There are several such rust-converter products on the market. I've seen somewhat mixed results, to be honest. It still takes elbow grease to remove as much loose rust and scale as possible for best results. One thing for sure, wear latex gloves! It will stain your skin black!
It seems I love the mountains and deserts more than my friends do. I sure miss them!
1971 Streamline Imperial project "Silver Snausage", 1985 Coleman tent trailer, 1964 Little Dipper, 1975 Northwest "Proto Toyhauler", 2004 Harbor Freight folding, still seeking my Airstream.