Which boiler will withstand the greatest working pressure based on diameter alone?

The working pressure a boiler can withstand is largely influenced by its design and the materials used in its construction. However, when considering diameter alone, the limits of how much pressure a boiler can handle can vary.

In general, a smaller diameter boiler has thicker walls relative to its diameter compared to a larger diameter boiler. This means that the smaller diameter boiler can often withstand a higher pressure, as the material is subject to less tensile stress due to the decreased surface area exposed to that pressure.

In this case, the 30-inch boiler, having a smaller diameter, will have more material per inch of radius compared to a 60-inch boiler. As a result, the structural integrity of the 30-inch boiler allows it to withstand greater working pressure based solely on diameter considerations.

Thus, for the scenario presented in the question, the 30-inch boiler is capable of withstanding greater working pressure.