Why are hollow stay bolts used on water legs?

Hollow stay bolts are designed with a small hole, allowing for the immediate detection of leaks in the water legs of a boiler. This feature is critical in maintaining the safety and efficiency of the boiler system. By enabling quick identification of any leaks, operators can take timely action to prevent potential hazards. This is particularly important because water legs are integral components that help support the structure of the boiler while also holding water needed for steam generation.

The other choices address different aspects of boiler design and function but do not accurately reflect the primary purpose of hollow stay bolts. While thermal expansion support and pressure handling are important considerations in boiler systems, they are not the primary reason for using hollow stay bolts. Additionally, the weight advantage of reducing overall boiler weight is not as significant compared to the essential function of leak detection.