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  • Salt water corrosion

    Lets say you wanted to make a piece of 304ss resistant to saltwater corrosion..
    Would you either:
    A) Bronze Plate it
    B) Chrome Plate it
    C) Just make it out of 316SS

    This is for a large batch of parts, not one off's, so cost is a consideration.
    And if plating works well, then forget the 304, just plate some 1018

  • #2
    D) Nothing... 304 if fine by itself.

    However, more info about intended use, if there are welds, how nice it has to look etc, will get you a better answer. Don't waste you time or money with plating tho.


    ME

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    • #3
      Make it from 316. Plating will cost more and isn't reliable.
      Free software for calculating bolt circles and similar: Click Here

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      • #4
        D) Nothing... 304 if fine by itself.
        304 isn't recommended for salt water duty. It's susceptible to chloride induced stress corrosion cracking.

        After a while it looks like this:

        Free software for calculating bolt circles and similar: Click Here

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        • #5
          It is for an exhaust mixing elbow
          Last edited by RB211; 04-29-2011, 01:24 PM.

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          • #6
            I got the Injun sign on this question. The Navy has to deal with saltwater in every way. They spend a billion or more on corrosion precention every year. Here's their stand:

            Salt water will eventually get every metal. The question is time.

            The conventail wisdom is stainless in spray where oxygen in available and nickel copper (monel) for immersion.

            Avoid galvanic couples like the plague. Stainless with bronze is a bad combination. So is stainless with cast iron or steel. If dissimilar metals are inescapable in salt spray or immersion the faying surfaces and attachments have to be electrically insulated, sacrifical metal protected, or actively protected with a cathodic protection system.

            I suggest titanium alloy Al4 7V. I've seen it hold up almost indefinitely in salt water. That's what the Navy uses in submarine ball valves. I've seen titanium alloy balls come out of valves that have seen 5 years in tropical waters. They looked almost new except where the seals rubbed.

            Plating, paint, and coatings heve limited benefit. If appearance is important, 304 will eventually "blood rust." 316L is preferred for enduring appearance in salt spray exposure. Welded austenetic stainless items should be furnace annealed and passivated for the most durable surface treatment.

            Regardless the best protection is sacrificial metal (zinc) anodes near and attached to the item being protected.
            Last edited by Forrest Addy; 04-29-2011, 01:41 PM.

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            • #7
              If you are going to weld it, 304L is preferable to 304.

              RWO

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              • #8
                Would a marine grade paint coating work in your application?

                Robert

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                • #9
                  I'd use 316.

                  316 is a lot less likely than 304 to rust, due (IIRC) to molybdenum in the alloy.

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                  • #10
                    For a coating.. Google TuffCor

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                    • #11
                      Originally posted by RB211
                      It is for an exhaust mixing elbow
                      As in the water cooling elbow on a marine diesel wet exhaust system right after
                      the engine exaust outlet?

                      If so then avoid 304, and 316 won't last that long either if its thin walled
                      hot salt water and exhaust fumes don't make it easy on any material in that
                      situation. Best thing you can do is use 316, make the item as heavy walled
                      as posible and have them passivated.

                      If its mixing sea water with exhaust further down the exhaust tube then it will
                      last longer

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