Plating stainless steel

[Ted]

A few years ago I had some custom fittings fabricated for my boat. They were made from stainless steel however I'm not sure what grade it is. I know it's not 316 or I wouldn't be asking this question. The stainless steel is showing signs of rust. The question is, can stainless steel be plated to prevent rusting in the future. Plated with what? My other option is powder coating. The stainless steel is in direct contact with bronze and salt water. They can be isolated if necessary but the proposed plating options should take this into consideration. Any other suggestions would be greatly appreciated.

 

[Guest]

Stainless Steel

Hi Ted, our 1991 model year boat came with a SS arch, which shows some signs of a light rust. Not the penetrating kind that you find with regular steel that flakes off over time, just more of a stain. It comes right off with a SS cleaner such as Bar Keepers Friend that most grocery stores carry.

I've never heard of plating stainless steel, but I suppose anything is possible. Our SS prop shaft has that same rust look at times, but again not that penetrating kind as I mentioned above, which comes right off with this cleaner.

Terry Cox

 

[Hermit Scott]

The latest powder coats are indestructible. I would and will have things powder coated that are on my boat. I am going to have the yacht specialties pedastal powder coated when I get around to tearing it down. Since I have started powder coating things, I will not paint anything. Some say you need to sand blast everything you powder coat. I don't sand blast anything and have had excellent results just having them phosphate wash the metal. Do not rely on sand blasting alone, this will not remove oil from the metal. It must be chemically removed.One word of caution about powder coating. If any silicone has touched the metal it will contaminate it. It will casue fish eye looking blemishes in the finish.
It could very well be 316. 316 will still "rust" it's really more like tarnish as guest said.
We cleaned our stern rail off really well, only to return a few weeks later and see that the rust was back. Others claim that they can stave off the rust by waxing the stainless. I am willing to give that a try.
I would hesitate before powder coating stainless. After all it is stainless.

 

[Ross]

You can electroplate anything with almost anything. But pacification is the best approach to dealing with stainless steel.

 

[Steve Dion]

Ted: This is the best thing I have found for surface rust on S.S.

http://www.miraclepolishingcloth.com/uses.html

They are under $5, so its not a big investment. Check out eBay, they are even less expensive.

Oxalic acid is also good for cleaning rust from S.S.

 

[BobM]

I have had very good results from Nevr-Dull polishing wadding on chrome on my cars and the stainless on my boat. It is very effective at removing light rust off with little effort. But be warned...use gloves or your hands will smell like polish the rest of the day. It is widely available...even from West Marine. It is very easy to use and protects your stainless too. Just wipe it over the surface, let it dry to a film and wipe off. Its been around for 70 years!

www.nevrdull.com

 

[sailingdog]

You can electroplate anything with almost anything. But pacification is the best approach to dealing with stainless steel.

I think Ross means passivation, not pacification.. Stainless steel is never very hostile or aggressive, so pacification is usually not necessary.

However, i don't know how much good passivation of the stainless steel will do if it is immersed in salt water and in close contact with bronze while immersed.

 

[BobM]

You might want to see if you can get it electropolished. We use electropolished tanks in the pharmaceutical industry, especially for biologics. The site below has a lot of information. The finish ends up like glass.

http://www.delstar.com/what.htm

A more local company that seems to do small volume marine jobs is:

http://www.seaboardmetalfin.com/

They seem uniquely qualified to advise you about your other options too.

Better Corrosion Protection

Electropolishing yields maximum tarnish and corrosion resistance in many metals and alloys. Stainless steel contains metallic and non-metallic inclusions, which are unavoidably included during manufacture. Mechanical polishing not only fails to remove inclusions, but also tends to push them further into the surface and even increase them by further pick-up of abrasive materials. These inclusions eventually can become points of corrosion.

 

[RichH]

You definitely dont want to be 'plating' stainless, nor coating it with anything for that matter. The reason is such coverings/coatings are always imperfect and the resultant corrosion that will inevitably form UNDER the coating/plating/etc. through the incomplete coating/plating (microscopic little holes) will be catastrophic as such coating 'trap' the continuing corrosion underneath and enhance its progress exponentially.

To prevent or lessen rust on ANY 300 series stainless, including 316, is to mirror polish it then follow with electropolishing. Rust on stainless is due to 'crevice corrosion' forming in the macro/microscopic surface irregularities. Passification is possible but unless these microscopic surface irregularities are removed the passification is only temporarily with respect to 'rust'.

