A tube expanding technique for securing a sleeve within a tube whereby fluid pressure is applied via an expander by incrementally decreasing the volume of the fluid system exclusive of the expander, or by incrementally increasing the mass of the fluid within the system. The system pressure and the rate of pressure increase as a function of incremental change in volume, or mass, are monitored. A decrease in the rate is indicative of the onset of plastic expansion of the sleeve or tube, as the case may be. By determining this point, the outer diameter of the tube may be accurately controlled to within six thousandths of an inch. A tube expanding device including a distensible sealed bladder for applying the expanding pressure and containing the system fluid.