PSI - Issue 47

L.A. Almazova et al. / Procedia Structural Integrity 47 (2023) 417–425 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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the distribution of corrosion defects and the degree of pit corrosion intensity on the plate surface have a substantial impact on the ultimate strength. A number of articles devoted to corrosion of spherical structural components. For instance, Zhao et al. (2019) investigated the impact of local corrosion defects that were randomly positioned on the loading capacity of welded hollow spherical joints showing that the loading capacity may be significantly reduced as a result of corrosion. Sedova et al. (2014) investigated the concentration of stresses near a single developing corrosion pit on the outer surface of a hollow sphere. Papers of Okulova et al. (2019, 2023) and Sedova et al. (2021) concern with a pressurized spherical shell weakened by multiple hemispherical corrosion pits. The maximum principal stress in the vessel is analysed with taking into account the uniform and random distribution of the defects, their number, and distance between them. These papers deal with usual static problems with defects of a certain geometry. However, it is well-known that processes of material transformation may be enhanced by mechanical stresses (see, for example, works of Abakarov and Pronina (2022), Anguiano et al. (2022), Javadi et al. (2020), Javanbakht and Ghaedi (2020), Kazemian et al. (2022), Shuvalov and Kostyrko (2021), Sedova and Pronina (2015, 2022), Song (2020), Wee et al. (2022), Xia et al. (2021)). Problems of thin- and thick-walled spherical vessels, made of elastoplastic material, subjected to uniform corrosion accelerated by stress, under internal and external pressures were considered by Gutman et al. (2016), Pronina (2013), Pronina et. al. 2018, Pronina and Sedova (2021). Stress corrosion cracking can also be caused by the combined action of loads and aggressive environments (Butusova et al., 2020). A special thermal treatment for steel sheets was suggested to stop the spread of cracks (originated from local defects) in unwanted directions; related fracture problem is discussed in Pronina et. al. (2020). Considering growing pits, it is necessary to have a mathematical model of their growth. The models of kinetics of corrosion pitting propagation are usually based on the anodic reaction responsible for dissolution, e.g. (Bard et al., 1980). Some of such models allow estimating pit depth in time (Valor et al. , 2007; Velázquez et al., 2009; Li et al., 2014). Microstructure heterogeneities may significantly affect the pit growth (Liu et al., 2008a; Shahryari et al., 2009). There are few models of pit’s propagation accounting for microstructure effect (Chen and Bobaru, 2015; Mai et al., 2016; Jafarzadeh et al.,2018a). The experiments show that in some conditions the rate of corrosion may depend on stress on the corroding surface (Gutman, 1994). Most of the research where propagation of pits is considered deal with the case of a single pit (see for example, work of Heurtault et. al. (2015)). A few efforts have been made to analyze the interaction of multiple growing pits (Budiansky et al (2005); Laycock at. al. (2006)). It was shown that the interaction between the two pits can have either a positive or negative effect on pit’s propagation (Laycock et. al. (2014)). Growth of corrosion pits based on a thermodynamically consistent phase field model is considered in (Ansari et. al. 2018). The cellular automata model is utilized for simulation of pit’s interaction with taking into account an anticorrosive coating (Liu X. 2021). Experimental (Ghahari et. al. (2015)) and numerical studies (Nguyen et al 2022) show that the dissolution kinetics of multiple interacting pits differ from that of a single pit. This paper is devoted to the estimate of the local strength of a spherical pressure vessel in the vicinity of two growing corrosion defects. Pits are considered to have a cylindrical form with hemispherical bottom. The rate of the pit growth linearly depends on the stresses at the pit’s bottom points . A series of 3D finite element analysis are performed. The effects of different geometrical parameters such as distance between defects; their depth and sizes of vessel are analysed. 2. Description of the model The interaction of two closely spaced growing pittings is investigated, the growth rate of which depends on the stress at their bottom point (Gutman, 1994). For this purpose, ANSYS software was utilized. A hollow sphere with the outer radius R and the inner r is built for the analysis. There are two cylindrical pits with hemispherical bottoms on the outer surface of the vessel, each pit has a radius δ =2 mm. Because of the symmetry, half of the sphere is constructed. Three sets of the vessel sizes are considered: R = 350 mm, r = 340 mm; R = 250 mm, r = 240 mm; and R = 150 mm, r = 140 mm. The distance between the edges of the defects, D, was assumed to be: 0.5 mm, 1 mm, 2 mm, 4 mm, 6 mm, and 8 mm. The initial depths of the pits, h1 and h2, are also variable values chosen from the set {0; 2 mm; 4