Ultrasonic Rail Testing test rail for defects including: transverse and compound fissures,
split web, piped rail, bolt hole cracks, head and web separations, vertical and horizontal split heads.
Ultrasonic rail testing was first offered by Sperry in 1949 with the equipment mounted on
a motor car to assist the then in use induction method of testing, at that time a hand inspection was made at each joint. In 1960 ultrasonic equipment was added to detect defects in the rail head. The first all ultrasonic detector car was tried for the first time in October 1959 on the New York City subway system.
Ultrasonic testing uses the transmission of high frequency sound waves into the rail head and web. These ultrasonic waves are at 20,000 cycles per second. The waves are sent into the rail,
then bounced back, the measure of time it takes to bounce back, also called reflected, indicates whether there may be a flaw.
Acoustic impedance is the resistance of a material to the passage of sound waves. The acoustic impedance determines how much sound is transmitted and reflected when the wave encounters a boundary with another material (flaw). It measures size of a fissure by that method. The larger the difference in acoustic impedance between 2 materials, the larger the amount of reflected energy is.