Failure analysis of a first stage IN738 gas turbine blade tip cracking in a thermal power plant

Sushila Rani, Atul K. Agrawal, Vikas Rastogi
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引用次数: 73

Abstract

This research paper deals with the investigation of causes of failure of the first stage gas turbine blade of 30 MW gas turbine having tip cracks at the trailing as well as leading edge. This blade is made of nickel based super alloy IN738LC, having directional solidified grain structure and contains aluminide coating (Pt–Al2) by diffusion process. The main focus of the paper is evaluation of tip crack at the trailing edge and further degradation of blade coating. The investigations included the visual observations, material composition analysis, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). During examination of the failed blade, it is found that the blade surface is completely degraded due to overheating. Corrosion pits are formed on the blade surface, these pits act as a notch to produce stress concentrations and cracks is initiated due to fatigue which further propagate due to hot corrosion. It is also reported that the Al-Pt coating is completely degraded, heavily oxidized. From these investigations, it is concluded that the failure of gas turbine blade takes place due to the combined effect of surface degradation caused by overheating, oxidation, hot corrosion and degradation of coating heavily oxidized.

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某火电厂IN738燃气轮机一级叶顶开裂失效分析
本文研究了30mw燃气轮机一级燃气轮机叶片尾缘和前缘存在尖端裂纹的失效原因。该叶片由镍基高温合金IN738LC制成,具有定向凝固的晶粒组织,并通过扩散工艺包裹有铝化物涂层(Pt-Al2)。本文的主要研究重点是叶片尾缘裂纹的评价和叶片涂层的进一步退化。研究包括目视观察、材料成分分析、扫描电子显微镜(SEM)和能谱分析(EDS)。在检查失效叶片时,发现叶片表面由于过热而完全退化。腐蚀坑是在叶片表面形成的,这些坑作为缺口产生应力集中,裂纹是由疲劳引起的,由于热腐蚀进一步扩展。也有报道称Al-Pt涂层完全降解,严重氧化。从这些研究中得出结论,燃气轮机叶片的失效是由于过热、氧化、热腐蚀和重氧化涂层降解引起的表面退化的综合作用而发生的。
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