Induction heating coil for heat-treating metallic tubes

An induction heating coil for heat-treating a metallic tube by leaving compressive residual stress in the outer surface of the tube, comprising:

• a plurality of electrical conductors for inductively heating the metallic tube, said conductors being hollow and connectable with a source of cooling water to allow cooling water to be supplied through said conductors during induction heating of the metallic tube, each of said electrical conductors being constructed in the shape of a ring and dividable into at least two segments along its circumference to allow said segments to be assembled around the metallic tube into said ring, said conductors surrounding the metallic tube and being spaced apart from each other a predetermined distance in the longitudinal direction of the metallic tube when said conductors are assembled around the metallic tube;
• and
• a plurality of cooling water tubes for cooling the outer surface of the metallic tube after having been heat-treated by said electrical conductors, each cooling water tube being shaped in a ring and dividable along its circumference to allow assembly thereof into said ring, each cooling water tube being disposed along a corresponding one of said electrical conductors and having in its outer surface a plurality of nozzles for forming water jets which produce an essentially uniform film of water on the metallic tube so as to uniformly cool said surface, said nozzles being inclined with respect to the outer surface of the metallic tube.