A method of manufacturing a coiled tubing string including uncoiling a flat metal sheet from an accumulator; bending the flat metal sheet that is uncoiled from the accumulator into a tubular form such that the edges of the flat metal sheet form a seam along a longitudinal length of the tubular form; welding the seam formed along the longitudinal length to form a tubing string; and coiling the tubing string onto a spool, wherein the tubing string is heat treated to meet specified material properties in a continuous operation from the accumulator to the spool.