Abstract: For the purpose of compressing by hammering a steam generator tube (1), a stream of gas at high velocity charged with particles having a particle size of between 50 and 500.10.sup.-6 m, is directed onto the inner surface of the tube (1) in radial directions and onto the whole of the periphery of the tube. The flow of the mass of the particles is higher than 0.008 kg/sec for tubes having an inside diameter of around 0.020 m. The device comprises a flexible sheath (20) movable inside a case (16, 18) fixed in a sealed manner under the tube plate (2) around the tube (1). An injection nozzle (21) is disposed at the end of the sheath (20) receiving the gas charged with particles.