Preventing Stainless Steel from Pitting

[keepondancin]

Spotless Stainless works pretty well, and is safe to use. I have been impressed, sure peat polishing and rubbing.

[skipmac]

Originally Posted by Browning

IIUC, a part made of welded Stainless Steel must get protected by a passivator immediately. Old welded parts, such as U-Bolts, that were not passivated accordingly, may have already developed crevice corrosion before the new owner gets to passivate them, right?

OTOH, "working" (ie. grinding and scratching) parts must be re-passivated continuously, right?

Hi Browning.

Yes I believe promptly passivating any SS part is the best plan. Beyond this I am afraid my metallurgical expertise is limited. Regarding old SS welds I am not certain you would call the problem crevice corrosion. Crevice corrosion occurs in a situation where there are places on a SS part that do not allow good flow of water, like in a crack, under a gasket, between two close fitting parts, etc. In the case of a weld, if the weld was done poorly and left cracks then there would be crevice corrosion and even passivating that weld would not be a permanent solution since the small crevices in the weld would create new corrosion.

However I believe welding SS itself has problems separate from crevice corrosion. Here my knowledge is limited but I think the heat of welding causes changes in the SS that weaken it or make it more brittle. Perhaps someone with more knowledge in this area can add some comments here.

[skipmac]

Originally Posted by Canibul

So am I screwing up my old stainless steel fresh water tanks by sanding them down to shiny again, and fiberglassing over the pitting that runs along all the welds? I've been filling the little holes with JB Weld Marine, and then glassing a layer of cloth over the seams. The welds are getting brittle and eaten up.

Good question. My guess, if the SS is completely clean and dry, and the glass completely seals to the SS so there is no crevice between the metal and resin then it might be OK.

It might be best to passivate the SS before glassing over since the protective oxide coating has been removed by the sanding. Here again maybe an opinion from a real expert would be beneficial.

[model 10]

Thin stainless is hard to weld without getting hot spots somewhere or even along the whole weld if the welder is not an ace. The more color get along the weld, the more prone to pitting corrosion that area is. The surface under a glass, is very rough and you can see why it would corrode . On some parts you can buff the surface smooth again
I'm trying citric acid these days. Seems to be working as well or maybe better than Phosphoric.

[hellosailor]

If you have stainless tubing, it was formed and curved with IRON tool steel tools, which leave plain iron grit in the stainless. That tool steel rusts, and leaves the rusted tool steel embedded in the stainless. The only real fix is to repassivate the stainless, and since the EPA can make that an expensive process most companies skip it.


So you clean the stainless, use a Dremel with a brass brush or similar to get into hard places, use something like 3M Finesse-It (which is just 3000 grit polish) if you want, then something like citric acid to "gently" repassivate it, and try to keep up with one of the specialty ss products or polishes afterwards.


Or, get rid the stainless. That's for landlubbers. Real yachtsmen use brass and bronze, and have the crew polish it up every morning.(G)

[skipmac]

Originally Posted by hellosailor

Or, get rid the stainless. That's for landlubbers. Real yachtsmen use brass and bronze, and have the crew polish it up every morning.(G)

Are you volunteering for the job? I will offer two meals a day of salt beef, hard tack, a ration of grog, plum duff on Sundays and $10/month.

Good pay for a seaman don't you think?

[hellosailor]

Nah, that's not for me. Yachtsmen do tings for the sake of tradition. Or conspicuous consumption, I'm not sure which. Another memo I missed.


Me? I'd rather do it all out of titanium. Faster, lighter, no rusting, no maintenance noises to disturb the peace and quiet.


And, an old FBI/DOJ uniform crime statistic said that 90% of the BIG robberies are never solved, because the pros plan them so well. So all you need to do is plan one good job, invest the proceeds in titanium, and Bob's your uncle.


You can get all sorts of pretty colors out of titanium, blues, greens, purples...

[skipmac]

Originally Posted by hellosailor

Nah, that's not for me. Yachtsmen do tings for the sake of tradition. Or conspicuous consumption, I'm not sure which. Another memo I missed.

