I replaced a water heater that was leaking. I've never had a w/h tank leak before.
It seems we had an electrolysis problem. The copper water lines to the w/h were directly attached to galvanized nipple and brass valve respectively, and had balls of corrosion growing on them the size of tennis balls.
Can this also damage the walls of the tank?
I had a similar problem about 10 years ago. I replaced a water heater tank and did not use dielectric unions. Within two years the fittings were so badly corroded the tank leaked, and could not be salvaged. My bad, I should have used the proper fittings. As to damaging the interior of the tank, I have no idea what mine looked like, however it was irrelevant since the threaded fittings were so badly corroded I could not get a seal.