Metals are protected against corrosion and pitting via the chemical processes of pickling and passivation. In both procedures, an acidic solution is applied to the metal surface in order to eliminate impurities and promote the formation of a continuous passive film of chromium oxide.
What is the Difference Between Pickling and Passivation?
Despite the fact that both pickling and passivation apply acids to metal surfaces, there are several very noticeable distinctions between the two procedures.
Steel loses corrosion resistance when heated by welding or other methods and a heat tint or oxide scale layer forms because the layer beneath has become chromium-depleted. Applying an acid solution to steel to remove heat-affected areas and the underlying chromium-reduced layer from stainless steel is known as pickling. Pickled steel is free from surface carbon steel contamination and embedded iron particles. Pickling removes the heat affected layer and prepares the surface for passivation.
Passivation is a process that is separate from pickling, which can be performed on its own or after pickling. The passivation procedure does not remove any metal, in contrast to pickling. Instead, an oxidizing acid is used to treat the stainless steel's surface in order to eliminate surface impurities. The acid further works to promote the formation of the chromium-rich passive film, which ensures the corrosion resistsance quality.
- Both pickling and passivation removes surface contamination
- Passivation maximizes corrosion resistance
- Pickling removes heat tint or weld discoloration
Pickling and Passivation Methodologies:
- Tank Immersion
- Spray Application
- Gel Application