Corrosion Failure Analysis of a Condenser on the Top of Benzene Tower in Styrene Unit

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.