Final answer:
Preheat temperature for welding a NPS 8 s40 pipe ASTM grade B at 30 degrees F typically ranges from 50 to 100 degrees F. Exact requirements should be based on the applicable welding codes or consultation with a welding engineer.
Step-by-step explanation:
The subject of the question concerns the preheat temperature required for welding a NPS 8 s40 pipe ASTM grade B when the ambient temperature is 30 degrees F. The recommended preheat temperature can vary depending on several factors such as the material's chemical composition, thickness, and welding procedure. However, according to codes such as the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section IX, as well as the American Welding Society (AWS) D1.1 Structural Welding Code, there are specific guidelines for preheating to mitigate the risk of cold cracking. Typically, for ASTM grade B steel and given the relatively low ambient temperature, a minimum preheat temperature of around 50 to 100 degrees F is often recommended to ensure proper weld quality. However, it's important to consult the applicable welding code or a welding engineer for the exact requirements tailored to the conditions of the project.