Experimental study of ultrasound characteristics in steel samples cut out of a pipeline that has been exploited during a long time
Abstract »Main oil pipeline is one of the examples of objects exploiting in cyclic loading conditions. The main changes that are happen with the material of the pipeline usually associated with a change in the density of dislocations. The utilization over the lifetime of the most grades of pipe steel is resulted in the significant changes of the dislocation structure.
When the density of dislocations are over the certain value, the various dislocation mechanisms of microcracks formation start activating. The microcracks can appear when the dislocation cross the slipbands, during the accumulating the boundary dislocations in a row. Hereafter such microcracks can turn to large cracks that poses threat for exploiting pipelines.
Thus the identification of high density areas of dislocations in steels for building main oil pipelines with the help of NDT is of practical importance.
For studying the characteristics for ultrasound propagation, hardware and software suite “Astron” was used. It is designed to generate and receive acoustic impulses as well as it has the capabilities for measuring their characteristics and conducting spectrum analysis.
The measurement of the speed of ultrasound propagation was performed. The spectral characteristics of the received and reflected pulses in steel samples cut from the pipeline, which was in service for a long period, were obtained. The correlation between the velocity of ultrasound propagation and the degree of degradation of the mechanical properties of the material was detected.