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Characterization of the Oxide Scale Formed on T12 Water Wall Tube After Long-term Service in Supercritical Power Plant

Authors
  • Zhong, Xiangyu1
  • Hamdani, Fethi1
  • Xu, Jian1
  • Shoji, Tetsuo1
  • Tatsuki, Tadashi2
  • Morii, Jun2
  • Sasaki, Wakako2
  • Ishii, Yasunori2
  • 1 Tohoku University, Frontier Research Initiative, New Industry Creation Hatchery Center, 6-6-10 Aza-Aoba Aramaki, Aoba-ku, Sendai, 980-8579, Japan , Sendai (Japan)
  • 2 Tohoku Electric Power Co., Inc., Sendai, Japan , Sendai (Japan)
Type
Published Article
Journal
Oxidation of Metals
Publisher
Springer US
Publication Date
Feb 22, 2019
Volume
91
Issue
5-6
Pages
705–727
Identifiers
DOI: 10.1007/s11085-019-09905-1
Source
Springer Nature
Keywords
License
Yellow

Abstract

Oxide scale control is one of the critical maintenance issues in fossil fuel power plant. Hence, the water treatment of the feed water has been changed from all-volatile treatment (AVT) to oxygenated treatment (OT) by added some amount of oxygen in the system to form a stable oxide and minimize the scale growth rate. In this work, the oxide scales formed on T12 water wall tube after one cycle of chemical cleaning treatment under OT condition in a supercritical coal power plant were characterized by using various methods. It was found that the oxide scale formed on the inner surface of the tube had a multi-layer structure with a porous outer layer consisting of Fe3O4 and Cr-rich α-Fe2O3 oxides and a dense inner layer consisting of Cr-rich spinel oxide. A Cr- and Mn-enriched outermost layer was also observed. Cavities, pits, and exfoliation were observed in the oxide scales. The cavities and grain boundaries behaved as the short path of the diffusion of oxygen into the metal. Intergranular oxidation was observed between the inner layer of oxide scale and matrix. The distribution, morphology, and chemical compositional of these oxides were assessed and discussed from a point of view of the suitability of current chemical cleaning solution and procedure which has been used for AVT descaling.

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