Stainless steel 316L with mirror finish vs Sea air.

[Jay_]

Hello everyone;
It has been such a long time without interacting with this forum I hope everyone is healthy and safe.
I have a project in hand that requires me to install 4 columns of stainless steel 316L mirror finish to hold up a canopy.
The canopy is located 30 ft away from the sea.
This canopy is highly architectural and the finish is what matters, I'm afraid that in a short time the passive layer of stainless steel will vanish and we will start to see grey pits all over the mirror surface.
is there any intervention or periodic maintenance we can do to AVOID defecting the mirror aspect of the shiny beautiful stainless steel?

Detailing is a hobby,

 

[EdStainless]

If the columns are under the canopy then they stand no chance of not rusting.
They will get damp with salt fog every night and dry off every day, but the salt stays.
It will build up and they will be dull and start to rust.
Look at using 2205. It is stronger and you can use thinner walls so the price difference should be small. It is more corrosion resistant and when polished it will look the same.
The polishing helps (I presume that it was done well and nitric acid passivated afterwards) since there are fewer places to catch debris.
To keep these shinny they will need to be regularly washed.

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P.E. Metallurgy, consulting work welcomed

 

[Jay_]

Dear Sir,
SAF 2205 isn't available in our local market.
How often do you think they need to be washed?
Will the salt and chloride contained in the air will cause abrasion of the ss surface?

Detailing is a hobby,

 

[weldstan]

Also if you have any crevices like attachments with bolting, expect to have crevice corrosion.

 

[EdStainless]

Washing and rinsing weekly should be enough for 316. Maybe a light scrub brush would help.
But over time there will likely be some pitting anyway.
Use non-abrasive Scotch-brite pads to remove staining.
If it gets too bad then use some very fine abrasive (4000 or finer grit) and citric acid to touch up the surfaces (maybe once a year).
Wash well afterwards. This won't quite be a mirror finish but over time you will lose that anyway.

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P.E. Metallurgy, consulting work welcomed

 

[Compositepro]

Use a brass polish, which also works for stainless. This applies a wax coating that protects the surface for a limited time. The only way to maintain a mirror polish in a salt spray environment is with constant cleaning. The same is true even for glass, where there is no corrosion concern.

 

[EdStainless]

Good point Stan, the base has to be designed to prevent any pooling, and to eliminate steel exposure at the base connections.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

Polished 316 stainless should hold up well, it's used for hand rails on yachts. It will require some maintenance.

If you want to reduce maintenance I would discuss this with your local electroless nickel plater. You'll have to build this in sections they can accommodate.

In both cases, gasket, bed, pot, seal, every joint. Get the fasteners coated as well or consider titanium fasteners with the electroless nickel option (with insulating washers) to eliminate sources of crevice corrosion. A dab of flowable silicone on the heads of fasteners works great, too but the clear does yellow overtime.