Evaluation of the Residual Life of Hydrogenated Pipes According to the Parameters of Acoustic Signals
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EVALUATION OF THE RESIDUAL LIFE OF HYDROGENATED PIPES ACCORDING TO THE PARAMETERS OF ACOUSTIC SIGNALS V. R. Skal’s’kyi,1,2 D. V. Rudavs’kyi,1 B. P. Klym,1 E. P. Pochaps’kyi,1 R. Ya. Yarema,1 and V. R. Bas1
UDC 593.375, 620.179.17, 669.788
We propose a technique for the evaluation of the residual life of a hydrogenated element of a pipe containing a cracklike defect on its inner surface. The kinetics of crack propagation is studied with regard for the influence of the hydrogen concentration on the pipeline wall. We establish the location of the cracklike defect in the pipe wall and its initial sizes by the acoustic-emission method. For the determination of the hydrogen concentration in the metal of pipeline, we propose to use the magnetoacoustic emission method. It is shown that the fluctuations of internal pressure in the oil (or gas) pipeline and the hydrogenation of its walls depending on the initial sizes of the cracklike defect may induce its fatigue propagation Keywords: surface crack, acoustic emission, hydrogen concentration, fatigue fracture, residual life.
To establish the time of safe operation of oil and gas pipelines and their elements, it is necessary to perform the engineering diagnostics of their dangerous sections. Among contemporary methods of nondestructive testing used for the detection of in-service cracklike defects, the acoustic methods are now most extensively applied and developed [1–3]. The aim of the present work is to develop a procedure for the evaluation of the residual life of an element of hydrogenated pipe of an oil (or gas) pipeline containing a crack according to the results of acoustic-emission and magnetoacoustic-emission diagnostics on the basis of a computational model. Computational Model Among most typical surface defects detected on the inner walls of oil and gas pipeline, we can mention the defects quite similar in shape to semielliptic cracks. This is why we consider the problem of growth of a surface semielliptic fatigue crack in the wall of a pipe (Fig. 1) under the conditions of cyclic changes in internal pressure p with a certain load ratio R . Let a0 and b0 be the initial sizes of the crack, let r be the inner radius of the pipe, and let h be the thickness of the wall (Fig. 1b). It is known [4–6] that the presence of even low concentrations of hydrogen in structural steels may strongly reduce their crack resistance, thus accelerating the process of growth of static and fatigue cracks. As follows from the practical experience, in the presence of hydrogen-containing components in oil and gas, the walls of oil and gas pipelines can be hydrogenated to high levels of hydrogen concentration, namely, 5–7 ppm. This is why, in the numerical analyses of the residual life of pipe elements containing cracks, it is necessary to take into account the influence of hydrogenation of the material on its crack-resistance characteristics. 1 2
Karpenko Physicomechanical Institute, Ukrainian National Academy of Sciences, Lviv, Ukraine. Corresponding author; e-mail: [email protected].
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