This work presents failure investigation of a prill-tower fan that was in service for about 20 years in a urea plant. All the fan-blades and the plummer blocks fractured catastrophically during the plant-operation, shocked the plant personnel, and caused a huge shutdown loss. Standard failure analysis procedure involving: site visit, visual inspection, microstructural analysis, fracture analysis, analytical stress calculation and FEM analysis was followed. The investigation confirms that the fan-blades having numerous dents and nicks were operating in a mild corrosive atmosphere of ammonium hydroxide. The fracture analysis suggests that a pre-existing dent on the trailing edge of a blade corroded to form a pre-crack that aligned perpendicular to the long axis of the blade. When the pre-crack grew to a critical size, a small chunk of the blade fractured from the vicinity and ejected towards the blade-tip by centrifugal force. Because of confined space around the fan and limited blade-tip clearance, this triggered a chain reaction of blade fracture and rattled the entire array of fan-blades. The analysis establishes that the plummer blocks failed due to mechanical imbalance of the fan-shaft caused by the blade failure. The investigation concludes that presence of dents and nicks on the fan-blades is the root-cause for this catastrophic failure. Grinding-off of the surface defects to eliminate stress raisers is recommended for averting such a failure in future.

这项工作提出了对在尿素工厂中服役约20年的射流塔风机的故障调查。在工厂运行期间，所有风扇叶片和垂直轴承座都发生了灾难性的断裂，震惊了工厂人员，并造成了巨大的停机损失。遵循标准的失效分析程序，包括：现场访问，目视检查，显微结构分析，断裂分析，分析应力计算和有限元分析。调查证实，具有许多凹痕和刻痕的扇叶在氢氧化铵的温和腐蚀气氛中运行。断裂分析表明，叶片后缘上的预先存在的凹痕被腐蚀而形成垂直于叶片长轴对齐的预裂纹。当预裂纹增长到临界尺寸时，叶片的一小部分从附近破裂并通过离心力向叶片尖端弹出。由于风扇周围的空间有限且叶片尖端间隙有限，因此引发了叶片断裂的连锁反应，并使整个风扇叶片嘎嘎作响。分析表明，由于叶片故障导致风扇轴的机械不平衡，导致立式轴承座失效。调查得出的结论是，风扇叶片上出现凹痕和缺口是造成这种灾难性故障的根本原因。建议消除表面缺陷以消除应力升高，以防止将来发生此类故障。这引发了叶片断裂的连锁反应，并使整个扇形叶片嘎嘎作响。分析表明，由于叶片故障导致风扇轴的机械不平衡，导致立式轴承座失效。调查得出的结论是，风扇叶片上出现凹痕和缺口是造成这种灾难性故障的根本原因。建议去除表面缺陷以消除应力升高，以防止将来发生此类故障。这引发了叶片断裂的连锁反应，并使整个扇形叶片嘎嘎作响。分析表明，由于叶片故障导致风扇轴的机械不平衡，导致立式轴承座失效。调查得出的结论是，风扇叶片上存在凹痕和缺口是造成这种灾难性故障的根本原因。建议去除表面缺陷以消除应力升高，以防止将来发生此类故障。