Stainless corrosion and maintenance - Page 7 - SailNet Community
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post #61 of 71 Old 4 Weeks Ago
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Re: Stainless corrosion and maintenance

Did anyone mention that one culprit is the use of non-stainless tools leaving residue? In-fact polishing with a steel wire wheel will make things a ton worse.

And just a scotchbright sponge soaked in water can go a long way.

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Re: Stainless corrosion and maintenance

I don't think anyone suggested polishing with a steel wire wheel - that for sure would be damaging.

Also have to be careful about scotchbright pads, because they come in many types, and some of them can really do damage to polished stainless. The soft white ones would probably be OK, but I'd still go gentle with them. Make sure you know which pad type, and how aggressive it is before hitting the stainless.

On the other end of the scotchbright pad spectrum, I have some that are made for deburring metal. These are more like sanding pad than polishing pad.

Mark

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Re: Stainless corrosion and maintenance

I got some Spotless Stainless and tried it out yesterday. It’s citric acid, and their website claims it won’t remove chromium from the surface of the stainless steel. I was pleased with the result.

The temperature was around 65F, which is a little cooler than the 70 degrees mentioned in the directions. It took about 1 hour to remove rust stains.

Here are a couple of pictures:






Here’s the backstory: A couple of months ago, I removed, inspected, replaced as needed, and rebedded all the structural 28-year-old fasteners on the frame of my folding trimaran. At the time, however, I didn’t clean the rust stains from the surrounding gel coat. So that was one of my goals.

I also took a look at other stainless one the boat. One fairly new SS item had quite a bit of rust, more than elsewhere on the boat. It was a 300 series Ubolt to which we welded a small tab in our shop about a year ago. We had not passivated it after welding. That’s consistent with the information about carbonizing chromium mentioned previously in the thread. (I’ll get before and after pictures next time I go to the boat)
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Re: Stainless corrosion and maintenance

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Originally Posted by jblumhorst View Post
I also took a look at other stainless one the boat. One item had quite a bit of rust, more than elsewhere on the boat. It was a 300 series Ubolt to which we welded a small tab in our shop about a year ago. We had not passivated it after welding. Thatís consistent with the information about carbonizing chromium mentioned previously in the thread. (Iíll get before and after pictures next time I go to the boat)
Judy, passivating the stainless after welding will not necessarily fix the problem if the stainless was sensitized. As a result of the weld, Cr is depleted near the grain boundaries in the vicinity of the weld making them very susceptible to corrosion. The best way to treat this is by another appropriate heat treatment that dissolves the chromium carbides that were inadvertently formed.
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Re: Stainless corrosion and maintenance

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Judy, passivating the stainless after welding will not necessarily fix the problem if the stainless was sensitized. As a result of the weld, Cr is depleted near the grain boundaries in the vicinity of the weld making them very susceptible to corrosion. The best way to treat this is by another appropriate heat treatment that dissolves the chromium carbides that were inadvertently formed.
We did the TIG welding at a friend's shop at his ranch. He's a skilled welder, and used to own/operate a fabrication shop. I myself know almost nothing about welding SS.

What can we do to address the susceptibility of the weld to corrosion? Is there a way to weld SS in ranch machine shop that produces welds that aren't very susceptible to corrosion?

TIA,
Judy

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Re: Stainless corrosion and maintenance

Donít know much about this subject but had a removable, hinged ladder we use on the dinghy. It had one weld that would rust. Told to clean it best I could then paint with zinc primer. Ugly but seems to have held up.

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Re: Stainless corrosion and maintenance

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Originally Posted by jblumhorst View Post
We did the TIG welding at a friend's shop at his ranch. He's a skilled welder, and used to own/operate a fabrication shop. I myself know almost nothing about welding SS.

What can we do to address the susceptibility of the weld to corrosion? Is there a way to weld SS in ranch machine shop that produces welds that aren't very susceptible to corrosion?

TIA,
Judy
Yes you can. The key is to not use any tools to cut or grind that have been used on any other metal like steel. Do not touch the SS with any thing steel like steel files, steel saw blades or carbon steel drill bits. clean the weld area to remove all oxides and weld with as much shielding gas as possible or in a vacuum chamber. Use 316L material and filler rod if possible. weld at the lowest heat that will still produce the weld size that is required. clean the surface after welding with clean scotchbrite pads or wheels and then passivate properly. any time the SS is touched with a mechanical polishing device, scratched or even wiped clean you are removing the chromium oxide from the surface and could be exposing the iron in the surface of the SS to the elements and it could cause rust. so frequent passivation is always recommended.
I have been in the fabricating business for 45 years and I use Spotless stainless because it works the best on boat hardware of any I have tried.

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Re: Stainless corrosion and maintenance

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Yes you can. The key is to not use any tools to cut or grind that have been used on any other metal like steel. Do not touch the SS with any thing steel like steel files, steel saw blades or carbon steel drill bits.
What kind of tools can we use to cut and form SS? We have band saws, drill bits, lathes, etc.

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Re: Stainless corrosion and maintenance

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so frequent passivation is always recommended.

I have been in the fabricating business for 45 years and I use Spotless stainless because it works the best on boat hardware of any I have tried.
Wait. What?

45yrs. Hmmm.

I agree(d).

Mark

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Re: Stainless corrosion and maintenance

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What kind of tools can we use to cut and form SS? We have band saws, drill bits, lathes, etc.
You can cut it with a band saw high speed steel drill bits and almost any tool that will cut it but the area that will be welded needs to be surfaced with a non steel tools in the area that will be welded, sanded, abrasive ground, machined, turned with clean non steel tools. and some times we passivate and chemically clean the surface to be welded prior to welding. don't want to introduce any iron to the weld that is not already in the SS
We use a lot of scotchbrite type products and sanding discs prior to welding
Our go to wheel is a 6" by 1" wide scotch brite wheel known as a "6s fine" grit medium density, good for cleaning and fine polishing before going to polish compounds. a bit expensive but a must for SS fab work this wheel is from Mcmaster carr and is the same wheel as 3m for less $
$71.44 Each
46575A71
yes I did say they are expensive
needs to be 6-7000 Rpm to polish

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