What is the minimum length of rail required for thermite welding in curves?

In thermite welding, particularly when welding rail in curves, it is essential to maintain a certain length of rail to ensure the integrity and strength of the weld. The minimum length of 18 feet is specified to allow for proper alignment and to accommodate the stresses that occur during both the welding process and the subsequent operation of the railway. This length helps in avoiding any potential distortion or misalignment that could arise due to the thermal effects of the welding process and the inherent flexing of rail on curves.

Using a length shorter than 18 feet could lead to issues in maintaining the necessary alignment to ensure a strong, durable joint, which is critical for the safety and reliability of the railway infrastructure. The choice of 18 feet strikes a balance between manageability of the rail sections while still providing enough material for a robust weld, particularly in curved sections where the dynamics of the rail can lead to additional challenges.