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I was thinking about interesting powder metallurgy method, hot isostatic pressing. Often thick steel walled vessel is required increasing costs and decreasing the prevalence of this technology.

This led me to consider say several metal spherical concentric tanks. I wonder if the inner most tank is at very high pressure more so than the metal wall could handle but was counter acted mostly by a second concentric tank pressurized nearly to the same pressure but slightly less, and so on so forth until finally the outer most tank was low enough pressure to be contained.

I'm not really sure of the net forces? Would there just be large compression forces on the tanks? Would there be a large net force inwards or outwards? I ask because it would be interesting if say I had two balloons and everything worked out such that say I had a 99% chance of rupturing balloon A at pressure P_1 but it balloon B had less than 1% chance of rupturing at pressure P_2 and I found both had low chance of rupturing at respective pressures with balloon A contained inside balloon B. Maybe this help to understand the idea I wonder about, perhaps it is a fallacy I'm not sure.

  • No imagine the scenario where you gradually make the concentric tanks closer to one another, making the gap between gradually thinner and thinner until the amount of gas between each one tends to zero... You're just describing a thick walled tank, with many more potential leak patha! – Jonathan R Swift May 31 '18 at 12:13
  • @JonathanRSwift this is not true, because for a single thick tank the internal stress field is continuous, but for multiple shells with small gaps between them the circumferential (hoop) stress can be discontinuous between the different shells. However making such a structure with small enough geometric tolerances so that it worked as the OP would hope would be a very hard problem. With "large" gaps between the shells, the OP also needs to think about how the pressurized fluid in the "gaps" will be contained! – alephzero May 31 '18 at 12:34
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    A better version of your idea would be to shrink-fit the shells around each other somehow, so that with no internal pressure, the inner shell is in compression. – alephzero May 31 '18 at 12:36
  • @alephzero best idea, in fact a technology already used in larger gun barrels for range and accuracy. – Solar Mike May 31 '18 at 13:50
  • @Jonathan R Smith, I had wondered if perhaps by some conservation requirement that the best case would simply be matching the pressure loads of a single homogeneous shell, but I think perhaps the mass, kinetic energy adds something from a chemical or continuum dynamical perspective? Any ways thanks all for taking time to entertain this concept, which is probably only fully explained in much more technical terms than I have made. It does seem open to empirical testing and experimentation though? –  May 31 '18 at 15:26
  • Maybe miniscule viscosity or something of the gas, or simply it's kinetic energy are usefully contributeing to structural integrity? –  May 31 '18 at 15:28
  • @marshalcraft and there was me thinking that a gas was good for propagating shock waves... – Solar Mike May 31 '18 at 15:38
  • @Solar Mike and alephzero, I have read about what you describe now. That would utilize the shells tensile strength where what I was describing would utilize the materials compression strength or even the principle that for suitable shapes compressing stress doesn't lead to significant tangential deformations. Now that I think about it, it seems that would be the limit to pressures obtainable at the inner shell, is as it deforms (sphere radius shrinks) under more and more compressive loads the imperfections in sphericalness would lead to larger and larger tangential deformations causing failure –  May 31 '18 at 15:52
  • @marshalcraft given that I read about 12” and 15” (sizes from memory) naval guns I think you have not understood how it works... – Solar Mike May 31 '18 at 15:54
  • Multiwall or wrapped pressure vessels have been made but solid walls were less expensive. The reason for the multilayers was to improve toughness. When we bought HIP parts , I don't remember it being so complicated; It was used to apply a high alloy to the inside of wellhead valves. – blacksmith37 Jun 01 '18 at 04:03

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