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Old 05-07-2020, 04:58   #1
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Question Mild steel chain plates rusting above deck

hey guys!

So have been looking at my chain plates, they have flaked a bit of steel, below deck they are encapsulated in foam and so no signs of corrosion.

So I had the idea of cleaning back the exposed chain plates to clean bare metal slowly and avoiding generating too much heat, take measurements as i go. Then make a set of patch plates with a few weld through holes on the face all out of 316ss as well as a pin sheath through the main hole for the clevis pin in 316ss so I have encapsulated the mild steel in 316 ss after welding it on....

Can anyone forsee any problems with my plan?

I will attempt to get some photos uploaded when its dried out up there 🌦

Will make another post about the other ideas as I get to them with the chipping hammer ⚒⚒⚒😅😅😅
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Old 05-07-2020, 05:19   #2
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Re: Mild steel chain plates rusting above deck

Are you up for welding mild steel to 316? I've done it, but it just about busted my butt.

Sounds like an unnecessarily complicated repair, if I follow you. Why not reinforce with welded on mild steel and then tackle the rust problem?
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Old 05-07-2020, 05:24   #3
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Re: Mild steel chain plates rusting above deck

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Originally Posted by tkeithlu View Post
Are you up for welding mild steel to 316? I've done it, but it just about busted my butt.

Sounds like an unnecessarily complicated repair, if I follow you. Why not reinforce with welded on mild steel and then tackle the rust problem?
Yea I have welded 316 to mild before, strange that now you mention just using mild im like huh that sounds easier 🤣

I think part of my reasoning was others with mild steel chain plates said they struggled to keep them from rusting so I was working on that basis!
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Old 05-07-2020, 05:33   #4
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Re: Mild steel chain plates rusting above deck

A lesson I learned by reading posts on the forum regarding painting rusting mild steel is don't finish prepping the steel with a powered wire brush - it leaves too smooth a surface for good adhesion of the paint. Finish with sandpaper after clearing the rust with whatever.
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Old 05-07-2020, 08:43   #5
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Re: Mild steel chain plates rusting above deck

I am not sure if this will work..........If you weld MS and SS together, you may have dissimilar metal or galvanic corrosion, especially if this assembly getting wet.
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Old 05-07-2020, 09:41   #6
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Re: Mild steel chain plates rusting above deck

I have welded stainless 316 to a mild steel boat above the waterline, using 316 rod. No problem and no galvanic reaction. This was about 5 years ago on someone else's boat.
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Old 05-07-2020, 12:30   #7
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Re: Mild steel chain plates rusting above deck

316 S/S is basically mild steel with additives and a saturated solution of carbon to the point the crystalline structure of the carbon no longer allows each crystal to contact another crystal. the structure forms spheroidal crystals of carbon separated from each other making it non ferrous and non magnetic. Magnetic S/S grades corrode to varying degres. When even T316 S/S is welded to itself this structure retracts slightly back and the weld seam (Heat affected zone) will degenerate and be able to corrode to varying degrees. Nitric acid added to the weld surface chemically pulls chrome up to the surface encapsulating and protecting the heated area below and to some extent protects the item from corrosion once more. When mild steel (lead free mild steel as leaded steel has a whole lot more issues but welded chainplates will not have lead) is welded to S/S with either 7016 rods or 316 rods will revert back to one or other forms of basic steel. Do not put Nitric Acid on mild steel however. The steel will corrode with nitric acid as the chrome is not present in sufficient quantity if at all. The join between the two metals will need to be well sealed as this point with seawater will corrode. O would personally replace the chainplates with T316 S/S but that is a much bigger job.
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Old 05-07-2020, 13:23   #8
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Re: Mild steel chain plates rusting above deck

Like most things, I guess you need to know what you're doing. I had a Fleming SS vane welded to my Temptresses 35. 316 to Aus10 steels. Half way up to the Reef, the welds started to give way. Hated putting extra holes in the boat, but then i thru bolted on the transom.
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Old 05-07-2020, 17:22   #9
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Re: Mild steel chain plates rusting above deck

