Method of manufacturing coiled tubing using multi-pass friction stir welding

A method of manufacturing coiled tubing, said method comprising:

• a. aligning end portions of two sheets of metallic parent stock so that a flush seam is established therebetween, said seam comprising a portion of each of the two sheets of parent stock;
• b. attaching a run-on tab to a first side edge surface of each of the two sheets of aligned parent stock, thereby forming a first tab interface;
• c. attaching a run-off tab to a second side edge surface of each of the two sheets of aligned parent stock, thereby forming a second tab interface;
• d. making a first friction stir welding pass, traversing said first tab interface, said seam, and said second tab interface, using a tool rotating in a first rotational direction and moving in a first longitudinal direction, thereby causing said seam to temporarily plastically deform, wherein a first edge defect is formed on an advancing side of the first friction stir welding pass within one of the sheets of metallic parent stock adjacent to the first tab interface, and wherein a second edge defect is formed on an opposite retreating side of the first friction stir welding pass within the other one of the sheets of metallic parent stock adjacent to the second tab interface;
• e. making a second friction stir welding pass offset from the advancing side of the first friction stir welding pass but within weld metal created during the first friction stir welding pass, traversing only said first tab interface using a tool rotating in a second, opposite rotational direction and moving in a second, opposite longitudinal direction, while said seam remains plastically deformed, thereby removing the first edge defect;
• f. making a third friction stir welding pass offset from the opposite retreating side of the first friction stir welding pass but within weld metal created during the first friction stir welding pass, traversing only said second tab interface using a tool rotating in said second, opposite rotational direction and moving in the first longitudinal direction, while said seam remains plastically deformed, thereby removing the second edge defect;
• and
• g. allowing said seam to cool in such a manner that the two portions of parent stock metal are thereafter seamlessly joined.