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Titanium metalworking technique options

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  1. Sep 2, 2015 #1

    rollingstein

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    What are the preferred, low-cost options for cutting & joining Titanium?

    I'll explain my use case: There's a fabricator with long experience working with Carbon Steel & Stainless Steel but now we want to assign him a Heat Exchanger project where the tubesheet & tubes must be Titanium. He has experienced welders & is willing to pay for whatever additional training is needed.

    But the preference is to go for techniques that have the lowest investment needed. e.g. No expensive CNC machines etc. There may or may not be future work involving Ti so no point investing in a $100k fancy machine.

    The welding and cutting work has so far been entirely manual and the quality is satisfactory. The part to be fabricated isn't very intricate, just a tubesheet and tubes joined to it. The strength requirements on the weld are minimal so long as seal welding has integrity.

    Any suggestions? Is this project practical?
     
    Last edited: Sep 2, 2015
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  3. Sep 2, 2015 #2

    Nidum

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    My best advice would be to turn job away or subcontract to specialists .

    Otherwise :

    Titanium can be welded by Tig and Mig processes but actually doing it requires a high level of practical expertise and of background knowledge .

    In particular weld preparation and effective use of welding and backing gasses has to be considered very carefully as does the complete heating and cooling cycle .

    Titanium can be cut and machined by conventional methods provided the actual cutting tools are of correct specification .

    Titanium swarf is a fire hazard .
     
    Last edited: Sep 2, 2015
  4. Sep 2, 2015 #3

    rollingstein

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    That's actually excellent advice in general but in this specific case the costs are not competitive. Except for not having handled Ti before this shop is really very good in their craftsmanship & welding skills.

    And they seem eager to learn & invest the time & money so there seems a thinking among Management that we ought to give them a chance.

    Luckily the equipment isn't safety critical (low pressure steam & brine boiling) so we can afford to make this a test case. If it works out it will mean bigger savings for us in the future. If they make a mess of it, of course, we go back the expert firm route.
     
  5. Sep 2, 2015 #4

    CalcNerd

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    This could easily be your main concern. Titanium is very combustible such that it can burn even typically inert N2 at a temperature well below its own melting point ie the metal can self combust if it becomes to hot. That is why it is usually (always???) worked in a vacuum or inert He atmosphere.
     
  6. Sep 2, 2015 #5

    rollingstein

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    Most handbooks I've seen describe Argon welding. Apparently arc stability is a problem with Helium.

    The typical procedure seems to be high purity Argon as shielding gas with a trailing jig to keep the still hot but cooling Ti surface also under an Argon blanket. The other jig seems to be the one to keep the back side of the welded piece also under Argon.

    Vacuums and glove boxes seem to be used for very complex pieces. For something like a simple tube to tube sheet weld I'm thinking Argon shielding should be ok so long as both sides are shielded and a trailing gas jig is used.
     
    Last edited: Sep 3, 2015
  7. Sep 4, 2015 #6

    f95toli

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    Do they have the equipment/know-how to TIG weld? If so they should be able to do it. However, if they don't they might have to invest quite a bit in training and equipment (mostly the former). TIG welding is -as I am sure you known a standard technique but it is still fairly specialized (it is something like a 2-year long course if you want to get all the permits) . It also depends on what the part will be used for, at least in the Europe the welders need to be certified before they are allowed to weld Ti pipes in e..g the oil/gas industry (which is a common application) and getting the required permits is quite expensive.

    (I don't know much about welding, but my dad used to be a welder for the oil industry, mainly working with titanium)
     
  8. Sep 4, 2015 #7

    rollingstein

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    Yes, they have the TIG know-how. This is to be installed in Asia and the end-use is non-hazardous so no extra rigorous Code Compliance is needed.
     
  9. Sep 4, 2015 #8

    Astronuc

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    This is a critical factor. One does not want to be near a sizeable mass of Ti (of Zr, Hf, or similar metal) if it catches fire.

    If not in a vacuum, Ti would have to be welded in inert gas, e.g., He or Ar, in order to avoid contamination of the weld. Oxygen and nitrogen are readily absorbed in the melt, and the contamination can lead to poor weld and subsequent failure.

    Here is an example of how a company prepares and fabricates a Zr-alloy heat exchanger.
    https://www.atimetals.com/businesses/atispecialtyalloysandcomponents/Documents/Tech-Serv-Library/1997-Conf-Proceedings/1997019.pdf [Broken]

    http://innomet.nl/docs/zirconium.pdf (Zirconium products fabrication similar to Ti product fabrication)
     
    Last edited by a moderator: May 7, 2017
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