It is a well-known “secret” that WFI systems with stainless steel piping can develop over time a very dangerous layer of Rouge. One step for prevention is to go on a regular schedule through a passivation process of the whole system. Our Sensor system monitors in a free selectable constant time frame the passivation layer and any buildup of Rouge to alarm the operator of the actual level. The measured results can be saved on any computer for long time trends and Report statistics.