Inspection method of square billet using electronic scanning

A method of detecting subsurface defects in a specimen by ultrasonic inspection, comprising the steps of:

• detecting both internal and surface defects by an angle beam inspection on the surface layer of said specimen using a phased array probe;
• determining the projection on the surface of the estimated position of a said defect located by said angle beam inspection utilizing the positional relation of said probe and said specimen, the incident angle of the ultrasonic beam, and the defect echo detecting time;
• detecting surface defects only using a surface defect inspection apparatus;
• determining a defect region for each surface defect detected by said surface defect inspection apparatus;
• comparing said estimated defect position information with said defect regions to determine surface defect position information;
• and
• detecting only subsurface defects by subtracting said surface defect region information from said estimated defect position information.