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Flash rust refers to the rapid growth of point like rust on the surface of steel substrates during the wet film stage before the paint film has dried and solidified after the water-based coating is applied. The fundamental principle behind its formation is that water, oxygen, and ions on the surface of the substrate together form the primary battery, causing electrochemical corrosion of the iron substrate. Water in water-based coatings belongs to the continuous phase. If the system contains corrosive ions such as chloride ions, it will greatly accelerate the formation rate of flash rust.

1、 Formula level

Firstly, choose specialized flash rust inhibitors. The sodium nitrite system has a strong inhibitory effect on flash rust, but there is a risk of generating nitrosamines, and its use has been restricted in many industries; Organic heterocyclic amines such as benzotriazole BTA and methylbenzotriazole TTA can adsorb onto steel surfaces to form passive films, which are environmentally friendly and safe. They are generally used in combination; Phosphates and phosphonates belong to the anodic passivation type, which generate a precipitation passivation film on the metal surface. The disadvantage is that they are sensitive to the pH of the system, and high addition amounts can easily affect pigment dispersion and cause paint film loss. At present, the mainstream solution for water-based industrial paint is the non nitrosamine composite flash rust inhibitor. Attention: Flash rust inhibitors should not be added excessively. Adding too much can affect the curing of the paint film, cause foaming, and reduce water resistance.

Secondly, optimize the resin system. Prioritize the use of low acid water-based resins to reduce the corrosion of carboxyl groups on metal substrates; Acrylic lotion with metal adsorption and passivation ability or epoxy modified lotion can be selected. The faster the resin film-forming speed, the shorter the wet film window time, and the lower the probability of flash rust occurrence.

Thirdly, pH regulation of the system. Maintain weak alkalinity of the system, control the pH within the range of 8.0-9.5, and reduce the corrosion rate of iron. Too low pH will easily lead to flash rust, but too strong alkalinity will damage the stability of lotion. Generally, ammonia or organic amines are used to adjust the pH.

Fourth, screening of pigments, fillers, and additives. Eliminate the use of pigments and fillers with high levels of chloride ions and sulfate impurities; Can be paired with anti rust pigments such as zinc phosphate and aluminum tripolyphosphate to achieve long-lasting anti rust synergy. Be cautious when choosing anionic surfactants, as some surfactants can enhance water permeability and increase the risk of flash rust.

2、 Substrate and pretreatment

The substrate needs to be sandblasted or polished to thoroughly remove rust, oxide scale, and oil stains. Soluble salts, especially chloride ions, are important inducers of flash rust, and the surface salt of the substrate must be cleaned and qualified. The surface of the substrate should not have visible water, as damp steel construction can easily produce flash rust.

3、 Construction and Environmental Control

Try to avoid construction in high humidity and low temperature environments. Under such conditions, the water evaporation rate is slow, the wet film retention time is significantly prolonged, and the risk of flash rust is significantly increased. Construction is prohibited during rainy weather or substrate condensation. The thickness of the wet film during a single construction should not be too thick. The thicker the wet film, the longer the drying time, and the more likely it is to cause flash rust. During construction, the temperature of the substrate should be at least 3 ℃ higher than the dew point to prevent condensation on the surface of the substrate.

Core Summary

The overall idea for controlling flash rust: shorten the duration of wet film existence; Quickly construct a passivation or adsorption protective film on the surface of steel in a wet state; Reduce corrosive ions in the system, regulate pH, and inhibit corrosion of electrochemical primary cells.  

Key distinction: Flash rust inhibitors only solve short-term rust prevention during the wet film stage; Long term rust prevention relies on resin film formation and anti rust pigments to form a shielding system, and the two cannot be replaced by each other.

Flash rust is the formation of rust spots during the electrochemical corrosion of steel substrates during the wet film stage of water-based paint. Solution: Add non nitrosamine flash rust inhibitor, maintain weak alkalinity of the system, use low acid value resin, reduce soluble salts on the surface of the substrate, and control the construction temperature and humidity to shorten the drying time of the wet film. Flash rust inhibitors only provide short-term wet protection, while long-term rust prevention requires a combination of coating shielding and anti rust pigments.