On 5/5/2013 9:51 PM, Doug Miller wrote:
woodchucker wrote in
:

Well, this tank hadn't been used for years the owner said. I let the
water out of my tank weekly, how long do you let it sit there.
I figure that years of sitting means deep rust inside. Based on the
stink of that water, I'd have to say it's been in there a long time.

When there's a lot of water in the tank, "hadn't been used for years" is waaaaay better than
"used it every week".

Water, by itself, doesn't cause rust. For iron to rust, two things are necessary: water and
oxygen. Once all the oxygen in the tank has been converted to iron oxide, there will be no
further rusting.

Case in point: hydronic (hot water) heating systems -- such as the one in my house --
typically have cast-iron boilers, and many (mine included) have cast-iron radiators as well.
Water normally sits in these systems for *decades* without any damage to the cast-iron
components. Yes, there's some rusting internally, but not much. Once the small amount of
dissolved oxygen is used up, the rusting process stops.

I would believe that a cast iron boiler is several times thicker that an
air compressor tank. I am sure the radiator is.