Pipe Axis Research Articles

Horizontal annular flow through orifice studied by X-ray microtomography

An X-ray microtomography (µCT) system was adapted so that 3D scans of fixed horizontal or vertical test sections can be performed. The mobile µCT system has been applied to measure the local, time-averaged volume fraction distribution of developing annular air-water flow in a horizontal pipe with µm spatial resolution. Based on the volume fraction data the liquid film thickness profile is computed and the accumulation, stripping and renewal of the annular liquid film at a circular orifice is studied. The development length of the annular flow downstream of the orifice is evaluated based on the integral volume fraction and the change of the film thickness profile along the pipe axis. Both parameters give a consistent result, indicating that liquid film renewal can be judged based on integral measurement techniques in this case. Further, the detailed 3D data enables the validation of computational fluid dynamics codes based on phase-averaged variables such as the Euler-Euler approach.Graphic abstract

Mechanical responses of bell‐and‐spigot joints in buried prestressed concrete cylinder pipe under coupled service and surcharge loads

AbstractPrestressed concrete cylinder pipe (PCCP) is widely used in hydraulic engineering. The bell‐and‐spigot joint is a weak point along a PCCP pipeline, since damage of joint can affect the operation of the whole pipeline. In this paper, a three‐dimensional numerical model of buried PCCP, considering the simulation of rubber gasket in bell‐and‐spigot joint is established. The fluid–structure coupling of PCCP is accomplished using the Mesh‐based parallel Code Coupling Interface (MpCCI), where the pipe and the surrounding soil are characterized in the software ABAQUS, and the pressurized water is modeled in the software FLUENT. The force and rotation angle at joints of PCCP under different conditions, including surcharge load, loading location, cover depth, and internal pressure, are analyzed. It is shown that the rotation angle of joint exceeds the allowable value, when the surcharge load is greater than 180 kPa. Compared with the effect of surcharge load, the offset distance (i.e., distance between the loading position and the pipe axis) has a greater influence on the development of horizontal displacement and rotation angle. As the offset distance increases, both the horizontal displacement and rotation angle at joints increase first, and they decrease after the peak.

Laminar flow through corrugated pipes: comparison of exact and approximate solutions

Exact flows are calculated for an infinite set of pipe cross-sections, each with variable corrugations, ranging from angular to smooth as a parameter varies. The results are compared with three ‘rules of thumb’ which give general but approximate formulae for the rate of flow through a pipe of given cross-sectional shape. These are (i) the Saint-Venant formula, in which the flow is related to the area and the polar moment J about the centroid of the pipe cross-section; (ii) the Aissen approximation, in which the flow is approximated in terms of the pipe cross-sectional area A and the diameters of the inscribed and circumscribed circles; and (iii) the area–perimeter or hydraulic radius approximation of various authors, which states that for a given pressure gradient and fluid viscosity the total flow rate through a pipe of given cross-section is proportional to A3/P2 where P is the perimeter length of a pipe section normal to the pipe axis. Formulae are given for the flows and pipe properties for corrugation number ranging from three to infinity.

IMPROVEMENT OF APPROACHES AND METHODS OF TURBULENT FLOW THEORY IN THE PIPES

Abstract. The article consideres the analysis of the literature about the development of the water turbulent flow theory in the pipes. According to the results of analysis and theoretical studies, we obtained mathematical models. These models described the kinematic structure of the water turbulent flow in the pipes for different regions of turbulence. For the first time, the hypothesis was accepted that the dependence obtained from the Navier-Stokes differential equation for constructing the velocity profile in the laminar regime is suitable for calculating the average velocities in the turbulent regime of flow, but for this, it is necessary to replace the molecular kinematic viscosity with the total turbulent kinematic viscosity, which includes kinematic viscosity on the inner surface of the pipe and turbulent kinematic viscosity , which occurs due to the movement of masses from one layer into another, as recommended in J.V. Boussinesq. Based on experimental data I. Nikuradze and F.O. Shevelev, we obtained a distribution of the total kinematic viscosity in the pipes, including the kinematic viscosity on the pipe inner surface and the kinematic turbulent viscosity. For the first time, we used the kinematic viscosity distribution equation in the pipes and obtained the averaged velocity profile equation. This equation corresponds to the boundary conditions on the pipe inner surface and on the axis of the pipe. The equation of maximum averaged velocity, the equation of distance from the axis of the pipe to the points having average velocity, the equation of the ratio of maximum velocity to average velocity was obtained. For the first time, the equation of the tangent stresses components ( , ) and the tangent stresses equation in radial coordinates ( ) were obtained. The equation of the maximum value of the tangent stresses located on the inner surface of the pipe was obtained. The tangent stresses assume a zero value on the pipe axis. The equation of the vortex components ( , ) was obtained. We have shown that vortex lines are concentric circles whose centers are located on the pipe axis. The equation of angular velocity of flow particles rotation relative to the vortex lines was obtained. The maximum value of the particle rotation angular velocity on the pipe inner surface is determined. It decreases monotonically to zero on the axis of the pipeline. It is zero on the pipe axis. In this article, all equations reveal the kinematic structure of the water flow. We described these equations by the Reynolds number and the pipe friction factor. Such equations are adopted to show the dependencies between the regimes and the flow kinematic structure. These equations make it possible to calculate the distribution profile of the total kinematic viscosity, averaged velocity, tangential stresses and angular velocity of flow particle rotation.

