Metal Permeability - Definition & Properties

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    Metal Permeability
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SUMMARY

The discussion centers on the concept of metal permeability, particularly in relation to the leakage rates of gases through steel, as highlighted by a conversation about the prototype used in the Saturn V's fuel tank. The terms "permeability" and "porosity" are critical in understanding how gases like LOX and H2 can seep through metals, albeit at extremely slow rates. The conversation emphasizes that while all materials are permeable to some extent, significant leakage often occurs through connections and welds rather than the metal itself. The importance of checking for porosity in cast parts, such as turbine blades and engine blocks, is also underscored.

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  • Understanding of metal properties, specifically "metal permeability" and "porosity"
  • Familiarity with gas leakage concepts in engineering contexts
  • Knowledge of casting processes and quality control measures
  • Basic principles of fluid dynamics as they relate to gas flow
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  • Research "metal permeability testing methods" to understand how permeability is measured
  • Explore "gas leakage rates in metals" to gain insights into practical applications
  • Learn about "casting defects and porosity" in manufacturing processes
  • Investigate "welding techniques for gas-tight seals" to prevent leakage
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Engineers, materials scientists, and quality control professionals involved in manufacturing and testing metal components, particularly in aerospace and automotive industries.

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Metal "permeability"

I went to the Von Braun planetarium the other day and was surprised to find out that their planetarium dome was a prototype for the Saturn V's Fuel tank! As a result, it wasn't exactly hemi-spherical which threw off come constellations, but that's another story.

I bumped into my friend who works on Aries. He said the prototype was most likely made to measure the leakage rate through the steel. LOX or H2 will seep through steel? Yes, everything leaks. This, among other reasons, is why there is a vented space between fuel tanks.

I believe it was "porosity" or "permeability" of the material that he spoke of. However, I've only been able to find information on the geological contexts of these words.

Am I looking for the right word?

Was he just joshing me?
 
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Yes, everything is permeable to everything, generally speaking. But the time it would take a significant amount of even the smallest gas atom/molecule (i.e., He) to permeate through 1 mm of metal is probably on the order of years (see Figure 10 http://www.devicelink.com/mddi/archive/00/01/015.html"). A more important leak path is through connections (which may not be completely gas-tight) and through welds (which can be porous if not made correctly).
 
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I've typically referred to this as porosity. The experience I've had with it has been cast parts. At Honda one problem they had was block porosity, where if the part wasn't cast correctly, high pressure oil lines could cause seemingly phantom oil leaks through the block.

I also just went to a plant that is casting some of our turbine blades, they mentioned how porosity is something that they check for to ensure they're doing a good job.
 

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