Rusted areas on a painted steel frame could also be treated with a phosphoric acid based rust passivator
after sanding with steel wool or scotchbrite down to the metal. Allow this to dry and then touch up
paint over this. In a pinch cola or dew soft drinks are basically low % phosphoric acid and will work if given
time, but area should be rinsed to remove other flavorants before painting. See youtube for cola based
rust treatment if interested.
Yes the phosphoric acid. Navel Jelly, Extend or auto body supplies rust etch.