Steel heat exchangers

When points for 20-ft-long tubes do not appear in Fig. 11-41, use 0.95 times the cost of the equivalent 16-ft-Iong exchanger. Length variation of steel heat exchangers affects costs by approximately 1 per square foot. Shell diameters for a given surface are approximately equal for U-tube and floating-head construc tion. 

For an all-steel heat exchanger AAith mixed design pressures the total extra for pressure is 0.7 X pressure extra on shell side plus 0.3 X pressure extra tube side. 

Figure 4.2 Severe localized wastage on a 316 stainless steel heat exchanger tube. Attack occurred beneath deposits, which were removed to show wastage.

Figure AAOA Deposits on a 316 stainless steel heat exchanger tube.

Figure 4.21 Internal surface (waterside) of alloy steel heat exchanger. Corrosion products and deposits partially cover pits. (Magnification 7.5x.)...

Figure 4.26 Internal surface of steel heat exchanger tube after removal of deposits. Note the mutually intersecting areas of metal loss.

Carbon steel heat exchangers, cast iron water boxes, screens, pump components, service water system piping, standpipes, fire protection systems, galvanized steel, engine components, and virtually all non-stainless ferrous components are subject to significant corrosion in oxygenated water. 

A 1-ft. (30-cm)-long section of steel heat exchanger tubing containing no failure was received. The section was submitted for evaluation of the internal surface, which was lined with a phenolic epoxy resin. 

Figure 6.5 Many small hemispherical pits on a 304 stainless steel heat exchanger tube end. The heat exchanger was removed from service and stored vertically for an extended period. Deposit accumulated at the lower tube ends where sulfate reducers flourished.

Figure 11.3 Sand dunelike erosion-corrosion patterns on the inlet end of a steel heat exchanger tube. (Magnification 7x.)...

Fig. 20-11 Potential-time curves of an enamelled container with built-in stainless steel heat exchanger as a function of equalizing resistance, R. Curve 1 container potential in the region of the heat exchanger. Curve 2 heat exchanger potential in the voltage cone of defects in the enamelling. Curve 3 heat exchanger potential outside the voltage cone of the defects.

B. A. Prine, Analysis of Titanium/Carbon Steel Heat Exchanger Fire, Paper presented at AIChE Loss Prevention Symposium, Aug. 1991. 

An alloy steel heat exchanger shell had been fitted with two large carbon steel flanges. The flanges were stamped as alloy. 

Stainless steel pipes (buried in the ground) and the interiors of stainless steel heat exchangers have been successfully cathodically protected, but CP is rarely used for materials other than steel. The protection potential usually adopted for steel is —850 mV to the saturated calomel reference electrode. This varies with temperature and the presence of other aggressive species in the environment. 

The presence of corrosion products is not always a negative event some small degree of surface corrosion of all steel heat exchanger surfaces is generally beneficial. Under the reducing conditions normally found on the surfaces of pre-boiler FW heaters, FW lines, and boiler surfaces, black magnetite naturally forms by the direct thermal reaction of water with steel. The development of this self-limited magnetite film is most desirable, and optimum formation is achieved at pH levels of 10.5 to 11.5. 

Solution From Equation 2.1 and Table 2.1, the capital cost of a carbon steel heat exchanger can be estimated from ... 

The cost of a carbon steel heat exchanger needs to be adjusted for the material of construction. Because of the low pressure rating, no correction for pressure is required (Table 2.5), but the cost needs to be adjusted for the material of construction. From Table 2.4, /m =2.9, and the total cost of the installed equipment can be estimated from Equation 2.6 and Table 2.7. If the project is a complete new plant, the contribution of the heat exchanger to the total cost can be estimated to be ... 

Washed solvent system The washed solvent tank is a grounded 55-gal drum. An elephant trunk positioned over the bung vents the drum to the exhaust system. Material fed to the drum is cooled from the POD operating temperature of approximately 190°F to 80°-110°F by a stainless steel heat exchanger. 

Waste water system The waste water tank is also a grounded 55-gal drum vented to the exhaust system. The heavy liquid out (HLO) stream from the POD system is cooled before discharge into the drum by a stainless steel heat exchanger. Disposal depends on the solvent used, its solubility in water, and environmental constraints. 

A 179 Seamless Cold-Drawn Low-Carbon Steel Heat-Exchanger and Condenser Tubes [Note (2)]... 

The hardness deposits coat the inside of the boiler s tubes, interfere with heat transfer, and overheat the tubes. The carbon dioxide, which is also generated from the dissolved solids, creates more serious corrosion problems in downstream heat exchangers. When the steam condenses, the carbon dioxide may remain trapped in the reboiler or preheater as a noncondensable gas. Actually, there is no such thing as a noncondensable gas. Even C02 is somewhat soluble in water. As the C02 dissolves in the condensed steam, it forms carbonic acid, a relatively weak acid (pH typically between 5 and 6). Strong acids will have pH values of 1 to 2. Pure water has a pH of seven. Carbonic acid is particularly corrosive to carbon steel heat-exchanger tubes. 

Example 1 A new heat exchanger is required and the lifetime of a carbon steel exchanger is 5 yr with a cost of 9500. The 316 stainless steel heat exchanger with a lifetime of 15 yr costs 26500, which can be written off in 11 yr. Assuming the minimum acceptable rate of 10%, tax rate of 48% and a straight-line depreciation, determine which unit is more economical based on annual costs. Using the equations... 

A carbon steel heat exchanger that costs 140,000 is expected to have a service life of 5 years before it requires replacement. If type 304 stainless steel is used, then the service life will be increased to 10 years. Which exchanger is the most economical if the cost of capital is 12% ... 

In this case, it would be more economical to buy the stainless steel heat exchanger. 

The relatively complex procedure that may be required and the associated safety considerations for chemical cleaning of heat exchangers is illustrated by a case study published by French [1981]. The deposit on the surfaces of a stainless steel heat exchanger had the aproximate composition given in Table 15.12. 

FIGURE 17.3. Simplified sketch of laboratory equipment to study the removal of particulate haematite particles from stainless steel heat exchanger tubes... 

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