PSI - Issue 47

L.A. Almazova et al. / Procedia Structural Integrity 47 (2023) 417–425 Author name / Structural Integrity Procedia 00 (2019) 000 – 000 5 example, for geometry with a single pitting with the initial depth 2 mm, the finite time, t*, is about 60 [ ], while for geometry with two pits of the initial depths h1=2 mm and h2=2 mm – 64 [ ] (radii in both cases are R=350, r=340 mm). With the growing distance between the defects, their influence on each other decreases. It was observed that for two initial geometries differing from each other only in the parameter D, the stresses at pits bottoms, and consequently, the propagation rate, were greater for smaller D. For example, in the sphere with R=350 and r=340 mm and initial pits depths h1=2 mm and h2=2 mm at time moment t = 32 [ ] pits at the distance D = 2 mm from each other propagated up to h1 = 5,622 mm and h2 = 5,606 mm, while at D=4 mm, pits propagated up to h1 = 5,575 mm and h2 = 5,588 mm. Meanwhile, the time before pit’s depth reaches 90% of vessel’s wall thickness almost has not changed. Calculation results were analyzed to investigate the influence of pit’s depth on the propagation rate. Table 1 shows the obtained values of pitting growth rates depending on the initial depth and distance between defects corresponding to different time moments, one of which is t=4 [ t c ]. It is seen from table 1 that in all cases the growth rates of both pits are close to each other in values. However, it is possible to notice a slight decrease in the growth rate of both pits with an increase in the distance between the defects. At the same time, it was often observed that for D > 2 mm the calculated propagation rates of the pits during some period of time practically do not change relative to the initial moment of time t (e.g., for h1=4, h2=4 and D=4 mm the rates are the same for both t=4 and 48 [ t c ]). Nevertheless, it is also shown that with an increase in the initial pitting depths, both growth rates slightly increase. This is explained by the fact that for the geometry with h1=4, h2=4 and D=4 mm at the time moment t=48 [ t c ] the depth of pits is less than the initial depth of pits of the geometry with h1=8, h2=8 and D=4 mm. Moreover, the increase of the propagation rates observed is also insignificant, only in the third decimal place. Thus, the results show that for considered parameters the depth of pits has hardly noticeable effect on the propagation rate. 421 3.2. Investigation of the effect of pitting depth on its growth rate

Growth rate of the first pit, mm / -

Growth rate of the second pit, mm / 0,127 0,133

Table 1. The dependence of the pits growth rate on the initial depths values

t, [ ] 4, 56

Initial depths, mm

D, mm

h1=0, h2=2

2

0,129 0,136 0,130 0,138 0,130 0,134 0,126 0,129 0,128 0,128 0,129 0,132 -

0,128 0,143 0,129 0,134 0,129 0,133 0,127 0,133 0,126 0,126 0,129 0,129 0,130 0,132

h1=2, h2=2

2

4, 64

4, 48

h1=4, h2=4

2

h1=8, h2=8

2

4, 16

4, 56

h1=0, h2=2

4

h1=2, h2=2

4

4, 64

4, 48

h1=4, h2=4

4

4, 16

h1=8, h2=8

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