How are the tubes in a water tube boiler typically fastened?

In a water tube boiler, the tubes are typically fastened by rolling and expanding them into drums and headers. This method is critical for ensuring a proper seal and structural integrity, which allows the boiler to withstand high pressure conditions.

Rolling the tube ends into the header or drum involves mechanically deforming the tube such that it tightly fits into the opening of the header. Expanding further secures the joint by increasing the contact surface area between the tube and the header, which enhances strength and thermal performance. This technique prevents leaks and promotes efficient heat transfer, as the tubes need to maintain consistent contact under varying thermal and pressure conditions.

Other methods such as welding and soldering are not typically used for fastening tubes in water tube boilers due to the extreme operating conditions and the potential for failure at welded joints. Similarly, while bolting and clamping can be effective in certain applications, they do not provide the necessary sealing and strength required in a high-pressure environment. Threading and fitting are generally not suitable for steam-tight applications, especially in the context of pressure vessels, as they can compromise the structural integrity and safety of a boiler system.