Analysis on Layer Cracking of Urea Reactors

A destructive explosion of a multilayered urea reactor on Mar. 21, 2005 in Shandong Province, China resulted in huge losses. About 10 urea reactors were scrapped in inspection and assessment after the explosion for the reason of layers severely cracking. Three scrapped urea reactors including the explosive reactor were anatomized layer by layer and 12 cracking reactors, and others were investigated for further study. Cracking morphology was observed in detail. Taking account of application conditions, the layer cracking can be divided into four categories: 1) severe cracking from the outmost layer inward, 2) severe cracking from the innermost layer outward, 3) randomly cracking from the outmost layer inward, or the innermost layer outward, or the middle layer, and 4) slight cracking. The reason for the layer cracking is SCC which is proved by means of visual observing the characteristics of the reactor cracking, metallographic experimenting on the samples taken from the cracking regions in the reactor and analyzing the corrosion products in the clearances between layers, the clearances of the cracks, and spills from air vent. The authors analyzed factors which caused different cracking categories from material, stress and media, gave advice on the leak detection of urea reactors: either the quality and flow of the leak detection steam should be strictly controlled, or better leak detection method should be used.