During the design of the boiler, the air in the container should be excluded in the manufacture, installation, maintenance and test of the boiler water pressure. Therefore, air pipes are designed in the drum or saturated steam lead, superheater, reheater and connected tubes. Many times, the air pipe leakage accident will occur after the boiler is put into use. Most of the leakage parts are the butt weld of the air pipe and the pipe joint and the angle weld of the air pipe and the air pipe. The causes of leakage are as follows: the air pipeline is usually discharged by the installation unit according to the site conditions, and the various kinds of supervision and inspection do not pay attention. There are many defects, such as the no slope, the counterpart deviation, the opening of the pipe as the gas cutting, the weld slags, the air hole and the non penetration, and the internal defects are developed into the leakage due to the vibration and thermal stress in the operation. Leakage.