Method for on-line welding repair of blast furnace charging bucket with coal gas

The method comprises the following steps that two steel plates are cut through gas cutting according to the outer diameter size of the blast furnace charging bucket, holes are formed in the two steel plates respectively, and phi 25 threading steel pipes are welded to the hole cutting positions; during blast furnace nitrogen pressure equalizing, one end of each steel plate is welded to the charging bucket shell, the two steel plates are wrapped on the charging bucket shell through a chain block and a steel wire rope, and a valve is installed on the threading steel pipe; opening an exhaust valve to exhaust, opening a gas inlet valve to connect a nitrogen hose to continuously purge and drive air in the space, enabling nitrogen to inhibit the formation of a gas explosion limit, carrying out comprehensive welding, and reducing the nitrogen amount during ending; after welding is completed, the nitrogen pipeline is dismantled, the exhaust valve and the air inlet valve are closed, and the overall cladding repair weld