Action Of Internal Pressure Research Articles

Finite-Element Modeling of the Dynamic Behavior of a Crack-like Defect in an Internally Pressurized Thin-Walled Steel Cylinder

This article presents one part of a study on the dynamic deformation and fracture of sections of steel gas pipelines with an external crack-like defect under the action of internal pressure. This work was performed on the basis of finite-element simulations using a cylindrical shell model executed by ANSYS-19.2 on the example of the section of the steel gas pipeline “Beineu–Bozoy–Shymkent” in the Republic of Kazakhstan. The propagation of the incipient crack-like defect along the pipeline and the resulting dynamic fracture in its tip area were investigated. The options of pipeline loading by working and critical internal pressure were both considered. It was found that, within the time of 1.0 ms, the formed crack expanded in the circumferential direction up to the maximum value, which depended on the value of the internal pressure. A further growth of cracks occurred along the longitudinal direction. At the operating pressure, the initial length of the crack increased by a factor of 5.6, while the equivalent stresses increased by a factor of 1.53 within 3.5 ms. Within the time of 3.75 ms, the equivalent stresses stopped growing due to the gas decompression. Specifically, there was a stop to the crack growth along the longitudinal direction. Vice versa, at the maximum pressure, the pipeline fracture did not change qualitatively, while at the time of the process, it decreased up to 3.5 ms. The finite-element results of the stress–strain state and pipeline fracture in the crack tip area at the working pressure showed that, within the time of 1.0 ms, the distance between the crack walls reached 23 mm at the free edge. Conversely, within the time periods of 2.25 and 3.5 ms, it increased two and three times, respectively. The crack elongation in the longitudinal direction occurred 5.8 times with time. Together, within the time of 3.5 ms, the equivalent stresses increased twice, after which the growth of the crack stopped due to the gas decompression. Moreover, studies on the growth of the crack-like defect in its tip area at the maximum pressure showed that additional considerations on the pressure on the crack edges led to an increment of 3.6% of the crack length. The results of this work can be used for the development of measurements for operating gas pipelines in the field of structural reinforcement.

DEVELOPMENT OF LOADING MODELS AND ANALYSIS OF THE STRESS-STRAIN STATE OF THE MAIN GAS PIPELINE WITH COMPOSITE LININGS

The operation of sections of main gas pipelines that are on the verge of developing a design resource is associated with a number of problems in ensuring industrial safety. One of the most acute problems is the occurrence of local defects. The main material for the manufacture of main gas pipelines is steel. During the operation of the pipeline, local defects occur due to metal corrosion or mechanical damage to the gas pipe. Such concentrators with high internal pressure in the gas pipeline can lead to the destruction of the entire structure. In this case, the situation of destruction is especially critical, since it can cause a man-made disaster. To increase the shelf life of damaged sections of main pipelines in places where defects are located, banding with composite linings is used. The article contains part of a comprehensive study, which consisted in the development of methods for modeling the main gas pipeline for oil and petroleum products under seismic loads, dynamic stress-strain state under the influence of seismic loads and stress-strain state of a damaged gas pipeline reinforced with composite linings under the action of internal pressure. The technology of manufacturing linings from composite material is also described in detail. At the same time, a geometric model of the section of the main gas pipeline with composite linings was developed and an analysis of the loading of the section of the main gas pipeline in ANSYS was carried out, provided that the lining is mounted without tension on the pipeline and provided that the lining is mounted with tension, where a comparative analysis showed that the installation condition of composite linings does not significantly affect the static stress state.

FEATURES OF THE CONSTRUCTION OF THE STIFFNESS MATRIX OF THE SPATIAL HEXAGONAL FINITE ELEMENT FOR COMPOSITE MATERIAL WITH DISCRETE INCLUSIONS BASED ON THE MOMENT SCHEME

An approach to numerical modeling of the stress-strain state of composite structures with discrete inclusions is presented in the paper. The finite element method is used as the main method, namely its modification – the moment finite-element scheme. The moment scheme, in contrast to the classic scheme of finite elements, allows to avoid such negative properties as not taking in consideration the rigid rotation of the finite element and “false” shear. If both the material of the matrix and the material of the reinforcing inclusions are weakly compressible, then problems arise due to the fact that some elastic constants approach very large values. The Taylor series expansion of the components of the displacement vector, the components of the strain tensor, and the volume change function is used in order to eliminate the mentioned shortcomings, after that, according to the moment scheme, certain sums are removed from these expansions. Homogenization of the material with lamellar inclusions, a small proportion of spherical inclusions, and a large proportion of spherical inclusions is used for modeling the elastic properties of the composite. The chaotic nature of the location of inclusions after homogenization makes it possible to present a non-homogeneous composite material as a homogeneous quasi-isotropic one. The described approaches are used in the construction of the stiffness matrix of the spatial hexagonal finite element. The obtained expressions for the stiffness matrix are done in the software package for calculating structures from composite materials. The calculation of a thick-walled pipe under the action of internal pressure from a composite material with lamellar inclusions, a small proportion of spherical inclusions, and a large proportion of spherical inclusions was carried out using the software package. For different volume fractions of discrete inclusions, the numerical convergence of the results with different finite element meshes has been investigated, which shows great congruence with analytical solutions.

