MATERIALS FOR HIGH TEMPERATURE METALLIC HEAT EXCHANGERS
Process efficiency and economics for heat exchangers in electricity generation, petrochemical, coal conversion and other industries are improved as the temperature of heat transfer and the plant lifetime are increased. These demands, however, aggravate materials problems in recuperative units working at temperatures in the range 500 degrees C to about 1000 degrees C. The materials of construction include ferritic and austenitic alloy steels, and nickel base alloys, the materials selection depending on the combination of temperature, mechanical loading and ? environmental factors for each application. The working environments encountered by these heat exchanger materials include normally oxidizing combustion gases, low oxygen containing gases, and coal ash slags. Other corrosive elements such as sulphur, chlorine, and vanadium may be encountered, particularly in coal conversion systems, oil fired boilers etc. Entrained solids may be found in all the environments. Exposure to these environments results in corrosion which is enhanced by any crevices formed during construction. Particularly serious is the local attack beneath deposited particulate material (fouling corrosion). When the velocity of the entrained solids in the gas stream rises sufficiently, erosion of the protective oxide, or even of the alloy itself, becomes serious. Furthermore, the heat exchanger material must have adequate mechanical properties for long term service, in terms of creep and fatigue strength and ductility. These properties may be affected by environmental attack; knowledge of the magnitude of the effect being necessary for efficient material usage. Thus, there is a need to achieve a balance between mechanical properties and corrosion resistance. The use of coatings or bimetallic tubes to enable heat exchangers to operate in particularly severe environmental conditions are discussed, as are the materials problems resulting from the forming and joining procedures which are needed to fabricate an engineering component.
Bibliographic Reference: ADVANCED COURSE ON HIGH TEMPERATURE HEAT EXCHANGERS, DUBROVNIK (YUGOSLAVIA) AUG. 25-30, 1985 WRITE TO CEC LUXEMBOURG, DG XIII/A2, POB 1907 MENTIONING PAPER E 32563 ORA
Availability: Can be ordered online
Record Number: 1989124095000 / Last updated on: 1987-01-01
Available languages: en