Corrosion problems in coal-fired boiler superheater and reheater tubes: fireside corrosion. Final report
This program was conducted to develop improved alloys for superheater and reheater tubes in direct coal-fired steam generators in order to extend the service life of the tubes, and to evaluate materials for use at higher operating temperatures than currently in use. The program consisted of a broad literature review and laboratory evaluation involving 19 commercial and semicommercial alloys, 19 custom-melted alloys and 18 types of high-temperature coatings, subjecting them to flowing flue gas and molten alkali-iron trisulfate ash at 1250 and 1450/sup 0/F (675 and 790/sup 0/C). The commercial and semicommercial alloys suffered severe attack and pitting under the laboratory fireside test environment at 1250/sup 0/F (675/sup 0/C). In the custom-melted group, the best alloy (25%Ni-20%Cr-2%Al-2.4%Si) generated a dense, adherent scale which reduced pitting by a factor of four when subjected to the molten trisulfate. The character of the pitting attack is best described as an electrochemical mechanism where the molten trisulfate provides the electrolyte and transfers away the metal consumed at the active anodic areas. Protective scales were observed only on a few alloys of higher silicon content; these alloys are believed to offer significant improvement in useful life in steam generators firing corrosive coals. The magnesium zirconate (MgZrO/sub 3/) coating was resistant to corrosive attack, providing a self-healing mechanism by the formation of high-melting sulfates within its pores. This pore plugging effect withstood exposure cycles which would seriously damage conventional stainless steel tubes.
- Research Organization:
- Foster Wheeler Corp., Livingston, NJ (USA)
- OSTI ID:
- 7080390
- Report Number(s):
- EPRI-CS-1653
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
200104* -- Fossil-Fueled Power Plants-- Components
36 MATERIALS SCIENCE
360105 -- Metals & Alloys-- Corrosion & Erosion
ALLOYS
BOILERS
CARBONACEOUS MATERIALS
CHEMICAL REACTIONS
COAL
COATINGS
CORROSION
CORROSION RESISTANCE
CORROSIVE EFFECTS
ENERGY SOURCES
FLUE GAS
FOSSIL FUELS
FOSSIL-FUEL POWER PLANTS
FUELS
GASEOUS WASTES
MATERIALS
POWER PLANTS
PROTECTIVE COATINGS
STEAM GENERATORS
SUPERHEATERS
TEMPERATURE DEPENDENCE
THERMAL POWER PLANTS
TUBES
VAPOR GENERATORS
WASTES