CONVECTION SECTION TUBE SHEET

CONVECTION SECTION TUBE SHEET

The convection section tube sheet is made by Casting, maximum size is 4 meters in length and 4 meters in width with minimum 25mm thickness. 

The convection section tube sheet is a critical component in various industrial applications, particularly for fired heater convection sectiona and heat exchangers. Its primary function is to hold tubes in place, facilitating the efficient transfer of heat between fluids. This article delves into the importance, design considerations, and maintenance practices associated with tube sheets in the convection section of fired heater and heat exchangers.

Design Considerations

The design temperature for tube sheet and guides exposed to flue gas shall be based on design operation of the furnace as follows:

a) for the radiant and shock sections and outside the refractory, the flue-gas temperature to which the supports are exposed plus 100 °C (180 °F); the minimum design temperature shall be 870 °C (1600 °F);

b) for the convection section, the temperature of the flue gas in contact with the tube sheet plus 55 °C (100 °F);

c) maximum flue-gas temperature gradient across a single convection intermediate tube sheet shall be 222 °C (400 °F);

d) where the radiant tube-support castings are shielded behind a row of tubes, the bridgewall temperature may be used.

No credit shall be taken for the shielding effect of refractory coatings on intermediate supports or guides.

10.1.2 Guides, horizontal radiant-section intermediate tube sheet and top supports for vertical radiant tubes

shall be designed to permit their replacement without tube removal and with minimum refractory repair.

10.1.3 The unsupported length of horizontal tubes shall not exceed 35 times the outside diameter or 6 m (20 ft), whichever is less.

10.1.4 The minimum corrosion allowance of each side for all exposed surfaces of each tube sheet and guide

contacting flue gases shall be 1,3 mm (0,05 in) for austenitic materials and 2.5 mm (0.10 in) for ferritic materials.

10.1.5 The following shall apply to end-tube sheets for tubes with external headers.

⎯ Tube sheets shall be structural plate. If the tube-sheet design temperature exceeds 425 °C (800 °F), alloy materials shall be used.

⎯ Minimum thickness of tube sheets shall be 12 mm (0.5 in).

⎯ Tube sheets shall be insulated on the flue-gas side with a castable having a minimum thickness of 75 mm(3 in) for the convection section and 125 mm (5 in) for the radiant section. (Anchors shall be made from austenitic stainless steel or nickel alloy  

⎯ Sleeves with an inside diameter at least 12 mm (0.5 in) greater than the tube or the extended-surface outside diameter shall be welded to the tube sheet at each tube hole, to prevent the refractory from being damaged by the tubes. The sleeve material shall be austenitic stainless steel.

10.1.6 The following shall apply to the supporting of extended-surface tubes.

⎯ Intermediate supports shall be designed to prevent mechanical damage to the extended surface and shall

permit easy removal and insertion of the tubes without binding.

⎯ For studded tubes, a minimum of three rows of studs shall rest on each support.

⎯ For finned tubes, at least five fins shall rest on each support. 

Advancements and Innovations

The continuous pursuit of efficiency and reliability drives advancements in tube sheet design and material science. Innovations in fabrication techniques, such as laser drilling and automated welding, contribute to higher precision and stronger bonds. Moreover, the development of new materials with enhanced thermal conductivity and corrosion resistance properties promises to further improve the performance and durability of tube sheets in high-demand industrial settings.