It should be passivation treatment, the last process step in chemical cleaning, is a key step, and its purpose is to prevent corrosion of the material.
Such as the boiler after pickling, water washing, rinsing, the metal surface is very clean, very active, easy to suffer corrosion, so it must be immediately passivation treatment, so that the cleaned metal surface to generate protective film, slow down corrosion.
In the field of automatic control, there is also a special name \"channel passivation\".
In a fail-safe system (F-SYSTEM), if... If the F-I\/O detects a fault, it switches the affected channel or all channels to ->. In a safe state, the F-I\/O channel is passivated.