Control of underground gas pipelines quality taking into account corrosive fatique, strength and normative documentation

2017;
: pp. 101-107
Authors:
1
Lviv Polytechnic National University, Ukraine
2
Lviv Polytechnic National University

The elements of the system of the corrosive monitoring (SCM) of metallic underground gas pipelines (UGP) are considered. This system (SCM) is intended for determining the locations of damages of protective cover, and also for measuring of electric potentials (corrosive, polarization, protective) on the surface of gas pipeline. The program of automatic calculation of corrosive activity of soil is represented in system of monitoring (SCM) and system of cathode defence of UGP software, id est for the evaluation of influence of soil on the current of corrosion on the external surface of metallic pipe. A formula over is brought for the evaluation of closeness of current of corrosion of metal of gas pipeline in the defect of protective covering. Polarization potential with the help of that optimize the system of cathode defence of metal of pipe in the conditions of corrosion is included in a formula. With the help of corresponding correlation for a current it is possible to estimate the resource of UGP. In equation for the current of corrosion a parameter enters also Tafel equation. Tafel equation binds the overpotential of electrode reaction of dissolution of metal (steel) with the density of corrosive (anodic) current. For the evaluation of speed of process of anodic dissolution of metal correlation that is entered in the monograph of Kaeshe and generalized is taken into account in the top of crack. Generalization relates to surface energy of plastic deformation and opening of crack.
The energetic criterion of mechanics of fracture is entered in basis of model of corrosive fatique of metal. In basis of criterion of opening of crack energy of plastic deformation, that is relatedto energy of fracture of material. Opening of top of crack is included in the criterion of strength, that has the name of the critical opening of crack. To opening of crack the coefficient of stress intensity factor (SIF) and overpotential of reaction of anodic dissolution of metal is related. Methodology of evaluation of resource is considered, id est to time of safe exploitation of material of pipeline (to the gas pipeline) with the damaged isolating coverage in a corrosive environment. Represented empiric criterion formula for the calculation of limit of corrosive fatique of metals. In a corresponding formula appear parameters, that characterize migration of electric charges, that goes to additional dissolution of the deformed metal. Evolutional equalization is offered for description of low-cycle fatigue of metal of UGP. In evolutional equation the integral by volume damaged of material (steel) is included and her critical value. Represented expressions that characterize connection of energetic and forced approaches in relation to fatique fracture of metal of UGP. Corresponding correlations are presented as elastic and plastic constituents for to the Rice’s integral. The geometrical size of crack, loop of hysteresis, coefficient of the deformation strengthening, is taken into account for a metal (in particular, for iron, steel)). The offered mathematical expressions are incorporated andused for development of the improved model of corrosion metry taking into account the low-cycle fatique of metals and corresponding information technology. Information technology of monitoring of UGP combines three types of mathematical models. The first type is a mathematical model of corrosion metry taking into account control of quality of underground gas pipeline and fracture of metal in surface defects (cracks, cavities). The second type is a modeling of physical and mathematical processes for UGP on the basis of control system by quality (CSQ). The third type is a modeling of processes for UGP from the point of view of organizational structures (personnel, engineering of quality, providing of operating safety of technological process). Represented in consideration integral index of efficiency of functioning of the system of monitoring of UGP. The flow diagram of informatively-computer technology is worked out for protecting of metal from an aggressive environment taking into account corrosive processes. For optimization of informative streams in the system of monitoring of underground gas pipelines and improvement of the system of anticorrosion defence it is recommended to take into account reverse copulas and principles of engineering of quality. The flow diagram of conceptual model of informatively-computer technology of defence of underground gas pipelinesis worked out taking into account corrosive processes near-by the top of crack and risk. The optimization models of corrosion metry are improved in basis of information technology, quality management (CSQ), behavior of workers (to the personnel), including quality and quantitative parameters. For optimization of informative streams in the system of monitoring of underground gas pipelines and improvement of the system of anticorrosion defence it is recommended to take into account reverse copulas and principles of engineering of quality.

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