Patent ID: 7707865

Claim:
A flaw detection apparatus for a mother tube which is manufactured by rolling a hollow shell in a mandrel mill having a plurality of stands, comprising a wall thickness gauge installed on the exit side of a mandrel mill for measuring the tube wall thickness of the mother tube along the longitudinal direction thereof in at least one of at least a first rolling direction and a second and different rolling direction of the hollow shell being rolled in the plurality of stands of the mandrel mill and producing a measured value corresponding to at least one of the at least first and second rolling directions, a rolling load measuring device installed in each of the plurality of stands, each rolling load measuring device producing a measured value representing a rolling load for each stand, and a decision unit which determines that a shape flaw has developed in the mother tube after rolling, based on: (1) a determination that the measured value of the wall thickness for any of the at least first and second rolling directions varies locally by a predetermined amount with respect to a wall thickness threshold amount and; (2) a determination that the measured value of the rolling load in any of the stands varies by a predetermined amount with respect to a rolling load threshold amount.