How do you know there's no sign of corrosion below if they're encapsulated in foam? Did you dig the foam back?
What is the hull material? If it's fiberglass, wouldn't it be easier to remove the mild steel chainplate and replace it with a proper bronze one? If the hull is steel, why not grind the existing chainplate to bare metal and weld a mild steel doubler to it and put a bead around the deck while you're at it so water doesn't get underneath the doubler?
I operated a steel schooner for some time, and while certainly an endless task, keeping up with rust wasn't impossible. Where SS was welded to mild steel, the weld seemed more brittle than mild to mild (stanchion welds would crack). But that might have been an accident of bad welding technique.
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Old 05-07-2020, 22:02   #10
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Re: Mild steel chain plates rusting above deck

Simple treatment of rusty chain plates. I served my apprenticeship in an English general engineering machine works with tradesmen born in the 1880's There a Victorian moulder in the iron foundry told me that they used to heat the metal dull red and quench it in moulten tar. ( the kind you buy in a 100lb keg and melt for roofing) Now I have tried heating the metal in situ with a propane torch and brushing melted tar on it, I found that works very well too. They used this method to stop drain grates and man hole covers from rusting.
works better than galvanizing the tar seems to burn into the surface of the metal.
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Old 05-07-2020, 22:56   #11
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Re: Mild steel chain plates rusting above deck

The problem with carbon steel chain plates is that the loaded pin causes the corrosion preventing coatings to fail where the pin enters the hole in the carbon steel allowing rust to form and lift the coating away from the steel thereby exposing the surface to further rusting.

The solution is simple.

Use a stainless steel rod to apply a bead of weld all the way around the hole in the chain plate. Then grind it back until you have about a 1/16 inch (1mm) raised bead left. Then ream or file out the hole so the pin fits.

Keep the chain plates painted and you won't have a problem again.
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Old 05-07-2020, 23:56   #12
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Re: Mild steel chain plates rusting above deck

Quote:
Originally Posted by tkeithlu View Post
A lesson I learned by reading posts on the forum regarding painting rusting mild steel is don't finish prepping the steel with a powered wire brush - it leaves too smooth a surface for good adhesion of the paint. Finish with sandpaper after clearing the rust with whatever.
This forum ROCKS!

Thanks guys so much useful information here I will try and respond to any posts that have not been answered by myself or someone else!

Quote:
Originally Posted by forgol View Post
I am not sure if this will work..........If you weld MS and SS together, you may have dissimilar metal or galvanic corrosion, especially if this assembly getting wet.
Picked up the 316 lining mild holes reading a boat building book so I think its more of a it has to be done properly 😁

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Originally Posted by Lancerbye View Post
I have welded stainless 316 to a mild steel boat above the waterline, using 316 rod. No problem and no galvanic reaction. This was about 5 years ago on someone else's boat.
Awskme thats that settled then thanks!

Quote:
Originally Posted by Pelican 2 View Post
316 S/S is basically mild steel with additives and a saturated solution of carbon to the point the crystalline structure of the carbon no longer allows each crystal to contact another crystal. the structure forms spheroidal crystals of carbon separated from each other making it non ferrous and non magnetic. Magnetic S/S grades corrode to varying degres. When even T316 S/S is welded to itself this structure retracts slightly back and the weld seam (Heat affected zone) will degenerate and be able to corrode to varying degrees. Nitric acid added to the weld surface chemically pulls chrome up to the surface encapsulating and protecting the heated area below and to some extent protects the item from corrosion once more. When mild steel (lead free mild steel as leaded steel has a whole lot more issues but welded chainplates will not have lead) is welded to S/S with either 7016 rods or 316 rods will revert back to one or other forms of basic steel. Do not put Nitric Acid on mild steel however. The steel will corrode with nitric acid as the chrome is not present in sufficient quantity if at all. The join between the two metals will need to be well sealed as this point with seawater will corrode. O would personally replace the chainplates with T316 S/S but that is a much bigger job.
Yes much bigger and also I think I'd want to drop the mast and go around doing all at once rather than one at a time!

