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Thread: Corrosion Treatment

  1. #1

    Corrosion Treatment

    Got a friend with an older alloy boat. He's let it go a bit, and turns out he's got pinholes in his hull from what is likely a combination of electrolysis and/or galvanic corrosion. It's speckled with white powdery sites all through the inside of his hull. I strongly suspect he's had a live short allowing current to flow through his hull and it's been nibbling. I've removed the battery from the boat to stop that process until we can backtrack every cable to find the fault, but in the interim whats the best method of treatment for this type of alloy corrosion ? Do "rust converters" work, but being that it's an alloy it's not your conventional red/brown iron oxidization. Any thoughts or suggestions would be appreciated.

    Cheers.

  2. #2

    Re: Corrosion Treatment

    Electrolysis and galvanic corrosion require a noble metal to contact the aluminium for the corrosion to take place.
    Both types are accelerated with a current leakage to the hull.

    Pitting with random round corrosion spots is usually under floors of boats where the humidity is high nearly all the time. It does not require any electrical charges to cause this, only high humidity especially in a salt rich moisture.

    Determine which type of corrosion you are dealing with.
    Jack.

  3. #3

    Re: Corrosion Treatment

    Quote Originally Posted by Fillet`n`Release View Post
    Got a friend with an older alloy boat. He's let it go a bit, and turns out he's got pinholes in his hull from what is likely a combination of electrolysis and/or galvanic corrosion. It's speckled with white powdery sites all through the inside of his hull. I strongly suspect he's had a live short allowing current to flow through his hull and it's been nibbling. I've removed the battery from the boat to stop that process until we can backtrack every cable to find the fault, but in the interim whats the best method of treatment for this type of alloy corrosion ? Do "rust converters" work, but being that it's an alloy it's not your conventional red/brown iron oxidization. Any thoughts or suggestions would be appreciated.

    Cheers.
    Light acid wash, allow to dry and then apply lanox mx4.

  4. #4

    Re: Corrosion Treatment

    Quote Originally Posted by tunaticer View Post
    Electrolysis and galvanic corrosion require a noble metal to contact the aluminium for the corrosion to take place..
    Not always. What is most likely happening is what is termed as pitting corrosion. The killer is salt. Aluminium is relatively corrosion resistant because it forms an oxide layer on the surface. The chlorides in the salt can break down the oxide layer, and prevent it from reforming which then results in a corrosion cell. Its a double edge sword, the salt also suck moisture out of the air, so now you have a nice little corrosion cell, and some good electrolyte.

    the problem is most likely from not cleaning the boat properly. Once the pitting has set in badly, its usually not recoverable. If there is pinholes all the way through, you could possibly try some sort of epoxy treatment. If its only mild pitting on the surface, taking it back to bare aluminium (use a scotchbrite) and the pickling it may stop further corrosion. You can buy pickling solutions, but I am pretty sure they are just phosphoric acid (rust converter)

    For aluminium to remain corrosion free, all the surfaces need to be exposed to oxygen. Anything that depletes that, ie dirt, fish guts, salt crystals etc will help in accelerating corrosion.


  5. #5

    Re: Corrosion Treatment

    I pulled the false.floor on my 2002 Bluefin when I purchased it 6 months ago. It had zero corrosion but I am pretty sure the manufacturer put on a clear coat. I washed it down with suds and water blasted and then put on 3 coats of Xtroll Rust Conqueror UV transparent paint and put the floor back down and put foam around the edges to stop anything rolling underneath. I have taken the foam away and had a look the other day and as I expected it looks no different. Once you have a complete barrier water condensate doesn't hurt the alloy. Good cheap protection. It's not an etching coating but stuck well...perhaps because of some previous coating but it seems to stick to everything well.

    Cheers

    Sent from my SM-G930F using Tapatalk
    Boat: Seafarer Vagabond
    Live: Great South East....love Moreton Bay fishing

  6. #6

    Re: Corrosion Treatment

    Cheers for all the thoughts and suggestions. Will relay them and see how things go.

  7. #7

    Re: Corrosion Treatment

    If you can get your hands on zine chromate its the go. Its toxic as all hell, but its the best stuff to prevent corrosion in aluminium. Like all things in corrosion prevention, regular reapplication is the key.


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