PSI - Issue 40

A.V. Burnashev et al. / Procedia Structural Integrity 40 (2022) 90–96 Burnashev A.V. at al. / Structural Integrity Procedia 00 (2022) 000 – 000

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0 10 20 30 40 50 60 70 80 90 100 220 230 240 250 260 270 280 290 300 K c MPa  m ½ T , K 1 2 3 4

Fig. 2. Crack resistance of MG pipe material: 1 – initial state; 2 – after operation for 20 years; 3 – after operation 50 years; 4 – after thermal deformation aging ε = 10% .

To assess the degree of embrittlement during long-term operation and strain ageing, we compared the values of crack resistance of the pipe material before and after the operation (Fig. 2). For the value of fracture toughness in the initial state of the material of the main gas pipelines, we employed the results of studies on the same steel grade, carried out after 5 and 10 years of operation, conducted by A.V. Lyglaev and A.I. Levin at the Institute of Physical and Technical Problems of the North, Siberian Branch of the Russian Academy of Sciences. As in the case of impact strength, there is a significant decrease in the material's resistance to brittle fracture. Ultrasound also showed a decrease in the speed of sound with changes in the state of tubular steel (Fig. 1, b). We can note the qualitative similarity of the results of tests on impact bending and ultrasonic measurements, which is related to the sensitivity of these characteristics to changes in the structure of the material during long-term operation.

Fig. 3. The speed of sound in MG steel after various states: 1 – metal pipe from emergency reserve; 2 – after operation 50 years; 3 – after 50 years of operation and additional thermal deformation aging.