PSI - Issue 36

Halyna Krechkovska et al. / Procedia Structural Integrity 36 (2022) 334–341 Halyna Krechkovska, Volodymyr Kulyk, Volodymyr Vira et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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a

b

c

d

e

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g

h

Fig. 4. Macrofractograms of Charpy specimens of the steel 17H1S in initial state (а – d) and after the operation on the main gas pipeline (e – h) obtained at different test temperatures, о С: +20 (а, e), – 20 (b, f), – 40 (c, g), – 60 (d, h).

On the fracture surfaces of impact specimens of exploited steel, obvious signs of its embrittlement were found. Only the relief of the fracture obtained by testing the specimen at room temperature did not practically differ from the relief of the fracture of steel in the initial state. It was dominated by signs of a ductile fibrous relief with a smaller amount, but deeper delaminations in the direction of rolling (Fig. 4e). But already at subzero temperatures (starting from – 20 °C), elements of a brittle crystalline relief with a characteristic bright shine of the cleavage facets appeared at the specimen fracture surface (Fig. 4f). With a further decrease in the test temperature, this relief began to prevail at the fractures, which is consistent with the low impact toughness of exploited steel at temperatures of – 40 and – 60 °C ( Fig. 4g, h).

b

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0,2 KCV op / KCV 0 0,4 0,6 0,8

0,00 0,05 0,10 0,15 0,20 0,0

a

Fig. 5. Ranking of various mechanical properties of a number of steels according to their sensitivity to operational degradation (a) and the correlation dependence of the brittle fracture resistance losses of exploited steels relative to inherent them in initial state (using to the KCV op / KCV 0 ratio) on the area of brittle fracture elements per unit of fracture surface area α for a number of steels after long -term operation on main gas pipelines (b). Data for 17H1S steel after 31 years of operation are marked with white symbols, and for other steels (Hredil 3 (2020)) - black ones (the decoding of the corresponding points is shown in Fig. a). On the base of comparison of the mechanical properties (strength, ductility and impact toughness) of a number of steels (X60, X70 and 17H1S) after their long-term operation (up to 51 years) on main gas pipelines for their sensitivity to operational degradation, it was concluded that the impact toughness KCV of steels decreases most