At what point does the boiler external piping end?

The end of the boiler external piping is recognized at the first stop valve. This designation is important because the first stop valve serves as a clear demarcation point between the boiler system and the external piping. The definition encompasses not just the physical aspects but also the operational significance.

In boiler operations, the stop valve plays a crucial role in terms of safety and maintenance. It enables operators to isolate the boiler from the downstream piping system. This isolation is essential for safely performing maintenance on the boiler and to ensure that any operation or failure within the downstream system does not impact the boiler's operational parameters.

Other options, while they may represent features or components of a piping system, do not fit the definition of where external piping ends. For instance, the last bend of the piping refers to geometric configuration rather than operational isolation, water level pertains to the internal conditions of the boiler rather than the external piping boundaries, and the pressure gauge is an instrument for monitoring system pressure but does not signify the endpoint of the piping. Thus, the first stop valve is the definitive point marking the transition from internal boiler components to external piping in terms of functionality and safety.