Abstract: An ultrasonic flaw detection method includes a condition setting step of setting a boundary echo detection threshold and a gate end point relative position, according to a type of a test object, a flaw detection signal obtaining step of obtaining a flaw detection signal by converting ultrasonic waves received from the test object to an electric signal, a boundary echo detection step of detecting a boundary echo detection time of the flaw detection signal by using the boundary echo detection threshold, a flaw echo detection gate setting step of setting an end point of a flaw echo detection gate by subtracting the gate end point relative position from the boundary echo detection time, and a flaw echo detection step of detecting a flaw echo by using the flaw detection signal within the flaw echo detection gate.

Abstract: A decision algorithm of discriminating a defect type and/or a defect level is automatically produced in a short time. The accuracy of defect classification in terms of a defect type or a defect level is improved.

Abstract: A soft-magnetic material is installed on the opposite side of the magnetism sensing face of magnetism sensing devices. This soft-magnetic material is larger than the magnetism sensing face. Then the detection coverage per sensor is enlarged, and the number of sensors and signal processing circuits are reduced across the width of the strip.

Abstract: A soft-magnetic material is installed on the opposite side of the magnetism sensing face of magnetism sensing devices. This soft-magnetic material is larger than the magnetism sensing face. Then the detection coverage per sensor is enlarged, and the number of sensors and signal processing circuits are reduced across the width of the strip.

Abstract: A flaw detecting method and apparatus for continuously testing a strip that is continuously carried through a liquid includes features for reducing air bubble generation in a liquid. The apparatus includes a liquid, carrying rolls for passage of the strip through the liquid, and ultrasonic testing probes arranged in the liquid for testing the strip. A carrying roll in contact with the liquid is fully immersed. Air bubble generation is inhibited to improve the testing reliability by at least one of (a) shielding the liquid dropping from the portion of the strip leaving the liquid, (b) reducing the dropping force of the liquid onto the liquid surface by inclining the strip, (c) installing the fully immersed carrying roll at a depth of at least 5 mm in the liquid, and (d) using a carrying speed of less than about 200 m/min. Upon manufacturing steel strips, testing is carried out in the stage of hot-rolled steel sheet, or, preferably, in pickling equipment.