What is a diagonal stay used for in boiler construction?

A diagonal stay is a critical component used in the construction of boilers, specifically designed to provide structural support. Its primary function is to brace right-angle surfaces within the boiler system. By doing so, diagonal stays help maintain the integrity and stability of the boiler's shape, especially under the stresses caused by high pressure and temperature.

The use of diagonal stays is essential in ensuring that the boiler can withstand various forces while maintaining its operational efficiency. They work by distributing loads evenly across the structure, effectively preventing deformation or failure of the corners where two surfaces meet at right angles. This is particularly important in vertical boiler designs, where the risk of buckling can be significant if proper bracing is not in place.

In contrast, the other options do not accurately describe the purpose of diagonal stays. They are not specifically intended to support horizontal surfaces, enhance water circulation, or reduce thermal efficiency, which highlights the distinct role that diagonal stays play in structural reinforcement within boiler systems.