More than 80% of the clean piping systems are affected by rouging. It can be seen easily or not, but rouging appears on the internal surfaces of ultra-clean pharmaceutical networks such as water for injection or pure steam networks. The stainless steel loses its corrosion resistant properties and iron oxide particles risk spreading into the network. Simply said, rouging means progresive stainless steel coloring, from reddish or orange to dark black.
The ASME-BPE defines rouging made of three distinct classes, depending of the state of iron oxides which attach themselves in the passive layer by substituting themselves for chromium oxides
This kind of phenomena's cause is not entirely known, but it was classified in 2000. The international ASME-BPE organization recognized and adopted this definition in 2009. If you don't fight rouging, you're going to have soon more serious problems.
ROUGING 1st CLASS