In the pharmaceutical industry purified water and steam systems have a frequent unwanted guest a certain reddish sometimes purple deposit. The specialized literature named it rouge after the french word, red.
But what is this rouge and how can it be removed?
In the pharmaceutical industry, the traditionally universal structural material is 316 L (low carbon content) stainless steel. Not by accident, since this austenic, acid resistant chrome-nickel-molybdenum steel, maximum 0.03% carbon content, has a high acid resistance. In solutions that contain chlorine moderately inclined to hole corrosion. It can be welded well without the need for follow-up heat treatment. Its ability for crystal corrosion is high, can be polished on glass surfaces, and ductile very well (bending, deep drawing, pressing).
Different opinions can be read in the specialized literature of the separation of rouge as the result of the corrosion process or not. Our company constantly develops its cleaning technologies including its chemicals, therefore, our fundamental goal is to understand the causes and composition of the contamination.
The above praised 316 L stainless steel’s one of the most important parameters is the ratio of Cr/Fe of the passive surface which is typically 1 in the surface 25-50 angstrom thickness. This passive protecting layer, namely the Cr/Fe ratio can change in some cases so metal ions can come out to the flowing medium continuously decreasing the quality of the stainless steel.
It is right to emerge a question: if the stainless steel is passive and unscathed, the water is pured in the best possible way, still how can rogue form?
The solution orients into three different forms according to the separation of rogue based on origin and appearance:
Type 1.:
Origin:
- mechanical impact, for example pump impeller house
- exterior originated metal contamination
- deposit from steam systems
Qualities:
- orange-red
- FeO
- Loosely, electronically link to the base metal
- The metal surface is not damaged under the rouge
- Most common appearance is the presser side arm of the pumps
Type 2.:
Origin:
- low ratio Cr/Fe stainless steel surface
- presence of chloride ions
- not properly passivated stainless steel surface
- surface, gap-, hole-corrosition
Qualities:
- red-brownish red
- Fe2O3
- tightly connected to the base metal
- rouge hides the corroded metal surface
- changed quality metal surface
Type 3.:
Origin:
- very high heat system, purified steam
Qualities:
- blackish blue-black
- Fe3O4
- strongly connected to the base metal
- low Cr/Fe ratio
Our company has a solution and technology for all three types of rouge removal. It is important to note that implying the type 3 qualities of the rogue where the base metal is damaged so the removal of the rouge will not treat this damage. Therefore, it is important to be convinced about if the surface was passivated perfectly at all technological reorganizations. Our company deals with passivation as well. Further information here...