As a specifier in the Petrochemical Industry, sometimes when working on Live Plant, we have to specify 'Non Impact' methods of surface preparation, we use Chemical Rust Removers after scraping the Loose Flaking or "Scabbing" Rust from the surface. These Rust Removers are not to be confused with Rust 'Convertors' They are not Single 'Solvents' but a 'chemical cocktail'
As an Example, we here use A.I.C. Rustex Gel succesfully, this is available from a company called A.I.C. their internet site can be found at:
Another useful contact is Trond Sivertsen, at a company called 'Sea to Sky Innovations' e mail is: trond.sivertsen@sea2sky.no This company has a fistfull of Useful chemicals, a couple of which are rust removers.
Hope this Helps....