Mathematical modeling of non-stationary deformation of cylindrical structures

The paper investigates the dynamic behavior of a hollow elastic cylinder of finite length, placed in a rigid cylindrical shell, under a sharp change in internal pressure. A numerical solution of a two-dimensional dynamic problem is obtained using the method of spatial characteristics. The stress-strain state of an elastic cylinder is described by a system of hyperbolic equations with two circular conical surfaces as characteristic surfaces. The outer cones correspond to longitudinal waves; the inner ones correspond to transverse waves. The calculations were carried out under various conditions at the ends and the outer (contact) surface of the cylinder and shell. An analysis of the results for a cylinder with load-free ends shows that the absence of gluing the outer surface of the cylinder with the shell leads to a significant increase in the velocities of the points of the cylinder. Under the action of internal pressure, the ends move apart, resulting in a significant increase in the radial velocities of the internal channel. Qualitative patterns of behavior of the structures under consideration, which are widely used in mechanical engineering, on impact-type impacts, can be used to improve and optimize them at the design stage.

Failure mechanisms of equipment hatch area in prestressed concrete containment vessel

The failure mechanisms of the equipment hatch area under two load cases (LCs), i.e. in-plane shear/tension and tension/tension to consider the combined action of ground motion and internal pressure and the action of internal pressure only, respectively, were experimentally studied with three specimens for each LC.The results show that the failure of the LC1 specimens is due to the eccentric tension in the vertical direction. The shear force in the lateral direction changes the stress distribution in the specimensand thus influence the crack nucleation and propagation. The failure modes of the LC2 specimens depend on the magnitude of the lateral tension. With the increase of the maximum lateral tension, the failure modes vary in the sequence of the horizontal cracking of concrete at the bottom of the specimen, the critical diagonal cracks on the top of the specimen and the failure of the narrowest part of the specimen.

Mechanical Behavior and Sealing Performance Study of Subsea Connector Core-Sealing Components under the Combined Action of Internal Pressure, Bending Moment, and Axial Load

A complete subsea production system (SPS) is assembled by interconnecting subsea manufacturing facilities through subsea connectors. To ensure the reliability and longevity of the SPS, it is imperative to thoroughly investigate the mechanical behavior and sealing performance of the subsea connector’s core-sealing components. In this study, the loading conditions of the subsea clamp connector are examined to analyze the load transfer relationship between its components under different modes. A mathematical model for the load transfer between locking torque and sealing contact pressure is developed for the preloading mode, and the concept of mechanical transfer efficiency is introduced. Another mathematical model for the load transfer between the locking torque and the design pressure is developed for the operation mode. Furthermore, a three-dimensional full-size finite element model of the subsea clamp connector is established to analyze the effects of complex loads on the mechanical behavior and sealing performance of its core-sealing components. The simulation results indicate that internal pressure loading positively affects the sealing of the subsea connector, and that the stress distribution in the core-sealing components under bending moment loading exhibits significant asymmetric characteristics. Additionally, the superposition of axial tensile loads reduces the effect of the bending moment on the strength of the core seal member but further weakens the seal. Finally, an experimental system is designed to validate the simulation results.

Fracture Response of X80 Pipe Girth Welds under Combined Internal Pressure and Bending Moment.

In order to determine the effect of defect size on the pipeline fracture performance of girth welds in oil and gas pipelines, ABAQUS was used to simulate the fracture responses of X80 pipelines with girth weld defects under internal pressure and bending moment conditions based on damage mechanics. In particular, the length and depth of defects were parametrically studied; the defect depth range was 20-80% of the wall thickness, and the circumferential length range of the defects was 5-20% of the pipeline circumference. The results show that, under the combined action of internal pressure and bending moment, the defect depth was more associated with adverse effects than the circumferential length of the defect. The failure load did not linearly decrease as the size of the defect increased, but when the depth of the defect reached a certain value, the failure load suddenly decreased.

