Protective coating system for high temperature stainless steel

1. Field of the Invention A method for protecting high temperature stainless steel from coking and corrosion at elevated temperatures in corrosive environments, such as during ethylene production by pyrolysis of hydrocarbons or the reduction of oxide ores, by coating the stainless steel with a coating of MCrAlX in which M is nickel, cobalt, iron or a mixture thereof and X is yttrium, hafnium, zirconium, lanthanum or combination thereof deposited onto and metallurgically bonded to the stainless steel by plasma transferred arc deposition of atomized powder of MCrAlX. The coating has a thick, dense, continuous and smooth transition region providing an effective metallurgically bond of the coating with the stainless steel. The coating retains a relatively high aluminum content which permits generation of an adherent alumina layer on the surface, providing good resistance to high temperature oxidation together with good anti-coking and hot erosion resistance properties.