How to verify passivation quality: blue-dot, salt spray and ASTM A967
The blue-dot test detects free iron, salt spray evaluates corrosion resistance, and ASTM A967 controls process parameters. Keep records and samples after passivation.
Passivation quality directly affects stainless corrosion resistance. Common verification methods:
1) Blue-dot (ferroxyl) test: detects free iron contamination on the surface; a blue spot indicates failure. Good for quick on-site screening.
2) Salt spray (NSS/AASS): per ASTM B117 or customer specification to evaluate corrosion resistance; takes time and is mainly used for type tests or dispute resolution.
3) Copper sulphate test: checks passive film integrity (referenced in some standards).
4) Visual inspection: no heat tint, no residual acid, no contamination; measure surface roughness where needed.
Process control (ASTM A967):
• Nitric or citric route with concentration, temperature and time per the standard and supplier procedure.
• Pre-treatment must remove oil, rust and free iron.
• Rinse thoroughly after passivation to avoid residual acid.
• Record batch, bath parameters and inspection results.
Purchasing advice: require the passivation procedure and inspection records; sample blue-dot tests on critical parts; do not accept “cleaning” as passivation.
Compiled by SteelWe editors and industry experts. For industry exchange only; not trading or investment advice. Cite the source when quoting.