Analysis of bulge failure of steel wire-reinforced thermoplastic composite pipe

A steel wire-reinforced thermoplastic composite pipe (SRTP) was used for water injection connecting line pipe had caused bulge failure of the external surface after 6 years of service. Investigations were performed to identify the most probable causes of the pipe failures. The study was conducted by reviewing the background of the failure, visual physical inspection, test production process analysis, and thermal analysis. The results revealed that the failure of this pipe was mainly caused by scratch defects on the inner surface and the poor resin stability near the cracking site compared to its basal resin. It has scratch defects forming a crack source under the combined action of internal pressure, the resin matrix on the inner surface appears brittle cracking. Subsequently, the medium to be corroded after contacting with the metal wire, losing the pressure bearing effect, and finally forming a bulge on the outer surface under the action of low internal pressure.

Instrumental inspection of pressure pipelines of the Amuzang-2 pumping station

This article discusses the main results of the field studies conducted to assess the technical condition of the pressure pipelines of the Amuzang-2 pumping station. The research aims to check the stress-strain state of the pipeline material, which occurs during long-term operation under conditions of corrosive and abrasive wear of the shell. The research objectives were as follows: measuring the thickness of the shell of pressure pipelines of the pumping station; verification calculation of the strength of pumping station pipelines. During the research, the method of carrying out full-scale measurements using an ultrasonic device to determine the thickness of the pipeline shell and the method of calculating the stress-strain state of the pipeline material that occurs during long-term operation under conditions of corrosive and abrasive wear of the shell were used. The verification calculation was carried out for the strength of the shell material and the stability of the shape of its section: from the action of external pressure (vacuum in the pipeline), buckling, like a rod, under the action of internal pressure. According to the studies carried out, the pipelines can withstand the maximum vacuum, and the static buckling strength of the pipelines is ensured.

Analysis of the limiting states of cylindrical elastic-plastic shells under tension and combined loading by internal pressure and tension

The elastic-plastic deformation, limiting states and supercritical behavior of cylindrical shells under tension and combined loading by internal pressure and tension to failure are studied theoretically and experimentally. This problem is characterized by the occurrence of large strains, shape changes and, as a result, an inhomogeneous stress-strain state. In the numerical solution of such problems, the problem arises of constructing true stress-strain curves of materials. In this regard, to study the deformation and strength properties of materials, it is important to use an experimental-computational approach, which makes it possible to take into account the non-uniaxiality and inhomogeneous of the stress-strain state without accepting simplifying hypotheses. The paper presents a new efficient algorithm for constructing a true stress-strain curve, which is based on the procedure of nonlinear extrapolation of the curve. Such an algorithm, in the process of direct numerical solution of the problem, consistently constructs a stress-strain curve without using repeated direct calculations, which significantly (at times) increases its efficiency. Based on the experimental-computational approach, the true stress-strain curves for solid rods and shells made of 10KhSND and 10G2FBYu steels were determined under tension and combined loading by internal pressure and tension to failure. The failure of shells under tension occurs at lower (at times) values of true strain than solid rods. Significant differences in true stresses and strains at the moment of failure are due to different localization of deformation of solid rods and shells after the loss of stability of plastic deformation in tension. It is shown numerically and experimentally that after loss of stability of plastic deformation according to Considerer in tension, the cylindrical shell contains two forms of loss of stability until the moment of failure. The first form of loss of stability, as in solid rods, is characterized by localization of deformations along the diameter of the sample in the form of a neck, and the second form is characterized by localization of deformations along the thickness of the sample, which determines the final stage of failure. Under the action of internal pressure on the shell, the first form of loss of stability of plastic deformation degenerates with the formation of a neck inside the shell, and only the form of loss of stability is observed, caused by the localization of deformations along the thickness of the shell.

Comparative analysis of the stress state of an equal slope shell by analytical and numerical methods

Works on the study of the stress-strain state of the shell of an equal slope with an ellipse at the base have not been widely performed. The present paper is a part of a series of articles on the analysis of the geometry and stress state of torses of an equal slope with a directrix ellipse by various methods under different loads and support conditions. The derivation of the differential equations of equilibrium of the momentless theory of shells for determining internal forces in the torse with a directrix ellipse under the action of internal pressure is presented. The analytical results are compared with results obtained by the finite element method (FEM) and the variational difference method (VDM). The advantages and disadvantages of three calculation methods are determined, and it is established that VDM results are more accurate compared to FEM, but FEM-based software is a more powerful tool to perform the structural analysis.

Prediction method based on strain monitoring for thread root crack in high pressure hydraulic fracturing manifold

There is a high stress concentration at the connection threads of high-pressure manifolds. Under the action of internal pressure(Pint) and rapid vibration, the root of the thread is prone to fatigue cracking. To study the variation in the damage of a high-pressure manifold with connection threading, this paper first analyzed the strain of the manifold with different Pint and with or without defects at different positions on the outer wall shaft. The potential fatigue crack damage of a high-pressure manifold of a hydraulic fracturing truck was monitored and analyzed by strain testing technology. The variation of the strain signals of defected and defect-free high-pressure pipe fittings were compared. The damage stress concentration point of the connection thread of the high-pressure manifold was analyzed. When there is a crack at the root of the thread, results show that there is a large difference in strain in the axial direction of the crack compared to the strain in threading thread without a crack. Meanwhile, the strain concentration coefficients of different stress concentration points change regularly. In this paper, the damage state of the thread is analyzed by strain monitoring. The results can provide a theoretical and practical basis for the prediction of root cracks in connection threads.

EXPERIMENTAL STUDIES OF ELEMENTS OF METAL CYLINDRICAL STRUCTURES STRENGTHENED BY EXTERNAL TRANSVERSAL CFRP REINFORCEMENT

One of the modern ways to increase the bearing capacity of the walls of metal cylindrical structures that perceive the action of internal pressure is the external transversely directed reinforcement by fiber reinforced plastics (FRP), the most effective type of which is made from carbon fibers (CFRP).

Optimization of structure matrix of mold forms

Purpose. Optimization of the method of design and calculation of the composite matrices of molds for the manufacture of products from powder materials.
 Research methods. Analysis of stresses in the walls of solid and composite thick-walled cylinders and their existing calculations.
 Results. The peculiarities of stress formation in the wall of solid and composite thick-walled cylinders under the action of internal pressure are investigated. The possibility of applying the obtained results to determine the strength and stiffness of the wall of the mold for the manufacture of products from powder materials is analyzed. Limitations in ensuring the strength of the matrix by only increasing its thickness are determined. It is shown that the use of a matrix composed of an inner cylinder and an outer holder allows to use optimal stress redistribution in the walls of such matrix in order to reduce the size and, accordingly, save materials for its manufacture. The possibility of using various, better adapted materials for the manufacture of the inner wall of the matrix and permiting the reduction of the cost of manufacturing the mold are analyzed.
 The method of calculation of stresses in dangerous points of walls of a matrix at an estimation of their strength and stiffness is generalized. Formulas for determination of the guaranteed tension which will provide effective redistribution of stresses in walls of the composite matrix under the set operating conditions are given.
 Scientific novelty. Approaches to the analysis of stresses in the walls of composite matrices of molds under the influence of internal pressure are optimized and generalized . Mathematical dependences are given, which make it possible to determine the optimal dimensions of mold elements at action of pressing pressure.
 Practical value. The principles of design and methods of calculation of composite matrices of molds for the manufacture of products from powder materials are proposed.

The influence of pressure changes on the integrity of tanks for storage of petroleum products and toxic substances

Tanks for the storage of oil products and toxic substances in warehouses are the main ones. They can be in the form of separate tanks or a group of tanks. The most widespread are vertical steel tanks with a stationary roof that a placed in open areas. The tanks heat up, and the intensity of evaporation of the oil product increases in case of fire. If there is a permanent roof, the pressure in the tank will increase. If the capacity of the breathing valves is less than the intensity of evaporation then there is a risk of explosion. Explosions in the tank often lead to the separation of the bottom, and the side cylindrical surface and the roof fly away instantly, spilling oil on neighboring tanks and the territory of the tank’s park. Then the combustion area increases intensively. The destruction of the integrity of the tank, due to the separation of the bottom, contributes to temperature and power stresses, the value of which increases with increasing temperature of their heating and increasing pressure, respectively. The values of temperature stresses are added to the power stresses caused by pressure, and when the critical value is reached, destruction occurs.
 We investigated the stress-strain state of a steel vertical tank for the storage of oil products and toxic substances. The analysis of the reasons for the occurrence of admissible pressure in the tank, which is the reason for the loss of its integrity, is carried out. Using the differential equation of a closed cylindrical shell, which is under the action of internal pressure, analytical expressions are obtained to find deformations and stresses in the side cylindrical surface and bottom. Were calculated axial and annular stresses for the tank of RVS-900. Based on the basic relations of the theory of elasticity of thin plates and shells analytical expressions of the stress-strain state of the cylindrical tanks are obtained for conditions for changing of pressure on their structural elements. It is shown that the greatest values of axial stresses are obtained on the surface of the connection of the cylindrical surface with the bottom. The researches results are presented graphically.

