Stainless Steel Question

[dreamer]

Hello Folks,

(I also posted this on the Materials forum)

I have a sailboat that I sail in freshwater with plans to someday take the boat offshore into saltwater. I recently inspected the chainplates and discovered a few of them were corroded. Fortunately I know someone who knows someone who was willing to fabricate a new set of chainplates from 304 ss for FREE. I would have preferred 316 ss but like I said...these were FREE!

My question is what type of finish would be a good choice? Would it be adequate to simply polish these or would it be better to plate them? The chainplates are about 15" and 2" of the material extends above the deck. The deck seal consists of polysulfide with a ss trim plate on top of that.

Thanks!

Rick

[casavecchia]

Go for 316!
Marco.

[dreamer]

I would love to...but 316 is not FREE. The 304 is FREE (meaning I would not have to pay any money...nothing...nada). So, since I am using 304, what would be the best way to finish it? Could I just leave it unfinished?

Again, 316 is out of the question in this particular instance.

[woodboat]

look here http://www.hghouston.com/Technical%20FAQs/TFAQ155.html

Type 304 SS is not a good material choice for seawater applications, particularly stagnant seawater

[marshmat]

304 stainless is not designed for marine applications. If you must use it, treat it as you would a plain low-alloy steel; its properties are closer to plain steel in the marine environment.

[dreamer]

Thanks guys.

In fact, I actually contacted the folks at HG Houston. They suggested that I paint the chainplates with a marine grade epoxy paint.

Also, is there a way to tell what type of stainless it is?

[marshmat]

Marine epoxy paints are used all the time on plain steel; they work just fine if applied right.
You can't tell the exact grade number by looking at it. However, a fridge magnet is a good tool for guessing- the higher-quality the stainless steel, the less the magnet will stick to it. Tapping your magnet on a few known samples and then tapping it on your unknown one will give you a pretty good idea what grade it is.

[DSmith]

The better the polish, the better the surface corrosion resistance.

[lenandval]

I had cause to weld an extension into a too short 304 aerial mast. The original had been electropolished and looked superb. The extension was welded to the base and was a section of the original construction metal but with the original linished finish. 19 years later the original remains untouched and unblemished while the extension requires seasonal cleaning to clean up the brown stains that a season at sea always produces. Electropolishing is an industrial process and is not cheap in the UK. It works beautifully.

[dreamer]

That's interesting (especially considering this is a 4 year old thread! )

Wikipedia's entry doesn't say a whole lot. I would think all the acids used are pretty expensive.

[lenandval]

How did your preferred solution work out?