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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in the technical specifications for the pipe manufacturer, as well as in building codes and rules. It is also confirmed by the results of visual inspection of the surface of destruction when 100% crystal fracture is detected in the sample. The speed of sound was measured using an acoustic device "ISAV-1" produced by Izhevsk State Technical University. This device allows measuring the speed of surface waves with an error of up to 0.01%. The sensors of the separate type, the emitter and the receiver are fixed in one base with a constant distance of 70.3 mm. The ultrasound frequency is » 2.5 MHz. Specific characteristics and principle of operation of the device are described in. The measurements were carried out on segments of pipes with dimensions of 200 – 250 – 9 mm (along the tube forming line), and the surface roughness was Rz £ 20. After the ultrasound, specimens were made from the same segments for impact bending tests. The tests were carried out at 20 °C. 3. Main results and conclusions Fig. 1 shows the dependence of the impact strength of KCV samples in different states, on the test temperature (a) and a separate graph plotted for the test case at room temperature (b). As the graphs demonstrate, there is a drop in the KCV value after operation compared to the KCV emergency reserve by up to 25% and more than 65% after additional ageing. There is a high sensitivity of KCV to changes in temperature and the course of ageing processes compared with the results of tests on KCU samples, which were in work Burnashev A.V et al. (2019).

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Fig. 1. Dependence of impact toughness on temperature (a) and various states of metal (b): 1 – metal pipe from emergency reserve; 2 – after operation 50 years; 3 – after 50 years of operation and additional thermal deformation aging; 4 – after thermal deformation aging ε = 8%; 5 – after thermal deformation aging ε = 10%.

The reduction in toughness during the operation was also confirmed on the results of tests for crack resistance. Like impact toughness, crack resistance is one of the important characteristics for evaluating the influence of operation time and the associated change in the mechanical characteristics of a metal. To determine the characteristics of crack resistance, we used the rectangular compact samples with an edge crack for testing for eccentric tension according to GOST 25.506-85 (2005). The tests were carried out at a temperature of +20 ° C.