Dynamic torsion of underground pipeline due to sudden rotation of foundation fragment

In the paper, we study the strength of underground pipelines, which are laid through tectonic faults, and, as a consequence, are operated in difficult mining and geological conditions. In such dangerous areas, in addition to the standard pressure load of the transported product, the pipe is subjected to additional effects from the movements of the inhomogeneous, often damaged, foundation. Predictably, the most dangerous situation is when such movements are transient. The paper aims at developing a model to describe the non-stationary process of pipeline deformation on a damaged foundation caused by sudden mutual rotations of rock blocks around the pipe axis. The dynamics of the pipeline was studied in a linear formulation, modeling it with a rod with a tubular cross-section. The momentless theory of cylindrical shells and the energy concept of strength were used while considering the issues of ultimate equilibrium. The soil backfill was considered as Winkler's elastic layer. Local continuity disturbances of the foundation are described by a sudden rupture of the angle of rotation of its fragment. This approach, developed on the problems of statics, makes it possible to dynamically assess the strength of the underground pipeline not by external load from the soil, which is usually unknown, but by the observed or predicted parameters of the fault edges. We formulated an initial-boundary value problem for a hyperbolic differential equation of torsion with a discontinuous right-hand side. Based on the analytical solution of the problem, constructed in the form of squares from Bessel functions, the influence of the sudden rotation of the foundation fragment around the pipe axis on the stress-strain state of the pipeline is studied. Plots of the space-time distribution of the angle of rotation, angular velocity, torsion deformation and equivalent stresses of von Mises in the prefrontal and postfrontal areas are constructed. It is established that considering dynamic effects leads to an increase in the torsion deformation maxima and the equivalent stress in the pipe wall in comparison with the case of static perturbation.

Numerical analysis of swirling turbulent droplet-laden flow and heat transfer in a sudden pipe expansion

The effect of swirling intensity on the structure and heat transfer of a turbulent gas–droplet flow after a sudden pipe expansion has been numerically simulated. Air is used as the carrier phase, and water, ethanol, and acetone are used as the dispersed phase. The Eulerian approach is applied to simulate the dynamics and heat transfer in the dispersed phase. The gas phase is described by a system of Reynolds-averaged Navier-Stokes (RANS) equations, taking into account the effect of droplets on mean transport and turbulent characteristics in the carrier phase. Gas phase turbulence is predicted using the second-moment closure. A swirling droplet-laden flow is characterized by an increase in the number of small particles on the pipe axis due to their accumulation in the zone of flow recirculation and the action of the turbulent migration (turbophoresis) force. A rapid dispersion of fine droplets over the pipe cross-section is observed without swirling. With an increase in swirling intensity, a significant reduction in the length of the separation region occurs. The swirling of a two-phase flow with liquid droplets leads to an increase in the level of turbulence for all three types of liquid droplets investigated in this work due to their intensive evaporation. It is shown that the addition of droplets leads to a significant increase in heat transfer in comparison with a single-phase swirling flow. The greatest effect of flow swirling on heat transfer intensification in a two-phase gas-droplet flow is obtained for the droplets of ethanol and water and smallest effect is for the acetone droplets.

About the Influence of the Corrosion Defect Geometry on Repaired Pipes Stress Distribution

Abstract This paper proposes a new approach in dealing with volumetric surface defects (VSD) in pipelines. Using three-dimensional (3D) scanning and reverse engineering techniques, along with finite element analysis, we studied and evaluated comparatively the stress distributions in the defect area for different shapes and positions of the machined VSD, in order to find the best solution for the repairing process using composite materials. Our main conclusion is that instead of machining the VSD such as to generate a rectangular shaped machined defect, with edges parallel/perpendicular to the pipe axis, it is better to mold the VSD. Another possible solution would be to machine the real VSD such as to generate an inclined rectangle that circumscribes the defect. This paper also studies the influence of the machined defect filet radius to the bottom of the VSD.

