Ultrasonic process for testing, by immersion, a metal piece and use thereof

An ultrasonic process for testing, by immersion, a condition of a metal piece, comprising the steps of:

• providing a plurality of transducers;
• activating the plurality of transducers to emit ultrasonic waves along respective axes of propagation;
• and
• focusing the ultrasonic waves on the metal piece;
• wherein each of said plurality of transducers has a frequency of 3 to 8 MHz, and a focal spot at -6 dB, each said focal spot having a section, perpendicular to its axis of propagation, of less than 25 mm.sup.2, said focal spots of said transducers being distributed in accordance with a depth of said metal piece which is to be tested, said focal spots of said transducers becoming covered after an observation depth interval of each of said transducers is controlled to a fraction of a focusing depth at -6 dB.

An ultrasonic process for testing, by immersion, a condition of a metal piece, comprising the steps of:

• providing a plurality of transducers;
• activating the plurality of transducers to emit ultrasonic waves along respective axes of propagation;
• and
• focusing the ultrasonic waves on the metal piece;
• wherein each of said plurality of transducers has a focal spot at -6 dB, each said focal spot having a section, perpendicular to its respective axis of propagation, which is no greater than 25 mm.sup.2, said focal spots of said plurality of transducers being distributed in accordance with a depth of said metal piece to be tested;
• wherein said focal spots of said transducers at -6 dB become covered in accordance with respective depths of said focal spots in said metal piece;
• wherein each of said plurality of transducers has an emitting surface, each said emitting surface having a point distanced acoustically such that, as measured in water and in said metal piece, distances from centers of said focal spots are identical;
• wherein said ultrasonic waves comprise longitudinal ultrasonic waves, each of said plurality of transducers emitting ultrasonic waves which are propagated in a direction adjacent to a line perpendicular to a surface of the metal piece, each of said plurality of transducers detecting waves reflected by said metal piece;
• wherein said metal piece comprises a titanium alloy bar having a diameter of 50 mm. to 400 mm.;
• wherein each of said plurality of transducers has a frequency of 3 MHz to 8 MHz;
• said method comprising the further step of controlling an observation depth interval of each of said plurality of transducers to a fraction of a focusing depth at -6 dB of each of said plurality of transducers, thereby improving the accuracy of the testing operation;
• wherein said metal piece comprises a bar having a diameter of 250 mm. to 400 mm., said observation depth interval being controlled to 1/15 to 1/2 of the focusing depth at -6 dB;
• and
• wherein an entire internal volume of said bar is tested, except for a superficial zone having a depth of less than 10 mm., by displacing an assembly of said plurality of transducers relative to said metal piece in such a way as to obtain a testing pitch which has a length no greater than 0.7 times a square root of the section of the focal spot at -6 dB of each of said plurality of transducers.