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Discussion Starter #1
So I’m replacing my chainplates and bids from various fabricators are starting to come back. Question: will hot cutting techniques degrade the metal? Using 316L and I think that will reduce the corrosion resistance at the cut. Thoughts?
 

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Hot cutting will have no effect on 316L ss stock. it was hot rolled when it was sized by the manufacture . what will have an effect on corrosion resistance is the surface finish. the finer the finish the less crevices for moisture to hid. if the metal is dry it will not corrode. The metal needs to be passivated after all metalwork is done, this needs to be done or it will corrode. passivation removes the surface iron and allows the chromium oxide to form on the surface which helps the metal resist corrosion. You can also electro polish which does reduce the crevices on the surface but is not necessary if the mechanical polishing is done properly and then passivated. passivation is always the last operation to be done to the metal. if you polish the parts at a latter date then passivation needs to be done after the polishing. mechanical or electro polishing removes the chromium oxide and exposes the surface iron and passivation restores it.
once on the boat it is best to use a product like Spotless stainless to remove any rust and restore the chromium oxide.
 

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So I’m replacing my chainplates and bids from various fabricators are starting to come back. Question: will hot cutting techniques degrade the metal? Using 316L and I think that will reduce the corrosion resistance at the cut. Thoughts?
Who have you contacted about new chain plates? I prob need to do some of mine soon.
 

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Discussion Starter #4
Thanks @overbored, exactly what I was looking for.
@sailforlife I've reached out to several shops local to the Tampa Bay area. I'll PM you when I get a feel for the ones worth dealing with. Ironically, the one that was recommended as go-to by Masthead in St Pete has a sign on the door saying they are maxed out and not taking any new work. (good for them)
 

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Thanks @overbored, exactly what I was looking for.

@sailforlife I've reached out to several shops local to the Tampa Bay area. I'll PM you when I get a feel for the ones worth dealing with. Ironically, the one that was recommended as go-to by Masthead in St Pete has a sign on the door saying they are maxed out and not taking any new work. (good for them)
I'm no expert on working with SS, but I just recently replaced several chainplates on my PSC34. Pacific Seacraft manufactured the chainplates themselves. Mine use carriage bolts to attach the chainplates to the hull. Something they did that apparently is supposed to reduce the potential for crevice corrosion is that rather than punching the square holes, they were cut with a water jet. So if you need square holes, you may ask whether your manufacturer has the ability to cut those with a water jet.
 

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Discussion Starter #6
I'm no expert on working with SS, but I just recently replaced several chainplates on my PSC34. Pacific Seacraft manufactured the chainplates themselves. Mine use carriage bolts to attach the chainplates to the hull. Something they did that apparently is supposed to reduce the potential for crevice corrosion is that rather than punching the square holes, they were cut with a water jet. So if you need square holes, you may ask whether your manufacturer has the ability to cut those with a water jet.
I don't know how a square hole would be more resistant to crevice corrosion vs a round hole. I'd be interested in hearing how that works.

Using carriage bolts would allow one person to work the bolts when both sides cannot be reached. In my application I can easily reach both sides of the chainplates so I'll stick with round holes.
 

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Consider titanium instead of stainless. Then you don't worry about corrosion again. In the scheme of a couple of chainplates that don't need a lot of machining, the cost difference should be minor. If they are external, they might not be mirror finish and look as good, though.

Mark
 

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Titanium is the best material for a chain plate but it is expensive . It does save on some labor in the polishing and fabrication. Titanium is about 5 times the price of 316L SS for the material. twice as expensive in the fabrication. we just purchased some 1/4" by 2" by 6 feet long titanium flat bar for a customer, our cost was $1045. the same material in #8 polished 316L would have been $250. so in boat dollars it is more but doable. in regular dollars it is expensive
 

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Titanium is the best material for a chain plate but it is expensive . It does save on some labor in the polishing and fabrication. Titanium is about 5 times the price of 316L SS for the material. twice as expensive in the fabrication. we just purchased some 1/4" by 2" by 6 feet long titanium flat bar for a customer, our cost was $1045. the same material in #8 polished 316L would have been $250. so in boat dollars it is more but doable. in regular dollars it is expensive
Interesting. I wasn't thinking the material cost was so different. Overall, though, what is the price difference from a final product point? Oftentimes labor is 3/4 of the price of anything.

I quickly looked at Onlinemetals.com and a 12"x12"x0.25" titanium plate was $380, and the same size 316L was $140.

Mark
 

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Discussion Starter #10
Consider titanium instead of stainless. Then you don't worry about corrosion again. In the scheme of a couple of chainplates that don't need a lot of machining, the cost difference should be minor. If they are external, they might not be mirror finish and look as good, though.