Wear of a high pressure layered pipe by a rough rigid bush

The article describes the solution to the problem of linear wear of a high pressure elastic pipe with an elastic coating by rigid bush worn on the pipe so that there is no gap between them. It is assumed that both the thickness of the coating in undeformed state and the shape of the inner surface of the bush are variable and depend on the coordinate along the axis of pipe. In the case when indicated characteristics are described by complex rapidly changing functions, standard approaches to solving such a problem turn out to be ineffective. The article describes an approach based on the use of special representations and basic functions that take into account the presence of complex characteristics. In the expression for contact pressures, which is the result of solving the problem and allows us to further evaluate the resource and durability of such a connection, the functions that describe the surfaces shapes are highlighted in explicit form. This allows us to perform exact calculations in cases where the forms are described by complex functions.

Study of Invelox Wind Turbine Considering Atmospheric Boundary Layer: Based on Numerical Simulation

The flow field characteristics of increased velocity (Invelox) system under different wind direction were studied by computational dynamic fluid (CFD) method. Since the Invelox wind turbine system needs to be placed in external space to operate, the atmospheric boundary layer (ABL) wind profile must be considered. The Invelox system was simulated with uniform velocity inlet and exponential wind profile inlet. The results show that when the wind direction is more than 90 degrees from the axis of the venturi pipe, the power generation efficiency of the system will decrease sharply. When the Angle exceeds 120 degrees, the system does not generate electricity. After considering ABL, the speed ratio (SR) of the system will decrease.

Advanced device for cleaning drain wells

The article presents cleaning technologies and considers an improved device for cleaning drainage wells, which allows to increase the productivity and quality of cleaning drainage wells, reduce labor costs, and water consumption. The device is simple, reliable, and highly maintainable, allowing you to operate it in the mode of economy and consumption of a large volume of water. The proposed device received a copyright certificate for the invention. A cable system is provided in this device, and a ruff head is stretched inside the drainage pipe, which has the ability to deviate and rotate along the longitudinal axis of the drainage pipe, the ruff is pulled by winches through adjustable and fixed blocks, and the mounting frames are installed in inspection wells and fixed with bolts and successively reinstalled from one well to another. Theoretical prerequisites have been developed for determining the maximum force in the closing, hoisting rope, the required power for closing the jaws and lifting the bucket, the diameters of the corresponding drums and ropes.

Study of the mechanical properties of the gas pipeline metal after long-term operation in conditions of the North

The residual strength and technical condition of the material of 530-mm steel pipe (14KhGS) of main gas pipeline are estimated to ensure the safety of long-term operation of pipelines in climatic conditions of the North. The mechanical properties are determined using standard methods of mechanical testing in laboratory conditions. A full-scale pressure test up to failure is used to determine the actual values of the fracture toughness and safety factor of the pipe. Full-scale tests were carried out on a test bench, a computer-measuring complex which displayed the reaction of the object to the load. A pipe fragment was cut from the linear part of the main gas pipeline and welded with spherical plugs. The outer surface of the pipe was notched along the pipe axis. The depth of the notch was calculated such that the breaking load on the ligament section at the notch site corresponded to the working pressure of the gas pipeline. No significant changes in the mechanical properties of the pipe metal were revealed in the absence of visible corrosion and deformation damage during long-term operation of the pipe in the North. Impact tests did not reveal embrittlement of the metal of the tested pipes. Full-scale tests of a pipe with an artificially applied defect made it possible to calculate the value of the critical stress intensity factor, which allowed us to estimate the residual strength of a pipe with a longitudinal crack. The value of the strength criterion of the fracture mechanics indicates the preservation of a sufficiently high viscosity of sheet metal pipes. Similar tests of the pipes (of other size and made of other materials) operating in the main gas pipelines should be continued taking into account temperature ranges and material degradation after long-term operation.

