You need proper understanding of Passivation and corrosion in order to find the ideal conditions for Passivation. You need to monitor such processes. There are different techniques to do that could control conditions.
In the biotechnology and pharmaceutical processes, rouge is actually the reddish or brownish deposit which is accumulated on tanks and pipes. According to the age of vessels, this product adheres to the surface. It is a corrosion product which causes corrosion at different areas of the system.
To remove this rouge form the surface properly, it is important to remove the organic residue before starting the process. This process involves removing metal oxides and the progress can be monitored well by looking at the concentration of Fe dissolved in the solution. With the dissolution of iron oxide, the constant value of Fe over time indicates the end of process. Monitoring the dissolved Fe concentration can be done with different techniques. Atomic absorption or spectrophotometry is the common and most convenient technique in the solution.
Degreasing is another process to Passivate the metal surface well. One can do it by treating it with alkaline detergent cleaner and get rid of any fatty or oily residue from the surface. Then inorganic non-protective oxide deposit is removed. Once the oily residue is removed, the inorganic oxides can now passivate.