Firetube ends are secured to the tube sheet by:

Firetube ends are secured to the tube sheet primarily through the process of expanding and beading. In this method, the tube ends are first expanded to create a tight fit against the tube sheet, establishing a strong mechanical seal. This expanding process ensures that there is minimal chance for leakage and that the tubes are firmly held in place during operation.

Following the expansion, a beading process is typically employed, where a bead is formed around the joint. This bead serves to further enhance the seal and provide additional strength, as it helps to distribute stresses evenly across the joint area. The combination of expanding and beading is particularly effective in maintaining the integrity of the firetube assembly under the high pressures and temperatures associated with boiler operations.

In contrast, welding and flaring, clamping and beading, or screwing and bolting involve different mechanisms that do not achieve the same level of secure connection or thermal efficiency necessary for firetube applications. Each of these alternative methods lacks the combination of tightness and durability provided by expanding and beading, which is essential in high-pressure environments.