Best metal or metal alloy for expansion?

[magee913ford]

Hello all. I am not a metal or materials expert and have a civil degree but I have been assigned a task to determine a material which can be used in the details described. Any suggestions would be greatly appreciated. Essentially I am trying to make an 0-ring approximately 6 inch diameter x 0.25" thick. I need something that can expand about 12% without losing its strength. Something malleable is ideal and will still hold an air tight seal after expansion. First thing that came to mind was gold, lead, zinc, or tin. Cost really isn't an issue.

 

[metengr]

Need More information. What is the expected service temperature for the o-ring material after expansion? What are other materials of construction that the o-ring will be placed against?

 

[racookpe1978]

What fluids will it be sealing?
How much movement of the joint and in what direction(s)?
How much pressure is "air tight" and for how long is the seal needed?
If the material - you imply metal! - expands once, does it need to keep sealing as it cools up and down in the future?

 

[magee913ford]

Thanks meteng. Temp not to exceed 450°F but operating will be around 150°F and the ring will be pressed against pretty corroded steel. Idea is to press the "o-ring" into the voids and create the seal. I appreciate your help

 

[magee913ford]

Fluids will essentially be water and gas. We will test the fixture to 1000psi. Not sure what kind of gases but potentially could be corrosive. H2S.. Joint will not move after expanding. Once it is expanded it will remain in that position indefinitely.

 

[racookpe1978]

Expanding a soft o-ring shaped material into corroded steel (base metal) is only going to work once. Once it contracts, the material is not going to re-expand into the exact same location the second, third, fourth, fifth time the system is heated and re-cooled. Result is the material is going to be tearing and pulling as parts get stuck into pockets and rises across the very uneven substrate, and the these "holes" and indents are not going to go back into the place they were before.

You apparently don't want to re-machine the surface to a flat even substrate, probably for time and money reasons, right? At 150 deg F operating temperature, you "might" get away a plastic or resin or epoxy fill very, very carefully applied to the corroded area to make it smoother. (Then sand or polish. Again, better choice is machining it.) Then use a conventional soft o-ring.

But if it is going to go to 450 deg F?

 

[dgallup]

Let me get this straight; you want a metal crush ring? And you want it to seal at 1000 PSI against a corroded surface? Good luck with that. Why not use an elastomeric seal? Even that will have a tough time sealing against a corroded surface but a better chance than metal.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[racookpe1978]

I know I was answering as you added the comment noting that the joint will only move once. If so, that helps, but I am very, very skeptical of success even with a low-strength (very soft) metal that might compress into the holes in the corroded surface.

 

[magee913ford]

May have to go back to the drawing boards. Thanks everyone for your help. This is a great website

 

[ornerynorsk]

There is a product called Xpando, if memory serves, that might just fit your application. It's good for one sealing, then it must be cleaned out of the joint and re-applied every time the equipment is disassembled.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[ornerynorsk]

Oh, it's not metal but the heat range will exceed lead or tin.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[Compositepro]

It sounds like a application where lead wool might be used.

 

[MagBen]

A metal expands 12% without phase/status change? I donot think it is possible. The alloy with the highest linear thermal expansion i know of and work with is called Hi-expansion 72 (72Mn-Cu-Ni) alloy. Linear thermal coefficient is about 29x10^-6 /C from RT to 300F, from RT to 700F, it can be 31x10^-6/C.