Mark
I think titanium would be serious overkill for my 1976 boat. The chainplates are original kit, and corrosion hasn't been a problem. Replacing mainly due to age. Discovered some point loading damage once I removed them.
 

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Hot cutting will have no effect on 316L ss stock. it was hot rolled when it was sized by the manufacture . what will have an effect on corrosion resistance is the surface finish. the finer the finish the less crevices for moisture to hid. if the metal is dry it will not corrode. The metal needs to be passivated after all metalwork is done, this needs to be done or it will corrode. passivation removes the surface iron and allows the chromium oxide to form on the surface which helps the metal resist corrosion. You can also electro polish which does reduce the crevices on the surface but is not necessary if the mechanical polishing is done properly and then passivated. passivation is always the last operation to be done to the metal. if you polish the parts at a latter date then passivation needs to be done after the polishing. mechanical or electro polishing removes the chromium oxide and exposes the surface iron and passivation restores it.
once on the boat it is best to use a product like Spotless stainless to remove any rust and restore the chromium oxide.
316L is no better than 316, just better corrosion resistance after welding due to less Chromium Carbides formed. But if cut and welded and passivated correctly, the corrosion resistance of 316L will be good. Read about how stainless works here and how to ensure the stainless performs well here - basically passivated and the smoother the finish better. And I agree with this post - electro-polishing makes a massive difference to corrosion protection.
 

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Discussion Starter #12
@jahunt Thanks for the references. The project has progressed a bit. The only bid that I recieved that included polishing was cost prohibitive (probably fair though) and the delivery time suggested they really didn't want the job. So I recieved the parts with a mill finish. I ground them down to a 3000 grit finish and buffed them to a mirror finish. Reading up to see if passivating is DIY feasable. Would appreciate any thoughts on that.
 

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passivation is a very big subject . even the scientists can't agree on the best method. typically on 316 the part are electro polished first which removes a slight amount of metal so you have a very clean surface and then passivate. the trick here is that the metal is clean before passivation. if the metal contains anything on the surface the acid used to passivate will not reach the surface and not do its job. you can clean it with solvents and have good results but never as good as electro polishing first. so when we make parts that require passivation we leave it to the pros. but when we are doing parts for our own use and don't want to spend the money for the pros we will clean the parts with both water and oil based solvents first and then DYI passivation. so far the best over the counter product I have found is Stopless Stainless. it removes the surface iron and allows the materials to form the protective oxide layer. Clean is the key, do mot touch the parts between cleaning them in solvents to cleaning in the acid to rinsing them and letting them air dry. not even with gloves. the water used for the rinse should also be pure water not tap water.
 

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Discussion Starter #14
Thanks @overbored ! Some questions; First, what would you suggest for a good oil based solvent? Is something like brake cleaner or mineral spirits suitable? Second, how does one with limited telekinesis skills best allow the parts to dry without touching them. I'm thinking a minimal contact arrangement to suspend them, and just accepting that there will be a few points that may not get the full benefit of the treatment. Any suggestions?
 

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the solvent we us is dry-cleaning solvent brake cleaner should work. we hang the parts with 316 welding wire or synthetic cord. its grease that keeps the acid form reaching the metal surface even finger grease and some time gloves contain a surface agents that contaminates the surface. sterile surgical gloves can be used but still best to avoid touching.
 

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If your chainplates are typical SS straps, you can buy the proper width and thickness in bar stock. That way they only have to be cut to length as the bar is already the proper width. When had my chainplates fabricated I bought the needed length of 1 1/2" x 1/4" bar stock. IIRC, the supplier cut the bar stock to length or into smaller pieces than the overall length to save on shipping.

Square holes that are punched have a tendency to develop crevice corrosion at the corners. Cutting them with a water jet or plasma cutter doesn't create this problem.
 

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Discussion Starter #17
If your chainplates are typical SS straps, you can buy the proper width and thickness in bar stock. That way they only have to be cut to length as the bar is already the proper width. When had my chainplates fabricated I bought the needed length of 1 1/2" x 1/4" bar stock. IIRC, the supplier cut the bar stock to length or into smaller pieces than the overall length to save on shipping.

Square holes that are punched have a tendency to develop crevice corrosion at the corners. Cutting them with a water jet or plasma cutter doesn't create this problem.

The old configuration was 4x 1 1/2" chainplates, But I opted for a larger plate to eliminate the deck penetrations and make it easier for me to raise the penetration site. Water intrusion is the whole reason I'm engaged in this massive project in the first place (also replacing bulkheads).

So the square holes aren't really any better than round but depending on how it's done, may be inferior.
 
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