Electron tube survival under hyperbaric conditions

Discussion in 'General Electronics Chat' started by Hypatia's Protege, Sep 6, 2015.

  1. Hypatia's Protege

    Thread Starter Distinguished Member

    Mar 1, 2015
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    Kind friends...

    This is to inquire as to the 'survivability' of electron tubes following several months exposure to ambient pressures of Ca. 54 PSI (372 kPa) (metered).

    The tubes are located in a (presumably) dry hold aboard a sunken vessel at ~ 20 fathoms (36.6 meters) fresh water --- I have been offered the contents of said hold (over six tons of assorted NOS 'transmitting', industrial and radiography/DRT tubes) contingent upon my (not inconsiderable) assistance with the salvage (refloating) effort...

    While most of said cargo is comprised of glass and ceramic high power 'transmitting' types - my principal interest is in the two dozen Coolidge RAs (a representative example of which is shown in the image below) --- FWIW, Owing to vertical stowage and the reasonably 'gentle' grounding of the boat, I don't anticipate breakage owed to excessive cantilever forces acting upon the anode seals --- Please note also that I am not concerned with the integrity of potted assemblies - merely the electron tubes contained therein (AKA "inserts" for those with a preference for 'trade speak') inasmuch as the envelopes must support well over four times manufacture-anticipated ambient 'storage' pressure... <<<Edit to clarify pressure ratio>>>

    Again, although the tubes are expected to be dry, the pressure is commensurate with depth inasmuch as the hold is not airtight - but, merely, airlocked...

    Inasmuch as 'geometry matters' where structural integrity is concerned -- here is an image of a typical Coolidge RA -- Please note that the volume ranges from Ca. 0.75 litre to 5 litres across various types...
    RA18.JPG

    Please understand this is merely a request for input -- For which I offer sincere gratitude - without regard to the outcome of my decisions!:):):) --- IOW: Should I accept the offer, and the week's work earns me nothing but a trailer full of shards - it's no one's fault but my own! -- I'm merely asking for opinions!:cool::)

    Very best regards
    HP
     
    Last edited: Sep 6, 2015
  2. Art

    Distinguished Member

    Sep 10, 2007
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    You want to retrieve some? Or you want to subject them to pressure?
    Or just curious?

    Since tubes can gas anyway, how would you know it was an effect of the pressure?
    I would guess some are ok and some are not just as if they were stored on land,
    but of course, only a guess.
     
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  3. Hypatia's Protege

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    Hello! Thanks for your reply!:)

    They've been subjected to increased pressure (54 PSI above atmospheric) since early June -- I'm merely wondering if such 'storage' is likely to have resulted in seal failure and/or implosion...

    The difference is the three months hyperbaric storage...:confused:

    Best regards -- And many thanks!:):):)
    HP
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The tube looks like a rotating anode X-ray tube to me.
    I do not know if the seal for the rotating anode is touched by the pressure difference.

    Bertus
     
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  5. Hypatia's Protege

    Thread Starter Distinguished Member

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    Thank you for your reply!:):):)

    Correct, as stated in the post, it is a Coolidge RA (Sorry for the abbreviation)...:oops:

    I expect to the same degree as any other electron tube --- the housing (i.e. potting assembly) offers no protection whatever against pressure inasmuch as it features a bellows/diaphragm to accommodate thermal expansion of the dielectric oil...

    To put a finer point on my question; Is it probable that tubes designed for operation at 1 ATM (absolute) will have survived three months storage at 4.67 ATM (absolute)???

    Many thanks!:)
    HP
     
  6. bertus

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  7. Art

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    Noone will be able to give a definitive answer. It's unlikely to have been tested.

    I have valve radios running here for 85 years in normal atmosphere,
    and intuitively think what's 3 months in those conditions?

    On the other hand, domestic radio and amp tubes aren't 5 litre volume, and I don't know about the anode seal.

    Implosion for domestic valves at least is quite difficult without a good shock.
     
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  8. Hypatia's Protege

    Thread Starter Distinguished Member

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    Yes, that's correct, the anode rotor and external stator constitute a (high slip) induction motor --- I am well 'versed' with the tubes' operation and construction -- I apologize that my question was not clear:oops:...

    My focus upon the Coolidge tubes owes both to their unique envelope geometry and to the high value I place upon them -- Their glass to metal seal technology is the same as that employed in other high power glass tubes...

    Again, I am merely inquiring as to the likelihood of any of the tubes' -- but especially the Coolidge tubes' --- survival of the above described protracted hyperbaric storage -- The Coolidge tubes alone are worth my effort!:cool:

    Many thanks!:)
    HP
     
    Last edited: Sep 6, 2015
  9. crutschow

    Expert

    Mar 14, 2008
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    My gut feel is that there is a large safety factor in the design of the tube envelope (just to survive normal handling at regular atmospheric pressure and to maintain their integrity at the operating temperature) so I would expect the tubes to be okay, but I have nothing objective on which to base that opinion.
     
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  10. Hypatia's Protege

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    Thanks for your reply!!!:)

    Indeed! -- Hence my request for opinions:cool: --- If I had more time I'd construct a test chamber, howbeit I've less than a week to decide...:rolleyes:

    But the tubes in question have been stored significantly in excess of atmospheric pressure...:confused:

    Agreed - Even more so RE: industrial types - Still --- Considering the tubes are at ~4.6 times 'normal pressure' seems reasonable cause for concern:eek::confused:

    Again many thanks for your response!:):):)
    Best regards
    HP
     
  11. Hypatia's Protege

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    That's my feeling (hope) as well --- I keep telling myself that storage (i.e. cold envelope) integrity is significantly greater inasmuch as the tubes must be designed against collapse owed to thermal 'softening' of the glass (a prominent characteristic of all amorphous 'solids') at operating temps...

