Stainless is protected by various elements working together to prevent the iron from being exposed to oxygen. Welding, grinding, sanding
all can expose the iron and cause some rust. In some cases where you have constant contact between water
and the stainless you can get corrosion
. Like where chain plates come through the deck
. There are pictures of almost completely gone chain plates and all of it was hidden.
You have to use a chemical or electrochemical process to prevent the rust from forming after certain types of work
I have limited experience in welding and working stainless so my above explanations are kind of general and may have some errors in them. You will need to research
to find the exact details.
I have done some early car restorations, 1931 Ford. So I know a bit about plating.
Here is a simplified thing on plating.
Chrome plating is really a clear coat over the base color metal. It is an ultra thin coating that gives a blue tint to the base metal. So typically you have a nickel plate for the silver color, but nickel will tarnish. So the chrome plate prevents moisture and the blue tint makes the yellow tint of the nickel look brighter. Chrome is porous with tiny holes in it. That is why you see some pock marks. Here is where some types of wax help keep the holes filled and reduce that green stuff that seems to spring up over time.
Potmetals are great at first. The problem with plated pot metal is the pot metal will just start to oxidize. Once it starts it is not easy to fix. The part will need to be ground down past the oxide layer and then plated up. Part of the reason form pot metal was it did ok at making accurate castings with some strength. It was cheap
and effective for manufacturing and lasted long enough. Of course, 20 years later the person trying to deal with it is not in a good place. Just imagine what it is like for the guy restoring a 1929 Ford that has an all pot metal wiper motor
and all the pot metal is bad. The only option is to make it all new ($$$).
in the steels is more about electric
currents at a micro level. If you have something that can act like even a tiny electric
circuit then you get a transport of ions. This is what causes corrosion. If you take a perfectly clean piece of steel
and dropped pure water
on it you would not get rust. Put a bit of something that makes the water conductive then you get rust. Salty dirty water like you find in areas with snow and salt
and you find the cars are real bad quick where the metal panels
overlap. They set up currents and you metal is done.
The only sure prevention is the never ending job of clean and polish.