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Thread: Inconel Spheres

  1. #51
    RBW Member Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike's Avatar
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    Re: Inconel Spheres

    Quote Originally Posted by cool_hardware52  View Original Post
    Scuba tanks are also "pressed" (bigger press than you need for a sphere)
    al scuba tanks arent pressed they are extruded from billet

    the 2 halfs of the sphere are made from rolled plate. this means after pressing the walls of the sphere can be thought of to have 'grain' in the same way a piece of wood does. the direction of the grain is parallel to the surface. this makes it very strong (just as wood is stronger in the direction of the grain)





    Not sure about the risks of greater temp rise. To start with the small spheres offer a pretty high surface area to volume ratio compared to most Scuba tanks, and inconel is a high nickel super alloy routinely used in the hot section of turbofan engines.
    compare a thick walled sphere to a thick walled scuba tank same internal volume and same heat input. the thin walled vessel has less material to absorb the same amount of heat - ergo each element will see a larger temperature rise. and a thin walled vessel will cool faster. It will see bigger and raster thermal gradients

    There is something called thermal fatigue which is brought on from changes in stress from rise and fall of thermal gradients in a material or a structure. In the case of the spheres its made worse because we dont have a homogenious structure like an extruded al tank. theres seam weld and the kneck weld and the kneck is thicker. these areas (particularly around the kneck) will be the site of thermal stress due to material geometry restraint there.

    These spheres wall are mm's thick....its not rocket science that they are not very robust and need to be treated with care
    Last edited by Drmike; 21st October 2010 at 02:40.

  2. #52
    Tobin George cool_hardware52 is a splendid one to behold cool_hardware52 is a splendid one to behold cool_hardware52 is a splendid one to behold cool_hardware52 is a splendid one to behold cool_hardware52 is a splendid one to behold cool_hardware52 is a splendid one to behold cool_hardware52 is a splendid one to behold cool_hardware52 is a splendid one to behold cool_hardware52 is a splendid one to behold cool_hardware52 is a splendid one to behold cool_hardware52 is a splendid one to behold cool_hardware52's Avatar
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    Re: Inconel Spheres

    Quote Originally Posted by Drmike  View Original Post
    al scuba tanks arent pressed they are extruded from billet

    True for aluminum tanks. Steels are drawn from a disk.

    Quote Originally Posted by Drmike  View Original Post
    the 2 halfs of the sphere are made from rolled plate. this means after pressing the walls of the sphere can be thought of to have 'grain' in the same way a piece of wood does. the direction of the grain is parallel to the surface. this makes it very strong (just as wood is stronger in the direction of the grain)

    I'm not sure I'd call the sphere blanks "plate" more like "sheet", but either way I agree the material will have a well developed grain as a result of the rolling process.


    Quote Originally Posted by Drmike  View Original Post
    compare a thick walled sphere to a thick walled scuba tank same internal volume and same heat input. the thin walled vessel has less material to absorb the same amount of heat - ergo each element will see a larger temperature rise. and a thin walled vessel will cool faster. It will see bigger and raster thermal gradients.

    There is a number of effects in play that differ between a thick scuba tank and a thin sphere that will impact the relative temperature rise.

    1) The relative volume of the scuba tank vs the Sphere

    2) The geometry, spheres offer the least surface area per unit volume

    3) The thermal mass of the sphere vs it's volume and the scuba tank vs it's volume

    4) The thermal conductivity of the materials, i.e. inconel vs aluminum or Cromo

    5) The Specific energy of the materials.

    Comparing the two is complex.

    If I owned a sphere I'd be tempted to run a few tests.


    Quote Originally Posted by Drmike  View Original Post
    These spheres are mm's thick....its not rocket science that they are not very robust and need to be treated with care
    No argument here.

    Tobin

  3. #53
    RBW Member Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike's Avatar
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    Re: Inconel Spheres

    Quote Originally Posted by cool_hardware52  View Original Post

    I'm not sure I'd call the sphere blanks "plate" more like "sheet",
    sorry i was using an engineering term specific to stress analysis. sheet isnt a very 'technical' term - we more commonly use 'plate' especially if its undergone some treatment such ar rolling, hammering etc



    There is a number of effects in play that differ between a thick scuba tank and a thin sphere that will impact the relative temperature rise.
    ..your being uneccessarily pedantic. at the end of the day - its mm thin - each element will see a bigger thermal range than a typical thick walled scuba tank for same input temp.

    i own 3 spheres and im not tempted to do a test. thats not to say thermal fatigue is the biggest concern - it isnt. scratching is - by far. it provides a nice stress raiser
    Last edited by Drmike; 21st October 2010 at 04:34.

