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http://dx.doi.org/10.3795/KSME-A.2016.40.4.423

Study for Fracture in the Last Stage Blade of a Low Pressure Turbine  

Lee, Gil Jae (Technical Solution Center, Technology & Information Department, Korea East-West Power)
Kim, Jae Hoon (School of Mechanical Engineering, Chungnam Nat'l Univ.)
Publication Information
Transactions of the Korean Society of Mechanical Engineers A / v.40, no.4, 2016 , pp. 423-428 More about this Journal
Abstract
The last stage blades of a low pressure (LP) turbine get frequently fractured because of stress corrosion cracking. This is because they operate in a severe corrosive environment that is caused by the impurities dissolved in condensed steam and high stress due to high speed rotation. To improve the reliability of the blades under severe conditions, 12% Cr martensitic stainless steel, having excellent corrosion resistance and higher strength, is widely used as the blade material. This paper shows the result of root cause analysis on a blade which got fractured suddenly during normal operation. Testing of mechanical properties and microstructure examination were performed on the fractured blade and on a blade in sound condition. The results of testing of mechanical properties of the fractured blade showed that the hardness were higher but impact energy were lower, and were not meeting the criteria as per the material certificate specification. This result showed that the fractured blade became embrittled. The branch-type crack was found to have propagated through the grain boundary and components of chloride and sulfur were detected on the fractured surface. Based on these results, the root cause of fracture was confirmed to be stress corrosion cracking.
Keywords
Thermal Power Plant; Low Pressure Turbine; Stress Corrosion Cracking; Intergranular Crack;
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Times Cited By KSCI : 1  (Citation Analysis)
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