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| Corrosion failure analysis of thin-film evaporator for caprolactam production |
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| 北京科技大学腐蚀与防护中心 |
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Abstract This paper mainly analyses the cause and principle of the failure of thin - film evaporator unit for purification processes in producing caprolactam. The device was forced to shutdown because of the decrease of wall thickness from 13.00 mm to 6.58 mm. The results of microstructrue and chemical composition analysis showed the failed component is eligible 304L stainless steel. By means of scanning electron microscopy it was found that there were corrosion ditches along the line of liquid flow and loose corrosion prduction layer on the surface of inner wall. Energy spectrum analysis showed the selective dissolution of elements Fe , Ni resulted in enrichment of Cr in the thinner corrosion production layer. According to the results of sample analysis and investigation of the operating conditions, it is confirmed that erosion - corrosion caused by high - speed liquid film containing organic acid is the main cause of the failure of the inner wall, and the corrosion thinned rate was accelerated after improving processing capacity. Moreover, corrosion resistance of stainless steels 304L,316,321 in acidic caprolactam solution was analyzed by potentiodynamic polarization curve measurement. It was confirmed that 316 stainless steel possessed better corrosion resistance to liquid flow.
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Received: 25 November 2005
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