What type of securing method is used for tubes in a water tube boiler?

In water tube boilers, the preferred method for securing tubes is through a process that involves rolling and then flaring. This technique ensures a tight, leak-proof fit between the tube and the tube sheet, which is essential for maintaining the pressure and integrity of the boiler system. The rolling process deforms the tube slightly, allowing it to fit snugly against the tube sheet. Following this, flaring the ends of the tube enhances the connection by increasing the contact area and creating a more secure seal, which is critical in high-pressure applications.

This method effectively accommodates thermal expansion and contraction that occurs during operation while maintaining a strong and durable attachment. The rolled and flared design minimizes the risk of leaks and allows for efficient heat transfer, which are vital factors in boiler design and functionality.

Other options, such as direct welding or bolting, do not typically provide the same level of flexibility and sealing efficiency required in high-pressure applications like those found in water tube boilers. While clamps may allow for some expansion, they do not create a secure enough attachment to handle the operational stresses experienced in these systems.