How are tubes attached to the tube sheet in a fire tube boiler?

In a fire tube boiler, the tubes are typically attached to the tube sheet through a process known as rolling and beading. This method involves the tube being rolled into place within a hole in the tube sheet, and then the end of the tube is beaded or flared to create a mechanical connection. This ensures a tight seal that can withstand the pressure and temperature conditions present in the boiler.

The rolling and beading method is preferred due to its ability to handle thermal expansion and contraction of the tubes during operation, which would be difficult to manage with methods like welding or bolting. Welding can create a rigid structure that does not allow for movement, potentially leading to stress and failure, while bolting does not provide a continuous seal and may not withstand high pressures as effectively. Screwing is also not used due to similar concerns about pressure and safety. This combination of mechanical connection methods provides the durability and reliability required for effective boiler operation.