The typical industry standard to prevent 'rust' on virtually all 300 series stainless (including 316, etc.) is to grind all welds and joints smooth, mechanically flat-sand the surface beginning with 180 grit, then down to 400-600 grit (or finer) removing ALL 'steel mill rolling marks', scratches, pits, ... then using large sewn fabric polishing wheels on high speed motors applying successively smaller and smaller polishing compounds (Tripoli - a mixture of extremely fine clay and diatomaceous earth) until the surface is like a MIRROR. THEN, the part is electro-polished to remove the still remaining 'ridges' left over from the 'bright' mechanical buffed mirror surface.

The technical standard is to produce a surface finish equal to or less than "10 micro-inches, Ra (root mean squared). .... and then where possible avoid ANY acid treatment that will enhance the removal of those 'attackable' metal microscopic 'grain boundaries' remaining after mirror polishing and electropolishing. Electropolishing is a 'reverse-plating' operation that further 'flattens' the 'hills and valleys' of a polishing operation. The result of electropolishing will produce a 'satinized' (not extremely shiney) surface.

Stainless 'rusts', because the supplier was cheap and omitted the important 'surface finish' (- probably a miserly and unknowing accountant involved). So, you dont want your stainless to rust, then put some sweat equity into it by 'grinding all the welds flat', removing ALL the surface irregularities, then MIRROR POLISH the surface. ..... or pay a fortune for already mirror polished material. The alternative is to spend an even greater fortune for monel, inconel or hastalloy material.

 

[Ross]

I think Ross means passivation, not pacification.. Stainless steel is never very hostile or aggressive, so pacification is usually not necessary.

However, i don't know how much good passivation of the stainless steel will do if it is immersed in salt water and in close contact with bronze while immersed.

Sometimes "spell check" takes me to strange places and I don't catch them.

 

[sailingdog]

You definitely dont want to be 'plating' stainless, nor coating it with anything for that matter. The reason is such coverings/coatings are always imperfect and the resultant corrosion that will inevitably form UNDER the coating/plating/etc. through the incomplete coating/plating (microscopic little holes) will be catastrophic as such coating 'trap' the continuing corrosion underneath and enhance its progress exponentially.

To prevent or lessen rust on ANY 300 series stainless, including 316, is to mirror polish it then follow with electroplating. Rust on stainless is due to 'crevice corrosion' forming in the macro/microscopic surface irregularities. Passification is possible but unless these microscopic surface irregularities are removed the passification is only temporarily with respect to 'rust'.

He obviously means ELECTROPOLISHING, not electroplating

The typical industry standard to prevent 'rust' on virtually all 300 series stainless (including 316, etc.) is to grind all welds and joints smooth, mechanically flat-sand the surface beginning with 180 grit, then down to 400-600 grit (or finer) removing ALL 'steel mill rolling marks', scratches, pits, ... then using large sewn fabric polishing wheels on high speed motors applying successively smaller and smaller polishing compounds (Tripoli - a mixture of extremely fine clay and diatomaceous earth) until the surface is like a MIRROR. THEN, the part is electro-polished to remove the still remaining 'ridges' left over from the 'bright' mechanical buffed mirror surface.

The technical standard is to produce a surface finish equal to or less than "10 micro-inches, Ra (root mean squared). .... and then where possible avoid ANY acid treatment that will enhance the removal of those 'attackable' metal microscopic 'grain boundaries' remaining after mirror polishing and electropolishing. Electropolishing is a 'reverse-plating' operation that further 'flattens' the 'hills and valleys' of a polishing operation. The result of electropolishing will produce a 'satinized' (not extremely shiney) surface.

Stainless 'rusts', because the supplier was cheap and omitted the important 'surface finish' (- probably a miserly and unknowing accountant involved). So, you dont want your stainless to rust, then put some sweat equity into it by 'grinding all the welds flat', removing ALL the surface irregularities, then MIRROR POLISH the surface. ..... or pay a fortune for already mirror polished material. The alternative is to spend an even greater fortune for monel, inconel or hastalloy material.

You should also avoid using steel tools on stainless steel fasteners, if you can avoid it. The steel tools will leave tiny inclusions of plain steel on the fasteners which become starting points for corrosion—much like using steel wool on a boat will leave tiny bits of steel all over the fiberglass and it will rapidly turn into rust pox.

 

[tommays]

Well

Somebody better tell Yamaha to stop using chrome plated SS bolts so there large outboards come apart


After a whole lifetime i have yet to meet anybody with a good SS tool set as it is way to soft most just go with a good plateing job

 

[RichH]

Sorry , typo removed/corrected

Nah, he definitely/obviously refers to plating .... then powder coating .... electropolishing (the reverse of electroplating) is not a common term that someone not involved in these techniques/methods would have idea or knowledge.

 

[tommays]

We do a passivation with nitric acid when we have to make products that use some kind of peroxide OR it goes bad

BUT you really DO NOT want to fool around with it unless you have a full MOON SUIT