Patent ID: 8550326

Claim:
A mandrel for use in friction stir welding of a pipe, said mandrel comprising: a plurality of hollow tubes; and at least two expandable mandrel shell stations coupled to the plurality of hollow tubes, each station separated from another by a station gap, and each station comprised of: a platform coupled to the plurality of hollow tubes; an expandable mandrel shell formed as a hollow cylinder having an outer diameter that is smaller than an inner diameter of the pipe, wherein the plurality of hollow tubes are coupled to the expandable mandrel shell, and wherein the expandable mandrel is disposed directly against a seam in a pipe in order to provide a force on an inside diameter that counteracts a force applied by a friction stir welding tool moving along the seam on an outside diameter of the pipe; wherein the expandable mandrel shell has a gap into which an expanding wedge is inserted, the expandable mandrel shell having two lips, each lip disposed adjacent to and on either side of the gap; a means for coupling edges surrounding the gap to the expandable wedge, wherein retracting the expandable wedge from the gap causes the edges surrounding the gap to move toward each other; a first and a second post disposed in first ends of the lips; a third and fourth post disposed in a first end of the expandable wedge; and a cable coupled to the third and fourth posts, and disposed around the first and second posts, wherein retracting the expandable wedge from the gap causes the cable to close the gap in the expandable mandrel shell; and a means for expanding the expandable mandrel shell by pushing the expanding wedge into the gap such that the gap widens to a desired width, the means being disposed on the platform.