Patent ID: 8056797

Claim:
A mandrel for use in friction stir welding of a pipe, said mandrel comprising: a mandrel shell formed as a hollow cylinder having an outer diameter that is smaller than an inner diameter of the pipe, wherein the cylinder has a gap therein that is perpendicular to a top edge and a bottom edge; a means for expanding the mandrel shell such that the gap widens to a desired width, the means comprising at least one hydraulic actuation device; and a wedge coupled to the at least one hydraulic actuation device and disposed so as to widen the gap by being inserted into the gap when the at least one hydraulic actuation device is actuated; and two lips welded onto the inside diameter of the mandrel shell, each lip disposed adjacent to and on either side of the gap such that the wedge contacts both lips as the wedge is inserted into the gap and continues to be pressed against the lips, wherein the wedge slides outwards through the two lips and the mandrel shell continues to expand until the wedge or the mandrel shell makes contact with the inside of the pipe.