# Stress Corrosion Cracking Analysis of a Hot Blast Stove Shell with an Internal Combustion Chamber
## 1 Introduction  
The long-term operation experience of hot blast stoves (HBSs) around the world reveals that stress corrosion cracking (SCC) is one of the main reasons for the failures of the structures that are exposed to acidic environments [1]. The stress corrosion cracking process has still not been fully elucidated, and several theories that predict SCC growth rates were set up to explain the causes of the structure collapse cases [2]. In addition, corrosion from condensed gases has been a problem in industries for long-term operation [3, 4]. Various types of corrosion reactions can occur due to factors such as the operation temperature, combustion stoichiometry, and burner design. For SCC to happen, the following conditions must be present: an aqueous corrosive media (typically chlorides and hydrogen sulfide) along with applied or residual stresses. Moreover, the elevated temperature is known to increase the SCC growth rate. The internal combustion-type HBS has a form in which a partition wall separates the combustion and checker chambers. During the HBS operation, the gas temperature undergoes cyclic changes ranging from 400 \({}^{\circ}\)C to 1200 \({}^{\circ}\)C. The duration of each cycle is approximately three hours, and over numerous cycles, the metallic shell may develop cracks. Despite the low internal pressure in the apparatus, a crack can pose a significant risk due to the high-temperature (1200 \({}^{\circ}\)C) oxygen-enriched air stream that can cause damageto the surrounding structures. Moreover, the corrosive atmosphere created by the flue gas inside the HBS, combined with the thermal stress, can lead to SCC. Such SCC can be assessed by non-destructive testing [5]. However, the size of the HBS is enormous, so checking all parts of the metallic shell is a challenging mission. Therefore, it is imperative to calculate the distribution of the higher SCC regions of the HBSs. According to recent research, even small non-uniformities in temperature can cause thermal stress cracks on the metallic shell [6]. When the flue gas contains high NOx concentration, thermal insulation in the HBS can result in nitric SCC [1]. Ammonium and calcium nitrates can form when nitric acid in the flue gas reacts with insulation material and carbon steel. In operating conditions with a possibility of nitrates and NOx condensation, carbon steels are at substantial risk of experiencing SCC sooner or later. Intergranular corrosion is associated with SCC due to the presence of nitrates. [PERSON] and [PERSON] [7] examined the susceptibility of ferritic stainless steels to intergranular corrosion in nitrate solutions in their study. It was observed that the environment was sensitive to intergranular corrosion. One of the critical parameters that affect the safety and efficiency of hot blast stoves (HBSs) is the acid dewpoint (ADP). ADP is the temperature at which acid vapours begin to condense and cause low-temperature corrosion (LTC), eventually threatening the HBS's safety. Although higher exhaust temperatures can relieve LTC by increasing ADP, higher exhaust temperatures can result in lower thermal efficiency. ADP is a crucial parameter that guides the safe and efficient operation of HBSs. While there have been numerous investigations into the ADP of HBSs, a comprehensive review is still needed [1]. As a result, the ADP continues to be a widely discussed topic in the realm of coal combustion and energy utilisation. SCC typically occurs at a microscopic or granular level, and even forces that would not typically damage the material can cause them to form and propagate. SCC can cause significant safety and economic issues, making it imperative to develop a model that can predict its growth rates. In recent decades, three primary methods have been used to define SCC growth rates: empirical, calculation, and deterministic. Classical statistical analysis and artificial neural network methods are commonly used to develop empirical models.