The explosion reason analysis of urea reactor of Pingyin

• Weiqiang Wang^{a, b, c, ,} ,
• Aiju Li^d,
• Yanyong Zhu^e,
• Xiaojing Yao^{c, f},
• Yan Liu^{a, b, c},
• Zhonghe Chen^{c, g}

• ^a School of Mechanical Engineering, Shandong University, 73 Jingshi Road, Jinan, 250061 Shandong, PR China
• ^b Research Center of Special Equipment Safety Guarantee and Assessment, Shandong University, Jinan, 250061 Shandong, PR China
• ^c Engineering and Technology Research Center for Special Equipment Safety of Shandong Province, Jinan, 250061 Shandong, PR China
• ^d Key Laboratory for Liquid Structure and Heredity of Materials, Ministry of Education of China, Engineering Ceramics Key Laboratory of Shandong Province, Shandong University, Jinan, 250061 Shandong, PR China
• ^e General Iron and Steel Research Institute, Beijing 100081, PR China
• ^f Shandong Special Equipment Inspection and Research Academe, Jinan 250013, PR China
• ^g School of Chemistry and Chemical Engineering, Jinan University, Jinan 250022, PR China

View full text

Purchase $31.50

---

Abstract

In allusion to the explosion of a urea reactor took place in a fertilizer plant at Pingyin, Shandong, China, a series of evidence collection and inspection jobs which includes collecting operation condition and parameters, sampling the explosion fracture, reactor body apart from explosion fracture, and leak detection medium and its hangover, etc., had been carried out firstly. Based on these jobs, farther analysis and computation work has been done to the structural and materials characteristics and the operation condition of the urea reactor, including compositions, metallographic phases, tensile properties, impact energy, strain ageing characteristics, and fracture toughness of the urea reactor steels, the compositions of leak detection medium and its hangover in the urea reactor, and explosion energy of the urea reactor. The most probable cause of the explosion of the Pingyin urea reactor may be: the severe stress corrosion cracking (SCC) and instable propagation occurred, which made the liner could not withstand the heavy load of internal pressure and produced tearing destruction, then caused the medium in the reactor leaking rapidly, and the BLEVE (boiling liquid expansion vapor explosion) happened in the reactor at last. The main medium reason which caused SCC is some minim alkali ions such as K⁺ and Na⁺ in the leak detection steam liquefied and concentrated. The structural reason to cause the explosive accident is the insufficient or uncertain seal of the conical thread connection between the leak detection nozzle and the first layer, which could not prevent the leak detection steam leaking and diffusing into the layer gaps. Finally, the leakage and concentration of the steam caused the SCC of many layers at the same time.

Keywords

• Urea reactor;
• Explosion;
• Stress corrosion cracking;
• Leak detection by steam

---

Figures and tables from this article:

Fig. 1. Schematic of urea reactor layers and weld.

Figure options

Fig. 2. The structure of leak detection hole of exploded urea reactor.

Fig. 3. The destroyed status of the foundation, the bottom formed head, and Cylinder 10.

Fig. 4. The destroyed status of Cylinder 9.

Fig. 5. The destroyed status of Cylinders 1–8.

Fig. 6. The fracture appearance at the northeast direction of Cylinder10.

Fig. 7. The fracture status of the cracks underneath and around thermoelement nozzle.

Fig. 8. Radial cracks around the leak detection hole.

Fig. 9. The fracture position of Cylinder 8.

Fig. 10. The appearance of tearing in Cylinder 8.

Fig. 11. The top shelf of trays remained at the original position of the flied off reactor body.

Fig. 12. The cracking status of 16MnR layer near to C8.

Fig. 13. The cracking status in C8 between NO7 and NI8.

Fig. 14. The fracture appearances of Cylinder 9 near the thermoelement nozzle by SEM.

Fig. 15. The intergranular fracture appearance at C10 near 16MnR layer of Cylinder 9 by SEM.

Fig. 16. The intergranular fracture around C9 near 15MnVR layer of Cylinder 8 by SEM.

Fig. 17. The intergranular fracture appearance of Q235-A annulus by SEM.

Fig. 18. The fracture intergranular appearance of 16MnR layer by SEM.

Fig. 19. The fracture intergranular appearances of 15MnVR layer by SEM.

Fig. 20. The exudation status of weep hole in Cylinder 10.

Fig. 21. The status of urea solution outlet pipe and thermoelement nozzle at the top of the reactor.