Passive Film Breakdown
If the passive film of your stainless steel has been broken, your equipment will begin the long walk down the dark road of corrosion. At its end; rust.
The first signs are on the microscopic level. If you were to look at them under a microscope or through a magnifying glass, you would see small pits and cracks staring back at you. Given time, these pits and cracks will grow and deepen while all the time exuding unsightly, red-orange rust. More severe and visible cracking can also take place.