Rails are joined in the field by either flash butt welding (a resistance welding process) or by thermite welding. In the shop, flash butt welding is used to weld the standard (1 1.9 m [39 ft]) lengths of rail into 300-ft sections. For additional information, refer to ANSUAWS D15.2, Recommended Practices for the Welding of Rails and Related Rail Components for Use by Rail Vehicles.

Rail joints are welded for the following reasons: smoother riding qualities, reduced track maintenance, and to eliminate the need for shimming and building up worn rail ends. Welded joints increase the life of ties and reduce the effects of vibration on cars and locomotives. Most American railroad systems are operating on trackage that has continuous welded rail. See FLASH WELDING and THERMITE WELDING.

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