Rouge, the reddish-brown iron oxide deposit found on stainless steel surfaces, is a persistent issue in many industries including pharmaceutical, food processing, and semiconductor manufacturing. Understanding what rouge is, how it forms, its different types, and effective removal techniques is key to maintaining equipment longevity and product purity.

This blog explores the causes of rouge, its classification, and how to tackle it effectively through derouging solutions and services.

What is Rouge?

Rouge is primarily composed of iron oxides that deposit on stainless steel surfaces exposed to steam, ultra-pure water, or high temperatures. Despite stainless steel’s corrosion resistance, rouge forms when trace iron contaminates the surface or system.

Causes of Rouge Formation

• - Contact with Carbon Steel: Using carbon steel tools or components can introduce iron particles.
• - Corrosion of Carbon Steel: Iron oxide particles migrate into stainless steel surfaces.
• - High Temperature Steam: Accelerates oxidation reactions on stainless steel.
• - Improper Cleaning: Residues from previous cleaning can encourage rouge formation.

Types of Rouge

• 1. Type I Rouge: Formed from iron oxides loosely adhering to the surface; easier to remove.
• 2. Type II Rouge: Denser, more tightly bound oxide layer formed under prolonged exposure; more difficult to clean.
• 3. Type III Rouge: The most tenacious, often a mix of iron oxide and embedded corrosion products; requires aggressive treatment.

Effects of Rouge on Stainless Steel Equipment

• - Corrosion and Pitting: Rouge deposits can create localized corrosion sites.
• - Contamination: Flaking rouge can contaminate process fluids, compromising product quality.
• - Equipment Wear: Accelerates deterioration of valves, fittings, and piping.
• - Increased Maintenance Costs: Requires frequent cleaning and repairs.

Effective Removal Techniques

Chemical Derouging

• - Use of derouging chemicals such as phosphoric and citric acid blends specifically designed for stainless steel.
• - Tailored solutions based on rouge type and industry requirements.
• - Requires controlled application and proper neutralization.

Mechanical Cleaning

• - Limited to superficial rouge, often with non-abrasive pads or brushes.
• - Risks damaging the chromium oxide layer if improperly done.

Combined Cleaning, Derouging, and Passivation

• - Best practice involves initial cleaning, followed by chemical derouging and passivation to restore surface integrity.

Selecting the Right Derouging Chemicals

• - Must be effective in removing all types of rouge without damaging stainless steel.
• - Should comply with industry-specific regulations (e.g., FDA, SEMI).
• - Environmentally safe and easy to handle.
• - Suitable for the facility’s equipment and operating conditions.

Preventing Rouge Formation

• - Avoid carbon steel contamination.
• - Use proper cleaning and maintenance schedules.
• - Employ passivation after welding or repairs.
• - Regular inspections and monitoring.

Conclusion

Rouge on stainless steel is a challenge that can compromise product quality and equipment lifespan if not managed properly. Understanding its causes and types helps in choosing the correct derouging solutions and service. Combining chemical derouging with cleaning and passivation offers the most effective strategy for keeping stainless steel equipment in peak condition, ensuring safety and compliance.