  4. #54
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    Re: Inconel Spheres

    Quote Originally Posted by Drmike  View Original Post
    sorry i was using an engineering term specific to stress analysis. sheet isnt a very 'technical' term - we more commonly use 'plate' especially if its undergone some treatment such ar rolling, hammering etc.
    Finish and dimensional tolerances are typically tighter on gage thickness (sheet) than for plate. Some (not all) consider 11 gage and lighter to be sheet and 10 and up to be plate, but I am splitting hairs.

    Quote Originally Posted by Drmike  View Original Post
    ..your being uneccessarily pedantic.
    maybe, wouldn't be the first time.

    Quote Originally Posted by Drmike  View Original Post
    at the end of the day - its mm thin - each element will see a bigger thermal range than a typical thick walled scuba tank for same input temp.
    The amount of heat input and the transfer rate out into the surrounding air / fluid will have some impact on the temperature rise. I have a buddy with access to very high end thermal imaging cameras. Some time lapse studies might be fun. (Probably end up proving you right.)

    Quote Originally Posted by Drmike  View Original Post
    i own 3 spheres and im not tempted to do a test. thats not to say thermal fatigue is the biggest concern - it isnt. scratching is - by far. it provides a nice stress raiser
    Given that the spheres spring from a design for hydraulic accumulators, which are routinely pressure cycled I would suspect that scratch and dent is a higher order concern than fatigue.

    Tobin

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    Re: Inconel Spheres

    Oooo, meandering engineering pissing matches make me moist...

  6. #56
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    Re: Inconel Spheres

    Quote Originally Posted by fireman  View Original Post
    Oooo, meandering engineering pissing matches make me moist...

    My rule-of-thumb is use 'em until they explode.

    Seems to have worked since 1996...



    Kevin.

  7. #57
    RBW Member Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike's Avatar
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    Re: Inconel Spheres

    Quote Originally Posted by cool_hardware52  View Original Post
    Given that the spheres spring from a design for hydraulic accumulators, which are routinely pressure cycled I would suspect that scratch and dent is a higher order concern than fatigue.
    just to continue to be pedantic (and to keep em moist).....surface scratches are only an issue exactly because they will reduce the fatigue life. They are stress raisers, just like a micro crack that could be incurred from a drop/dent. Both flaws reduce the fatigue life because fatigue life is the time taken for a micro crack (that exists in all things) to grow (with each pressurising/depressurising) until the crack is sufficiently long to cause a catastrophic rapid failure (critical crack length) by having a scratch or a micro crack from dropping you effectively leapfrog in time to the point where a normally occuring micro-crack normally would reach after x number of pressuring/deperssurising cycles. in other words the scracth/crack reduces the remaining fatigue life.

    ok, pedantic mode off
    Last edited by Drmike; 22nd October 2010 at 05:11.

  8. #58
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    Re: Inconel Spheres

    Quote Originally Posted by Drmike  View Original Post
    just to continue to be pedantic (and to keep em moist).....surface scratches are only an issue exactly because they will reduce the fatigue life. They are stress raisers, just like a micro crack that could be incurred from a drop/dent. Both flaws reduce the fatigue life because fatigue life is the time taken for a micro crack (that exists in all things) to grow (with each pressurising/depressurising) until the crack is sufficiently long to cause a catastrophic rapid failure (critical crack length) by having a scratch or a micro crack from dropping you effectively leapfrog in time to the point where a normally occuring micro-crack normally would reach after x number of pressuring/deperssurising cycles. in other words the scracth/crack reduces the remaining fatigue life.

    ok, pedantic mode off
    Err, ah, well of course. It appears we have both taken he same side of this argument.

    Tobin

  9. #59
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    Re: Inconel Spheres

    Quote Originally Posted by heyydude  View Original Post
    My rule-of-thumb is use 'em until they explode.
    Still got both thumbs? I guess there's still life in mine yet then :D

  10. #60
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    Re: Inconel Spheres

    Quote Originally Posted by lizardland  View Original Post
    Still got both thumbs? I guess there's still life in mine yet then :D
    Yup. But I DID stop crouching over them when I'm filling...





    Kevin.

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