Abstract: A pressurized-fluid workhead for permanent belling of end portions of plastic pipes. A die has a cavity for receiving a thermally plasticized end portion of a pipe. A forming buffer is insertable into the end portion of the pipe and arranged centrally of the die. A flange is mounted coaxially and slidably with respect to the buffer and die and has a striking surface which can be associated to an edge of the end portion of the pipe. Sealing elements are located on the die and the buffer. These interact with an external surface and an internal surface of the end portion of the pipe. The die, the buffer and the flange together peripherally define a forming chamber for the end portion of the pipe. The forming chamber is subdivided by the pipe into first and second pressure chambers for a fluid. The first pressure chamber is arranged between the lateral surface of the buffer and the internal surface of the pipe.