A crack was observed on an outlet elbow of the pre-converter in coal gasification unit during operation. This paper details the investigation into the failure and highlights the most probable cause of failure based on available documents and experimental analysis. Visual examination, chemical components analysis, energy spectrum analysis, fracture analysis, metallurgical analysis, mechanical properties test and residual stress measurement were performed. The experimental results show that the primary crack initiated from inside and propagated to outer surface of the elbow. The content of titanium element was lower than the requirement in GB/T 14976-2002. Corrosion products were rich in O and S elements. Amounts of secondary cracks and strain induced martensite were observed. Furthermore, the residual stress on the inner surface near the crack tip was extremely high. According to the experiment results and the analysis of operating condition and history, the failure mechanism of the elbow is stress corrosion cracking. Sensitization of the stainless steel due to low Ti content and the faulty heat treatment contributed to the intergranular stress corrosion cracking.
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机译：在操作期间在煤气化单元中的煤气化单元的出口弯头上观察到裂缝。本文详细介绍了对失败的调查，并突出了可用文件和实验分析的最可能失败原因。进行视觉检查，化学成分分析，能谱分析，断裂分析，冶金分析，机械性能试验和残余应力测量。实验结果表明，初级裂纹从内部发起并传播到肘部的外表面。钛元素的含量低于GB / T 14976-2002中的要求。腐蚀产品富含O和S元素。观察到二次裂缝和菌株诱导马氏体的量。此外，裂纹尖端附近的内表面上的残余应力极高。根据实验结果和操作条件和历史分析，肘部的故障机理是应力腐蚀裂缝。由于低Ti含量，不锈钢的敏化和故障的热处理导致晶间应力腐蚀裂缝有助于。
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