During the reliability validation process of a specific natural gas engine,a fracture of the exhaust valve occurred.The fracture cause was analyzed by using methods such as morphology observation,chemical composition analysis and hardness testing,and improvement measures were proposed.The results indicate that the chemical composition and hardness of the exhaust valve material meet the requirements of GB/T 12773-2021.The hardness test shows that the maximum actual working temperature of the exhaust valve is 725-735 ℃.The oxide layer generated on the valve stem under high temperature extends to the substrate and forms microcracks on the surface of the valve stem.High temperature causes layered precipitates to precipitate along the grain boundary,further accelerating the propagation of microcracks along the grain boundary,and gradually developing into deeper cracks,ultimately leading to fatigue fracture of the valve stem.It is recommended that reducing the operating temperature of the exhaust valve through optimizing the combustion system parameters,or alternatively,selecting NCF 3015 or Inconel 751 materials with superior temperature resistance can ensure the exhaust valve meets the operational requirements.
natural gas engineexhaust valvefracturefailure analysis
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