316 to mild rod?

Discussion in 'Metal Boat Building' started by Nick.K, Oct 5, 2013.

  1. Nick.K
    Joined: May 2011
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    Location: Ireland

    Nick.K Senior Member

    I have 316L bar which I intend to use for fore and back stay attachment points on my steel hull. Are 316L rods OK for welding stainless to mild in this situation or is there another rod I should use?
    My intention is to slot the deck and insert the bar through about three inches, the welds will be along the sides of the bar in shear to the hull structure.
    Nick.
     
  2. pdwiley
    Joined: Jun 2008
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    Location: Hobart

    pdwiley Senior Member

    You should use E309 rods ideally but the truth of the matter is, for something like yours or mine that doesn't have to meet any building codes etc for commercial survey (no picky engineers), you can get by with 316L rods.

    If you were closer I'd send you a few E309 rods as I've got a lot of them (and 316L) and have nearly finished all my welding.

    PDW
     
  3. Nick.K
    Joined: May 2011
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    Location: Ireland

    Nick.K Senior Member

    Thanks for the reply PDW. I had read a reference in Gerr's boat strength book about the 309. What is the issue with the 316?


    You kindly posted photos of your tube bender... I found the cap rail section I wanted (flat side oval) but in the end I did the bending with an ancient hydraulic pipe bender, a tiny bend about every 50mm. It took a whole weekend to do all the tube! I was happy with the results except that the bender left two small indentations with each bend on the inside edge. Now that it is all fitted, you don't really see them and it is acceptably fair. For the stanchions I have made up SS tube sockets which sit on a small SS doubler on the deck. The top of the socket is welded to the cap rail. The bulwarks lean in so there is about an 80mm gap for cleaning behind the socket. The sockets will brace the bulwark and I have made them heavy enough to tie things to them if I want.

    I'm concerned about the cap tube rusting out. It is a very light section. Any ideas for preventing this?
    I am thinking of filling the tube with epoxy paint, then draining out the paint and using it as a second coat somewhere in the boat.
    Nick.
     
  4. pdwiley
    Joined: Jun 2008
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    Location: Hobart

    pdwiley Senior Member

    Sorry Nick, I'm flat out ATM so I don't have time to dig into my welding references. You should be able to find the differences between 316 & 309 rods online anyway, Lincoln Welding is a good source of information.

    As for the cap tube rusting out, you have 2 options. Keep any water out, or make sure it can drain easily and quickly. Not sure what you mean by light section but if it's under 3mm wall, I foresee many dings in it in your future.

    Filling it with epoxy paint can't hurt but as you've no good method to ensure 100% coverage, you can't rely on it to do much.

    If you want to go to ridiculous extremes, weld in a pressure fitting, purge and then fill to say 3 psi with argon. Check periodically for leakage via pressure drop. This will also test how good your weld technique has been.....

    Needless to say that isn't a serious suggestion... would work, though.

    PDW
     
  5. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member

    Too much nickel in the transition causes the mild steel side of the transition to be crack prone. 309 is formulated for an ideal alloying in the transition zone.

    Be wary of 316L unless dual certified ie yield equiv to std 316 but with reduced Carbon. Standard 316L yields at around 20% lower stress than 316 which catches a few people out. A lot of suppliers now supply what they call dual grade 316/316L.
     

  6. Nick.K
    Joined: May 2011
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    Location: Ireland

    Nick.K Senior Member

    I did some reading and bought some 309 rods..!
    Mike, thanks for the info on the dual 316, I will do some reading on that too.

    I had to bring in the tube in from the UK, it was collected for me; the suppliers cut and loaded the tube to the vehicle before mentioning that they had run out of the section I had ordered and had substituted a lighter one!
    The bulwarks lean in and there is a substantial rub rail so I'm hoping it won't be dinged too much.
    Nick.
     
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