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A form of pitting corrosion found in pharmaceutical water for injection (WFI) systems. It must be removed chemically, either by electropolishing or re-passivation.

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The presence of rouge in hygienic pipe systems is a significant concern, especially in industries where purity and cleanliness are crucial, such as pharmaceuticals, biotechnology, and food processing. It’s a form of corrosion that typically appears as a red or black deposit on stainless steel surfaces. Understanding and managing this issue is vital to maintain system integrity, product quality, and compliance with industry standards.

Understanding Rouge in Hygienic Pipe Systems

What is Rouge? 

Rouge is a form of iron oxide that develops on stainless steel surfaces over time. It can occur in various forms, ranging from a thin translucent film to thicker, visible deposits. The formation of rouge is influenced by factors such as temperature, the chemical composition of the fluids in contact with the steel, and the quality of the steel itself.

Types of Rouge

Type I

Often found in high-temperature steam systems, appearing as a loose, powdery red oxide.

Type II

Typically seen in water systems at lower temperatures, characterized by a harder, black or grey oxide.

Type III

Occurs in systems where purified water is in use, appearing as a thin, translucent film.

Causes and Effects

The primary cause this issue is the interaction between stainless steel and the chemicals or substances transported within the system. Factors like water quality, flow velocity, and temperature changes can accelerate formation.

Its presence can compromise the purity of the product being processed, as particulates may detach and contaminate the product. It can also indicate more severe corrosion issues, potentially leading to system failures.

Managing and Preventing Rouge

Regular Inspection and Monitoring

  • Routine inspections of pipe systems are essential to identify early signs of this issue.
  • Implementing a monitoring program helps in tracking the progression and determining the severity of its formation.

Proper Material Selection and System Design

Using high-quality stainless steel and designing systems to minimize areas where fluid can stagnate can reduce the likelihood of its formation.

Chemical Treatment and Cleaning

Periodic chemical cleaning (passivation) can remove rouge deposits and help restore the passive layer of stainless steel, reducing the chances of rouge reformation.

Implementing Water Treatment Processes

Treating the water used in the systems to remove impurities can significantly reduce the risk of formation.


Rouge in hygienic pipe systems poses a serious challenge in industries where contamination control is critical. By understanding its nature, regularly inspecting and maintaining systems, and employing appropriate prevention strategies, industries can mitigate the risks associated with rouge and maintain the high standards required in their operations.

Find out more

To find out more about this issue and derouging visit Inox Passivation.

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