Abstract: For removal of the sludge deposits on the tube sheet of a steam generator which comprises, in a vertical cylindrical enclosure closed by said sheet, a bundle of parallel heat exchange U-shaped tubes sealingly connected to said sheet at both ends and distributed to form parallel sheets of tubes, a lance is radially moved from the center of the tubular plate between two parallel sheets of tubes rather than in the tube lane. Movement occurs in a direction parallel to the tube sheet and in close proximity to the latter. Two streams at least of cleaning fluid under a high pressure are directed toward the plate from the end portion of the lance and in directions which are fixed and symmetrical with respect to the direction of the two sheets of tubes. The streams are cut off as they confront the tubes during radial movement of the lance. And the cleaning fluid is flown out of the enclosure of the steam generator from the periphery of the bundle of tubes.