Phosphoric acid question

[GSJake]

I filled my rusty tank with a 1 part phosphoric acid 2 parts water solution. Does anyone have an idea how long i need to leave the solution in there to get rid of all the rust?

[uudfourty]

Until all of the rust is gone.:-D

Actually, I have no idea. But I'm sure someone will come along and deliver a fact rather than a smartassed comment.

[J_C]

It really DOES depend on how much rust you have. Peek in periodically to check it out

[Nessism]

How long depends on how strong the acid is and how much rust.

I used POR metal clean (phosphoric acid) in one of my tanks and it took several days - rotating the tank several times each day. The rust was eventually converted but it left a chalky residue on the metal. Dumped in a bag of aquarium rocks, along with some denatured alcohol followed by vigorous agitation, and the tank came out clean. I don’t trust the metal to stay rust free after all this monkey motion so I used Caswell tank sealer to lock it all down.

The key to doing this job is to come up with a positive way to seal off the tank while the solution is doing it’s job. I used a rubber stopper in the main tank opening and a plate with rubber gasket over the petcock holes.

Good luck.

[themess]

I worked in a factory that made oil seals. One of the early stages was making steel stampings. The steel coils often had some rust on them. Steel can get quite warm when it is stamped, which increases the rate at which it rusts. Stamping oil covers the parts, but it only slows rust, it won't eliminate it. So we had to remove rust all the time. Roughly about a half ton of parts were put into a cylinder with perforated walls. This was put into a tub of hot caustic (sodium hydroxide, pretty concentrated) to remove the stamping oil. The caustic was washed off, and it was then put into phosphoric acid to remove rust, then into a solution that would leave a phosphate coating that both inhibited rust and left a surface that rubber adhesive and rubber would stick to. Finally, it went into a rubber adhesive.

If one trip through the bath didn't removed all of the rust, we'd run it through again and again. Once in a while something was too badly rusted, and we'd have to throw it out, but that was rare. So try it, and look at it, and try it again until you can't see any rust, then leave it about twice as long to get the stuff that you can't see.