Metal Permeability - Definition & Properties

In summary, the conversation discussed the concept of metal permeability and how it relates to the construction of the Von Braun planetarium dome, as well as its importance in ensuring the integrity of fuel tanks. The term "porosity" was mentioned as a possible alternative to "permeability" and its significance in the casting process was also discussed.
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flatmaster
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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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  • #2
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.
 

1. What is metal permeability?

Metal permeability is the measure of a metal's ability to allow the flow of magnetic flux through it. It is a property that varies among different metals and can be influenced by factors such as composition, temperature, and magnetic field strength.

2. How is metal permeability measured?

Metal permeability is typically measured using a device called a permeameter, which applies a known magnetic field to a metal sample and measures the resulting magnetic flux. The ratio of the applied magnetic field to the resulting flux is known as the permeability of the metal.

3. What are the units of metal permeability?

Metal permeability is typically measured in units of Henry per meter (H/m) or Tesla per ampere (T/A), depending on the measurement system used. These units represent the ratio of magnetic field strength to magnetic flux density.

4. How does metal permeability affect the performance of magnetic materials?

Metal permeability plays a crucial role in the functionality of magnetic materials. Higher permeability metals allow for a stronger magnetic field to be generated, making them more suitable for applications such as electromagnets. Lower permeability metals, on the other hand, are better suited for shielding against magnetic fields.

5. Can metal permeability be changed?

Yes, metal permeability can be changed through various methods such as heat treatment, alloying, and mechanical processing. These can alter the microstructure of the metal, impacting its magnetic properties and therefore its permeability. The ability to manipulate metal permeability makes it a valuable property for a wide range of industrial and scientific applications.

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