氨合成塔冷管失效分析

Failure Analysis of Cooling Tubes in Synthetic Ammonia Tower

采用金相、电子探针成分分析和显微硬度检测手段研究了断裂冷管段 ,同时进行现场硬度检测 ,说明断裂冷管形成了深度达 1mm的渗氮层 ,且由于渗氮致使氮化层严重脆化和开裂 ,同时氮化层在腐蚀氧化和冷热疲劳作用下 ,导致冷管表面形成了较深的冷热疲劳或氮化脆化裂纹 ,导致冷管的韧性降低 ,甚至断裂。建议严格控制合成塔的操作温度 ,定期检验塔内件承压元件的渗氮程度 。

The broken cooling tube was investigated by adopting metallographic analysis electron probe chemical component analysis and microhardness testing methods. In the meanwhile, the hardness of the cooling tubes was tested in site. The results showed that the nitriding layer with depth reaching 1mm had formed in the broken cooling tube surface. The action of nitriding makes the nitriding layer brittle and cracking. And as a result the deeper thermal fatigue or nitrided brittle cracks were formed on the cooling tube surface because the nitriding layer was acted by corrosively oxidation and thermal fatigue. This reduced the toughness of the cooling tubes and led the tubes fractured. In order to ensure the device safely operated, it is suggested to strictly control the operation temperature of the synthetic ammonia tower and inspect the nitriding extent of the undertaking pressure elements of the tower inner parts periodically.