Beading the tube ends in a firetube boiler:

Beading the tube ends in a firetube boiler serves a specific function, particularly in preventing the overheating of the tube ends. When the tube ends are beaded, they are formed into a shape that increases the surface area and thickness at the end of the tube. This design feature helps to distribute the heat more evenly along the tube end, which ultimately reduces the risk of overheating. Overheating can lead to tube failure or leaks, which are critical concerns in the safe operation of boilers.

The beading process also improves the mechanical strength of the tube and provides a means to secure the tube more effectively against the tubesheet. While this action does have benefits related to leakage and securing the tube, its primary role in the context of preventing overheating is what makes this option stand out. By enhancing the thermal management at the tube ends, beading contributes significantly to the overall reliability and safety of the boiler operation.