I'm going for inconspicuous consumption.

Originally Posted by hellosailor

Me? I'd rather do it all out of titanium. Faster, lighter, no rusting, no maintenance noises to disturb the peace and quiet.

I agree titanium is the way to go. Unfortunately I have titanium taste but a galvanized budget.

Originally Posted by hellosailor

And, an old FBI/DOJ uniform crime statistic said that 90% of the BIG robberies are never solved, because the pros plan them so well. So all you need to do is plan one good job, invest the proceeds in titanium, and Bob's your uncle.

I can believe that. Watching the local news and occasionally one of the TV networks reports on real crimes it is pretty obvious that the majority of the crimes are committed by idiots. Also can prove that from personal experience.

Had a break-in at my house a few years back. I actually caught the guy (just a kid really) and he was locked up for a couple of years. When he got out on probation he went back to school and got a high school degree so thought he might have straightened out and maybe wasn't so dumb after all.

Wrong.

Within weeks of getting off probation this genius posted a recruiting video on the internet showing him holding an AK-47 looking for volunteers to start a local chapter of the Crips. I think it only took a day before the local authorities saw it and a few days later he was locked up again.

So, yes I see some great opportunities in crime for a few smart guys. Just let me know how it works out for you.

[Seymore]

Originally Posted by bcboomer

So I'm new to salt water sail boat maintenance. I find that most places where I have close fitting stainless to stainless there is a rust film and/or pitting between the two. For example between the steering wheel and its shaft, between the control levers and their shafts, between any stainless clamped to stainless etc etc.

How old is your O'Day 40?

[bcboomer]

1986
It was a California boat with lots of Newport to Ensenada races and I don't think it was babied.

[Cheechako]

Originally Posted by hellosailor

Nah, that's not for me. Yachtsmen do tings for the sake of tradition. Or conspicuous consumption, I'm not sure which. Another memo I missed.


Me? I'd rather do it all out of titanium. Faster, lighter, no rusting, no maintenance noises to disturb the peace and quiet.


And, an old FBI/DOJ uniform crime statistic said that 90% of the BIG robberies are never solved, because the pros plan them so well. So all you need to do is plan one good job, invest the proceeds in titanium, and Bob's your uncle.


You can get all sorts of pretty colors out of titanium, blues, greens, purples...

I actually made a bilge fuel tank out of Titanium for my Tanton 44 cutter. The original bilge located SS one corroded through in about 5-6 years. Surprisingly not in the weld but right in the center of the plate!
I had 6AL4V Ti available in 1/8" so had it made out of that.

[skipmac]

Originally Posted by Cheechako

I actually made a bilge fuel tank out of Titanium for my Tanton 44 cutter. The original bilge located SS one corroded through in about 5-6 years. Surprisingly not in the weld but right in the center of the plate!
I had 6AL4V Ti available in 1/8" so had it made out of that.

Titanium fuel tank. Wow bet that was not cheap, unless you had a source for free titanium sheets.

[seandepagnier]

I just spent 6 hours drilling out the 3/8" stainless pin that goes through a stainless block (hinge pin for monitor wind vane rudder) My electric drill broke so I was forced to use a hand drill, and the two parts were completely seized.

I think it's a bad design to put a high stress part like this where it is constantly submerged then stick stainless inside stainless with a very tight fit.

[Canibul]

Isn't titanium so expensive over here because we have to buy it from the Russians? It's so cheap to them that they make entire submarine hulls out of it.

[Cheechako]

Originally Posted by skipmac

Titanium fuel tank. Wow bet that was not cheap, unless you had a source for free titanium sheets.

I managed the Aerospace shop. There were a few "G jobs" going on from time to time. The 6-4 Ti was surplus and going to scrap. That's when the "light went on"!
Had one of my welders weld it up after work for $100. All the pieces were either shear cut or laser cut for the holes and access port stuff.

When I retired, the boys in the shop made me a custom metalwork plaque stating "From the "marine" division. haha