Ultrasonic Inspection System

An ultrasonic inspection system comprising:

• an ultrasonic sensor having a piezoelectric element that transmits and receives an ultrasonic wave;
• and
• a control device that acquires a propagation time of a reflected wave reflected on a surface of a subject opposite to a side of the piezoelectric element, and calculates a thickness of the subject based on a propagation time of the reflected wave and sound velocity of the subject,
• wherein the ultrasonic sensor includes first and second plate portions which are arranged so as to contact either a surface of the piezoelectric element on a side of the subject or a surface of the piezoelectric element opposite to the side of the subject and are different in at least one of a thickness and a sound velocity, and
• the control device acquires a propagation time of a first reflected wave reflected on a surface of the first plate portion opposite to the side of the piezoelectric element and a propagation time of the second reflected wave reflected on a surface of the second plate portion opposite to the side of the piezoelectric element, calculates a sound velocity of the first plate portion using the propagation time of the first reflected wave and a thickness of the first plate portion, corrects the sound velocity of the subject and acquires a sound velocity of the second plate portion based on the calculated sound velocity of the first plate portion, and calibrates a time axis based on the propagation time of the second reflected wave, a thickness of the second plate portion, and the sound velocity of the second plate portion.