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| Failure Analysis on Main Steam Valve Stem of An Ultra-supercritical Turbine |
| Received:January 04, 2021 Revised:January 12, 2021 |
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| DOI：10.7643/issn.1672-9242.2021.06.020 |
| KeyWord:22Cr12NiMoWV (C422) steel valve stem stress concentration segregation mechanical property fracture failure |
| Author | Institution |
| ZHANG Jian |
Anhui Xinli Power Technology Consulting Co.Ltd., Hefei , China |
| MIAO Chun-hui |
Electric Power Research Institute, State Grid Anhui Electric Power Co.Ltd., Hefei , China |
| QIN Xiao-long |
School of Materials Science and Engineering, Hefei University of Technology, Hefei , China |
| WANG Ruo-min |
Anhui Xinli Power Technology Consulting Co.Ltd., Hefei , China |
| CHEN Guo-hong |
Electric Power Research Institute, State Grid Anhui Electric Power Co.Ltd., Hefei , China |
| TANG Wen-ming |
School of Materials Science and Engineering, Hefei University of Technology, Hefei , China |
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| Abstract: |
| Fracture of the nominal 22Cr12NiMoWV (C422) steel main steam valve stem of the ultra-supercritical turbine took place, which brought about an adverse influence on power generation security of the thermal power station. Based on the failure analysis of the valve stem, improvement approaches should be put forward in order to avoid the occurrence of similar accidents. Appearance inspection, composition and metallography tests and fracture surface observation, combining with hardness and impact toughness tests, were employed to investigate the fracture causes of the main steam valve stem. The results show that Composition of the valve stem meets the requirement of the 22Cr12NiMoWV steel. However, there are net-like distributed segregation microstructures in the steel, leading to that the mechanical properties of the steel cannot meet the standard requirement. Moreover, other disadvantages such as unreasonable mechanical design and manufacturing and unreasonable heat treatment of the valve stem were also found. Both right-angle transition at the location of reducing diameter and apparent machining tool mark through the cross-holes result in stress concentration in the valve stem, even induce microcracks over there. The microcracks preferentially propagate through the segregation microstructures of low mechanical properties, leading to fracture failure of the valve stem. Accordingly, reasonable proposals were put forward from quality control, process normalization and so on. |
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