What's titanium worth to you?

Discussion in 'Materials' started by Stumble, Nov 24, 2012.

  1. myark
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    myark Senior Member

    US NAVY TO USE TITANIUM TO MAKE SHIP HULL

    To fabricate the ship hull structure, more than 70 feet of welded linear joints were made, the longest known welds in titanium made with the friction-stir process.
    This friction stir welding achievement showed a noticeable improvement from previous similar processes. It was made at a high linear speed, indicating reduced manufacturing time; showed excellent weld penetration, indicating a secure connection; and had no distortion of the titanium adjoining the weld.

    http://world-defece-review.blogspot.com/2012/04/us-navy-to-use-titanium-to-make-ship.html
     
  2. myark
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    myark Senior Member

  3. upchurchmr
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    upchurchmr Senior Member

    Be careful of ONR's claims of success, they are in the research business and it is necessary for them to claim success even though there are practical issues with a piece of research.
    It is typical to claim success when the technology never gets picked up and used in business.
    Note the caution about reduced material properties when the steel pins erode and leave steel particles in the Ti. Note also the use of "lower grade" ti which reduces the strength, requiring more material for the job. Note again the general words used to talk about "success" but no actual final material properties or actual costs.
    Friction stir requires a modified numerically controlled milling machine which is a big investment just to start. There is nothing like a hand held welding unit like a common MIG welder.

    Frosty,

    You can Friction Stir Weld various materials together like Ti and Aluminum you just can't tell what the material properties will be. Although the material doesn't melt, it does get hot, and the two materials together will make what's called intermetallics - which are odd combinations of ti an aluminum which sometimes are extremely strong and brittle (very brittle). So failure at the joint can start at relatively low strengths. You would never know without expensive testing. Aerospace is not using it because so little is known.
     
  4. Stumble
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    Stumble Senior Member

    Frosty,

    No typically titanium cannot be welded to other materials. The tempratures it takes to weld titanium would destroy most metals. Depending on grade titanium has a service temprature in excess of 1200 Farenhite. Just the melting point of the metals alone shows the problem, alluminium melts at around 1200 degrees F, while titanium melts at over 3000 F.



    In special applications there are some concerns with using titanium and its ability to ignite. And there are real concerns about storing large quantities of titanium fines from processing and milling work. I don't feel qualified to get into detail, so I would recommend reading http://www.titanium.org/files/ItemFileA4650.pdf which is a safety guide for dealing with them.

    Generally speaking titanium parts don't have the surface area to burn, and it is only with quantities of dust/powder that you have a problem.



    I have been following the friction stir welding research for a while, which is pretty easy since I know Dr. Dong who heads it up at UNO. But I don't see it coming to industrial production levels in the near future, figure at least five years out at a minimum. That being said, there are huge advantages to making a hull from titanium once it is proven effective which is why the research is being funded by everyone from the Navy to major shipping lines. A titanium hull could realistically cut the weight of a ship by about 50%, allowing for huge increases in fuel efficiency, reduced drag, smaller engines, ect. That would all effect the bottom line positively.

    Plus it would eliminate all painting on ships, other than that required for cosmetic purposes, and anti-fouling below the water line.
     
  5. BMcF
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    BMcF Senior Member

    That sounds about right..if our experience with the introduction and adoption of stir welding for aluminum ship structures serves as a guide.
     
  6. Charly
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    Charly Senior Member

    Greg, Thanks for taking the time to post here. Your knowlege is very valuable to many readers here I am sure.

    In light of the above perhaps I should reconsider using Titanium pins in my composite chainplates? For my application, the 1/2 inch pin is held to the deck with several layers of wrapped fabric and epoxy. The pin, of whatever metal, basically would replace the 1/2 inch clevis that would normally go through the jaws of the turnbuclke. I guess it boils down to the question of which is the greater danger- crevice corrosion on the stainless pin, which is partly buried in the glass deck,-- OR -- galvanic interaction between a 316 turnbuclke, or a silicone bronze turnbuckle, and a titanium pin. It seems that the contact point would be difficult to insulate properly. Have you any opinion on this comparison?

    Maybe this question belongs in a riggers forum. Perhaps there is some good way to insulate the turnbucle from the pin?

    Thanks and sorry for the drift.
     
  7. Frosty

    Frosty Previous Member

    If titanium is corrosive free then I might be able to seperate my hand from my hard earned cash for sea cocks that I know are corrosion free and always will be.

    I have never heard of titanium sea cocks but many sinkings are because of corrosion of them.

    I am surprised therfore that this would not be included in Lloyds certification.
     
  8. Stumble
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    Stumble Senior Member

    Why not just use titanium turnbuckles and Dynex Dux standing rigging? Give John Franta a call at Colligio Marine, he has experience putting this together.

    Frankly the questions you are asking come awfully close to providing engineering assistance, which I am prohibited from doing. I can provide information, but I can't make sugestions based on engineering data. It's a legal liability thing.


    Frosty,

    We are looking for a valve engineer right now to design a series of seacocks. We have the flanges and thru-hull fitting now, but until we have a complete system I can't recommend them. And because we can't mass market them they are still being machined not cast. Hopefully by the spring we will have something ready to market, and I would be happy to take your money when the products are ready.
     
  9. powerabout
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    powerabout Senior Member

    if you need to bolt through carbon structure are you better off with Titanium as SS will desintegrate if there is sea water around?
     
  10. upchurchmr
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    upchurchmr Senior Member

    Titanium is the best possible fastener for use in carbon because it is closest on the galvanic potential charts. Like anything, it needs to be sized properly. You can't always just put the same size fastener as a replacement.

     
  11. Milehog
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    Milehog Clever Quip

    Would an oversize titanium pin be a good idea in case it were lost and needed to be replaced and only stainless or bronze available?
     

  12. Stumble
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    Stumble Senior Member

    You could, but it probably makes more sence to either confirm supply of the titanium pins, or to carry a spare if you are worried about it.

    One of the advantages of titanium is that it is so strong for its size it allows for much smaller parts to be used. In actual designs I have seen engineers have reduced the cross section area of parts by as much as 75% from stainless originals. This allows the parts to be made even lighter, and smaller, saving even more weight and reducing the cost. A re-engineered part in titanium may actually be the same cost or less as the stainless it replaces simply because there is so much less material that needs to be used.

    Just as an example, take a look at keel bolts, and lets say a current boat is using 1.5" 316 bolts. There is a cross section area of 1.77 square inches, so the nominal tensile strength of that bolt is 1.77*33kps = 58,410pounds.

    To replace that bolt in Grade 5, we just work the formulas backwards, and get...

    Ca=58,410lbs/128,000 psi. = .456 cross sectional area

    A=(pi)r^2
    .456=3.14r^2
    .145=r^2
    r=.381

    So we need a 3/4" bolt to replace the 1.5" stainless bolt. At a massive weight reduction, and a similar reduction in the cost of the bolt, since it is so much smaller.

    If you were to just directly replace the stainless with titanium, the issue is you would have a bolt that is massively oversized. With a yield strength of roughly 226,560 pounds (versus 58,000 pounds for the stainless).
     
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