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| Microstructure and Formation Mechanism of Inner-wall Oxide Layers of TP347H Steel Tube in Long-term Service Involving Deep Peak-load Shaving |
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| DOI：10.7643/issn.1672-9242.2023.06.015 |
| KeyWord:deep peak-load shaving TP347H steel tube oxide layer microstructure formation mechanism |
| Author | Institution |
| WANG Bo |
School of Materials Science and Engineering, Hefei University of Technology, Hefei , China |
| ZHANG Jian |
Anhui Xinli Electric Technology Consulting Co.Ltd., Hefei , China |
| YANG Ping |
Department of Technology, Wenergy Hefei Power Generation Co.Ltd., Hefei , China |
| WANG Ruo-min |
Anhui Xinli Electric Technology Consulting Co.Ltd., Hefei , China |
| HU Yu-zhang |
Department of Technology, Wenergy Hefei Power Generation Co.Ltd., Hefei , China |
| TANG Wen-ming |
School of Materials Science and Engineering, Hefei University of Technology, Hefei , China |
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| Abstract: |
| The work aims to study the inner-wall oxide layers of the TP347H high-temperature superheater and pendant superheater tubes of a super critical unit involving deep peak-load shaving to master and handle the new safety issues brought with deep peak-load shaving. Phase composition and microstructure tests were conducted to clarify microstructure and its formation mechanism of the oxide layers. The results showed that the oxide layer was divided into the inner and outer sub-layers by the medium layer of pores. The outer-sublayer had a loose structure, and consisted of Fe2O3; meanwhile, the inner-sublayer was dense, and mainly consisted of (Fe, Ni)Cr2O4, in which the Cr-rich grain-boundary phase partly reacted with the vapor containing oxygen, and then gasified to form the in-situ pores. The vapor diffused through the pores, and reacted with Cr in the steel, resulting in formation of the thin discontinuous Cr2O3 layer. On the other hand, the Fe atoms in the steel diffused into the inner/outer sublayer interface though the voids in the thin Cr2O3 layer, and reacted with the vapor to form Fe2O3, promoting the growth of the outer sublayer. Deep peak-load shaving accelerates oxidation of the inner-wall of the TP347H steel tubes and formation of the pores in the oxide layers, and also induces microcracks in the outer sublayer. As a result, exfoliation of the inner-wall oxide layer is promoted. |
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