Where is the disagreement?   Looks like about the same answer except your example is at approximately twice the application rate and therefore half the acres.     It does look as if I stated 100# N when I meant 100# NH3 though. 

Ammonia is non-corrosive to mild steel.  It plays heck with some other materials.   It will remove paint if it drips down from a leaky fittting, I think mostly due to the extreme temperature.  This is especially a problem the first couple years after the tank is painted, seems to become more durable as it ages.   The N Serve is what ruins tanks and equipment.   It doesn't go into our tanks.  

Most NH3 tanks you find on lots around here will have ASME plates dated in the '60s and be on their second or third set of running gear.  I can't say that I have ever seen one which was retired unless it was a 500 gallon.  Lots of them are around converted to air tanks or (this ought to give you something to talk about, Mike  lol:) LP.