Ultrasonic inspection method and system therefor

A method of ultrasonically inspecting a turbine wheel having a central hub bore, a plurality of bolt holes radially spaced outward from the central hub bore and circumferentially spaced from each other along a circle concentric with the central hub, and an annular-shaped web region between the central hub bore and the bolt holes, the wheel being formed such that the web region potentially contains axial-radial oriented defects, the method comprising the steps of:

• mounting a plurality of ultrasonic transducers to form at least one transducer unit;
• placing the transducer unit in a first of the bolt holes of the turbine wheel;
• performing a pulse-echo diagnostic technique on the turbine wheel by causing the ultrasonic transducers to emit ultrasonic signals that intersect radials of the turbine wheel at angles of approximately ninety degrees to the radials, the ultrasonic signals intersecting the radials at points located within the web portion of the wheel between the central hub bore and the first bolt hole so that each of a plurality of the points is located on a corresponding one of the radials, all of the plurality of points being located within the web portion;
• and
• placing the transducer unit in a sufficient additional number of the bolt holes and performing the pulse-echo diagnostic technique on the wheel to locate additional points throughout the web portion;
• wherein at least one of the ultrasonic transducers receives at least one reflected ultrasonic signal returned from at least one of the plurality of points at which an axial-radial oriented defect is present and oriented substantially perpendicular to the ultrasonic signal that returned the reflected ultrasonic signal;
• and
• wherein each of the bolt holes has a center located a constant distance R from a center of the central hub bore along one of the radials of the turbine wheel, each of the plurality of points is located a distance d from the center of the bolt hole and a distance r from the center of the central hub bore, the distances R, d and r define sides of a right triangle with an angle of ninety degrees between the sides corresponding to the distances d and r, an angle α between the sides corresponding to the distances d and R, and an angle θ between the sides corresponding to the distances r and R, and the plurality of points are located within the turbine wheel by the equation:
• cos2 θ+cos2 α=1.