Rust on stainless rub rail

B

BillWilliams

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Our Formula has a rusted area on the starboard corner of the swim platform. It's about 2 inches long.

I took some wet/dry sandpaper starting at 600 working my way up to 2000 and sanded it out. It looked great but the rust is coming back.

I don't understand how stainless can be rusting given the metal is not sealed and is exposed to the air.

Any ideas?
 
Stainless steel is a mixture of steel and chromium with a process to remove some of the carbon. A few other elements can be added. Either its cheap stainless steel or the alloy was not manufactured properly.

I am not an expert but I do not see how you can fix this. Replacement is the only solution.
 
Did you try Collinite?

https://www.overtons.com/collinite-metal-wax-pint-351343.html?msclkid=23cd7fbfea69140294b920139a4548c7&utm_source=bing&utm_medium=cpc&utm_campaign=SHB%20%7C%20Repair%20Maintenance%20%26%20Hardware&utm_term=4580840328171862&utm_content=O%20-%20Repair%20Maintenance%20%26%20Hardware%20-%20Product%20IDs&gclid=23cd7fbfea69140294b920139a4548c7&gclsrc="3p.ds
 
First of all, there are different grades of stainless. Maybe you have one of the cheaper grades.
Second, there's a reason it is called stainless...not stainfree
 
Are you sanding the SS or fiberglass? I believe sanding SS may help it be more susceptible to rust by removing the chromium oxide protective outer surface.

304 SS is a bit more likely to rust than 316 in my experience but both will rust. You can try applying wax or a corrosion block , but passivation is likely a better solution.
https://www.theruststore.com/Can-stainless-steel-rust-W71.aspx

https://www.theruststore.com/CitriSurf-C64.aspx

That said, ....I haven't tried it yet.
 
Flitz on stainless steel. Takes the rust off and polishes it.

Why do you think they call it "Stain Less"? :-)

Ken
 
Stainless Steel is a classification of steel that is still composed of iron but has alloying ingredients to reduce the iron oxide build up, RUST.
Non-magnetic SS is typically the 300 series. 304 is more the generic but 316 is better in Chloride environments like salt water. After the alloy is machined, formed or welded it must be Passivated or electropolished to establish a Chromium Oxide layer on the surface. This inert outer layer prevents the iron oxide from forming.
If this passive layer is removed (sanding, drilling etc...) you have opened up the surface for the oxygen to combine with the iron to make RUST. Sure sanding with fine grit makes it look shiny but in time it will appear again. Waxes and polishes help but you must be vigilante with re-applications.
BTW, SS has 68% iron in its content ~ roughly.
304L or 316L has lower carbon content (<.3%) for improved welding. Normal 304 - 316 has <.8% Carbon content.
 
Thanks. My guess is the previous owner must have scuffed it since the spot is on the aft starboard corner of the swim platform and that started the rust issue.

Sandy, I'll probably give the CitriSurf a shot.
 
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