THE biggest mistake made in ID scarf blowout operations is over-sizing the blowout portion in an attempt to remove 100 percent of the ID scarf scrap. This isn't meant to imply that 100 percent ID scarf removal isn't desirable, but that oversizing the blowout is based on a misconception. The culprit in this scenario is an attempt to compensate for deficiencies elsewhere. When the weld seam and the ID bead scarf mandrel are not in line with each other-when either of them moves away from the normal (12 o'clock) position-the scarfing process does not cut the weld bead from the tube wall completely. When the cutoff process has welded the ID bead to the pipe end inadvertently, no amount of compressed air or water can remove it. You might get lucky and break the strand free from the tube wall or tube end, but the tube is still a candidate for rejection. Remember, it takes just one unscarfed section hanging onto an inside bending mandrel to cause a customer to reject a truckload of pipe. The bottom line is the ID scarf scrap must be free to exit the tube for the blowout process to be successful.
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