尿素合成塔缺陷评定

为确保尿素合成塔安全运行，采用失效评定图对尿素合成塔进行了缺陷评定。鉴于有限元分析技术可以针对尿素合成塔这一特定结构建立精细的分析模型进行参数分析，能够大大地提高结果的准确度，采用有限元方法计算评定参数。建立含裂纹结构的尿素合成塔缺陷三维分析模型，通过节点位移插值计算应力强度因子；基于塑性屈服和裂纹稳态扩展准则求得结构的极限载荷；利用SINTAP中的失效评定曲线进行缺陷评定与1～4年后的安全预评定。结果表明，目前设备处于安全状态，安全裕度为0．2026，1—2年后设备仍安全，第3年临界安全，第4年设备失效。

Defect Assessment on Urea Synthetic Reactors

The failure assessment diagram （FAD） method was applied to conducte a defect assessment of urea synthetic reactor in order to ensure its safe service. Considering the detailed analysis model of urea synthetic reactor could be created through finite element analysis, and the accuracy of results could be improved largely, finite element method was used to determine the assessment parameters. The 3 D defect analysis model of the cracked structure was created and the stress intensity factor （SIF） was calculated by nodal displacement interpolation. The collapse load was investigated through the plastic yield and crack steady propagation criterions. The defect assessment on the structure and the safety predictions were carried out via a FAD of SINTAP procedure. The results show that the urea synthetic reactor is currently safe with a margin of 0.2026, in the first 2 years it is still safe, and in the state of critical safety in the 3th year, and failed in the 4th year.