JB Marine Weld and Crevice Corrosion

[rognvald]

For any "Metal Junkies" out there . . . do you think JB Marine Weld will seal very minor crevice corrosion on a stainless shaft after it has been treated with a metal rust remover to neutralize the rust? Is it even necessary? Will it hold up in a marine environment? Any comments will be appreciated.

[skipmac]

Is the corroded area under the packing in the stuffing box? If yes, then I would think the friction would wear the JB Weld and not the shaft.

If the area is in an open part of the shaft then I don't see any reason not to give it a try.

By the way, JB Weld Marine grade? Have not seen that. Is it any different than plain old JB Weld (other than charging more to say marine on the tube)?

[rognvald]

Originally Posted by skipmac

Is the corroded area under the packing in the stuffing box? If yes, then I would think the friction would wear the JB Weld and not the shaft.

If the area is in an open part of the shaft then I don't see any reason not to give it a try.

By the way, JB Weld Marine grade? Have not seen that. Is it any different than plain old JB Weld (other than charging more to say marine on the tube)?

Skipmac,
It is at the juncture of the top of the rudder and the rudder shaft where the shaft enters the rudder. Here's the info on Marine Weld.
www.jbweld.com/product/j-b-marineweld

[skipmac]

OK, rudder shaft. I was thinking prop shaft although a rudder post can also have a stuffing box.

So the corrosion was right where the shaft exits the rudder itself as in the part of the shaft that is normally exposed to the water?

What about down into the rudder as well? Did you dig out a little to see if the corrosion penetrated beyond the exposed, visible part of the shaft?

My understanding of crevice corrosion is that it occurs on SS that is enclosed in a wet environment where the water is stagnant and becomes oxygen depleted. SS exposed to open water I would not expect to show true crevice corrosion so I would question what caused the corrosion and if it will continue.

Either way, it sounds like it's not a wear area so answers that concern. My only question is whether or not the JB weld will absorb any moisture or allow moisture to seep under the margins of the repair and stay damp against the underlying SS shaft. That would just exacerbate the problem. Why not just leave it as is, exposed so you can keep an eye on it?

[model 10]

I have a similar problem but it's pitting not crevice corrosion (I hope.) I have tried JB weld, 4200, 5200 and epoxy and filler. At every haul out they have all been leaking around the shaft. I must not be cleaning the shaft well enough.

[boatpoker]

JB Weld is great stuff, it does not however, halt corrosion in stainless steel.
The black and white photo below is an x-ray of a stainless steel shaft with one very small visible pit. The other photo is a broken ss shaft with microscopic pits on the surface.

[Cheechako]

I cant zoom the image, but that second pic looks like a very suspect type of break. Almost looks like it was defective to start with. Too much cold drawing?

[boatpoker]

Originally Posted by Cheechako

I cant zoom the image, but that second pic looks like a very suspect type of break. Almost looks like it was defective to start with. Too much cold drawing?

Wish I had a higher resolution shot of that one but it was taken years ago on a Sony Mavica 1.6 megapixel camera. Lab tests gave no indication of manufacturing flaws ...... strictly corrosion. This shaft was on a boat that had not moved in about ten years, the stagnant water sitting in the cutless bearing was the culprit.

[skipmac]

Originally Posted by boatpoker

Wish I had a higher resolution shot of that one but it was taken years ago on a Sony Mavica 1.6 megapixel camera. Lab tests gave no indication of manufacturing flaws ...... strictly corrosion. This shaft was on a boat that had not moved in about ten years, the stagnant water sitting in the cutless bearing was the culprit.

Do you know the scale of the black and white photo?

[boatpoker]

Originally Posted by skipmac

Do you know the scale of the black and white photo?

Don't know the scale but I could barely fit a pin head in the pit.

[OceanSeaSpray]

Cleaning out the pits, using a drill bit if needed, and filling with high-strength epoxy filler, is normally a successful way of dealing with pitting/crevice corrosion (same mechanism and process), but on a stainless stock it leaves open the question of why it is pitting. This is not really a location with stagnant water anyway.

In this sense, it is unlikely to solve the actual problem. Here are a couple of questions I would try answering first:

- What is the grade of the metal in the rudder stock?
- Is it solid or hollow?

If I got the wrong answer to either of those, I would think about building a new rudder on a new stock.

I remember a yacht arriving in the Marquesas many years ago with no rudder (and a piece of floorboard at the end of the spinnaker pole hanging off the stern): the rudder stock was a heavy wall stainless pipe pitted all around at the insertion point in the fiberglass foil.

If you decide to patch up the corroded area, you need to go back to bright metal and then passivate the surface using pickling paste (not some hardware store DIY rustkill stuff). Get some from a workshop and be careful, it is highly corrosive.

[Cheechako]

The problem with corrosion is you don't know how far the damage has gone. The pits may be from end of a micro crack. They may not also.

[model 10]

You bet and there are way more pits than cracks. If every pit had a crack there would be no ships, bridges, airplanes or spaceships.

[Cephious1]

I once had a neighbor who forgot to winterize His 4 cylinder engine . In the spring the-expanding ice had cracked his block. He cleaned and ground the crack and then used j b weld on it. It was cast metal. I thought no way--this will never hold as it was a large crack. He used the boat every summer for 4 years with no issues..that made a believer out of me





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[Cheechako]

Yeah the stuff is pretty good sometimes. The custom Aluminum triple sheave on a watermaker /gen set I built cracked on the end sheave in the Bahamas. I JB welded it and it lasted until I returned to the States a month or so.