Which boiler will withstand the greatest working pressure if one is 30 inches in diameter and the other is 60 inches?

In evaluating which boiler can withstand the greatest working pressure, it's important to consider the relationship between the diameter and the pressure-carrying capacity of a boiler. The ability of a boiler to withstand pressure relies on several factors, including the material it is constructed from and its geometry, but primarily, it’s influenced by the thickness of the walls relative to the diameter.

A smaller-diameter boiler, like the 30-inch one, often has walls that can be designed to be thicker relative to its size, allowing it to endure higher pressures. The key here is that as the diameter increases, the circumference also increases, leading to a greater stress on the walls of the boiler under pressure.

In this context, the 30-inch boiler, with its relatively smaller size, can be constructed to handle pressures that are high enough for most applications while maintaining structural integrity. Moreover, the design of pressure vessels follows guidelines that often favor thicker walls in smaller diameters for safety and strength.

Therefore, the reasoning behind the conclusion is that the smaller-diameter boiler (the 30-inch boiler) can indeed withstand greater working pressures than a larger-diameter one, given appropriate design and construction standards are followed.