Rail inspection

Rail inspection is the practice of examining rail tracks for flaws that could lead to catastrophic failures. According to the United States Federal Railroad Administration Office of Safety Analysis, track defects are the second leading cause of accidents on railways in the United States. The leading cause of railway accidents is attributed to human error. The contribution of poor management decisions to rail accidents caused by infrequent or inadequate rail inspection is significant but not reported by the FRA, only the NTSB. Every year, North American railroads spend millions of dollars to inspect the rails for internal and external flaws. Nondestructive testing (NDT) methods are used as a preventative measures against track failures and possible derailment.

The first rail inspections were done visually. Many sources cite that the need for better rail inspections came after a derailment at Manchester, New York, in 1911. That particular accident resulted in the death of 29 people and injuries to 60 others. The investigation of the accident revealed that the cause was a transverse fissure (a critical crack which lies perpendicular to the length of the rail) in the rail. Further investigation in the late 1920s showed that this type of defect was quite common. With increased rail traffic at higher speeds and with heavier axle loads today, critical crack sizes are shrinking and rail inspection is becoming more important. In 1927, Dr. Elmer Sperry built a massive rail inspection car under contract with the American Railway Association. Magnetic induction was the method used on the first rail inspection cars. This was done by passing large amounts of magnetic field through the rail and detecting flux leakage with search coils. Since then, many other inspection cars have traversed the rails in search of flaws.

There are many effects that influence rail defects and rail failure. These effects include bending and shear stresses, wheel/rail contact stresses, thermal stresses, residual stresses and dynamic effects.

Defects due to contact stresses or rolling contact fatigue (RCF):

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