Results 1 to 13 of 13

Thread: Metal corrosion question

  1. #1
    Member
    Join Date
    Mar 2008
    Location
    Fairbanks
    Posts
    203

    Question Metal corrosion question

    I was wondering which metals hold up well in saltwater use. I know that stainless steel is popular. Brass has been a nautical mainstay for centuries. How does copper (like tubing) or aluminum hold up over prolonged marine use? I was thinking of using copper tubing (since I have a bunch on hand) and some aluminum for some projects on deck but don't want a corroded mess after one season. Any experiences/input would be appreciated before I create an expensive, short-lived mess.

  2. #2

    Default

    In my opinion, stainless is among the best. None of our choices are maintenance free, but I think aluminum and copper tubing will be an issue. Could you use a poly tubing in you application?

  3. #3
    Member ironartist's Avatar
    Join Date
    Jun 2006
    Location
    Meadow Lakes
    Posts
    1,182

    Default 5086

    if your using aluminum 5086 is for a salt water application
    Visions Steel/841-WELD(9353)
    "Rebellion is in my blood, I was born an American"
    Μολών λαβέ

  4. #4
    Moderator Paul H's Avatar
    Join Date
    Apr 2006
    Location
    Anchorage
    Posts
    5,594

    Default

    That's a good question, but it leads to more questions than a simple answer. There are many, many different alloys of a given metal, and a big spectrum of corrosion resistance depending on the alloy. Also it depends on the application as there are factors other than just the base material that can lead to corrosion, such as galvanic action (mixed materials). Also is the material above or below the waterline, and does the boat live in a marina, or is kept inland on a trailer.

    There are aluminum alloys that are designed for corrosion resistance in a marine environment, but if you bolt stainless or worse yet copper to the aluminum, you've created essentially a battery and the aluminum will corrode at the joint unless it is electrically isolated from the disimilar material.

    So, look into exactly what you plan to do with these materials and the application. It could work great, or the material on hand could cause more damage and hence cost more than buying the proper material for the application.

    It won't cost you anything to bring the materials you plan to use on your boat for a couple day trip and see if they start corroding.

  5. #5
    Member
    Join Date
    Mar 2008
    Location
    Fairbanks
    Posts
    203

    Default Thanks for the input

    My project is building a frame over the aft fishing deck. I have lots of heavy walled 3/4" copper tubing and tons of fittings from a few plumbing projects. I was looking at builing the frame just like I'd solder up for a major plumbing project. I could build it very easily then have tent and tarp make me up a nice cover. If I build it strong it will keep rain off us while we're fishing and maybe even put my 10' inflatable upside down on top of the cabin and frame. I don't plan on mixing metals (other than the solder) and will cover the tubing with white rustoleum. The only reason I'm looking at copper tubing is I have it on hand and have everything necessary to make the frame.
    The boat stays in Valdez at a storage lot during the summer and not in a slip. Winter it's up in Fbks.

  6. #6
    Member
    Join Date
    Nov 2009
    Location
    California
    Posts
    335

    Default corrosion

    If you are in fresh water you've not much to fear, salt is the killer.
    as a practice anything metal I care about , I mount a zink annode to any where on the circut. the electrollisis attacks that first, pretty much leaving every thing else alone. ( till the zink annode is no longer in electrical contact) so don't hide it . don't paint over it . Zink annodes came with your drive ,some as installed in the cooling circut of the engine . Navy ships are nuts with them,on every part of the ship, especially on water circuts(plumbing) The copper might be fine but I'm not sure about the modern solders,(there not lead any more) . expiriment

  7. #7
    Moderator Paul H's Avatar
    Join Date
    Apr 2006
    Location
    Anchorage
    Posts
    5,594

    Default

    I'd be both concerned that that 3/4" tubing isn't large enough in diameter to provide sufficient rigidity. Small dia tubing even with a heavy wall is prone to buckling when you put a compressive load on it. Even though you'll paint it, you'll end up with a big green mess when the copper starts corroding under the paint.

    Personally I'd use 1" stainless tubing. I used 304 ss for my hand rails, but my boat lives on a trailer inland. If the boat was to kept near salt water I would have gone with 316 ss. Not cheap, as I recall the 316 was $10/ft and that was with a discount and a few years ago. But if you're going to the trouble of building up a frame, it better be stout enough for the application.

  8. #8
    Member
    Join Date
    Mar 2008
    Location
    Fairbanks
    Posts
    203

    Default Thats what I thought

    Thanks. I was affraid that might be the case. There's a company in town that has 1-1/2" square tube 3/16" thick walled and I'll most likely bite the bullet and buy that then weld up a nice unit. I'm glad I asked. Thanks Paul.

  9. #9

    Default

    Didn't they use copper on submerged parts of wooden ships way back when?
    As much as the copper is worth you might be better off taking the scrap money and putting it towards common marine materials?

  10. #10
    New member
    Join Date
    Aug 2009
    Location
    Anchorage
    Posts
    2

    Default make sure you have the right weld

    I you go with stainless, such as 316, make sure you have a welder that will use stainless 316L welding wire for all the welding. If you don't do this, your welds will corrode around the stainless.

  11. #11
    Member Michael's Avatar
    Join Date
    Oct 2007
    Location
    Anchorage / Glennallen
    Posts
    162

    Default

    Try going to sailrite.com. With the dimensions you can provide, they can fab all the stainless you need. and provide the proper fittings. Worth a look.

  12. #12
    Member
    Join Date
    Apr 2006
    Location
    Anchorage
    Posts
    3,246

    Default

    Andy,does make a good point just because you are using SS or Aluminum does not guarantee you will not have problems. I have seen SS exhaust, gas tanks, and railing eating by corrosion, because the builder did not know how to properly build or install a device on a boat use in salt water.

  13. #13
    Moderator Paul H's Avatar
    Join Date
    Apr 2006
    Location
    Anchorage
    Posts
    5,594

    Default

    Quote Originally Posted by Tealer View Post
    Thanks. I was affraid that might be the case. There's a company in town that has 1-1/2" square tube 3/16" thick walled and I'll most likely bite the bullet and buy that then weld up a nice unit. I'm glad I asked. Thanks Paul.
    That would definately be robust, but methinks very heavy! Adding weight up high is bad for a boat. I think for stainless, 1" dia 0.90" wall would be plenty strong, 1/8" wall at the most. For aluminum, I could see going larger dia, say 1 1/4 or perpaps 1 1/2" diameter, but I wouldn't go over 1/8" wall.

    Square tubing is approximately 25% heavier than round tubing of the same size, but you really don't gain much strength for the added weight.

    You don't have to weld stainless, you can use fittings to attach the tubing. The tubing can also be bent. I had my handrails bent, which not only saved me four 90 deg elbows, it also provided a stronger and cleaner installation.


Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •