Tag Archives: трубопровод
Underground main oil pipelines are very extended objects which pass not only through stable areas with steady soil, but also areas with active manifestations of soil changes, including through bogs, the rivers, seismic breaks, is long-term – frozen soil, sites with karst manifestations, slopes and ravines. At long operation of pipelines on such sites it is necessary to watch the happening changes and to take anticipatory measures for safety of pipelines.
In article research of dependences of interaction of the pipeline with soil in a landslide zone from various factors is considered. The problem is solved by method of physical and mathematical modeling. The model of interaction of the pipeline with soil in a landslide zone represents a valuable contribution to the solution of the actual scientific and technical problem connected with safety of pipeline systems.
As a result of work the state equation in the form of the differential equation is received. Methods and features of the decision in some simple cases when reaction of soil is expressed by analytical expressions are investigated. At determination of tension from external forces difficult correctly and precisely to describe regularities of interaction of a pipe with soil which besides change at soil changes. Other complexity that in many cases boundary conditions for the considered pipeline site are in advance unknown; they are defined only during the solution of a task. Therefore in article decision methods in real cases when reaction of soil can’t be described by means of simple analytical expressions are considered. For these cases the algorithm based on numerical methods with consecutive approximations is made.
SCALING DETECTION IN A PIPELINE WITH FLUID UNDER PRESSURE USING NATURAL FREQUENCIES OF FLEXURAL VIBRATIONS
Pipelines can form scale deposits on their walls. Erosion-corrosion processes in pipelines are characterized by the fact that deposition of corrosion products in some of their portions occurs simultaneously with wall thinning in the others.
In this paper consideration is given to natural frequencies of flexural vibrations in a pipeline clamped at both ends and subjected to the action of tension force. The pipeline has wall scale deposits and is filled with fluid under pressure. The scale deposits are supposed to be uniformly distributed on the inner surface of the pipeline. Here, the Kirchhoff’s equation for flexural vibrations is applied. The frequency equation has been derived from the equation that dictates the type of flexural vibrations and also the boundary conditions for a pipeline clamped at its ends. Solutions have been found to the primal problem to determine the first and the second natural frequencies of flexural vibrations in the pipeline for the given scale density in the pipeline, axial force, wall thickness, inside pressure of the pipeline and uniform scale thickness on the pipe wall as well as to the inverse problem to determine scale density on the pipe wall and deposition thickness using two natural frequencies of flexural vibrations in the pipeline.
It has been found that an increase in the density of scale deposits on the pipe wall results in smaller natural frequencies of pipe flexural vibrations. Besides, the research has shown that a reduction in the pipe inside area or an increase in the scale thickness results in smaller natural frequencies of pipe flexural vibrations. Using two natural frequencies of pipe flexural vibrations we can determine the density of scale deposits on the pipe wall and pipe inside area or scale thickness.
The investigation outcomes can be applied to assess axial loading and pipe wall thickness using two natural frequencies of flexural vibrations.
DETERMINATION OF PARAMETERS OF CHANGE OF PRODUCTIVITY OF TRANSFER TAKING INTO ACCOUNT SAFETY OF OPERATION OF THE PIPELINE
The article considers determination of parameters of change of productivity of transfer of a product through the pipeline taking into account safety of operation. Conditions of prevention of inadmissible deformations by restriction of the maximum equivalent tension with a limit of metal ductility and safety of the pipeline with achievement of the acceptable margin of safety on a ductility limit are formulated. Parameters of change of the mode of transfer are characterized by the length of the pipeline segment which is under the change of speed of the movement of the pumped-over product and the period of change of the specified speed. As a result of researches the analytical dependences of length of the pipeline segment which is under the change of speed of the movement of a product and the period of change of this speed from change of productivity of transfer, internal pressure inside the cavity of the pipeline, its geometrical characteristics and mechanical properties of metal of pipes taking into account conditions of ensuring durability of pipes and safe operation of the pipeline are received. Because the specified analytical dependences depend on geometrical characteristics of pipes and their connections, the connections of pipes with equal and different thickness of walls, and also connections of pipes with the element having very big rigidity on deformation, for example, with shutoff valves are considered. The quantitative and qualitative analysis of influence of geometrical characteristics of pipes and their connections, properties of metal, necessary margin of safety on values of parameters of the mode of transfer at which durability of pipes and safety of operation of the pipeline is provided were carried out. Increases in parameters of change of productivity of transfer of a product are necessary for all considered schemes of connection of pipes for the purpose of prevention of inadmissible deformations and achievement of the acceptable margin of safety on a limit of ductility. At the same time, on a site of connection of the pipeline with an element, rigid on deformation, higher values of parameters of change of the mode of transfer are necessary for prevention of inadmissible deformations and achievement of the acceptable margin of safety. The increase in value of change of productivity of transfer results in the need of increase of a period of change of speed of the movement of a product and extent of the site of the pipeline on which there is a change of this speed.
Foamed plastics are an effective material for pipe insulation. Among the advantages of this material include the ability to form heat-insulating coating with a given density distribution through the thickness, to obtain a so-called integral foams. This allows to increase the density and hence the strength of external insulation layers most exposed to external mechanical influences. This decreases the moisture permeability of the coating, which is important for underground laying underground pipeline. Insulation effect of the inner layers, and consequently the coating is enhanced through reduction of their density, since there is a direct correlation between the density of the insulation and its thermal conductivity. Achieved such a redistribution of density by influencing the technology of production of foam during the polymerization. In the presented work are given the solution of the heat conduction equation for a stationary case at the steady state temperatures at the inner and the outer surfaces of the insulation. The thermal conductivity of the insulation was considered as a variable depending on the density of the insulation, which is distributed in a certain way through the thickness of the coating. The formula allowing to calculate the equivalent thermal conductivity of the coating at any possible density distribution along its thickness. Taking into account the linear character of the dependence of the thermal conductivity of polyurethane foam is its density, obtained a modification of this formula for the case when the heat-insulating coating consists of two layers: the inner, fixed minimum allowable density, and external, where the density increases to the maximum value on the surface of the coating. A recommendation to determine the thickness of each layer at a known specific weight of foam per unit of pipe length. On the example of thermal insulation of polyurethane foam with an integral structure for medium diameter tubing shown the ability to reduce heat loss by nearly 14% compared with homogeneous insulation of the same specific gravity.
The purpose of this experimental study was to determine the reduction in contact resistance of underground pipeline coatings over time, as well as to analyze the effect of cathodic protection on pipeline coatings.
Investigation was carried out in the laboratories USPTU under normal conditions with the use of special facilities, developed on the basis of GOST R 5116 – 98 «Assessment of the contact resistance».
Experiment bears out that, CP current intensify the deterioration of the coating, i.e. form all experiments the use of cathodic protection about 100 times decreased the contact resistance of pipeline coatings during the first of operation, compared with operation without cathodic polarization. Therefore, it is requested to consider the necessity of applying cathodic protection on pipelines once again. In the operation of field pipelines special problems with external corrosion is not observed. Alternative means of electrochemical pipeline protection would be the use of anodic grounding according to patents № 125673 and № 146246 along the entire pipeline in the most dangerous places after appropriate investigations.
It is known that the negative effect of cathodic polarization on the properties of the metal pipeline is the magnetization of metal, the increasing speed of occurrence of Stress Corrosion Cracking (SCC) and others. In addition, in previous decades, many studies have found reduction of individual properties of the protective coating when applied cathodic polarization: it’s a decrease in adhesion and an increase in water permeability and others. Now it’s proven that integral Rпер decreases about 100 times in the first year of operation. Conducting large-scale field experiments will allow the industry to draw definitive conclusions.