Quote:
Originally Posted by KenB
During my work with a leading stainless supplier in US, they alway reminded people that it was stainLESS steel, not stain free. Under the right temperature and humidity conditions, plus say road salt, a thin surface red rust can form in hours., particularly on the 4xx series (ferritic) grades. And not just in a lab😀
Most of time, ferritic meets the need, though the grade chosen by an OE varies depending where in the exhaust (hot end gets “better” grades) the component is located.
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As I recall, a chemical process called "passivation" is used to stabilize the naturally-protective oxide films that make stainless stainless. I think this is common on machined parts that can have contaminant particles embedded but is also used on "cosmetic" applications like appliances.
Do you know if tubing used for exhaust would be treated this way and how well it might prevent rusting?
I expect exhaust tubing is made from alloys at the "low" end for chromium content (low cost stainless). This might make them even more susceptible to corrosion than other 400-series alloys.