Influence of Steam-Side Oxid Scales on Creep Life of Boiler Superheater Tube

článek v časopise ve Web of Science, Jimp

en

Creep life is a limiting factor in case of boiler tubes operating above creep temperature, and, for a given material, it generally is determined by the actual operating temperature and stress. Standard approaches to calculation of tube creep life take into account mainly the stress caused by pressure loading and mean temperature in the tube wall. However, estimation of the temperature and stress may be difficult in water tube boilers, because oxide scales tend to form on inner surfaces of the tubes exposed to steam and indirectly affect the resulting creep life. Because scales increase thermal resistance of a tube wall and, consequently, also wall temperature, creep life is reduced. Moreover, presence of oxide scales leads to higher hydraulic resistance of the tube, which can cause further increase in temperature in some tubes of the bundle if the oxide scale growth rate is not uniform. Additionally, elements increasing creep strength may leach out of the surface should the scales be porous, thus inducing even more pronounced decrease in creep life. This paper investigates effects of oxide scales on creep life of boiler tubes in cross flow. Thermal and stress conditions in tubes are thoroughly investigated using analytical as well as numerical approaches.

Creep life is a limiting factor in case of boiler tubes operating above creep temperature, and, for a given material, it generally is determined by the actual operating temperature and stress. Standard approaches to calculation of tube creep life take into account mainly the stress caused by pressure loading and mean temperature in the tube wall. However, estimation of the temperature and stress may be difficult in water tube boilers, because oxide scales tend to form on inner surfaces of the tubes exposed to steam and indirectly affect the resulting creep life. Because scales increase thermal resistance of a tube wall and, consequently, also wall temperature, creep life is reduced. Moreover, presence of oxide scales leads to higher hydraulic resistance of the tube, which can cause further increase in temperature in some tubes of the bundle if the oxide scale growth rate is not uniform. Additionally, elements increasing creep strength may leach out of the surface should the scales be porous, thus inducing even more pronounced decrease in creep life. This paper investigates effects of oxide scales on creep life of boiler tubes in cross flow. Thermal and stress conditions in tubes are thoroughly investigated using analytical as well as numerical approaches.

oxide scale, creep, superheater, tube, CFD, FEA

31.01.2018

Institute of Metals and Technology, Ljubljana, Slovenia

Ljubljana

1580-2949

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