Thermite welding is a specialty practice using molten metals to join rail segments. It requires specialty tooling, gases, and safety equipment to get the job done.
Throughout the 1920s, railroad rails were joined by steel connections and bolts. But over time these bolts would come loose, requiring regular maintenance and repair. Eventually, thermite welding was developed as a method to join and repair rails. This type of welding requires high temperatures and specialized equipment.