Y Gong et aL/Engineering Failure Analysis 31(2013)203-210 已品是 site A ao w spot loan set NO ERS Fig. 7. SEM micrograph of cross-section of the 'Yin-Yang corrosion on failed tubes. (a)" face, (b)narrow deep, (c)elliptical, (d) wide& shallow, (e) subsurface, (f undercutting, and 2Nacl+2H20 2NaOH+H21+Cl2↑ As for the mechanism of pitting corrosion, it was so familiar and didnt deserve repeatedly discussed in detail. Now the focus should turn to the reason why this pitting corrosion eventually brought about such a peculiar "Yin-Yang ' morphology on the failed tubes. According to the process parameters, concentration of the wet Pta filter cakes was only 38.7%, i.e. the humidity was as high as 61.3%. Meanwhile, the rotation rate of the dryer cylinder was only 2. 2 r/min, a little bit lower than the designed value 2. 4 r/min. Also, inside it, the motion mode of the dryers heat exchanger tubes was translational, rather2Nacl þ 2H2O ! electrolysis 2NaOH þ H2 " þCl2 " ð2Þ As for the mechanism of pitting corrosion, it was so familiar and didn’t deserve repeatedly discussed in detail. Now the focus should turn to the reason why this pitting corrosion eventually brought about such a peculiar ‘Yin-Yang’ morphology on the failed tubes. According to the process parameters, concentration of the wet PTA filter cakes was only 38.7%, i.e. the humidity was as high as 61.3%. Meanwhile, the rotation rate of the dryer cylinder was only 2.2 r/min, a little bit lower than the designed value 2.4 r/min. Also, inside it, the motion mode of the dryer’s heat exchanger tubes was translational, rather Fig. 7. SEM micrograph of cross-section of the ‘Yin-Yang’ corrosion on failed tubes. (a) ‘Yang’ face, (b) narrow & deep, (c) elliptical, (d) wide & shallow, (e) subsurface, (f) undercutting, and (g) horizontal. 208 Y. Gong et al. / Engineering Failure Analysis 31 (2013) 203–210