Abstract: There is provided an apparatus for forming a weld joint between abutting ends of first and second tubular members. The welding apparatus includes a support ring defining an aperture therethrough. The support ring has first and second sides defining a channel therebetween. The first and second sides of the support ring define a plurality of supports spaced about the circumference of the support ring, each of which defines a gripping surface for contacting at least a portion of the exterior surface of a corresponding tubular member to thereby secure the abutting ends of the first and second tubular members at least partially within the aperture of the support ring. The welding apparatus includes at least one friction stir welding tool, which is movably and rotatably mounted within the channel defined by the support ring and projects toward the abutting ends of the first and second tubular members.

Abstract: An apparatus and method for friction stir welding a seam in a hollow container from the inside. The apparatus includes a weld head convertible between a retracted state to an expanded state. The retracted weld head fits through an opening in the container and then expands to enable formation of the weld. The weld head includes a frame and a least one friction stir welding spindle convertible between a retracted position adjacent the frame and an expanded position away from frame. The container may be a pressure vessel tank, with a circular weld being formed between a tubular mid-section and a hemispherical end cap. Desirably, multiple friction stir welding spindles that expand into a common plane are provided, and relative rotation between the weld head and container forms the circular seam. Force balance arms intermediate adjacent friction stir welding spindles expandable to contact the interior of the container may also be provided to help maintain the position of the weld head.