ИСТИНА

The purpose of this study is to develop the experimental and theoretical foundations of the stochastic method for assessing of longevity and diagnostic periods of the technical conditions of various long structures. The section fracture at the internal pressure of the pumped product, the action of mass forces, temperature field and natural-climatic and technogenic influences, is considered at each moment of time as the sum of probabilistic fracture of its generalized structural elements (of base metal, welded joints, bends, tees, adapters, plugs). For this purpose, the problem is a mathematical representation of the random mechanical loading of structural sections, random chemical and biological effects during soil and stress corrosion, random natural (aerohydrodynamic, geodynamic and seismic) influences and the effects of third parties on structural sections. Further, the constitutive relations are constructed for the distribution function of the element failure probability on the various defect levels at mechanical loading. The considered approach uses the results of studies of the physical and chemical interactions between an aggressive medium and the metal. The fundamental problem is to develop the safe operation criteria for long structures, taking into account the influence on people, technosphere objects and the environment at possible fracture. The research relevance is associated with considering of complex processes of multiscale fracture of structural elements at the resource estimation of long structures. The durability of long structures at operational loading is described by random processes taking into account the potential stochastic element fracture, random mechanical loading, random environmental influences, etc. Therefore, a stochastic approach and methods of the theory of random processes and statistical analysis are chosen. As a toolkit for numerical experiments and solving practical problems, finite element methods of the ANSYS are used. There is proposed a stochastic method of safe operation assessing on the basis of a system of safe operation criteria for long structures, taking into account the determination of the structural element life using a stochastic model of fatigue scale-structural failure. The model predicts the probability that a certain function of the structure, depending on the density and size of multilevel defects, reaches the limiting values during loading. The basic experiments for identifying of material functions are based on the standard tests of materials for long-term and fatigue strength. Here are plotted the fatigue curves of metals and alloys on defect levels at high-cycle and gigacycle fatigue and various types of proportional loading with a symmetric and asymmetric cycle. The algorithm for durability calculation of various sections of main pipelines on the basis of the proposed method, taking into account the influence of natural and technogenic factors and aggressive media, as well as the negative consequences of their possible destruction is proposed. The algorithm is implemented for a number of main gas pipelines (for linear parts between adjacent compressor stations, strapping pipelines).