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Purpose: of this paper is to reveal the mechanisms of corrosion processes of outer surfaces of low-emission steam boiler evaporator tubes. Examinations were performed to find the reasons of different corrosion susceptibility of tubes situated at combustion chamber on various levels. Design/methodology/approach: Examinations were conducted on several segments of Ø 57 x 5.0 mm evaporator tubes made of 16M (16Mo3) steel grade. Segments were taken from level of 10 meters and 18 meters from the chamber bottom of low-emission coal fired steam boiler after two years operation. Microstructure degradation of base material was estimated. Metallographic evaluation of scale morphology, its micro sites chemical composition analysis and distribution of elements on cross sections have been performed. Findings: Eexaminations of evaporator tubes indicated that reduction of wall thickness was considerable at the segments taken from level of 10 m, when at level of 18 m this reduction was small. The morphology of scales consisted of external layer which was porous and weakly connected to the tube surface, and internal layer, which was dense and adherent to the base metal. In these two layers the bands reach in sulfur were detected. The sulfide corrosion seems to be the main degradation mechanism of the tube surface at the level of 10 m. Research limitations/implications: Corrosion of the water wall tubes in low-emission steam boilers is a result of reaction of steel tube surface with the aggressive substoichiometric environment contains sulfur. The chemical composition of flue gases changes along the water wall. The exact compound of flue gases has not been determined in this study. Practical implications: Prevention of water wall tubes corrosion can be achieved by changing in operation conditions or replacement of tube materials. The first mentioned action is limited to accurate burner's adjustment or introduces a flow of additional air along the walls and create air curtain between reducing environment and tubes surface. These efforts often are insufficient. The replacement of more corrosion resistant material on Cr rich steel or Cr-Ni steel is possible but other problems appear connected with high costs of installation and low heat transfer coefficients of such materials. Knowing the mechanisms of corrosion allows adjusting combustion process at low emission steam boilers. Originality/value: Information available in literature does not clearly indicate what mechanism of corrosion is dominant at different parts of combustion chamber. The current study shows which corrosion mechanisms are the most dangerous for evaporator tubes.
Słowa kluczowe
Wydawca
Rocznik
Tom
Strony
85--92
Opis fizyczny
Bibliogr. 15 poz.
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autor
autor
- Institute of Engineering Materials and Biomaterials, Silesian University of Technology, ul. Konarskiego 18a, 44-100 Gliwice, Poland, santina.topolska@polsl.pl
Bibliografia
- [1]G. Y. Lai, High-temperature corrosion of engineering alloys, ASM Internationa, 1997, 1.
- [2]Metals Handbook, Failure Analysis and Prevention. ASM International, 1995, 11.
- [3]Metals Handbook, Corrosion, ASM International, 1987, 13.
- [4]Hernas, Creep resistance of steel and alloys. Silesian University of Technology, Gliwice, 1999 (in Polish).
- [5]J. Łabanowski, Mechanical properties and corrosion resistance of dissimilar stainless steel welds, Archives of Materials Science and Engineering 28/1 (2007) 27-33.
- [6]J. Nowacki, P. Rybicki, Corrision resistance of SAW duplex joints welded with high heat input, Journal of Achievements in Materials and Manufacturing Engineering 23/2 (2007) 7-14.
- [7]J. Łabanowski, S. Topolska, J. Ćwiek, Assessment of evaporator tubes corrosion in low-emission steam boilers, Advances in Materials Science 8/4 (2008) 14-21.
- [8]S. Król, M. Pietrzyk, Formation of corrosion products protecting surfaces of the boiler proper tubes from the combustion chamber, Journal of Achievements in Materials and Manufacturing Engineering 21/2 (2007) 45-48.
- [9]J. Okrajni, K. Mutwil, M. Cieśla, Steam pipelines effort and durability, Journal of Achievements in Materials and Manufacturing Engineering 22/2 (2007) 63-66.
- [10]J. Pacyna, The microstructure and properties of the new bainitic rail steels, Journal of Achievements in Materials and Manufacturing Engineering 28/1 (2008) 19-22.
- [11]S. Mrowec, T. Weber, The modern heat resistant materials, WNT, Warsaw, 1982 (in Polish).
- [12]A. Zieliński, J. Dobrzański, G. Golański, Estimation of the residual life of L17HMF cast steel elements after long-term service, Journal of Achievements in Materials and Manufacturing Engineering 34/2 (2009) 137-144.
- [13]J. Nowacki, P. Zając, Microstructure and corrosion resistance of the duplex steel wide-gap one-side fluxcored wire welded joints, Journal of Achievements in Materials and Manufacturing Engineering 28/2 (2008) 191-198.
- [14]D. Renowicz, A. Hernas, M. Cieśla, K. Mutwil, Degradation of the cast steel parts working in power plant pipelines, Journal of Achievements in Materials and Manufacturing Engineering 18/1/2 (2006) 219-222.
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Typ dokumentu
Bibliografia
Identyfikator YADDA
bwmeta1.element.baztech-article-BSL7-0048-0021