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：在运行过程中，在煤气化装置中，预转化器的出口弯头处观察到裂纹。本文详细介绍了对故障的调查，并根据可用的文档和实验分析突出了最可能的故障原因。进行了外观检查，化学成分分析，能谱分析，断裂分析，冶金分析，力学性能测试和残余应力测量。实验结果表明，初次裂纹是从内部开始并扩展到肘部的外表面。钛元素含量低于GB / T 14976-2002的要求。腐蚀产物中富含O和S元素。观察到大量的二次裂纹和应变诱发的马氏体。此外，裂纹尖端附近的内表面上的残余应力非常高。根据实验结果和工作条件及历史分析，弯头的失效机理为应力腐蚀开裂。低钛含量引起的不锈钢敏化和错误的热处理导致晶间应力腐蚀开裂。
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