Preheating should be applied and extend at least how many inches on either side of the weld?

To ensure adequate preheating for welding procedures, it is critical to apply heat not just to the immediate area where the weld will be made but also to the surrounding base material. Preheating serves multiple purposes, including reducing the thermal gradient, preventing the formation of cracks, and improving the overall quality of the weld joint. Extending the preheat at least two inches on either side of the weld is a standard practice because it helps to ensure that the heat penetrates sufficiently to maintain a uniform temperature across the heat-affected zone. This practice helps in mitigating the risk of problems such as hydrogen-induced cracking or hardening of the base material. Therefore, specifying a two-inch extension on either side provides a balance between effective preheat coverage and practical application in the field, making it the most widely accepted guideline in welding procedures.