(57) [summary] [purpose] even when large temperature difference between the high temperature side of the furnace wall tube and the cold side of the furnace wall tubes, cracking of the occurrence of by reducing it due to the stress to the both furnace wall tube to be able to prevent, and is to provide a reinforcement structure around the boiler furnace wall tube fin end portion to be able to make long lifetime. [Configuration] high-temperature side of the furnace wall tubes and cold side of the furnace wall tube, both made from the cross-section square tube with a square, and the upper end portion is welded to the fin, the furnace one sides of the high-temperature side is welded to the outer surface of the wall tube, the other side is welded to the outer surface of the cold side of the furnace wall tubes, and a tapered plate provided so as to cover the vicinity of the fin end portion partially.
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