PURPOSE: To provide a method for continuously applying a protective layer for coating the longitudinal weld seam of metal tubes.

CONSTITUTION: A hot-melt mass continuously passes, as blexible hot-melt threads 28 and 58, the inside of a welding arm 18 of a welding machine, is bent to the inner side of the longitudinal weld seam of the metal tubes, is press bonded by coating applicators 40 and 54, is melted and is applied uniformly over the entire part of the width of the longitudinal weld seam. More preferably the protective layer on the outer side is applied simultaneously with the coating on the inner side, by which the need for a baking or drying oven requiring a large space and energy as in the case of lacquer coating is eliminated. A more advantageous application example of the method includes the coating application of a sterilization-resistant hot-melt strip to the inner side or the inner side and outer side of the longitudinal weld seam of cans for canned goods.