Corrosion Failure Analysis of a Condenser on the Top of Benzene Tower in Styrene Unit
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CASE HISTORY—PEER-REVIEWED
Corrosion Failure Analysis of a Condenser on the Top of Benzene Tower in Styrene Unit Y. G. Zheng • G. Q. Liu • Y. M. Zhang H. X. Hu • Q. N. Song
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Submitted: 5 January 2014 / in revised form: 30 January 2014 / Published online: 25 March 2014 Ó ASM International 2014
Abstract Corrosion and scaling of heat exchanger is a severe problem in oil refinery industries. In this paper, the corrosion mechanisms of tubes in the condenser at the top of the benzene tower have been investigated by elemental analyzer, optical microscopy, and scanning electron microscopy (SEM) with energy-dispersive spectrometry (EDS) and X-ray diffraction (XRD) analysis. It is concluded that corrosion occurred outside the tube due to a trace amount of acidic water containing chloride ion which condensed on the surface of tubes. Then the condensed acidic water led to electrochemical corrosion during heat exchanging process in the condenser at the top of the tower. Chloride ion plays a very important role in the tube corrosion. The most important point is that chloride ion could cause the depassivation of material. Moreover, chloride ion is easily absorbed onto the surface of tubes due to the negative charge. Later, the corrosion of tubes is accelerated due to ion migration if the concentration of chloride ion increases. In addition, the loose scales of corrosion product also accelerate the electrochemical corrosion since it makes the acidic aqueous solution easier to stay and concentrate on the tube surface. Keywords Corrosion Reflux tank Styrene unit Condenser Chloride ion corrosion
Y. G. Zheng (&) G. Q. Liu Y. M. Zhang H. X. Hu Q. N. Song State Key Laboratory for Corrosion and Protection, Institute of Metal Research, CAS, 62 Wencui Road, Shenyang 110016, Liaoning, China e-mail: [email protected]
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Introduction and Background Information Heat exchangers are widely used in the petrochemical industry for energy reducing and improving efficiency. However, it is well known that the corrosion of heat exchanger is a severe problem in the oil refinery industries. Previous studies have shown that corrosion usually occurred in the tubes due to the presence of chlorine, sulfur, and/or other impurities in oil mixture or cooling water [1–3]. Tawancy [1] found that small amount of water in the media led to the corrosion. Kuznicka [2] considered that the corrosion of the tubes in heat exchanger was attributed to chlorides. Kou et al. [4] discovered that high content of salt in the oil-water mixture led to the perforation of the tube. However, there is no perfect explanation for this problem. In this work, the corrosion process of the tubes in heat exchanger has been systematically analyzed and a reasonable explanation was put forward. The schematic diagram of benzene tower and the top condenser is shown in Fig. 1. The condenser on the top of benzene tower is a kind of shell-and-tube heat exchanger with benzene mixture passing through it. The top condenser beyond reflux tank of benzene tower was replaced by a ne
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