PSI - Issue 33

D.D. Okulova et al. / Procedia Structural Integrity 33 (2021) 1055–1064 Author name / Structural Integrity Procedia 00 (2019) 000–000

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of thin- and thick-walled spherical vessels subjected to mechanochemical corrosion under internal and external pressures were proposed by Pronina et al. (2018) and Pronina et al. (2021). Note that combined action of loads and aggressive environment can also initiate stress corrosion cracking (Butusova et al., 2020). To prevent propagation of cracks (originated from local defects) in undesirable directions, special thermal treatment of the steel sheets was proposed (related fracture problem is discussed in the work of Pronina et al., 2020). The effect of interaction of neighbouring defects and the influence of the distance between them on the stress state of the pressure vessel must also be taken into account. Metal structures with several interacting defects have been investigated in a few publications, for example, by Ahmed et al. (2019). It is shown in some papers that if there are several defects on the surface of the pressure vessel located far enough from each other, then the local stresses in the vicinity of each of them differ a little from the stresses arising in the vicinity of a single defect (Sun et al., 2021). However, the stress-strain state of spherical pressure vessels with multiple interacting defects remains insufficiently studied. Since in reality the defects arise in a random way, it is necessary to simulate random patterns of their location for the analysis. In the present paper, a spherical vessel under internal pressure with multiple defects on its outer surface is considered. The defects are assumed to have a shape of nearly hemispherical notches of equal sizes with the depth equal to half of its curvature radius. Corrosion pittings of this shape were obtained, for example, testing commercial 800 HT alloy (see the paper of Fabas et al. (2015)). Random arrangement of defects along the equator of the sphere and different numbers of notches are considered. The stress state of the shell is analysed by finite element method using the ANSYS Workbench package. Calculations are made within the frame-work of bilinear plasticity hardening model and linearly elastic model.

Nomenclature r

inner radius of the shell outer radius of the shell

R p δ h n

internal pressure

curvature radius of the notches

depth of the notches number of notches

Fig. 1. Sketch of a hollow sphere with a notch

2. Model considered A spherical vessel with an inner radius r and an outer R is considered. Pressure p is applied to the inner surface of the shell. There are multiple nearly hemispherical defects on the outer surface, with curvature radius δ and depth h = δ /2 (Fig. 1). A pseudo-random arrangement of defects along the equator of the sphere and different numbers of defects