PSI - Issue 21

M. Hredil et al. / Procedia Structural Integrity 21 (2019) 166–172 M. Hredil, H. Krechkovska, O. Stud nt, I. Kurnat / tr ct r l I t it Procedia 00 (2019) 000 – 000

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Fig. 3. ( а ) Rate of loss of brittle fracture resistance V with operation time τ and (b) its dependence on the parameter  = S brittle / S ductile for pipeline steels of different strength.

Fig. 4. Fracture surfaces of Charpy specimens of the steel 17H1S from gas mains after (a, b) 30 years and (c) 51 years of their operation illustrating typical fractographic features of the steel degradation. 4. Conclusions Pipeline steels of different strength after their long term service were analyzed. Their mechanical properties, especially impact toughness, are worsened as a result of operation. The relationship was noticed between structural/fractographic features of steel degradation and their mechanical characteristics. The structural peculiarity of steel degradation was supposed to be damaging inside pearlite grains, and fractographic features – non-structured areas of delaminations against the background of typical ductile relief, transgranular cleavage with a typical river patterns and their combinations observed at fracture surfaces of Charpy specimens. Correlation was found for steels 17H1S , Х60, Х70 between the rate of loss of brittle fracture resistance and the area of brittle elements at the fracture surfaces of specimens after the Charpy testing. Acknowledgements The research has been partially supported by the NATO in the Science for Peace and Security Programme under the Project G5055.