An elongated tool device adapted for use in installing a tubular sleeve within a tube and forming a pressure-tight seal therebetween. The tool device includes a housing having a reduced-diameter forward extension portion attached to a front cylinder, and containing a rear piston. The front cylinder is attached to a collet having multiple radially expandable fingers and contains a front piston attached to a tapered mandrel which is axially movable within the fingers, and has a forward tapered nose portion to facilitate inserting the tool into a tube. The rear piston is attached to the front piston by an elongated rod. By pressurizing the tool front piston by a hydraulic fluid pressurizing unit, the mandrel is forced forward through the collet fingers to expand the fingers and sleeve tightly into the tube to form the seal joint. After withdrawing the tool from the tube, the tool rear piston is similarly pressurized to retract the front piston and attached mandrel back through the collet expandable fingers to reset the tool prior to its further use. A method for utilizing the tool device to locate a sleeve within a tube and then pressure-tightly seal the sleeve within the tube is also disclosed.