A process for producing a metallic protective layer whereby a metal-containing plating, cladding, paint or other coating is applied to at least a portion of a reactor system and then contacted with a gaseous stream containing hydrocarbons, such as impure hydrogen, thereby producing a continuous and adherent metallic protective layer. The gaseous stream preferably comprises hydrogen, which may be recycled. A preferred embodiment of the invention is directed to touch-up procedures where a portion of an already protected reactor system is replaced or rewelded and the protective layer is formed as the replaced portion is brought on-stream.