Double walled metal tube, metal band and strip, and method of coating a metal strip

The invention relates to a double walled metal tube comprising a tubular roll formed metal band having a brazing layer between the metal layers of the tubular roll formed metal band, wherein the brazing layer consists of a copper alloy. According to the invention, the copper alloy is a copper-tin alloy, wherein the copper-tin alloy contains 3 - 12 wt% tin. The invention also relates to a metal band for forming such a double walled metal tube and to a metal strip for producing such metal bands, and to a method of coating a metal band and strip.