What makes stainless steel stainless is that it corrodes quickly, uniformly and forms a dense rich en Cr carbide coating (I dont know how it is called in english). This reduces the rate at which it corrodes enormously. This is the same on most “corrosion resistant” metals and alloys, like aluminium, titanium and zirconium.

There are multiple grades of SS, some of them are better at halting corrosion than others. And given the right environment (chemical + temperature) it will ultimately corrode.

Some geometrical obstacles* can produce other, more localized, types of corrosion… again, sorry, I dont know the technical words in english.