# Stress Corrosion Cracking Analysis of a Hot Blast Stove Shell with an Internal Combustion Chamber
## 3 Results and Discussion
### Prediction Results Combined with Acid Corrosion Rates  
When the on-blast period begins and the HBS is pressurised, NO diffuses towards the metallic shell through the refractory linings. As the on-blast period continues, the concentration of NO reduces due to the oxidation of NO\({}_{2}\). Moreover, NO\({}_{2}\) diffuses back into the combustion chamber, contributing to the reduction in NO concentration. At the start of the next on-blast period, the concentration of NO\({}_{2}\) increases due to the higher NO concentration and the subsequent increase in pressure resulting from the reaction. It is worth noting that, according to the reaction mechanisms for obtaining sulfuric and nitric acid, one mole of SO\({}_{3}\) could lead to the formation of one mole of H\({}_{2}\)SO\({}_{4}\). Meanwhile, one mole of NO\({}_{2}\) could cause two moles of HNO\({}_{3}\). It can be seen in Figure 6 that the condensation of water, sulfuric, and nitric acids occurred at the bottom of the burner under the hot blast outlet for the reference blast temperature. Meanwhile, H\({}_{2}\)O and H\({}_{2}\)SO\({}_{4}\) would condense at the conical part where the low-temperature region occurred. However, HNO\({}_{3}\) would not expect a higher dew point at the upper region of the combustion chamber. The average surface temperature difference ranged from 20 \({}^{\circ}\)C to 50 \({}^{\circ}\)C. The binary system of nitric acid/water and sulfuric acid/water had dew points of 56 \({}^{\circ}\)C and 115 \({}^{\circ}\)C, respectively. Additionally, as previously stated, the condensation of acids leads to the corrosion of materials. The aim of this study was to predict this corrosion by conducting parametric studies on the condensation that occurred. Figure 5: (**a**) Maximum principal stress [28] and (**b**) average crack propagation velocity through an operation cycle of the shell for the reference blast temperature. The crack propagation velocity was calculated based on the original SCC SMM. As mentioned above, the corrosion rate of the material is not only due to metallic material by the parameter of mass transfer coefficient of the interface but also depends on the environmental components present in the flue gas condensate. Therefore, in this study, the main variable parameters were the material and surface temperature, and the corrosion rate was considered as a function of the acid's mass fraction and the temperature. Furthermore, once the location of the condensation region and the mass composition of the components in the target condensate are determined, the corrosion rate can be calculated using the diagrams developed by [PERSON] et al. [39] and [PERSON] et al. [40]. The weight distribution showed the acid corrosion rates caused by the condensation, as shown in Figure 6d. Figure 7 shows the comparison of crack propagation rate for the reference blast temperature while not considering the weight and considering the weight factor. By combining the weight, a high region disturbed at the hot blast outlet was affected throughout the operation by high temperature (above 400 K), where acid condensation should not exist. For the same reason, the crack propagation rate disturbed at the upper checker chamber decreased. Similarly, another important thing, as shown in the conical part between the checker chamber and the combustion chamber, was influenced by two main reasons:  
Figure 6: The average deposition rates of (**a**) the water, (**b**) sulfuric, and (**c**) nitric acids through an operation cycle for the reference blast temperature and (**d**) corresponding weight value. The weight value was calculated based on the deposition rates. (i) thermal stress caused by the high temperature and (ii) acid condensation caused by the low temperature. Figure 8 shows the crack propagation rate results according to the rise in the blast temperature deviation with the reference case, increased 45 K case, increased 90 K case, and the maximum crack propagation rate-raising tendency.