Rouging is a thin film,of iron oxide or hydroxide, usually reddish-brown or golden in color, typically found on stainless steels. Rouge can also consist of iron, chromium, nickel and other elements. Rouge is prevalent in the Biotech and Pharmaceutical industry because most of their systems are made up of stainless steel, typically 316/316L grade and the operating temperature is high. Rouge normally builds up on the interior surfaces of high purity water distillation units, storage tanks, distribution systems (piping, valves, pump housings, fittings, etc.) and process vessels. Many drug manufacturers are concerned about the particulate matter from build-up contaminating their products and sterile systems. An effective way to deal with this problem is monitor the rouging rate on-line in case of process upsets to prevent contamination.