Ultimate pressure determination in hydraulic fracturing of boreholes for different rock failure criteria

The problem on elastoplastic deformation and rock failure around boreholes under the action of internal pressure is considered. The stress state in the intact rock mass is assumed to be hydrostatic. The hydraulic fracturing pressure is conventionally determined by the maximum normal stress criterion. However, the experimental studies described in scientific articles show that this criterion is not consistent with the results obtained in the course of laboratory tests on failure of cylindrical and spherical cavities made in rock samples. It has been known that test results on complex loading for solid samples of various materials are not confirmed by the theory of maximum normal stress both in terms of ultimate load value and direction of failure surface propagation. In this case, for the complex stress state of rocks, it is proposed to determine the ultimate pressure by the experimentally substantiated fracture criteria which are in good agreement with the results of laboratory tests on hydraulic fracturing of boreholes.

Analysis of the stress state of solid propellant grains under internal pressure load

In order to determine the stress state of the solid rocket motor grain under the internal pressure load, based on the finite element numerical simulation calculation, the length and size requirements of the grain under the internal pressure simplified to a plane strain problem are obtained. Numerical simulation calculations are further carried out for the grains in plane strain state that meet the simplified conditions, and the radial and circumferential stress states of the grains are obtained. The numerical simulation results are compared with the viscoelastic theoretical solution of the grains under the same material parameters. The results show that when the aspect ratio exceeds 2.5, the axial strain is approximately 0, which can be equivalent to a plane strain problem. In addition, the analysis shows that under the action of internal pressure, the plane strain grains are in a bidirectional compression stress state with a radial and circumferential stress ratio of approximately 1:1. Finally, by comparing the numerical solution and the analytical solution, it is found that the relative error is within 3%, which verifies the correctness of the numerical simulation calculation results.

Stress-strain state of spherical shells with two unequal holes

This article presents the results of a numerical study of the stress concentration around two equal and unequal holes in an orthotropic spherical shell made of composite materials under the action of internal pressure. The influence of geometric (hole radii, shell thickness, distance between holes) characteristics, as well as material orthotropy and shear stiffness, on the stress state of spherical shells made of composite materials is studied. A numerical algorithm based on the finite element method has been developed and a software package has been implemented on a computer that allows solving the problem of stress concentration near two unequal holes in spherical shells made of composite materials.

Numerical Investigation of the Damage Mechanism of Offshore Pipeline Impacted by the Lump-Shaped Falling Object

AbstractDamage mechanism analysis of the exposed offshore pipeline impacted by lump-shaped falling objects plays a significant role in offshore pipeline design, inspection, maintenance, and protection. A series of three-dimensional (3D) coupling models are established and simulated to investigate mechanical behaviors and responses of exposed offshore pipelines impacted by lump-shaped falling objects. The effects of both offshore pipeline parameters and lump-shaped falling object parameters were discussed under the joint action of internal pressure and external seawater pressure. The results demonstrate that seabed soil could absorb partial impact energy and act as a cushion. Indentation on the pipeline top and stress concentrations on the pipeline bottom starts to appear when the impact velocity is larger than 10 m/s and 14 m/s, respectively. The critical impact energy before pipeline failure is around 9733.339 J. A variation in contact area has a noticeable influence on the dent depth, but a slight influence on the global deformation. An increase in pressure difference mitigates the impact damage. The depression rate increases with the rise of the radius-thickness ratio, and the most severe plastic deformation occurs when the radius-thickness ratio is 40. Besides, the eccentric distance is an essential factor influencing the damage mechanism of the offshore pipeline.

Modeling of stress-strain state of piping systems with erosion and corrosion wear

The problems of modeling the stress-deformed state of erosion or corrosion-worn rectilinear sections and the ball-shaped bends of pipeline systems are proposed to solve in a cylindrical coordinate system. For this purpose, formulas of Christophell type II, non-zero components of the strain tensor and a system of equilibrium equations in the framework of linear torsional theory are given. The system of equilibrium equations is reduced to one equation, which is the basic equation of the Lame’s problem. Formulas for the calculation of ring stresses that occur in the wall of erosion or corrosion worn rectilinear sections, and the removal of pipelines from the action of internal pressure are derived. The influence of the change in the wall thickness of the pipeline bends in the place of their erosion or corrosion wear on the amount of ring stresses is determined.