Durability evaluation of protection coatings on water-wall tubes of low-emission boilers

• Autorzy: Ćwiek J.
• Języki publikacji: EN

Abstrakty

EN

Purpose: of the paper is presentation of diagnostic research on durability of protection coatings on water-wall tubes in low-emission boilers. Design/methodology/approach: Thermal spraying Al2O3/Ni-30Cr and hybrid paint coatings were evaluated. Durability of the coatings was evaluated after one and two years of service in direct action of flame, flue gas, and air flux from a blower. For evaluation of a level of degradation examinations of chemical composition and morphology of coatings and scales have been performed with the use of scanning electron microscope (SEM) equipped with EDS (energy dispersion X-ray spectroscopy) spectrometer. Findings: Ceramic Al2O3/Ni-30Cr coatings are resistant to flame corrosion, but failed due to cracks generated by thermal stresses. Hybrid paint coatings do not protect steel tubes against hot corrosion (flame corrosion) since oxygen, sulphur and chlorine can easily diffuse throughout the coating. Resulting sulphide scale under the coating causes spalling of the coating. Sulfidation attack results in accelerated corrosion (wastage rate). Research limitations/implications: Initial state of the coatings, and chemistry of combustion atmosphere have not been exactly known. Practical implications: Generation of NOx is limiting by firing fuel with lower amount of oxygen than required for complete combustion, i.e. under sub-stoichiometric conditions. Under these conditions carbon and sulfur present in coal are released as CO and H2S gases. Additionally, unburned carbon particles arrive at water walls, which lead to high temperature oxidation, sulfidation and sometimes molten salt attack. Sulfidation mechanism results in accelerated corrosion rate, and additional costs due to unscheduled outages and replacement of water-wall tubes. Originality/value: It has been found that the coatings do not protect heating surface of water-wall tubes from hot corrosion, including sulfidation under sub-stoichiometric burning. Durability of the coatings is from one to two years of exploitation of a boiler only.

Słowa kluczowe

EN

corrosion; low-emission boilers; hot corrosion; protection coatings

PL

korozja; kotły niskoemisyjne; korozja wysokotemperaturowa; powłoki ochronne

• Wydawca: International OCSCO World Press
• Czasopismo: Archives of Materials Science and Engineering
• Rocznik: 2012
• Tom: Vol. 56, nr 2
• Strony: 69--74

Twórcy

autor

Ćwiek J.

• Institute of Engineering Materials and Biomaterials, Silesian University of Technology, ul. Konarskiego 18a, 44-100 Gliwice, Poland

Bibliografia

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