| 摘要 |
A metal structural element such as a pipe or tube is provided with a plurality of protective layers including an external sheath of thermoplastic resin surrounding and in contact with a layer of viscous adhesive. The tube may first be coated by immersion in bitumen, which is smoothed by passage through a ring, and a layer of viscous adhesive is applied similarly. The adhesive may comprise a mixture of resinic acids, e.g. abietic or pimaric, with saturated fatty acids, e.g. myristic or palmitic, non-saturated fatty acids, e.g. those having from 20 to 22 carbon atoms per molecule, and blown bitumen. One or more layers of thermoplastic resin, e.g. vinyl resin, are then applied in an extrusion zone. The metal element may be pre-treated by pickling, sand-blasting or peening.
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