By how many inches must the flow (lip) be removed before performing a weld on head worn rail?

The correct answer, which indicates that 4 inches of the flow (lip) must be removed, aligns with the requirements for ensuring a proper weld on head worn rail. Removing this amount of lip allows for adequate penentration of the thermite weld material into the rail surface, ensuring a strong bond that can withstand the stresses of rail operations.

The removal of 4 inches is sufficient to ensure that any deformations or inconsistencies on the surface of the worn rail are eliminated, providing a clean, smooth surface for the weld. This step is crucial as it helps to minimize defects in the weld and ensures that the weld adheres properly.

This amount is also guided by industry standards and practices that emphasize the need for preparing the rail surface adequately before welding to achieve optimal strength and durability of the welded joint.