    Thanks for your reply! --- It is most reassuring to hear my 'rationalizations' reinforced via the considered observations of another!:):):)

    Best regards
    HP
     
  12. PackratKing

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    Jul 13, 2008
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    HP... How old are these tubes you seek... current tech, or from when things were really made well...??? If the latter, I would think they will survive intact...
     
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  13. KeepItSimpleStupid

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    Mar 4, 2014
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    I lost my post with references. The basic ideas are the tube is weak at one area and one might try to calculate the force on that area of the tube. The materials are all over the map.

    I doubt that leakage will be an issue.

    I worked with quartz lamps that supposedly saw 10-15 atmospheres when in operation. That glass was thick though.

    I sealed quartz under vacuum at 1e-6 Torr and worked a bit with Pyrex.

    I also worked with ion pump, cryo-pumps, diffusion pumps, turbo pumps from the low end of 1e-9 to 1e-6 Torr.

    What did amaze me was the pressure, on say a 8-10" vacuum port at 1e-6 Torr. I wondered why so many bolts. Well, there is about 750 lbs of force on that flange. ( I did not re-do the calcs - from memory).
     
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  14. Kermit2

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    Considering the type of manufacturing practices around the time these were made, I would guess that they will be just fine. Nothing back then was considered properly engineered unless OVER engineered. ;)
     
  15. Hypatia's Protege

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    Thank you for your replies!:) ---- The prospect is looking better and better!:):):):cool:

    While it's difficult (for me, anyway) to determine the dates of manufacture - I'm guessing the oldest (i.e. the octal 'beam-power' amplifier types) may date from the early 50s whereas the newest (i.e. certain high-power ceramic and radiography types ) are no newer than the late 80s - early 90s

    For those wiser in the ways of component dating than I - here's a summary based upon a cursory perusal of the manifest:

    The internal anode types range from 'octal style' (i.e. 6146, 6L6, etc...) through the 8166/8189 and their ilk --- While the external anode (ceramic) types range from the 3CX1500 (8877), etc through the 4CX24000A (8916) and others of their 'geometric style'

    Most of the radiography tubes are NOS Varian A256 and G256 potted in B-150 housings - in addition to some vintage non-potted NOS EBRT/DRT FAs of Machlett and Picker manufacture...

    Many, many sincere thanks!
    HP:)

    PS --- Lest I be mistaken for a 'textie':eek: -- Here's an expansion of abbreviations used in this post:
    NOS= New Old Stock
    FA = Fixed Anode
    EBRT = External Beam Radiotherapy
    DRT = Deep Radiotherapy
     
    Last edited: Sep 6, 2015
  16. Hypatia's Protege

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    Of course quartz (i.e. fused silica) is a true solid -- as opposed to an ultra-viscous liquid (as is room-temperature glass) -- Though that could work in my favor in that the structural design of glass envelopes must be consistent with the highest anticipated operating temperatures (and, so it would seem, exhibit considerable 'margin' at room temps)???

    It's just such considerations that has me worried - especially for the large volume types:eek:

    With many sincere thanks!:)
    HP
     
  17. KeepItSimpleStupid

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    In any event, stress may be the biggest problem. For the "tubes sake, you might have to "decompress". "Decompress" meaning to let the pressure and temperature equalize and don't bring stuff up too fast. That might not be allowed to happen though?
     
  18. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    @Hypatia's Protege

    I would say they survived. The laboratory glass easily handles 100psi internal pressure - just to give reference to thickness vs. strength.

    Vacuum tubes need strength against external pressure and are designed for that by geometry. Because it is air pressure, the pressure is applied evenly just as it is designed to withstand (with, as mentioned above, with several orders of safety factor most likely).

    A glass bulb is generally sealed with glass-to-metal seal, the alloy is commonly KOVAR or similar alloy with the same thermal-expansion co-efficient as glass. The potting compound is generally just used to attach the wires exiting the evacuated envelope to the connector in such a way that gives significant strength while installing or, more importantly, removing the bulb (tube) from the socket.

    Good luck.

    I am interested, are these tubes in the frigid fresh waters of Lake Superior or in salt water?

    https://en.wikipedia.org/wiki/Kovar
     
    Last edited: Sep 6, 2015
  19. Hypatia's Protege

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    Unfortunately that's beyond my control -- Once the ballasts are sufficiently inflated things tend to happen rather quickly!:eek:

    Thanks for the info and for placing matters in perspective!:)

    Correct --the the boat containing the tubes is submerged in Lake Superior (fresh water) -- however the tubes are almost certainly in a dry hold (based upon sonar/acoustic imaging findings of <10° starboard 'list' and negligible 'pitch') --- Owing to ventilation to the bilge, however, the pressure in the hold necessarily corresponds with depth (≅120 Ft ≅ 54 PSI [metered])

    Thank you both for your responses and interest!!!:)

    Best regards
    HP
     
    Last edited: Sep 6, 2015
  20. Hypatia's Protege

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    ADDENDUM to post #19

    As an aside - it is curious that the (sunken) boat is clearly visible from the surface - It seems surface refraction (i.e. that attendant to the air/H2O 'interface') produces a 'telescopic' effect in that the 'wreck' appears significantly closer than it is...
     
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