What commonly available alloy has the best corrorsion resistance properties?

There are a lot of good suggestions in this thread. Having said that, I think it is unlikely you will be truly successful making something that will last 500 years if you just get a bunch of opinions and don't spend any further effort on it. At minimum, you need to do a bunch of research to find out what applicable work has been published. I'll be so bold to suggest you might actually want to do some accelerated aging tests on sample containers.

The shell material is one issue. Two others are seals and environment. You've mentioned seals--again, how in the world do you know your seal material will last 500 years (more research needed...)? How do you know it will be indoors all that time? Will the building last 500 years? If you really expect 500 years out of it, you need to protect against the possibility it won't be indoors.

There was a new motel going up near work about 10 years ago. The building frame and walls were up (no exterior finish yet, insulation hanging out), lots of window holes, many covered with plywood, looked pretty ratty. My friend Phil says "Just think, in 100 years, it will look exactly the same".

Steve

James wrote:

Your concern about corrosion is not understandable. Stainless should withstand thousands of years without any type of preservation under the conditions you've described. . Simply have it passivated after it has been manufactured. I doubt you'd see enough change in the appearance in 100 years to know it's even been stored. I have remnant pieces that I've had for well over 30 years, all of which went through 4 years of storage in a damp container. They don't look any differently today than they did 30 years ago, and they didn't have the luxury of being passivated. That's the beauty of stainless.

You're on your own where seals are concerned, but I think I'd research various O ring compounds. Surely one of them would suit your needs.

Harold

CD's and DVD's don't last forever. They sometimes don't last very long at all. There is a fair bit of info on the web.

There is also a serious consideration of how you will ensure there will be equipment to read your storage media available and working. This could easily be a problem in 20-50 years.

Steve

James wrote:

I agree that stainless is a bargain in the short term. If you figure cost in relation to time monel is cheap compared to stainless. I've seen 80 year old monel deck hardware (chocks and cleats) look and act like it had been installed last week and I've seen 5 year old stainless deck hardware (chocks and cleats) look like it had been installed last week, but act like it was made of peanut brittle.

Eide

Excuse me if this is repitition (I haven't read this thread), but stainless is vulnerable to stress-corrosion cracking, especially in a marine environment. If it's under constant load and it's exposed to salt water, or even to salt air, it's likely to fail sooner or later.

OTOH, I have monel trolling lines that are now 50 years old and they don't break. That isn't constant load, of course, but it's remarkable nonetheless.

-- Ed Huntress

Monel is good stuff, I've been using a 55 gal monel strainer for a burn barrel for 30 years and it was old when I inherited it.

James, the ultra-whacko Scientologists use titanium sheets or something like that to keep the priceless mumblings of their drug-ridden founder for future alien invasion fleets to read. They have oodles of money (hint: get stupid rich folk like Cruise and Travolta to sponsor you) and probably have done a lot of this preservation research already. Google them and you might find something useful...

You should use a commercially available copper ConFlat high vacuum seal. No elastomers and it will provide an excellent leak-tight seal.

Jim

That shouldn't be an issue in the circumstances described. Salt water is tough on stainless because of chlorine. There should be none of that present as the device was described. For that reason, the expenditure for monel is likely a waste. Remember, the original post said: "I cannot afford some rare exotic metal." My one inquiry on monel a few years back disclosed a price of something like $15/lb. Could be it's more now, what with copper prices having gone through the ceiling.

Monel would raise the cost of materials in excess of 400% as opposed to stainless, and would likely serve no better. Were it used on a boat that saw a sea environment, I'd agree with you.

Harold

Just include plans to build the retrieval apparatus.

.......... ... ..

A hard copy of the plans on archivally correct paper.

C'mon, a lot of that is readily available. I still have a perf tape reader, and recently disposed of a working 8-track player. The card readers went out years ago, but you can physically read cards by looking at them! Still need to read 8" or

5.25" odd format floppies? I'll sell you a Compaticard disk controller, the drives, and Uniform software to do it. 8mm and 16mm movie projectors show up at garage sales all the time. If you don't have a Beta VCR (I have 3) there are services that will transfer the tapes to another format for you.

I'd avoid using something completely proprietary for long term storage. But you can still get 7 and 9 track computer tapes read if you want. Odds are pretty good that you'll be able to read standard CD's and DVD's in 50 years if the media don't deteriorate significantly.

I'm a s> The problem with long term media storage is not deterioration but lack of

The New York Times (Magazine?) commissioned a time capsule for the Millennium (2000), and wrote a long article that appeared in either December 1999 or January 2000. The capsule was intended to be opened in

1,000 years, and was made of investment-cast stainless steel.

Joe Gwinn

Chuckle!

I assume you have proof they really existed? Allow me to be the first to step forth and say BS.

There's not so much as one thing in the Book of Mormon that can be verified scientifically. The Bible has a much better track record, and even it's suspect.

Harold

He'd be crazy to use elastomer O-rings when commercial conflat flanges are there.

They use a flat OFHC gasked which is trapped between two stainless knife edges. They will withstand high temperatures, low temperatures, and unless the thick flat copper gasket completely rots away are quite long-lasting I would think.

Jim

I prefer Thomas Jefferson's edition, the one he edited with a pair of scissors.

-- Ed Huntress

Hard to argue with that, Jim. I'm not familiar with them in the least, so I had no clue. When I think about it, a dead soft copper gasket alone would likely serve quite well, assuming the surfaces were well prepared. It wouldn't take much in the way of creativity to machine some sealing grooves on the lid.

Harold

But bear in mind that the gaskets *must* be replaced every time you open it for inspection. So -- be sure to stock enough gaskets to deal with the inspection schedule, as replacements may not be available one hundred years or so down the line.

The O-rings, however, can probably be re-used some number of times -- if you can find a material which satisfies your other requirements.

Enjoy, DoN.