Abstract: A method of nondestructively inspecting a magnetic substance such as metal pipe and bar stocks, wherein the method provides a detection coil having a diameter which is specified based on the length of existent peripheral surface flaws such that the directional sensitivity of the detection coil relative to those flaws is improved. The magnetic substance is moved along an axis thereof and has an eddy current induced therein. Relative rotation of the detection coil around the magnetic substance is effected to permit detection of surface flaws.

Abstract: A method of producing a stepped tube, the method including the steps of preparing a straight mother tube with a stepped wall portion of a smaller inside diameter on the inner periphery thereof at a predetermined position in the longitudinal direction of the tube between opposite straight portions of a larger inside diameter; inserting the mother tube in a clearance a split die having a die cavity between bearing portions provided at opposite ends thereof and separable into first and second halves in the longitudinal direction at a median point of the die cavity and a plug member extensible through the die cavity; gripping a mouth portion of the mother tube by a carriage while positioning the plug member at one of the die bearing portions on the side of the carriage; moving the carriage in the longitudinal direction of the tube until the stepped wall portion on the inner periphery of the mother tube aligns with the die cavity, thereby expanding and stretching one of the straight portions; next moving the plug