Study of Modified Layer on Exterior Surface of Superheater Tubes

Abstract:

Renewal of overhaul period of power plants equipment, especially superheater tubes, is important problem in energy sector of every country. Investigation of processes on tube’s surfaces is necessary to obtain information of equivalent temperature during maintenance. In this work the austenitic chrome-manganese steel 10Cr13Mn12Si2Ni2Cu2Nb (DI59) and chrome-nickel steel 12Cr18Ni12Ti were studied. Application of these steels provides the desired heating resource of the steam superheater (100000 h) and reliable exploitation of the boilers at high temperature (~650°C). Between the oxide layer and the base metal layers with different crystal structure compared with matrix are observed. Qualitative and quantitative electron microscopic techniques, optical metallography and X-ray phase analysis are employed to investigate the morphological evolution, elemental redistribution in the alloy system and formation and growth of discovered layers. In steel DI59 the discovered layer had a ferrite structure. In steel 12Cr18Ni12Ti it was first shown that this layer is consist of different sulfides which disposed in FeNi₃ matrix. This intermetallic phase and ferrite layer are ferromagnetic. Changes in the structure of steel on its surfaces are caused by high exploitation temperature and type of fuel which is used in power plants (combination of natural gas and mazut). This opens the possibility to use connection between thermal irregularity in metal and thickness of discovered layers in order to search most damaged part of tubes with ferrite meter.

• Periodical: Materials Science Forum (Volumes 706-709)
• Pages: 890-895
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.706-709.890
• Online since: January 2012
• Authors: Dmitry Zmienko, Aleksey Korneev, Vladimir Bogachev
• Keywords: Austenitic Steel, High Temperature Oxidation, Phase Transformation, SEM, Structure, X-Ray Diffraction (XRD)

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