What are the Yellow Metal Balls Found in Demolished Cryogenic Tanks?

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We are demolishing some old cryogenic tanks and inside them were large metal balls. The metal is very hard and dense and has a yellowish tint. The tanks are large upright and cylindrical. Need information on the purpose of the balls and what material(s) they might be made of. I would appreciate any help.
 
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Could they be made from brass? What stops the balls from dropping into the liquid withdrawl line?
 
It could be brass/bronze type alloy. I apologize because most of the information I am getting is second hand. I was brought into the game late and am trying to deal with a 5 foot orb of metal. I was able to actually find one of the workers who was there when it was removed. He stated that it was not free floating inside of the tank but was stationary. Apparently the orb itself is double walled and might be the actual container for the liquid N2 (similar to a Dewar). If this is the case I am not sure what the purpose of the more traditional outer upright cylindrical tank would be. Maybe as insulation but the tanks were very tall and there would be a lot of wasted space. This material is very dense and hard. When they tried to use a mechanical shear to cut it up (the type mounted to a Track hoe), they were unsuccessful. The cutting blades could not shear the metal but they could pull off small pieces. The issue comes down to a worker protection (especially if we have to take a cutting torch to it) and waste disposition issue.
 
So this is a 5' diameter "double walled" vessel? Let me play back to you what I think you're saying. You have an inner vessel that contains the cryogen, a vacuum space and this second 5' diameter vessel that might be made of brass or bronze, then another vacuum space and then an outer vessel.

If that's the case, it sounds like you may have some kind of vessel with an unconventional radiation shield. These are typically used for liquid helium but I haven't seen a solid shield before. Typically the shield is just a copper foil wrap that's thermally tied into into a shield gas. That shield gas is either a liquid nitrogen shield or the gas that's vented off the tank when it boils. The shield gas could even be supplied by the liquid withdrawl as an option. At any rate, the copper is there to intercept radiation heat transfer through the vacuum space and remove that heat through the shield gas by conduction from the shield to the shield gas piping. Copper is used because it has good thermal conductivity at low temperature. Brass and other copper alloys could also be used. I've not seen a solid vessel used as a shield before, but I don't see any reason it wouldn't work very well as a shield.

So I guess the question is, is this vessel an ultra low heat leak vessel such as might be used for liquid helium or perhaps a type of test vessel used for very low temperature tests?

There are ways of easily identifying what type of metal it is. I've seen hand held 'guns' that look a bit like police radar guns. They fire x-rays (I think?) at the metal and thereby are able to determine the composition. They're very expensive (tens of thousands of dollars) but you could probably get someone with one of these devices to test it for you very inexpensively. It should only take a few minutes if you have one of these. May I ask where the tank is located?
 
We are in Oak Ridge, TN although the tanks themself are a thing of the past, all that remains are two of these orbs. Thanks for the info and advice. Am kicking myself because I should have thought of a hand held XRF (x-ray fluoresence) myself. I used one called Niton (Thermo Scientific?) about 8 to 9 years ago to analyze painted surfaces for lead content. They were fairly new at that time. I probably know some one aroud here that owns one if I ask around. Based on what I am hearing from the workers who were there your guess is most likely correct. It would make sense. I do not have all the history of the use of these tanks nor could I really go into detail. You info helped me make some sense of the tank design and gave me some directions to go. Thanks again!