What type of ASME stamp is required when welding high pressure piping in boiler external piping?

The requirement for a specific ASME stamp when welding high pressure piping in boiler external piping is best represented by the Power Piping (PP) stamp. This is because the Power Piping code includes regulations and standards that apply to piping systems transporting fluids under pressure, particularly in power generation and similar applications.

The Power Piping code sets the framework for the design, materials, fabrication, and installation of such piping systems, ensuring they meet safety and performance standards necessary for high-pressure conditions. Boilers are typically involved in power generation, thus aligning the need for a Power Piping stamp in this context.

While the other choices are related to specific areas within piping, they either focus on different applications or do not encompass the full scope and requirements pertinent to high-pressure systems associated with boiler external piping.