To locally clean only the black skin generated on the inner face of a pipe by welding, etc., by inserting the sealing devices connected to surround the opening of the pipe and the area to be cleaned into the pipe, expanding the devices to the inner face by air to seal the space between the devices and cleaning only the inner face from the opening.

The sealing devices A1 and A2 are drawn into a pipe with a wire 15 so as to place the socket 18 of the pipe 13 and the black skin C between the devices A1 and A2. Air is supplied to an air hose 17 from the outside to expand the rubber band of the devices A1 Aand A2, and the space between the devices A1 and A2 is sealed. A claning hose 14 is then inserted into the pipe 13 from the socket 18, a cleaning soln. to remove the black skin C generated when the pipe 12 is welded to the pipe 13 is filled or injected from the hose 14 to remove the black skin C, and the waste liq. is discharged from the hose 14.