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Plating onto rusted steel procedure?

we are upgrading some Caterpillar marine diesel engines and have steel expansion tanks (coolant) that are pitted and rusty internally. Instead of replacing them (very expensive), is there a metal coating (chrome?, nickel?) we could bond to the entire part (inside and outside) that would retard further corrosion? in other words, is it possible to plate onto rusted/corroded steel surface?

BENJAMIN Victor
osf - irvine, California, USA
2003

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A qualified "no" to that. It is possible to repair pits or other small damaged spots one at a time by brush plating with nickel and then grinding smooth. And it's also possible to clean a rusted item and electroplate it or electroless nickel plate it. But the general concept of trying to electroplate rusted steel to restore its integrity is probably impractical.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

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No matter what you do, you must start by removing all the rust and getting back to bare metal. In all metal finishing operations, the key to success is good surface preparation; any cutting of corners here will result in premature failure of your hard work. I agree with Ted that it is probably impractical to do a remetalling job, but perhaps you may consider lining or spraying the tank with a corrosion resistant resin such as epoxy paint, butyl rubber or something similar. However, you must first remove all the rust. I have no idea how big your tank is, but it may be feasible to thoroughly clean it with a good steel wire brush and then remove the final bits of rust with a suitable acid. I recall seeing in a very old edition (probably published just before or just after WW2!)of "The Rubber Book" a formulation for removing rust and passivating the steel surface. I think it was based on sulfuric acid and phosphoric acid, but I am not sure. When I used it (30 years ago! !), I remember it turned the steel almost black, but it did the job - at least it kept my old car on the road when I was a student! The phosphoric acid offers protection to the steel by phosphating it. Can anyone else help in remembering this very useful solution?

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2003