What is the minimum preheat and inter-pass temperature required when plug welding a 1-1/4" thick plate onto a flange?

The specified minimum preheat and inter-pass temperature for plug welding a 1-1/4" thick plate onto a flange is consistent with the requirements set forth in the AWS D1.1 Structural Welding Code. For thicker plates, a higher preheat temperature is generally necessary to help minimize the risk of cracking and to promote proper weld fusion.

In this case, the choice of 225°F aligns with the guidelines recommending a minimum preheat temperature that helps to alleviate thermal stresses and improve the overall weld quality. Preheating aids in reducing welding thermal gradients, which can make a significant difference in the performance of the welded joint.

Using a temperature that is too low could lead to issues such as lack of fusion or cracking, which is crucial when connecting thicker sections. Therefore, the correct answer of 225°F reflects an understanding of these welding principles as they apply to thicker materials, ensuring better weld integrity and performance.