Fixed tube sheet

Functional Definitions Heat-transfer equipment can be designated by type (e.g., fixed tube sheet, outside packed head, etc.) or by... 

Construction Codes Rules for Construction of Pressure Vessels, Division 1, which is part of Section T11 of the ASME Boiler and Pressure Vessel Code (American Society of Mechanical Engineers), sei ves as a construction code by providing minimum standards. New editions of the code are usually issued every 3 years. Interim revisions are made semiannually in the form of addenda. Compliance with ASME Code requirements is mandatoiy in much of the United States and Canada. Originally these rules were not prepared for heat exchangers. However, the welded joint between tube sheet and shell of the fixed-tube-sheet heat exchanger is now included. A nonmandatoi y... 

Fixed-Tube-Sheet Heat Exchang ers Fixed-tube-sheet exchangers (Fig. 11-36Z ) are used more often than any other type, and the frequency of use has been increasing in recent years. The tube sheets are welded to the shell. Usually these extend beyond the shell and serve as flanges to which the tube-side headers are bolted. This construction requires that the shell and tube-sheet materials be weldable to each other. 

The U-tube bundle has the advantage of providing minimum clearance between the outer tube hmit and the inside of the shell for any of the removable-tube-bundle constructions. Clearances are of the same magnitude as for fixed-tube-sheet heat exchangers. 

The number of tube holes in a given shell is less than that for a fixed-tube-sheet exchanger because of hmitations on bending tubes of aveiy short radius. 

The bonnet (Fig. 11-35B) bolts to the shell. It is necessary to remove the bonnet in order to examine the tube ends. The fixed-tube-sheet exchanger of Fig. 11-36Z has bonnets at both ends of the shell. 

Tube-Side Passes Most exchangers have an even number of tube-side passes. The fixed-tube-sheet exchanger (which has no shell cover) usually has a return cover without any flow nozzles as shown in Fig. 11-35M Types L and N are also used. All removable-bundle designs (except for the U tube) have a floating-head cover directing the flow of tube-side fluid at the floating tube eet. 

In very large fixed-tube-sheet units, in which concentricity of shells decreases, baffles are occasionally welded to the shell to eliminate bypassing between the baffle and the shell. 

Tube-Bundle Bypassing Shell-side heat-transfer rates are maximized when bypassing of the tube bundle is at a minimum. The most significant bypass stream is generally between the outer tube limit and the inside of the shell. The clearance between tubes and shell is at a minimum for fixed-tube-sheet construc tion and is greatest for straight-tube removable bundles. 

Clad Tube Sheets Usually tube sheets and other exchanger parts are of a solid metal. Clad or bimetallic tube sheets are usecito reduce costs or because no single metal is satisfactory for the corrosive conditions. The alloy material (e.g., stainless steel, Monel) is generally bonded or clad to a carbon steel backing material. In fixed-tube-sheet construction a copper-alloy-clad tube sheet can be welded to a steel shell, while most copper-alloy tube sheets cannot be welded to steel in a manner acceptable to ASME Code authorities. 

Fabrication Expanding the tube into the tube sheet reduces the tube wall thickness and work-hardens the metal. The induced stresses can lead to stress corrosion. Differential expansion between tubes and shell in fixed-tube-sheet exchangers can develop stresses, which lead to stress corrosion. 

I Fixed-tube-sheet construction Anth Vi-in OD tube on i-Vift-in triangular pitch provides 36 percent more surface. 

Fixed Tube Sheet Both tube sheets fixed to shell Condensers liquid-liquid gas-gas gas-liquid cooling and heating, horizontal or vertical, reboiling Temperature difference at extremes of about 200°F. Due to differential expansion 1.0... 

In. sclcciing an exchanger, one must know the advantages and disadvantages td each type. The three basic types of shell-and-tube exchangers are fixed tube sheet, floating head, and U-tube, Table 3-1 summarizes the comparison between these three exchangers. 

Fixed Tube Sheet Outside Packed FloatinoHeod "U"- Tut Shell Fixed Tube re Iside Packed Flodtino He[Pg.68]

From Table 3-4 for 1-in. OD, 114-in. square pitch, fixed tube sheet, four passes, shell ID = 29 in. 

Tube Sheet Layout FIXED TUBE SHEET EXCHANGER (Also Non-Removable Flaating Head) Tube Passes Two Tube Size a Pitch 3/4 on I5/I6"A... 

Select Fixed tube sheet vertical unit... 

Shell Tubes 1-10 bar x 1.0 Floating head x Fixed tube sheet x 1.0... 

Reboiler forced convection type, fixed tube sheets, area 18.6 m2, carbon steel shell, stainless-steel tubes, operating pressure 1 bar. 

Reactor, three off shell and tube construction, fixed tube sheets, heat transfer area 50 m2, design pressure 5 bar, materials stainless steel. 

The simplest and cheapest type of shell and tube exchanger is the fixed tube sheet design shown in Figure 12.3. The main disadvantages of this type are that the tube bundle cannot be removed for cleaning and there is no provision for differential expansion of the shell and tubes. As the shell and tubes will be at different temperatures, and may be of different materials, the differential expansion can be considerable and the use of this type is limited to temperature differences up to about 80°C. Some provision for expansion can be made by including an expansion loop in the shell (shown dotted on Figure 12.3) but their use is limited to low shell pressure up to about 8 bar. In the other types, only one end of the tubes is fixed and the bundle can expand freely. 

A fixed tube sheet will be used for a vertical thermosyphon reboiler. From Figure 12.10, shell diametrical clearance = 14 mm,... 

Figure 8.4. Example of tubular heat exchangers (see also Fig. 8.14). (a) Double-pipe exchanger, (b) Scraped inner surface of a double-pipe exchanger, (c) Shell-and-tube exchanger with fixed tube sheets, (d) Kettle-type reboiler, (e) Horizontal shell side thermosiphon reboiler, (f) Vertical tube side thermosiphon reboiler, (g) Internal reboiler in a tower, (h) Air cooler with induced draft fan above the tube bank, (i) Air cooler with forced draft fan below the tube bank.

L<30, 3/8 type Material 316 SS Operating pressures <300 psig... 

Figure B.l shows the American TEMA (Tubular Exchanger Manufacture Association) standards that are largely accepted. The codification makes use of three letters that indicate the type of stationary head, shell and rear head, respectively. One of the most common types is AES or AEL that designate removable channel and cover (A), one-pass shell (E) and fixed tube sheet (L) or floating-rear (S). A similar...

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