Passive Layer Regeneration
Passive layer repair is the restoration of damaged oxide layers on stainless steels to ensure lasting self-protection.
Physical-Chemical Mechanism of Action
Stainless steels such as austenitic or duplex grades form a thin oxide layer on their surface that acts as a passive film. This layer prevents direct contact between iron and air or water, which stops corrosion. If this layer is damaged (e.g., by mechanical damage or chemical attack), it can spontaneously repair under the right conditions.
Metallurgical Relevance & Welding Risks
A damaged passive layer can lead to increased corrosion susceptibility. During welding, the passive layer can be interrupted or altered, making the weld more prone to corrosion. It's important to restore the passive layer after welding to ensure the component's service life and safety.
Workshop Practice & Instructions
After welding stainless steels:
1. Clean: Remove all weld residue, paint, and contaminants with a fine polishing abrasive.
2. Passivate: Apply a passivation solution (e.g., 10 % nitrate solution) for at least 5 minutes. This reactivates oxidation and forms a new, dense passive layer.
3. Dry: Thoroughly dry the surface to ensure a clean and correct passive layer.