Originally Posted by Luddite

Hydrochloric acid (up to a 10% solution) is used to clean titanium but it is recommended that it is used with a corrosion inhibitor (such as ferric chloride) to protect the metal. Having said that, an inhibitor is also recommended when using hydrochloric acid to clean stainless steel but, for our purposes, with the frequency we use it and the short time the acid is in contact with the metal, I don't think we need to worry.

If you are concerned, citric acid (for descaling kettles, etc.) used in a 25% solution, or nitric acid in a 10% solution can be used with no need for corrosion inhibitors.