1. Introduction
Passivation is a controlled chemical process used in industrial and boiler systems to form a stable, protective oxide layer on metal surfaces, primarily carbon steel and stainless steel. This layer reduces the metal’s reactivity with water, oxygen, and contaminants, thereby minimizing the risk of corrosion during operation.
Passivation is required before commissioning or during lay-up to protect newly installed or cleaned equipment from rapid oxidation and corrosion. During these periods, metal surfaces are highly active and vulnerable. Proper passivation ensures long-term equipment integrity, improves reliability, and supports safe, efficient start-up and shutdown of boiler and auxiliary systems.
2. What Is Passivation?
- Passivation is a chemical process that creates a thin, stable oxide layer on metal surfaces to reduce corrosion activity.
- Metallurgically, it stabilizes the metal surface by removing free iron and reactive sites prone to oxidation.
- Passivation differs from cleaning; cleaning removes contaminants, while passivation protects the cleaned metal surface.
- Cleaning prepares the surface, whereas passivation ensures long-term corrosion resistance.
- Systems requiring passivation include boilers, steam and condensate piping, heat exchangers, economizers, and auxiliary equipment.
3. Purpose of Passivation
- To form a uniform, protective oxide layer on metal surfaces, reducing direct contact with corrosive agents.
- To remove free iron and eliminate active corrosion sites that can initiate pitting and localized corrosion.
- To stabilize metal surfaces after installation or cleaning, ensuring readiness for long-term, safe, and efficient operation.
4. Importance of Passivation
- Prevents corrosion and pitting by protecting metal surfaces from oxygen and aggressive contaminants.
- Extends equipment life and enhances operational reliability of boilers and associated systems.
- Reduces maintenance costs and minimizes unplanned shutdowns caused by corrosion-related failures.
- Ensures compliance with industry standards, safety requirements, and recommended engineering best practices
5. When Passivation Is Required
- During new boiler installations to protect freshly fabricated and exposed metal surfaces.
- After major repairs or component replacements that expose bare metal to corrosive conditions.
- Following acid or chemical cleaning to stabilize active metal surfaces and prevent flash corrosion.
- Before initial start-up to ensure safe and reliable operation from commissioning.
- Prior to long-term shutdown or lay-up to protect equipment during idle periods.