Wheel swaps are conducted when a wheel is deemed unserviceable. The purpose for this is to prevent wheel failures which could result in the possibility of the locomotive and its cars derailing.
There are a variety of components that must be checked to ensure that they are in compliance with minimum standards set by the Federal Railroad Administration (FRA). These components must be thoroughly inspected for defects like cracks, breaks, and improper placement and alignments.
A variety of factors can cause wheel defects, but the most common pertain to the integrity of the material the wheels are composed of, and overheating.
Subsurface defects pose a major concern to safety. They can form naturally over time, or because of poor manufacturing. The first indication that you may have a subsurface defect is if you notice cracks forming on the sides of the wheel rims. If left untreated, these cracks can expand and shatter the entire rim. These cracks usually start off small and can be easily overlooked. However, the longer they are left untreated, you will notice more blatant indicators of damage like rusting, larger cracks, and pieces of the tread breaking away.
Another common reason why wheels must be replaced is overheating. Overheating in locomotives is most commonly caused by traveling at excessive speeds, traveling shorter distances, and heavy use of the brake system. One of the main concerns pertaining to overheating is the formation of thermal cracks in the wheels.
Wheel thermal cracks are formed by excessive heating which typically run parallel to the wheel’s axle. These cracks pose a serious threat to the wheel’s overall integrity and can result in the wheel rims shattering. Thermal cracks should be reported immediately and should be replaced as soon as possible, or at the inspector’s discretion.