Evaluation of the durability of a pipe of oil pipeline with surface crack under biaxial block loading
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SCIENCE FOR PRODUCTION
EVALUATION OF THE DURABILITY OF A PIPE OF OIL PIPELINE WITH SURFACE CRACK UNDER BIAXIAL BLOCK LOADING O. E. Andreikiv, Ya. L. Ivanyts’kyi, Z. O. Terlets’ka, and M. B. Kit
UDC 539.375
We propose an energy approach to the evaluation of the residual service life of structural elements with cracks for the two-frequency loading mode of biaxial tension-compression. This approach is applied to a pipe of oil pipeline containing a crack on its inner surface. The pipe is regarded as an infinite plate with surface semicircular crack loaded by longitudinal tension-compression caused by the processes of heating and cooling of the pipe. The pipe is also squeezed by the soil and subjected to the action of internal pressure formed in the process of pumping of oil. The two-frequency variations of pressure in the pipe are caused by the turbulence of the flow of oil (high frequency), opening and closing of the gate valves, and the shutdowns of the pumps (low frequency). It is shown that if we neglect the longitudinal tension-compression of the pipe and the oscillations of pressure of oil in the evaluation of durability of the pipes of oil pipelines, then we can get strongly overestimated predictions of the residual service life.
The prediction of the residual service life of structural elements under variable loads is an urgent problem of engineering practice. This is especially true for variable loads [1] (multifrequency, package, with known law of variation of amplitudes, etc.). Since the theoretical aspects of this problem are developed insufficiently and the required amount of experimental data is not accumulated due to significant technical difficulties, the required dependences that can be used for the evaluation of the service life of structures are absent. In the present work, on the basis of the energy approach developed in [2–4], we propose a method for the determination of the residual service life of structural elements with cracks under block loading by bilateral tension-compression. The proposed method is applied to the evaluation of the residual service life of a pipe with surface crack subjected to longitudinal bilateral tension-compression caused by the processes of heating and cooling of the pipe, its squeezing by the soil, and the action of internal pressure formed in the process of pumping of oil. The two-frequency variations of pressure in the pipe are explained by the turbulence of the flow of oil (high frequency), closing and opening of the gate valves, and shutdowns of the pumps (low frequency). Model of Loading of a Pipe Oil mains are, as a rule, very long (at least 50 km). The diameter of pipes is never smaller than 500 mm. The pressure of oil in the mains can be quite high to guarantee their high throughput capacity. The deviations of working pressure caused by the startups and shutdowns of the pump stations can be as large as 2–3 MPa [5], in the case of successive pumping of different types of oil, these deviations do not exceed 1 MPa, the deviations caused by the startups and sh
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