Evaluation of the Residual Service Life of Main Pipelines with Regard for the Action of Media and Degradation of Materia
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EVALUATION OF THE RESIDUAL SERVICE LIFE OF MAIN PIPELINES WITH REGARD FOR THE ACTION OF MEDIA AND DEGRADATION OF MATERIALS O. Ye. Andreikiv,1, 2 I. Ya. Dolins’ka,3 I. P. Shtoiko,3 O. K. Raiter,3 and Yu. Ya. Matviiv4
UDC: 539.375; 539.4
We proposed new procedures for the evaluation of the residual service life of main pipelines with surface cracks under the action of a long-term constant gas pressure in gas pipelines, a variable pressure in oil pipelines, hydrogenation, and soil corrosion. The degradation of the materials is taken into account. Since the time dependence of the degree of degradation is insignificant, it is analytically described by linear dependences. The energy approach is used to determine the residual service life of the pipes. The corresponding computational models (differential equations with initial and final conditions) are developed. For specific pipe materials (Kh52, Kh60, and Kh70 steels), the residual service life is computed under long-term static and variable loads, in the presence of hydrogenation and soil corrosion with regard for the degradation of the materials for 30 yr. Keywords: residual service life of main pipelines, hydrogenation, soil corrosion, degradation of materials, Kh52, Kh60, and Kh70 steels.
Introduction The application of main pipelines proves to be the most cost-efficient method of transportation of oil, gas, and oil products. Pipeline systems can be regarded as the most important part of the power-generating complex whose trouble-free functioning is of exceptional importance for the state. Thus, the main task is to guarantee their reliability. However, the solution of this problem is complicated by the fact that the service life of more than 37% of all main pipelines exceeded the term of amortization of the linear parts (33 yr) and 38% of pipelines are in service for 20–33 yr. In general, the system of main pipelines with so "solid age” entered the third period of their life cycle, i.e., the period of total degradation of the metal and frequent failures. Therefore, in analyzing the residual service life of pipelines, it is necessary to take into account the degradation of their materials, i.e., the changes in their mechanical, fatigue, and strength characteristics in the course of operation. At present, the problem of degradation of the materials of pipelines operating for 30–60 yr is extensively investigated and the variations of their mechanical characteristics are analyzed (see, e.g., [1, 2]). However, in order to determine the residual service life of pipelines with regard for the operating conditions, it is necessary to know various important characteristics of materials of the pipes, such as the static and cyclic crack resistance of the materials, their behavior as functions of time, and the influence of soil corrosion and hydrogenation on these characteristics. 1 2 3 4
I. Franko Lviv National University, Lviv, Ukraine.
Corresponding author; e-mail: [email protected].
Karpenko Physicomechanical Institute, Ukrainian National Academy of Sciences, Lviv, U
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