- Rouging is seen in many water systems, usually high temperature (80°C) distilled water and clean steam systems. Rouge is not limited to storage and distribution systems; it also can be found in distillation and clean steam generating equipment.
- The main constituent of the rouge film is ferric oxide, but it can contain iron, chromium, and nickel of different forms.
- From Auger Electron Spectroscopy, it has been found that the outer layer of a rouge film is carbon rich, and the underlying region is iron and oxygen rich, probably iron oxide.
- Over time, the film uniformly distributes itself throughout the system. The exact mechanism of the rouge formation and proliferation is unknown. Because the phenomenon occurs in systems that offer the most corrosive environment, it is thought that low molecular weight ions of the stainless steel, such as iron, are drawn to the metal surface or are dissolved and uniformly re-deposited throughout the system.
- Others feel the rouge is an external contaminant probably colloidal in nature that once in the system, uniformly deposits itself.
- Rouging would seem to be very site (facility) specific because of the variety in appearance and texture. Rouge can be observed in a variety of colors including; orange, light-red, red, reddish-brown, purple, blue, gray, and black.
- It can be a very loose film, dust like in appearance and texture that can be readily wiped off to a tight pertinacious film that requires scraping with a sharp instrument to be removed. In addition to the diversification already discussed, rouge can be multi-layered exhibiting different colors and textures.
- Traditionally the red rouges are most common in high purity high temperature water systems, while the blue/black rouges are typically found in clean steam systems.
- Evidence of the migration of rouging in distribution systems can be demonstrated by monitoring a system over a period of time. Key places to look for rouging are still and clean steam generator discharge lines, tank water/vapor interface, pump heads, Teflon diaphragms on diaphragm valves, interior surface of tank spray ball, and heat effected area of welds. Rouge deposition seems to have an affinity for Teflon and would be one of the first places to look for signs of system rouging.
- In some cases, the rouging appears as quickly as a month or two after system start up. In other cases, it is several years before rouging is observed.
- In either case rouging is an industry wide phenomena. In a specific case, a facility cold WFI system would re-rouge within a week of being derouged and passivated. The system was derouged and passivated a total of three times. Each time, within a week, the system was totally rouged again. The specific cause was never determined.
- The presence of rouge in high purity water systems has not been proven to effect water quality. The FDA has no written position addressing rouging, its existence, or presence in high temperature high purity water and clean steam systems. Their criterion has and remains to be in meeting established USP standards for water quality. There is some fear that as the unwanted film develops, it might eventually slough off and be dispersed throughout the system. This, in fact, does occur and is manifested in systems with filtered use points.
- Filters become discolored with the typical reddish-brown rouge color. Phosphoric, citric, oxalic acids, and ammonium citrates are used depending on the severity of the problem.
- Oxalic acid solutions are used for the worst cases of rouge. Passivation with nitric acid is required after an oxalic acid rinse.
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