Failure Analysis of a Railroad Rail
(Published in Claims Magazine, October 2013)
Charles C. Roberts, Jr., Ph.D., P.E.
Private railroad turn-outs service many industrial facilities. Rail failure can occur for a variety of reasons causing substantial property loss, along with possible personal injury. Figure 1 is a view of a rail failure that occurred at the lead truck (front wheels) of a diesel locomotive on a private rail siding. The locomotive derailed, resulting in damage to the traction wheels as well as loss of usage of the turn-out while repairs were made.
Figure 2 shows the fracture surface of the rail, characterized by an older rusted fracture and the fresh final fracture of the 150 lb/yard steel rail. It was apparent there was sufficient mechanical stress in the rail to cause in a metal fatigue related fracture.
In Figure 3A, a railroad truck (set of wheels) is rolling on a moderate curve. Figure 3B shows a truck rolling on a curve of lesser radius, which causes increased stress in the rails (red arrow) as a result of the truck trying to straighten the curve. Many railroads have minimum radius specifications for private rail facilities. For instance, Reference 1 requires a minimum radius of 574 feet for acceptable operation in private railroad yards. This tends to minimize the mechanical stress in the track, reducing track maintenance and track failure. For the failure shown in Figures 1 and 2, the radius of the track was significantly less than recommended, suggesting a design defect is the probable cause of failure. Other evidence of a low radius curve is the existence of several wheel burns on the track.
Figure 4 shows the mechanics of a rail burn. Short radius curves increase the rolling resistance of rail cars, making it harder to move. A locomotive starting to move a train may encounter traction wheel slippage, which causes a characteristic scuffing mark on the track called a rail burn, as shown in Figure 5. Rail burn sites may be a future origin of a rail fracture.
1. Standard Specification for the Design and Construction of Private Sidetracks, CSX Transportation, Office of the Vice-President - Engineering, Jacksonville, Florida, June 1, 2007