# The Corrosion Failure Mechanism of a Peak Load Boiler in a District Heating System
## 3 Results
### Simulation on Gas Temperature Distribution  
The CFD simulation was conducted under the most severe operating conditions, corresponding to the design pressure and design temperature of the PLB. In practice, the boiler typically operates under less extreme conditions; however, selecting these parameters ensures that the analysis encompasses worst-case scenarios where degradation is most likely to occur. A key challenge in evaluating the internal thermal environment is the lack of direct temperature measurements within the convection section. The only available temperature data are from stack emissions, which does not provide insight into localized temperature distributions inside the tubes. This limitation necessitated a numerical approach to estimate thermal gradients, gas flow behavior, and heat transfer characteristics within the system. While the simulation was performed under specific conditions, the \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Unit: ppm** & **Na\({}^{+}\)** & **Fe2\({}^{+}\)/Fe3\({}^{+}\)** & **Al3\({}^{+}\)** & **Mg2\({}^{+}\)** & **Silicate** & **Cl\({}^{-}\)** & **PO4\({}^{3-}\)** & **NO3\({}^{-}\)** & **SO4\({}^{2-}\)** \\ \hline
1 & 66.99 & 23.13 & 0.699 & 1.29 & 2.329 & 50.39 & \textless{}0.1 & 5.707 & 71.61 \\
2 & 63.91 & 0.777 & \textless{}0.1 & 0.37 & 1.65 & 47.08 & \textless{}0.1 & 11.47 & 23.83 \\
3 & 65.17 & 5.384 & 0.105 & 0.593 & 1.943 & 48.71 & \textless{}0.1 & 11.75 & 33.52 \\
4 & 72.37 & 0.216 & \textless{}0.1 & 0.141 & 1.355 & 65.50 & \textless{}0.1 & 7.099 & 18.60 \\
5 & 66.0 & 6.7 & 0.6 & 0.2 & 1.4 & 57.7 & \textless{}0.1 & 6.9 & 18.1 \\
6 & 66.0 & 0.1 & \textless{}0.1 & \textless{}0.1 & 1.5 & 58.4 & \textless{}0.1 & 6.6 & 17.9 \\
7 & 68.9 & 1.2 & 0.5 & 0.6 & 2.2 & 57.5 & \textless{}0.1 & 6.8 & 21.5 \\
8 & 61.9 & 1.0 & 0.1 & \textless{}0.1 & 2.3 & 52.4 & \textless{}0.1 & 6.9 & 16.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: IC and ICP analysis results of boiler feedwater collected eight times during \(11\) months. Figure 8: Comparison of non-leaked and near-leak turbidator shapes in the convection section of the PLB. **(a,b)** Non-leaked turbidator and its corresponding upper plate surface, **(c)** SEM image of the turbidator cross-section in the non-leaked region (270\({}^{\circ}\)), **(d,e)** Near-leak turbidator and its corresponding upper plate surface, **(f)** SEM image of the turbidator cross-section in the near-leak region (90\({}^{\circ}\)). results provide a basis for understanding the thermal environment and identifying areas prone to potential degradation. Figure 9 presents the simulation results, showing a generally symmetrical temperature distribution across the lower plate. However, a slight temperature deviation was observed near 0\({}^{\circ}\), where the gas exhibited a lower temperature compared to other regions, with a reduction of approximately 200 K. This was likely due to inertial effects, as the combustion gas shifted toward 180\({}^{\circ}\) while entering the convection section. Despite the lower temperature at 0\({}^{\circ}\), leakage did not occur in this region due to the flow dynamics preventing boiler water intrusion. This indicates that the occurrence of leakage is more influenced by the transport dynamics of the leaked boiler water rather than solely by the local temperature distribution. The affected tubes near 90\({}^{\circ}\) experienced a higher degree of exposure to vaporized water due to gas flow patterns, leading to more significant condensate formation and corrosion progression in this area. Figure 9b illustrates the temperature variation from the center to the wall (edge) direction. The temperature gradually decreased toward the boiler wall due to reduced gas introduction inside the plumbing located on the wall. Due to symmetry, a similar result was obtained at 90\({}^{\circ}\) and 270\({}^{\circ}\), confirming that regions near the boiler walls experienced lower temperatures compared to the central area.