Evaluation of the Kinetics of Fracture of Elements of a Gas Pipeline After Operation
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EVALUATION OF THE KINETICS OF FRACTURE OF ELEMENTS OF A GAS PIPELINE AFTER OPERATION E. I. Kryzhanivs’kyi,1 R. S. Hrabovs’kyi,1, 2 I. Ya. Fedorovych,1 and R. A. Barna3
UDC 620.191.33: 620.193
The efficiency of the numerical-analytic approach to the evaluation of the kinetics and changes in the shapes of corrosion fatigue cracklike defects in the course of their propagation in the wall of the pipeline is experimentally demonstrated. An experimental-numerical method is proposed for the estimation of the conditions of fracture of gas pipelines after long-term operation with regard for the influence of the expected evolution of in-service defects in given media and the degradation of the properties of pipe metal. We determine the conditions under which the catastrophic failures of pipes of the “Kyiv– Western Ukraine” gas main become possible after long-operation. Keywords: gas pipeline, stress-corrosion cracklike defects, corrosion-fatigue cracks, through cracks, cracks of critical sizes.
The gas-transportation network of the Ukraine is as long as 38,500 km. In the course of long-term operation of gas mains under the simultaneous action of static, cyclic, and dynamic loads and corrosive media [1–4], we observe the initiation and propagation of stress-corrosion cracklike defects (pits and grooves) and corrosionfatigue cracks mostly located along the axis of the pipe (Fig. 1) [2, 5]. According to the statistical data, the periodic diagnostics of gas mains in the course of long-term operation reveal about 5000–6000 defects per 100 km of length. These defects are classified into certain categories. Then the corresponding management decisions are made with an aim of their removal [1, 6]. It is worth noting that the serviceability of gas-transportation systems intended for long-term operation is substantiated by using various approaches to the evaluation of the number of stress-corrosion defects in the pipe metal [3, 5, 7–11]. However, the available methods do not take into account the kinetics of propagation of these defects since the operation of gas mains under the actual conditions is characterized by a certain periodicity and insignificant amplitude (which may become high in some cases [12]) of variations of the working pressures [2–4]. This may lead to emergency situations as a result of the propagation of defects [2, 4, 5]. Therefore, in order to determine the schedule of maintenance aimed at the removal of defects and increasing the reliability of the numerical estimates of residual durability of defective pipelines, it is necessary to take into account the subcritical growth of stress-corrosion cracklike defects caused by the fatigue or the corrosion fatigue of the material under the long-term action of operating conditions. Since 75% of gas mains in the Ukraine operate for at least 30 yr, the problem of analysis of the defects revealed in the course of technical diagnostics proves to be quite urgent.
1 2 3
National Technical University of Oil and Gas, Ivano-Frankivs’k, Ukraine. Corresponding author; e-mail: hrab
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