Tube sheets

When a tube is rolled or expanded into the tube sheet three different wall thicknesses are created on the tube in the near drum region. They are the thickness of the tube within the tube sheet, the thickness of the tube from the tube sheet to the roll mark, and the thickness of the tube above the roll mark. 

Roll marks and the edge of the tube sheet provides distinct reference points as scan characteristics and tube thickness may change dramatically at these points. 

Figure 1 is a cross section of a typical generator tube showing the tube sheet, the location of both the soft and hard roll marks and the typical location of wastage. 

Figure 5 is a photo of a sectioned tube removed from a tube sheet. Within the tube sheet the wall thickness of the tube is 3,35 mm on the left and 4,37 mm on the right (elevation A). Immediately above the tube sheet (elevation B), but still within the roll, the left wall is 2,74 mm and the right 4,67 mm. Immediately above the roll mark (elevation C), there is a significant reduction in the tubes eccentricity, as the left wall is 4,67 mm and the right 4,83 mm. 

The wastage is 2,6 mm below the nominal wall thickness of 4.2 mm. On the rare occasion this type of wastage may also penetrate into the tube sheet for up to 6 mm. 

Wastage all around the tube is seldom seen near the tube sheet in recovery boilers. Figure 9 shows a sean of a tube that has gradual thinning around the full circumference of the tube with the wastage stopping at the tube sheet. 

Tube sheet C-steel with stainless steel liner... 

Fig. 12. OxyTech Systems MDC cell a, brine feed rotometer b, head sight glass c, cell head d, cathode assembly e, tube sheet f, grid plate g, cathode...

Fig. 13. Exploded view of an OxyTech MDC-55 ceU a, end plate b, rim screen c, side screens d, tube sheet e, full-cathode tube f, half-cathode or end tube g, side plate h, lifting lug i, punched and coined stiffener strap j, bosses k, end plate, operating aisle end 1, hydrogen outiet m, connector bar n,...

Fig. 8. Shell-and-tube heat exchanger A, shell of high strength B, tube sheet C, tubes (normally small diameter tubes are seamless, but large diameter tubes (>1 in.) are welded tubes) D, boimets E, baffles to assure more efficient circulation by providing minimum clearance between tubes and tube holes...

Explosion-bonded metals are produced by several manufacturers in the United States, Europe, and Japan. The chemical industry is the principal consumer of explosion-bonded metals which are used in the constmction of clad reaction vessels and heat-exchanger tube sheets for corrosion-resistant service. The primary market segments for explosion-bonded metals are for corrosion-resistant pressure vessels, tube sheets for heat exchangers, electrical transition joints, and stmctural transition joints. Total world markets for explosion-clad metals are estimated to fluctuate between 30 x 10 to 60 x 10 annually. 

The location of exchangers is the key to maintenance. Usually the back head is kept at a distance of about three meters from the piperack support columns. Access equipment must be able to get in and remove the sheU cover and flange head. Access area must also be provided to handle and remove the sheU cover usually located under the piperack. The tube-pulling or rodding-out area must be kept clear to allow access to the channel end. This space should be at least equal to the tube length and about two meters from the tube sheet location. Tube removal space should be allowed for but is not mandatory if grade-mounted heat exchangers are used and mobile maintenance equipment employed to pick up the entire unit and transfer it to the repair shop. 

Galvanic corrosion can be controlled by the use of sacrificial anodes. This is a common method of controlling corrosion in heat exchangers with Admiralty tube bundles and carbon steel tube sheets and channel heads. The anodes are bolted direcdy to the steel and protect a limited area around the anode. Proper placement of sacrificial anodes is a precise science. 

External Dilute-Phase Upflow Cooler. The external ddute-phase upflow design (68) offers some control in the range of heat removal duties but generates relatively low heat-transfer coefficients [60—170 W/(m K)]- This design substantially increases the surface area requirement and thereby reduces the ultimate duty that can be achieved from a single bundle. In addition, poor mechanical rehabdity has been continuously experienced because of excessive erosion at the lower tube sheets as a result of the high catalyst fluxes and gas velocities imposed. 

The cod wound heat exchanger consists of multiple tubes heHcally wound on a mandrel, usually with spacers between each tube layer. The tubes are inserted into tube sheets at both ends of the tube bundle, with separate tube sheets to accommodate each tube circuit. The tube bundle is enclosed ia a sheU with inlet and outlet no22les for the sheUside fluid. This type of heat exchanger is usually constmcted of aluminum or stainless steel. Large aluminum... 

Flat head. UG-34. Fig. UG-34. UG-39 Tube sheet. No code. TEMA acceptable. U2 (g)... 

Details are provided for head-to-shell welds, tube sheet-to-shell welds, and nozzle-to-shell welds. Acceptable forms of welded stay-bolts and plug and slot welds for staying plates are given here. 

Appendix 4 gives definitions and rules for stress analysis for shells, flat and formed heads, and tube sheets, layered vessels, and nozzles including discontinuity stresses. Of particular importance are Table 4-120.1, Classification of Stresses for Some Typical Cases, and Fig. 4-130.1, Stress Categories and Limits of Stress Intensity. These are veiy useful in that they clarify a number of paragraphs and simphfy stress analysis. 

It is assumed that process conditions and physical properties are known and the following are known or specified tube outside diameter D, tube geometrical arrangement (unit cell), shell inside diameter D shell outer tube limit baffle cut 4, baffle spacing and number of sealing strips N,. The effective tube length between tube sheets L may be either specified or calculated after the heat-transfer coefficient has been determined. If additional specific information (e.g., tube-baffle clearance) is available, the exact values (instead of estimates) of certain parameters may be used in the calculation with some improvement in accuracy. To complete the rating, it is necessary to know also the tube material and wall thickness or inside diameter. 

C) Pull-through floating-heat-kettle-type rehoder having stationary head integral with tube sheet, 584-mm (23-in) port diameter and 940-mm (37-in) inside shed diameter with tubes 4.9-m (16-ft) long. SIZE 23/37-192 TYPE CKT. 

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

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