Corrosion on stainless steel

Discussion in 'Materials' started by gonzo, Jan 8, 2011.

  1. gonzo
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    gonzo Senior Member

    These bolts came out of a 1972 Swan. They were on the toe rail. It is mainly crevice corrosion but I think that there may be also electrolysis caused by the two SSB radios they used to have.
     

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  2. michael pierzga
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    michael pierzga Senior Member

    They were exposed to water...electrolyte. When SS is deprived of oxygen in a wet area, electrolyte, ... ......such as in a keel bolt, a rudder shaft, ss fastener in a wooden hull , a propeller shaft—it’s suffers pit corrosion, . In this pitted state the surface is no longer "passivated" ...it becomes ACTIVE and as a result is much less noble on the Galvanic Scale. This is why you don't use ss fasteners in wooden boat construction below the waterline.
     
  3. gonzo
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    gonzo Senior Member

    Unless something horrible happened to the boat, toe rails are usually above the waterline.
     
  4. michael pierzga
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    michael pierzga Senior Member

    Read again.....IN THE PRESENTS OF WATER.. anerobic......depassivation....Galvanicly active. WATERPROOF THE JOINT.
     
  5. gonzo
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    gonzo Senior Member

    Capital letters means you are yelling at me. You did that on the previous post too. Learn some manners, and grow up boy.
     
  6. baeckmo
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    baeckmo Hydrodynamics

    Would you have any idea about what SS quality it´s all about, Gonzo? And how far from each other were they mounted? One observation I make is that the corrosion occurrs at ~the same depth in both bolts; is there any kind of "moisture-carrying" structure at that level? You also see some free ferro-oxide near the bolt head, indicating a possible galvanic potential along the bolt length, also supporting the thought of differing oxygen concentration in the moisture at varying levels.
     
  7. michael pierzga
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    michael pierzga Senior Member


  8. gonzo
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    gonzo Senior Member

    It is A4/316 stainless. They were about 5" apart. The boat had at least two SSBs installed with through-deck insulators with bare connection nuts on top. The corrosion is at the base of the toe rail, where water intrusion is most likely.
    Michael: what is your disagreement with my statement that this is crevice corrosion with maybe electrolysis too?
     
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