JPS5669327A - Annealing method of seam welding portion of electric welded tube - Google Patents

Abstract

PURPOSE:To save energy and permit an effective annealing by disposing a plurality of heating devices at a predetermined interval in accordance with an even heat keeping time required in advance in a moving direction of a pipe and annealing it in a preset heat pattern. CONSTITUTION:In annealing of a seam welded portion 3' of an electric welded tube 3, in a rear stage of a seam welding machine 1 of an electro-unite production line, for example, three sets of heaters 21, 22, 23 are disposed at a predetermined interval 11 in a direction of a line considering a preliminarily obtained uniform heat keep time required (t) based on a tube production size, material, tube producing condition and the like. When said tube 3 subjected to welding is fed said portion 3' is heated in the first heating area K1 by said heater 21, then stopped heating in the first cooling area L1, heating and heating stop are repeated during the movement of the tube, and said portion 3' is annealed in a wave shape heat pattern relatively small in difference between maximum heating temperature T1 and minimum heating temperature T. Thus, an effective annealing obtained without raising the maximum heating temperature more than necessary.