METHOD FOR LOCALLY ANNEALING WELD ZONES OF TUBE GROUP

摘要

PROBLEM TO BE SOLVED: To provide a method for easily locally annealing weld zones of a heat transfer tube group in a heat exchanger consisting of the long-length heat transfer tube group of ferritic high strength heat resistant steel containing >=9% Cr without giving damage caused by an excessive tensile load to the heat transfer tube system regardlessly of the structure of the weld zone. SOLUTION: When a stub tube 7 welded to a header 1 and the butt weld zone 5 of heat transfer tubes 2 are locally annealed, a box heater 6 is set with the butt weld zone 5 as the center. Further, a compact auxiliary heater 11 is set so as to be close to the header side face 13 on the side opposite to the weld zone 5 to the central axis 12 of the header 1. The temperature measuring point 9 on the side of the weld zone at the side face of the header 1 and the temperature measuring point 10 on the side of the auxiliary heater are decided. The temperatures in the temperature measuring points 9 and 10 are measured. The butt weld zone 5 is locally annealed while controlling power supply to the auxiliary heater 11 so that the temperature difference between the measuring points 9 and 10 is within a tolerance.