Waterborne Industrial Coatings Functional Additives – Flash Rust Inhibitors

Water based  coatings have gained widespread application, yet their use in metal anti-corrosion coatings remains limited. When applied to steel surfaces, waterborne coatings are highly susceptible to corrosion during drying due to the presence of water and oxygen, a phenomenon termed flash rust. This issue proves particularly challenging on high-carbon steel or cast iron components.

Selecting Flash Rust Inhibitors for Different Substrates

The rate and severity of flash rust formation during water-based coating application vary across different metal substrates, necessitating tailored inhibitor selection and dosage. For instance, cast iron is widely regarded as an exceptionally challenging substrate. At humidity levels exceeding 85%, conventional sodium nitrite proves largely ineffective. Similarly, aluminium sheets are highly susceptible to flash rusting, though this is a relatively manageable substrate where sodium nitrite can exert a beneficial effect.

For most metallic substrates like steel, flash rust suppression is not inherently problematic. However, achieving a balance between flash rust inhibition, in-can corrosion protection, and long-term corrosion resistance necessitates the combined use of sodium nitrite with other flash rust-inhibiting additives.

Rapid Evaluation Method for Flash Rust Inhibitors

Given the complex composition of water-based acrylic anti-corrosion coatings, each component influences flash rust phenomena to varying degrees. The practice of discarding a flash rust inhibitor after one or a few trials at its recommended dosage due to unsatisfactory results is unscientific. A straightforward method is proposed: add the flash rust inhibitor at its recommended dosage to deionised water, then directly apply droplets onto the substrate requiring coating (previously treated according to standard substrate preparation protocols). Ensure droplets remain undried for at least 24 hours. Variants that prevent rust formation under these conditions may proceed to further testing. This approach eliminates interference from other coating components that could skew flash rust inhibition assessments, offering simplicity, speed, and low cost.