This kind of rust is normal and as was stated, it's called surface rust. This light layer of rust actually prevents rust from forming... I know, sounds crazy!

It's the same principle as Aluminum and how it gets a light haze of oxidation on the surface. That light haze actually protects the metal from there on out.

It's perfectly normal.. Trust me! I run a boat and my trailer leaf springs and axles get dunked every time in salt water. They're doing fine and after the light rust set in, corrosion stopped... Now, if' you're pulling substantial chunks out and there is definite corrosion going on where the metal integrity is being compromised, then ya got a problem!

Hope this eases some of your fears...

Later,
Chris