberglass reinforced plastic (FRP), stainless steel, or plastic-lined steel panels.