74 Y Gong, Z-G Yang/ Materials and Design 32 (2011)671-681 (a Fig. 5. External appearances of the manhole door B(a) two perforations, (b)size of the bigger perforation and (c)scaling on the edge of manhole door. (a) Fig. 6. External appearances of the primary superheater(a)manhole door and(b)steam piping. tion occurred on the primary superheater was uniform corrosion; superheats; on the other hand, decrease of temperature increases the hardness of these ash particles. Thus, the economizer is always Then, observation was conducted on the secondary superheater. subjected to erosive wear in service. As is shown in Fig 8a, trace of Compared with the primary superheater, the manhole door here erosive wear was indeed observed on the piping surfaces in this exhibited no obvious rust phenomenon, seen in Fig. 7a. However, economizer, and they were covered with large amount of ash dust it can be learned from Fig. 7b that uniform corrosion also occurred as well(Fig. 8b). However fortunately, no obvious corrosion was on the steam piping within this superheater detected. This may have been accounted of &s In summary, extent of degradation, ie the uniform corrosion in the fin-type configuration for the piping, which could effectively these two superheaters was not pretty serious. This may have been relieve the corrosion extent on its surfaces. To sum up, as for the relevant to the service conditions of them. As the predominant economizer, no serious corrosion but erosive wear had occurred medium that superheaters contacted was only high temperature on the piping surfaces, and only removing of the ash dust was steam, in other words, no severe corrosive environment would needed be generated under this condition. As a result, merely uniform cor Compared with the superheaters and the economizer, the air rosion that was caused by the effect from high temperature oxida- preheater suffered severer uniform corrosion on its piping wall tion was engendered upon the iron-based piping, and its extent ( Fig. 9a), and lots of brown rust had already scaled off and accumu- was acceptable lated on its bottom(some of it was then collected for further anal- Economizer is usually installed on the lower part of the steam ysis of its chemical compositions), seen in Fig. 9b. In fact, the system. Consequently, on one hand, concentration of the ash parti- service conditions of the air preheater were not as harsh as that cles in it is relatively higher than that in the upper equipments like of the upper steam equipments, why the corrosion extent of it ) Fig. 7. External appearances of the secondary superheater (a)manhole door and(b) steam piping.tion occurred on the primary superheater was uniform corrosion; however its extent was not severe. Then, observation was conducted on the secondary superheater. Compared with the primary superheater, the manhole door here exhibited no obvious rust phenomenon, seen in Fig. 7a. However, it can be learned from Fig. 7b that uniform corrosion also occurred on the steam piping within this superheater. In summary, extent of degradation, i.e. the uniform corrosion in these two superheaters was not pretty serious. This may have been relevant to the service conditions of them. As the predominant medium that superheaters contacted was only high temperature steam, in other words, no severe corrosive environment would be generated under this condition. As a result, merely uniform cor￾rosion that was caused by the effect from high temperature oxida￾tion was engendered upon the iron-based piping, and its extent was acceptable. Economizer is usually installed on the lower part of the steam system. Consequently, on one hand, concentration of the ash parti￾cles in it is relatively higher than that in the upper equipments like superheats; on the other hand, decrease of temperature increases the hardness of these ash particles. Thus, the economizer is always subjected to erosive wear in service. As is shown in Fig. 8a, trace of erosive wear was indeed observed on the piping surfaces in this economizer, and they were covered with large amount of ash dust as well (Fig. 8b). However fortunately, no obvious corrosion was detected. This may have been accounted for the application of the fin-type configuration for the piping, which could effectively relieve the corrosion extent on its surfaces. To sum up, as for the economizer, no serious corrosion but erosive wear had occurred on the piping surfaces, and only removing of the ash dust was needed. Compared with the superheaters and the economizer, the air preheater suffered severer uniform corrosion on its piping wall (Fig. 9a), and lots of brown rust had already scaled off and accumu￾lated on its bottom (some of it was then collected for further anal￾ysis of its chemical compositions), seen in Fig. 9b. In fact, the service conditions of the air preheater were not as harsh as that of the upper steam equipments, why the corrosion extent of it Fig. 7. External appearances of the secondary superheater (a) manhole door and (b) steam piping. Fig. 5. External appearances of the manhole door B (a) two perforations, (b) size of the bigger perforation and (c) scaling on the edge of manhole door. Fig. 6. External appearances of the primary superheater (a) manhole door and (b) steam piping. 674 Y. Gong, Z.-G. Yang / Materials and Design 32 (2011) 671–681