Why is it necessary to have stays in the construction of certain boiler surfaces?

Stays are critical components in the construction of certain boiler surfaces, primarily because they provide structural support essential for maintaining the integrity of the boiler under the conditions of high internal pressure. When water is heated in a boiler, it converts to steam, which can generate significant pressure. Without proper support, the surfaces of the boiler could bulge or even rupture, leading to dangerous failures. Stays help distribute the stress caused by this pressure, ensuring that the boiler can operate safely and effectively.

The other options do not accurately reflect the primary purpose of stays in boiler construction. Enhancing aesthetic appearance is not a relevant function of boiler stays, as their design focuses on functionality rather than looks. While assembly is important, facilitating easier assembly is a secondary consideration that does not justify the use of stays. Minimizing materials is also not the goal; rather, stays are used specifically to provide additional support where it is needed, which can require careful material usage to achieve the right strength and safety levels.