What structural feature is used to support flat surfaces above tubes in fire tube boilers?

In fire tube boilers, diagonal stays are essential for maintaining the structural integrity and strength of the boiler. These diagonal stays are tension members that help transfer the weight and any operational loads from flat surfaces, such as the boiler's shell and its supporting structures, down to the foundation or base of the boiler.

The purpose of diagonal stays is to counteract the various stresses that can occur during operation, such as pressure and thermal expansion. By using a triangulated design, diagonal stays effectively distribute forces and prevent deformation or failure of the flat surfaces. This setup is particularly important in maintaining the safety and efficiency of the boiler.

Other structural features, such as reinforced plates, support brackets, and cross beams, may also play roles in the overall support and design of a boiler, but they do not specifically fulfill the same function as diagonal stays in terms of buckling resistance and maintaining flat surface stability in fire tube designs.