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Industry's usual approach to evaluating the design of heat transfer equipment is to look for failures that have occurred in existing equipment of the same design, try to determine their causes, and then develop design modifications to prevent them from recurring. This is referred to as "failure analysis."
In general, there is more than one cause for heat exchanger failures. Two major problems are poor manufacturing and incorrect equipment operation. Because these causes are not always obvious, the design may be blamed for a failure. When this happens, the heat exchanger invariably is modified and a perfectly good design is sometimes lost.
There is a tendency in industry to overlook successful designs of existing equipment that have operated for many years without major failures. A manufacturer of this type of equipment that also repairs and retubes heat exchangers is in a unique position to analyze and evaluate the designs used. Data on the condition of individual components and materials used, and operating conditions, types of fluids and specific design features can all be compiled to develop a complete evaluation. In addition, calculations can be made to verify the validity of currently established design parameters from various sources.
Utility heat exchangers cover a wide range of equipment, including feedwater heaters, evaporators, condensate coolers, lube oil coolers, turbine oil coolers, air preheaters, generator coolers, service water exchangers and air ejector condensers. The piece of equipment selected to be analyzed is a horizontal three-zone feedwater heater. Four major areas will be covered: tubeside, desuperheating, condensing, and subcooling zones of heat exchangers. The analysis...