The method for making cold-drawn seamless pipes involves taking a round "billet" or bar of steel and boring it in the center, turning it, cutting it, heating it to make it more pliable, then "drawing" it (extruding or pulling it) to make it a longer and thinner tube. As the tube cools, "cold working" begins. Cold working involves pulling the tube over a stationary die and a mandrel. This increases the pipe's hardness and improves its surface condition and grain structure while reducing the pipe to the desired size and thickness.
By Laurie J. Brenner