crevice corrosion: the weakest link

Discussion in 'Fiberglass and Composite Boat Building' started by Charly, Oct 22, 2012.

  1. Charly
    Joined: Dec 2009
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    Charly Senior Member

    I have one final question to resolve before I start the layup of my composite chainplates.

    The pin that the turnbuckle attaches to is stainless. It is "wrapped" up inside the layers of cloth. The whole idea of composite chainplates is to do away with stainless parts that are buried away somewhere, making them more susceptible to crevice corrision. So this pin then, it seems to me, must be the weakest link. The only redeeming thing is that it would be easier to remove periodically and inspect.

    Ok so here is the question: which is better? wrap the pin up tightly in the cloth so that there is little room for movement from vibrations and wear, etc., or leave a miniscule airspace around the pin so that it is less apt to corrode?

    Thanks
     
  2. lewisboats
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    lewisboats Obsessed Member

    Why not use a bronze pin?
     
  3. gonzo
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    gonzo Senior Member

    These are toerail bolts from a Swan I worked on a couple of years ago. It is a good example of crevice corrosion. As you can see, some of the bolt heads corroded right off; those are not nuts.
     

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  4. charlyIII
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    charlyIII Junior Member

    :idea: :D

    I guess I was so fixated on my crevice question I didn't consider the obvious

    Thanks
     
  5. gonzo
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    gonzo Senior Member

    Titanium has come down in price and may be cheaper than bronze.
     
  6. BMcF
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    BMcF Senior Member

    I saw a lot of the same with some of the "stainless" fasteners on some boats I helped to build in Norway. I have to wonder what alloy those are.

    If 316L is not available and/or not not strong enough...we'll opt for some other material wherever possible....titanium being one of those.
     
  7. Stumble
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    Stumble Senior Member

    Charly,

    I of course would recommend titanium as opposed to bronze. And frankly the price difference may amaze you. Depending on the production numbers of the specific part we may actually be cheaper if you are using high quality bronze.
     
  8. Landlubber
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    Landlubber Senior Member

    certainly burying stainless steel is going to cause crevice corrosion, it is just a matter of time.

    Go the titanium, monel or bronze in that order.
     

  9. Petros
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    Petros Senior Member

    it seams to me an airspace around the pin gives it a place for moisture to get trapped. this can not be good. I would make it a net fit, and seal it with some kind of easily removed flexible sealant. So the inspection process would be to peel off the sealant and remove the pin.

    There is almost no place where moisture will not eventually find its way into, air spaces tend to not only trap and hold it, but condensation can also occur even if it was not directly exposed to moisture, but just moist air. Are you thinking the tiny space would allow it drain and dry out?

    Going with monel or some other corrosion resistant materiel is your best defense, but I would not have any gaps anywhere if I could avoid it.
     
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