OT. Rust removal in gas tanks

"Balders" wrote: I remember reading on here about removing slight rust from petrol tanks. (clip)I think muratic (SP?)

I'm surprised no one has responded to this. Muriatic acid will remove rust--its chemical name is hydrochloric acid. But I hesitate to see you try it. It is fairly aggressive against steel--if there are any pits or thin spots, it could eat through. I have used a product called Evaporust, which does a beautiful job of dissolving rust, without attacking the underlying metal, and which is not even hard on skin. It is made by a US company, and I'm not sure whether it is available where "petrol" is sold.

Phosphoric acid is used commonly to change iron oxide to iron phosphate, which does not spread. It will probably attack whatever zinc galvanizing is still there. I would have it cleaned with caustic soda at a radiator shop, dry it well with acetone, and coat with Red-Koat or a similar slosh compound. I have done plenty of them.

Thanks guys. I have Phosphoric acid (Jenolite is a properitery brand in the UK) & also caustic soda. Now I have two solutions (sorry 'bout that ;-) ). It's only a surface rust, more like spots than the entire surface.

Electrolysis is a much better idea than acid dips.

You'll need to arrange an internal electrode though, and make sure it doesn't short out against the tank. I used a length of steel chain pushed through a length of plastic pipe. Place the tank vertical with the tank filler facing horizontally, then stick the pipe through horizontally. The chain can now dangle vertically on the inside, without touching anything. Repeat with it the other way up.

Ummm, sounds interesting! What would you use as electrolyte? ISTR reading about using washing soda, that had totally slipped my mind. Would a 6 amp battery charger be sufficient?

Google has been my friend. Thanks guys.