additives and fillers usually used in fluoropolymers a common pvdf plasticizer a dye or an acrylic impact modifier or triblock copolymer which may be chosen from the impact modifiers of l1 described above may also be added the proportion of impact modifier in this layer 3 may be from 5 to 15 parts by weight per 95 to 85 parts respectively of fluoropolymer the thicknesses of the various layers may be from 50 to 150 u03bcm for the layer 1 from 100 to 500 u03bcm for the layer 2 and from 1000 to 5000 u03bcm for the layer 3 the thicknesses are preferably in u03bcm starting with the layer 1 80 250 1500 the metal surface may be of any type however the invention is particularly useful for the outer surface of tubes these tubes possibly having an outside diameter for example of up to 0 8 or 1 5 m and a thickness of from 2 to 25 mm as regards the coating of tubes the preferred process breaks down as follows preparation of the steel tube degreasing shot blasting and optionally surface treatment chromatation etc treatment of the tube in an infrared oven so as to reach a temperature of between 180 and 220 u00b0 c application of the epoxy primer powder.