Abstract: The invention provides a composite protective coating applied to a steel pipe, the coating comprising an epoxy resin primer bonded to the outer surface of the pipe, a polyolefin outer sheath, and an interlayer consisting of a mixture of epoxy resin and polyolefin. The composition of the mixture forming the interlayer is graded throughout its thickness, being substantially all epoxy resin adjacent to the primer coating and substantially all polyolefin adjacent to the sheath.

Abstract: Two methods are provided for applying and forming a protective composite coating on a metallic substrate. In the first method, the substrate is heated to a temperature between about 175.degree. C. and 275.degree. C. and a powdered coating of epoxy resin between 100 and 400 microns thick is applied to the outer surface of the heated substrate. A premixed powder coating of epoxy resin and polyolefin is applied directly onto the epoxy resin coating, forming an interlayer of interspersed domains of epoxy and polyolefin between about 100 and 400 microns in thickness. On to this, powdered polyolefin is sprayed to produce a polyolefin sheath coating for the metallic substrate between 200 and 1000 microns in thickness. In the second embodiment of the method, the interlayer is formed by spraying pure epoxy resin powder and polyolefin powder from separate sources simultaneously onto the substrate. By these methods, a metallic substrate coated with a composite epoxy/polyolefin protective coating is produced.