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

In a fire-tube boiler, the tubes are typically attached to the tube sheet by a process known as rolling the tubes and beading the ends. This method ensures a tight and secure fit, which is crucial for maintaining the integrity and safety of the boiler.

Rolling involves deforming the ends of the tubes against the tube sheet to create a mechanical seal, preventing fluid leaks and maintaining pressure. The beading procedure further enhances this connection by forming a bead or flare at the tube ends, distributing forces more evenly and providing additional sealing capability. This construction technique is essential in handling the high temperatures and pressures typically found in fire-tube boilers, ensuring their efficient and safe operation.

The other attachment methods mentioned, such as welding or using bolts, are not standard practices for fire-tube boilers due to the stresses and thermal cycles that could lead to failure at those connection points. Adhesives are impractical for this high-pressure application, as they do not provide the necessary mechanical strength or durability under extreme conditions.