If you dispense your beer with a party pump, which uses air instead of CO2 to drive the beer, you can only expect your beer to remain fresh for 8-12 hours. If you keep your kegs warm, and drive them with CO2 through a jockey box or other faucet, they will most likely last a couple of months.
Rust by definition is the result of the oxidation of metal. One engine manufacturer refers to the process of corrosion in aircraft engines as galvanic corrosion which is a type of corrosion caused by dissimilar metals being in close proximity of each other. In this process an electrolyte such as water also needs to be present. Almost all metals will oxidize or corrode.
Corrosion is one of the main causes of reduced reliability in steam generating systems. It is estimated that problems due to boiler system corrosion cost industry billions of dollars per year. Many corrosion problems occur in the hottest areas of the boiler-the water wall, screen, and superheater tubes.