PSI - Issue 71

Poshadri Chathri et al. / Procedia Structural Integrity 71 (2025) 309–316

310

1 Introduction In several applications, components experience a combination of corrosion and mechanical loading; this synergistic effect can lead to early failure before the expected life. Corrosion is a physio-chemical interaction leading to the deterioration of the material's functional property; hence, this degradation is chemical or electrochemical in nature. Amongst corrosion mechanisms, pitting is a form of localized corrosion of a metal surface where small areas corrode preferentially leading to the formation of cavities or pits. Pitting corrosion is very dangerous, widespread, and difficult to detect (Souto, 2015). Pitting corrosion is influenced by the physical, chemical, metallurgical, and biological factors when it is subjected to different kinds of aggressive conditions (Jiang et al., 2017). Steel is widely used in various applications due to its availability and excellent mechanical properties. Among steels, stainless steel is particularly valued for its extensive use in aggressive environments. Austenitic stainless steels, especially SS304, are widely applied across numerous chemical, marine, and nuclear industries because of their superior corrosion resistance, high temperature resistance, and robust mechanical properties (Jian et al., 2015a). Increasing the salinity of the aggressive media has been observed to result in a decrease in tensile strength (Eken and Oktem, 2016). In steels, the corrosion pits form firstly circular and then they grow on the surface with 15 minutes in the solution. After 15 minutes, the pits tend to be deeper, but the size of them tends to be stable (Eken and Oktem, 2016). The corrosion rate was in general high at lower pH levels. So, lower pH and a combination of CO 2 + H 2 S with 3.5% NaCl has the most fatal effect on the corrosion resistance property (Abdo and Seikh, 2021).In pitting corrosion, the exposure time initially leads to an increase in impact and tensile strengths; however, after a certain period, these strengths begin to decrease due to microstructural changes (Lakkam et al., 2019). The corrosion rate of SS-304 remains low at 20 °C, increases at 40 °C and 60 °C, and rises significantly at 80 °C. At 20 °C, passivation dominates, whereas at 40 °C and above, pitting corrosion becomes the primary mechanism (Jian et al., 2015b). The stress at the corrosion pit is significantly higher, indicating that the stress concentration in this area is also elevated compared to other regions on the infinite plate (Mu et al., 2011). In previous studies, the effects of mechanical properties and stress concentration factor (SCF) have been extensively analyzed for plates with a single pit (Santos, 2013). The aspect ratio, defined as the ratio of pit depth to pit diameter, as shown in Figure .1, is a critical factor in pitting corrosion. Higher aspect ratios are associated with increased risk, as they notably influence the SCF in thin-walled spherical vessels subjected to internal pressure (Cerit, 2019). Fig.1 The aspect ratio for the pit (Cerit, 2019). The aim of this study is to generate pits in the model using MATLAB, employing both spherical shapes and various other shapes of pits with inline and random orientations in accordance with ASTM G46-21 for the three sets of aspect ratios. Subsequently, the study will simulate for following conditions: spherical pits with inline, spherical pits random, different shapes of pits with inline, and different shapes of pits with random orientations to observe the mechanical properties and determine the SCF for each pit. 2. Materials and methods Stainless Steel has wide applications due to good mechanical properties and better corrosion resistance, especially austenitic stainless steels in marine, aerospace, pipping, oil, and natural gas extraction. In this study the austenitic stainless-steel grade SS304 is examined to observe the failure of the material with and without pits (Liu et al., 2023).TTable.1 shows the composition of the material, and the stress-strain data are taken from the reference paper (Liu et al., 2023).