A new transient analytical model for heat transfer of earth-to-air heat exchangers

In the present paper, a simple but accurate transient model to evaluate the thermal performance of earth to air heat exchangers (EAHEs) is developed. Governing equations for both pipe flow and soil surrounding the pipe are derived for the transient state and are solved using Laplacian transform. To validate the analytical model, the 3D numerical model of the EAHE is also simulated. Results of the analytical model and numerical simulations are compared with already reported experimental data. In heating period at velocity of 2 m/s, the discrepancy between the analytical model and reported experimental results is 0.87% and 1.31% for steel and PVC pipes, respectively. For velocity of 5 m/s this was as low as 0.4% for both pipe materials. For the cooling condition, a maximum discrepancy occurs for PVC pipe at 2 m/s equal to 9.55%. Analytical results were compared with numerical simulations for both constant and time-varying inlet temperatures, and great correlation was observed. Thermal diffusion into the soil was also investigated after 6 h and 120 h of continuous operation. Results revealed that for the fluid velocity of 5 m/s, after 6 and 120 h of continuous operation, heat diffused up to 10 cm and 50 cm distance of the pipe axis, respectively, which showed the thermal saturation of the soil with passing the time in continuous operation mode. Results show that thermal saturation of the soil should be taken into the model as ignoring it can cause an overestimation in system performance.

Mechanical behavior of buried composite pipelines subjected to strike-slip fault movement

Buried composite pipelines crossing active faults can be deformed significantly due to strike-slip fault movement. Because of the problem complexity arising from material mechanical behavior and imposed large deformation, a numerical analysis was conducted using a nonlinear finite element approach. The lateral displacement incrementally was imposed normal to the pipe axis until one of the pipe layers failed based on the Hashin failure criteria. The effective factors on the buried composite pipeline performance, such as the pipe dimensions, composite lay-up, and soil stiffness, were studied parametrically. The results showed that the winding angle of the composite pipe has significant effects on the response of the pipe subjected to the fault movement, therefore determining an optimum winding angle is very important for practical engineering designs. In addition, the results show that the effect of changing the pipe diameter cannot be predicted easily, and also it is depended on the winding angle. However, changing the soil stiffness did not change the optimum winding angle. Furthermore, the comparison conducted for the studied composite and steel pipes at the similar simulation conditions showed that the composite pipe has a better response until the onset of the failure, and the composite pipe could be considered as a suitable replacement for the conventional buried steel pipeline.

Investigating the migration law of aggregates during concrete flowing in pipe

During pumping fresh concrete pipes, aggregate migration is occurred under the action of various forces. In order to study the migration characteristic of aggregates during concrete flowing in pipes, in this paper, we built the test system based on particle tracking technology. Transparent concrete was prepared. The particle capture function of high-speed camera was used to track particle motion. Results showed that the radial displacement of particles depended on the initial location and aggregate size. Small aggregates near pipe wall or center axis had fewer motion. For the particles with larger diameter, the migration direction almost pointed to the axis of pipe. The migration displacement of nature aggregates was smaller than that of ground grinding ball. The migration displacement firstly increased and then decreased with increasing the diameter of particle. Moreover, the effect of particle shape on migration was explored. Finally, the wall effect, gravity induced particle migration and shear induced particle migration were compared based on the phenomenon of flow induced particle migration, results showed that the phenomenon of shear induced particle migration played the main role in the formation of lubrication layer. This study was of great significance to reveal the transport law of dense particle flow in the pipeline.

An experimental study on a horizontal-vertical pneumatic conveying system using oscillatory flow

To reduce the power consumption of a horizontal-vertical pneumatic conveying system, an oscillator is mounted with a 45° oblique plane through the pipe axis in this study. This experimental study focuses on the effect of oscillatory flow using the oscillator on the horizontal-vertical pneumatic conveying system in terms of the overall pressure drop of the system, power consumption, local pressure drop, and particle velocity. Compared with conventional pneumatic conveying (axial-flow), the pressure drop and power consumption can be reduced using the oscillatory flow in a lower air velocity range. Meanwhile, the particle axial velocity of the oscillatory flow is higher than that of the axial-flow near the bottom of pipe. This outcome indicates that the accelerating effect of oscillatory flow is obvious near the bottom of the pipe, and the particle vertical velocity of the oscillatory flow is positive, whereas the particle vertical velocity of the axial-flow is almost negative. This result shows that the particles of the oscillatory flow are suspended sufficiently, but the particles of the axial-flow have a tendency of deposition. Furthermore, the fluctuation intensity of the particle velocity of the oscillatory flow is higher than that of the axial-flow, especially near the bottom of the pipe.

A Simulation of the Post-Bending Process of the Pipe Billets for Welded Pipe Manufacturing

The paper presents a result of the simulation of the post-bending process of the pipe billet, using the MSC.Marc software package. It was shown that the use of a standard method for carrying out post-bending process leads to the formation of various defects, such as a variable gap between the edges along the pipe axis, vertical waves and bends at the edges, as well as a decrease in a sheet thickness on the edges.

