How are tubes secured in a tube sheet in a fire tube boiler?

In a fire tube boiler, tubes are typically secured in a tube sheet using a rolling and beading process. This method involves mechanically rolling the ends of the tubes into the tube sheet to create a tight, leak-proof seal. Beading involves creating a raised edge at the end of the tube, which also helps in securing the tube within the sheet. This mechanical action is essential because it ensures that the tubes remain firmly in place even under high pressure and temperature conditions.

The rolling and beading process not only provides structural integrity but also allows for the necessary thermal expansion and contraction of the materials involved without compromising the connection between the tubes and the tube sheet. This is critical for the efficient and safe operation of the boiler.

Other methods mentioned, such as welding or gluing, are not typically used for tube attachment in fire tube boilers due to concerns about potential failure at high temperatures and pressures, as well as the difficulty in disassembling for maintenance.