Machine Design And Shop Practice (MDSP) Inhouse Practice Exam

The main concept is how shape controls stress under internal pressure. In a thin-walled pressure vessel, the circumferential (hoop) stress governs how thick the wall must be. A spherical shell distributes the load evenly in all directions, so the hoop stress is uniform around the surface and is lower than in a cylinder (for the same internal pressure and dimensions). Specifically, the sphere has about half the circumferential stress of a cylinder, allowing the same safety with a thinner wall or less material. That uniform, lower stress state is why spherical vessels are favored in design. The other options aren’t the primary design reason: fabrication cost isn’t guaranteed to be lower, the hoop stress isn’t higher, and while a sphere can enclose more volume per material, the key advantage in design is the uniform, reduced circumferential stress.