Numerical simulation of gas-liquid two-phase flow in gas lift system

The gas-lift system has a lot of significant advantages in sewage treatment, deep well oil recovery, liquid metal cooled reactor and magnetohydrodynamic power converters. The densities of different liquid media and gas media have great influences on the performance of gas lift system. Therefore, based on Fluent simulation software, using Euler model and <i>k</i>-<i>ω</i> SST (shear stress transport) turbulence model, the gas-liquid two-phase flow behaviors in nitrogen-water, nitrogen-kerosene, nitrogen-mercury and air-water, argon-water, nitrogen-water of gas lift system are studied. The rules of gas volume fraction and liquid flow rate at lifting pipe, liquid radial velocity at lifting pipe outlet, promoting efficiency are analyzed. The results are shown as follows. 1) In the nitrogen-water, nitrogen-kerosene and nitrogen-mercury system, the higher the density of liquid medium, the smaller the gas volume fraction in the lifting pipe is; the greater the flow rate of lifting liquid, the higher the promoting efficiency is. 2) In the air-water, argon-water and nitrogen-water systems, the higher the density of gas medium, the smaller the gas volume fraction in the lifting pipe is; the larger the flow rate of lifting liquid, the smaller the peak value of promoting efficiency is. 3) With the increase of gas flow rate, the liquid radial velocity at the lifting pipe outlet increases with overall fluctuation rising. Finally, the liquid velocity near the center of pipe axis is large, near the pipe wall is small. These research results provide the scientific theoretical basis for optimizing the gas lifting technology in applications such as sewage treatment, deep well oil recovery, liquid metal cooled reactor and magnetohydrodynamic power converters.

Brittle fracture manifestation in gas pipeline steels after long-term operation

Gas pipelines are exposed to operational loads combined with corrosive environment action during their long-term service. Complicated service conditions lead to a worsening of steel properties, a reduction of serviceability of the whole object, therefore, a risk of its premature failure rises. Aware of the importance of the existing problem, the aim of this study is the analysis of various mechanical properties of steels after their long-term operation on gas pipelines, and detecting and evaluating fractographic signs of this degradation.Mechanical properties of operated pipe steels characterizing their brittle fracture resistance were significantly decreased. Delamination areas as one of a feature of brittle fracture were identified on the fracture surfaces of specimens after SSRT of the operated steels in corrosive environment. Fracture was initiated from the outer surface of the specimens along the boundaries of ferrite and pearlite grains with significant secondary cracking.The obvious texture in the steels affects noticeably the results of the impact tests. Higher KCV values for the specimens cut in the longitudinal direction relative to the pipe axis comparing with the specimens of transversal orientation were obtained. This was explained by different length of narrow pearlite strips alternated by wide ferrite bands and interrupted by individual ferrite grains depending on the orientation of the specimen fracture surface relative to the pipe axis. Thus, a proper direction of specimen cutting to achieve the maximum sensitivity of KCV parameter to operational degradation of steels is discussed. The effect of specimen orientation on the results of the Charpy testing becomes much more pronounced with steel operation. Defects accumulated in steels during their service are preferentially oriented in the pipe axial direction along the boundaries between ferrite and pearlite strips. Analyzing the fracture surfaces of the Charpy specimens after their impact testing, certain signs of embrittlement were found for long term operated steels in the form of delaminations varying in size and shape, and some cleavage fragments. Furthermore, their percentage of total fracture surface (generally formed by dimples) correlates well with a drop in the impact toughness. The established relationship could be the basis for the introduction of fractographic criteria of the steel serviceability.

Shadow-Based Operation Assistant for a Pipeline-Inspection Robot Using a Variance Value of the Image Histogram

This paper presents a shadow-based operation assistant method for a pipeline-inspection robot using a variance value of the image histogram. By displacing the position of the head camera relative to that of the illuminator, a crescent-shaped shadow appears in the images captured in a bent pipe. The size, position, and orientation of the shadow depend on the robot’s orientation around the pipe axis. By applying the pathway direction of the bent pipe obtained from the image processing to the rolling movement, the robot can automatically adjust its roll-orientation. Experiments were conducted in four types of pipeline environments to verify the autonomous navigation. These include a complex winding pipeline, a long straight pipe, and pipelines with replicated dust and dirt.

Laminar viscous flow through pipes, related to cross-sectional area and perimeter length

It has been proposed, as a rough rule of thumb, that for a given pressure gradient and fluid viscosity the total flow rate through a pipe of given cross-section is proportional to A3/P2 where A is the area and P is the perimeter length of a pipe section normal to the pipe axis. This dependence on perimeter length as well as on area allows for the additional friction which comes from more contact of fluid with the walls of pipes which are corrugated or highly deformed from a circular cross-section. Comparison is made with exactly calculated flows for a variety of different pipe shapes.