Lots of cool info there thank you! How do you know this stuff?

Quote:
Originally Posted by Benz View Post
How do you know there's no sign of corrosion below if they're encapsulated in foam? Did you dig the foam back?
What is the hull material? If it's fiberglass, wouldn't it be easier to remove the mild steel chainplate and replace it with a proper bronze one? If the hull is steel, why not grind the existing chainplate to bare metal and weld a mild steel doubler to it and put a bead around the deck while you're at it so water doesn't get underneath the doubler?
I operated a steel schooner for some time, and while certainly an endless task, keeping up with rust wasn't impossible. Where SS was welded to mild steel, the weld seemed more brittle than mild to mild (stanchion welds would crack). But that might have been an accident of bad welding technique.
I have dug random spots over the foam to check pajnt still solid she is steel hulled, yes part of my idea there except the "doubler" would cover both sides and edges in SS

Yes brittle was my only worry, not something I want to snap off! But it sounds like its doable!

Thanks there will be many more questions I can assure you! Haha

Quote:
Originally Posted by coastalexplorer View Post
Simple treatment of rusty chain plates. I served my apprenticeship in an English general engineering machine works with tradesmen born in the 1880's There a Victorian moulder in the iron foundry told me that they used to heat the metal dull red and quench it in moulten tar. ( the kind you buy in a 100lb keg and melt for roofing) Now I have tried heating the metal in situ with a propane torch and brushing melted tar on it, I found that works very well too. They used this method to stop drain grates and man hole covers from rusting.
works better than galvanizing the tar seems to burn into the surface of the metal.
Now thats cool! (pun?) I think the clevis pin will wear through the tar in no time 😔 but seriously cool history there!

Quote:
Originally Posted by RaymondR View Post
The problem with carbon steel chain plates is that the loaded pin causes the corrosion preventing coatings to fail where the pin enters the hole in the carbon steel allowing rust to form and lift the coating away from the steel thereby exposing the surface to further rusting.

The solution is simple.

Use a stainless steel rod to apply a bead of weld all the way around the hole in the chain plate. Then grind it back until you have about a 1/16 inch (1mm) raised bead left. Then ream or file out the hole so the pin fits.

Keep the chain plates painted and you won't have a problem again.
Ohhh so my idea of a machined ss sleeve for the pin would work! its easier for me to machine a sleeve up and weld it on and I won't have to buy a reamer 😁

OK cool thank you guys, seriously good info there! I will ponder a bit more, I've some chipping to do around my steering gear after iv cut teplates to replace the bits that fail the hammer test!
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Old 06-07-2020, 00:42   #13
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Re: Mild steel chain plates rusting above deck

IIRC, lots of alloy boats use s/s sleeves (bits of tubing) epoxied into their alloy chainplates to reduce wear and corrosion. If it works for them, why not in mild steel plates? Makes replacement when worn much easier, no reamer needed if tube size is selected carefully, and no embrittlement worries.

No experience, just observations of others efforts.

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Old 07-07-2020, 07:08   #14
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Re: Mild steel chain plates rusting above deck

Some mild steel chain plates use 2 316L washers welded to the mild steel with 309 rod. I use Tefgelled bronze bushings from McMaster Carr in mine and haven't had an issue in ten years.
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Old 09-07-2020, 02:52   #15
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Re: Mild steel chain plates rusting above deck

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Originally Posted by s/v michaela View Post
Some mild steel chain plates use 2 316L washers welded to the mild steel with 309 rod. I use Tefgelled bronze bushings from McMaster Carr in mine and haven't had an issue in ten years.
cool thanks am learning lots
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