Boiler jacket finish

[rkcarguy]

SS will eventually rust.

If a 300 series is selected (it normally is) it won't rust if it is passivated before being placed in service. That should happen after ALL work is done in fitting the jacket. Rusting of austenitic stainless is caused by free iron on the surface. Passivation removes the iron and creates the impervious surface finish that prevents further rusting.

Note that the grades of stainless are strictly controlled (and certification is generally provided upon request) so the notion that the alloy has, somehow, changed, isn't true unless the material has been procured from a questionable source. Note, also, that if the finished surface is scratched by a ferrous source (after passivation), it may still rust, but only where the surface has been damaged. The rust is the result of deposited iron.

H

Agreed.
FYI, passivation is the application of an acid product in spray or paste form that "eats" the ferrous metal from the surface of the stainless.
Its common to get good stainless that has been warehoused with steel or had work done in shop that also works on steel. Little bits of steel will fly around from grinding and other processes and land on the SS, and the first time it gets wet you have your rust speckled stainless.

[Harold_V]

FYI, passivation is the application of an acid product in spray or paste form that "eats" the ferrous metal from the surface of the stainless.
Its common to get good stainless that has been warehoused with steel or had work done in shop that also works on steel. Little bits of steel will fly around from grinding and other processes and land on the SS, and the first time it gets wet you have your rust speckled stainless.

Depends on the requirement, of course. Mil spec includes a heated bath of dilute nitric acid and potassium dichromate, a process I've had to performed on a government contract. It came at a time when I had a fume hood and a supply of the required reagents. Couldn't do it today.

H