In practice, it is not unusual for rouging to affect stainless steel surfaces. The stainless steel pipe systems that are mainly used in the pharmaceutical and biotech industries do not escape rouge either. On WFI systems, layers of reddish coating are visible in most cases, while on pure steam systems, the coating that disrupts the system appears as a rough black layer that is firmly attached to the inside of the pipe. These situations often produce rouge particles, some of which can be carried over by the flow of product into other areas of the pipework where they may be deposited. Especially in the "clean" pharmaceutical sector, all of this means that rouge is not a subject that can be taken lightly.

Removal of rouging: stay "on the ball"

Passivation of new systems is an important factor in the prevention of rouging. Even so, it does not offer protection for ever. Various factors such as an insufficient percentage of oxygen combined with warm or hot operating conditions can cause rouge to form again after a certain time. The only way to guarantee a safe solution is regular derouging and repassivation of the system.

Problems caused by rouging at a glance:

> particles of heavy metal oxides that can contaminate
   the medium
> microcorrosive attacks on the stainless steel surface
> germs are encouraged to breed on the stainless steel
   surface/a biofilm is formed.