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Laboratory corrosion testing of coatings and substrates simulating coal combustion under a low NO x burner atmosphere
Author(s) -
Agüero A.,
Gutiérrez M.,
Muelas R.,
Plana D.,
Román A.,
Hernández M.
Publication year - 2014
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.201307096
Subject(s) - metallurgy , materials science , combustion , boiler (water heating) , oxidizing agent , slurry , atmosphere (unit) , high temperature corrosion , combustor , coating , reducing atmosphere , decarburization , corrosion , waste management , composite material , chemistry , physics , organic chemistry , engineering , thermodynamics
It is certainly a difficult task to evaluate new materials and coatings to be used for boilers in power plants, as conditions are extremely complex, comprising a highly erosive environment, high temperature, highly corrosive gases, and reactive deposits. In particular, early catastrophic failures, as well as higher degradation rates have been observed on different power plant boiler components when operating under atmospheres containing low levels of oxygen. These atmospheres are typical of low NO x burners, and can be more corrosive than normal oxidizing conditions. The presence of a sulfidizing atmosphere as well as ash deposits present in boilers, are in part responsible of this accelerated damage. In this work, testing under a low oxygen atmosphere has been carried out on T22 and P92 uncoated and coated specimens. The atmosphere was equal to that measured in a Spanish coal‐fired power plant (ENDESA, Compostilla, León) and the test temperature was 580 °C. Tested coatings were slurry applied aluminides, as well as two HVOF sprayed coatings including a commercially deposited Cr 2 C 3 NiCr, and a newly developed Cr 2 O 3 ‐Cr composite coating. The specimens were covered with ash (taken from the plant) prior to testing. After testing, the uncoated substrates exhibited high thickness oxides with some sulfide inclusions whereas all tested coatings were very protective. Exposed samples of T22 tubes employed in the Compostilla power plants were analyzed and compared with the corresponding specimens tested in the laboratory. In both cases, the scales contained Fe 3 O 4 and FeS but the sulfide content was significantly higher in the scale formed in the plant. Moreover, ash particles were found embedded in the both scales.