Corrosion Pits

Q. What is the best procedure for replacing hard chrome on carbon steel substrates that have corrosion pits 0.10” in depth? The issue relates to hydraulic cylinder repair where extensive grinding would exceed base material removal tolerances. The vendor has proposed nickel plating and grinding before chrome plating. What are my options in this case?—B.N.

A. Filling in pits tends to be a challenge, and a pit with a depth of a 0.10” is even more of a challenge than what is routinely found. The vendor’s suggestion of nickel plating the cylinder and then grinding back to specification might work. Usually for non-critical work, copper is used for this purpose, however. Copper is softer than nickel and easier to machine. But whether this would work for hydraulic cylinders that are a more-critical application is dicey. You don’t say whether there are a few pits on the surface of the hydraulic cylinder or if the pits are distributed over the entire surface. If there are only a few pits on the surface, you would save yourself a lot of grinding by selectively plating the pits and building up the deposit in the pitted areas. You would only have to grind the areas that are plated. If the entire cylinder is pitted, the entire cylinder will have to be ground to specification. This is a more labor-intensive process, and your client might not want to drop the money involved.

If any readers have a suggestion for solving this problem, please let me know.