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  1. #1
    gr8life is offline Cast Iron
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    Default What kind of metal to use for salt water?

    I am in the process of making a fitting to keep a reserve diving tank attached to the main diving tank. Think of this as a quick change tool post for underwater use. First I thought alum. anodized, no good the ano. will wear off. Next thought of chrome plate, same problem. Should I use stainless and if so what am I looking for. New problem hope there is someone here who knows.
    thanks
    ed

  2. #2
    gregormarwick is online now Stainless
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    I'm not sure what you mean by "quick-change" but if this is something that is threaded and going to be screwed and unscrewed often then stainless is only an option if that mating parts are NOT stainless. Stainless on stainless threads will gall up and seize in short order if you're not careful. If this is the case then brass would be a good candidate.

  3. #3
    Dave Johnson is offline Aluminum
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    My first choice would be 316 SS. Readily available, good for corrosion resistance, sometimes called "marine grade stainless". Welds fine.
    Be forewarned, you CANNOT let a cutting tool rub on the surface. If it's not cutting it will work harden the surface, and destroy the cutting edge.

    Do not let it contact other metals, especially Aluminum, galvanic corrosion will be a problem. Use an insulator between dis-similar metals.

  4. #4
    DigiSnapMark is offline Plastic
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    Stainless, even 316 is subject to crevice corrosion... still water corrosion. Bronze would be my suggestion.

  5. #5
    gr8life is offline Cast Iron
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    This is 2 mating dove tails like a quick change tool post. The tanks are aluminum painted or powder coated.
    ed

  6. #6
    split tenth is offline Cast Iron
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    I think they use Naval Bronze alloy 464 for ship propellers and salt water applications

  7. #7
    machine1medic's Avatar
    machine1medic is offline Titanium
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    Default Same trouble with stainless on stainless.

    Quote Originally Posted by gr8life View Post
    This is 2 mating dove tails like a quick change tool post. The tanks are aluminum painted or powder coated.
    ed
    I would make the dovetail Male out of 300 series stainless.
    Make the Female out of brass / bronze / tobin-bronze / what-have-you.
    3 to 4 thou clearance....any locking threads still need to be
    one of each as well.

    Regards
    M1M

  8. #8
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    Forestgnome is offline Stainless
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    H-1 is the latest and greatest for marine use. Spyderco uses it for knife blades. Don't know how you get it or how machinable it is.

  9. #9
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    Alloy 903 bronze is listed as being particularly resistant to saltwater exposure. It's weldable, if that matters.

    I haven't used it, since I don't do any saltwater stuff.

    - Leigh

  10. #10
    adama is offline Diamond
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    Some of the better alloys will hold up for a long time if well anodized. Failing that some of the better enginering plastics are vertualy imune from corrosion, just may swell a small fration. There also a lot nearer netural bouancy.

  11. #11
    SAG 180's Avatar
    SAG 180 is offline Titanium
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    Why not use what they use on most saltwater boats for valves and fittings: LG2 bronze. It's considered pressure tight for castings and machines really well. If it's an application requiring great hardness as well as corrosion resistance then opt for AB2 aluminium bronze instead although that would be tough to machine.

  12. #12
    gnorbury is offline Hot Rolled
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    Delrin or a bronze alloy.

    If you use stainless, its eventually going to come in contact with the aluminum tank and cause the tank to corrode.

  13. #13
    PixMan's Avatar
    PixMan is offline Diamond
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    Here's an interesting website with some good information about stainless steel in salt water. There's a PDF document you can view or download. I was only disappointed that the article didn't seem to mention 321 or 347 stainless. I was told by some engineer a number of years ago that those are more corrosion-resistant than 316.

    http://www.ssina.com/publications/salt_corrosion.html

  14. #14
    PixMan's Avatar
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    Quote Originally Posted by machine1medic View Post
    I would make the dovetail Male out of 300 series stainless.
    Make the Female out of brass / bronze / tobin-bronze / what-have-you.
    3 to 4 thou clearance....any locking threads still need to be
    one of each as well.

    Regards
    M1M
    I agree with this. Dissimilar metals will be strong enough for almost any load but resist galling when the members slide against each other.

  15. #15
    Hdpg is offline Stainless
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    Anodizing will not wear of aluminum and as mentioned some alloys are very good for saltwater exposure; after all diving tanks ar made from aluminum and so are boats.

    Make the receiver out of aluminum and the insert out of Delrin which does not absorb water; actually the insert could be aluminum with Delrin inserts for the contact areas on the receiver.

  16. #16
    Carl Darnell is offline Titanium
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    Since your talking dovetails I don't see a problem with both metals being the same. I may be best to use one of the bronze alloys suggested. The clamping system could be of the same material.

  17. #17
    gr8life is offline Cast Iron
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    Just to clarify there is little stress on this attachment. The current operation uses a strap which is clumsy and takes too long to hook up. The only thing he is looking for is a faster system.
    thanks for all the info.
    ed

  18. #18
    Steve Seebold is offline Banned
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    Default What kind of metal to use for salt water?

    347 stainless steel. It's a little gummy to machine, but you can drop it in hydrochloric acid and the acis has no effect in the stainless.

  19. #19
    Jackmo is offline Hot Rolled
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    Monel 400 is a good metal for marine use.

    Found this web site: http://www.megamex.com/monel-400-nickel-alloy.htm

    Jackmo

  20. #20
    jabezkin is offline Stainless
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    Titanium doesn't rot too quickly.........

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