„Derouging – or not Derouging“ – Ein Faktenabgleich
Dipl.-Ing. Dr. techn. Georg Henkel1 und Dipl.-Ing. Benedikt Henkel2
1 Henkel Beiz- und Elektropoliertechnik GmbH u. Co. KG, Waidhofen a. d. Thaya (Österreich)
2 Henkel Beiz- und Elektropoliertechnik GmbH u. Co. KG, Neustadt-Glewe
Korrespondenz: Dipl.-Ing. Dr. techn. Georg Henkel, Henkel Beiz- und Elektropoliertechnik GmbH u. Co. KG, Stoissmühle 2, 3830 Waidhofen a. d. Thaya (Österreich), e-mail: firstname.lastname@example.org
“Derouging – or not Derouging” – Comparing the Facts
Commercial stainless steel alloys like 316L or similar which are frequently used for manufacturing equipment for hot WFI (water for injection) or clean steam show after some weeks or months effects of chemical de-passivation followed by Rouging on the media side of the equipment, which is based on the known mechanism of uniform corrosion.
The observable and undesired change of the related stainless steel surface characteristic (morphology) is followed by the creation and generation of Fe-oxide enriched particles. The growth of the Rouge layer leads to an increasing particle generation in the media flow (WFI, clean steam) contaminating downstream equipment and process systems.
This media contamination needs special attention regarding elevated heavy metal oxide contaminants and often causes typical contamination effects like schlieren optics on the stainless steel surfaces in downstream equipment, e. g. bottling systems, which is influencing applied visual criteria of acceptance during validation operations after SOP defined CIP-cleaning procedures.
Recurring chemical de-rouging- and re-passivation operations of affected stainless steel equipment carried out by well trained specialists with experience in the de-rouging process allow perfect rehabilitation. On-site service operations like de-rouging and re-passivation of stainless steel systems can be performed quickly and effectively during regular service stops including documentation for revalidation.
This article highlights “pros and cons” of different risks of Rouging concerning stainless steel surfaces, the influence of Rouging on media quality and de-rouging as rehabilitation processes including cost impact from different aspects of view.
Key words Derouging • Edelstahl 1.4435/316L • Korrosion • Passivschicht • Rouging