(Restoring purity, strength, and lasting corrosion resistance.)
Purpose: – Stainless steel naturally forms a thin, protective layer of chromium oxide passive film (2-5 nm thick). During fabrication processes (such as welding, cutting, and heat treatment), this layer can be damaged, leading to the formation of rust, scale, and reduced corrosion resistance. Pickling and passivation are chemical treatments used to restore maximum corrosion protection. Removes welding scale, heat tint, oxides, and embedded iron. Restore a clean, metallic surface for further passivation. Rebuilds /enhances the chromium-rich oxide film. Improve corrosion resistance, especially in chloride-rich environments.
Methods:-
- Immersion – for small parts.
- Spray Pickling – for large fabrications.
- Pickling Paste/Gel – for weld seams & localized treatment.
Process Flow:-
- Degreasing / Cleaning – remove oils, grease, dirt.
- Pickling – dissolve oxides, rust, heat tint.
- Rinsing (DI water preferred) – avoid contamination.
- Passivation – rebuild protective chromium oxide layer.
- Final Rinse & Drying – prevent water stains.
Applicable Standards: –
- ASTM A380 – Cleaning, Descaling & Passivation of Stainless Steel.
- ASTM A967 – Chemical Passivation Treatments for Stainless Steel.
- ISO 16048 – Passivation of Corrosion-Resisting Steels..
Applications :-
- Welded stainless steel equipment (tanks, pipelines).
- Food, dairy, and pharmaceutical equipment.
- Chemical process plants.
- Marine and architectural stainless structures.
Final Inspection: –
- Water-break test → surface should retain a continuous water film (no beading).
- Surface should appear clean, uniform, free from scale or discoloration.
- Optional: Use a salt spray or ferroxyl test to determine corrosion resistance”.
Result
- The formation of a stable, self-healing passive layer with a high chromium concentration of at least 12%.