Top Of Pipe Research Articles

Dynamics of large cavity induced by valve closure in an undulating pipeline

The dynamics of large cavity and the accompanied water column separation and rejoining induced by fast closing of a butterfly valve in an undulating pipeline system are investigated in this study. The three-dimensional computational fluid dynamics numerical simulations are performed using a newly developed interfacial surface tension-based model (ISTM) that accounts for the surface tension effect on large cavities. The applicability of the ISTM model is validated with the experimental data, showing better accuracy in predicting pressure fluctuations and cavity evolutions than three typical cavitation models. Differences in cavitation characteristics are observed between upstream and downstream of the valve. Upstream the valve, cavitation primarily appears at the pipe top, with the vapor volume fraction varying sharply due to the rarefaction pressure waves (maximum value of 0.0073). Downstream the valve, the complete water-column separation occurs, and vapor volume fraction changes slowly correspond with the growth and collapse of the large cavity (maximum value of 0.647). The maximum length of the large cavity can reach about six times the pipe diameter, with a minimum water vapor interface angle of 16°. The cavitation evolution displays a transition from a clustered inception to a sheet-like growth and collapse pattern. These findings contribute to the design and operation guidance for complex hydraulic systems during transient processes.

Flow Performance Analysis of Double-Chamber Gas–Liquid Transferring Device under Gas Inlet Condition

Gas-liquid mixed transportation technology is the core technology and plays a key role in the development of oil and gas production and transportation industry. Three different models of double-chamber gas-liquid transferring devices for gas field were selected as the research objects of this paper, and Fluent software was used to analyze the flow performance under the 100% gas content inlet condition. The gas-liquid two-phase distribution and the periodic relationship between pressure, temperature, tank liquid height with time of the device were calculated. The analysis revealed that the internal flow law of different models of devices is similar. A device’s operating cycle generally includes three processes ′ suction-compression-discharge ′, the pressure and liquid height within the two tanks change alternately, and the calculation formula of the cycle period has been provided. The highest temperature in the device appears at the top pipe during the compression process. The velocity at the vertical pipe at the device’s outlet is the fastest. The research methods and results can offer a theoretical reference for the design, optimization and application of the double-chamber gas-liquid transferring device.

Comparative Analysis of Buried Pipe Under Heavy Train Loads

With rapid development of railway transportation and increasing demand of oil and gas in China, the heavy haul train load becomes an important factor that threaten the safe operation of pipe. The mechanical behavior of buried pipe subjected to heavy haul train load was investigated in this study. A finite element model was established to investigate the effect of train load. Finally, the multiple train loads were also discussed. Results show that the high stress area occurs under the train track. In the pipe segment below the track, the top of pipe is under compression and the bottom of pipe is under tension. The cross section of pipe is still circular. The maximum vertical and horizontal displacement are at the top and side of pipe. The maximum von Mises stress, axial strain, and displacement of pipe increase with the increase of train load. Under the multiple train loads, there are two high stress and high strain areas at the top and bottom of pipe. With the increase of multiple train loads, the maximum von Mises stress, axial strain, displacement and ovality increase.

Characterization of local parameters of inclined upward air–water bubbly two-phase flows in a round pipe

The present work seeks to develop a detailed experimental database and characterize the local effects of inclination on horizontal and upward bubbly air–water two-phase flows. Experimental conditions are selected to investigate bubbly flows at a variety of orientations while reducing the influence of flow regime transition. Detailed time-averaged data is collected using state-of-the-art four-sensor conductivity probes for measurements across the flow area for five flow conditions at five inclination orientations in a 25.4 mm inner diameter pipe. Using the newly established database, effects of inclination on bubbly flows are analyzed, as are changes in liquid and gas flow rate at different orientations. The observations include (1) bubble migration and agglomeration at the top pipe wall as orientation changes from vertical to horizontal; (2) reducing the angle from vertical reduces the local gas velocity, and correspondingly reduces the global slip from greater than unity at 90° to less than unity for 60° and lower; (3) changes in the bubble size distribution are primarily at the interface between the bubble cluster and the liquid region of the pipe, not coalescence within the bubble cluster. Physical mechanisms for these observations are proposed, and the present trends at different orientations support previous experiments in horizontal two-phase flows.

Experiment on bubble characteristics of turbulent bubbly jets in pipe crossflow

Air-water bubbly jets in crossflow are commonly encountered in various practical applications such as artificial aeration in oceans and submarine pipelines. This study reveals the bubble characteristics for bubbly jets in pipe crossflow by conducting a series of physical experiments. It was found that the horizontal distance from nozzle exit to where bubble centerline touches the top pipe wall can be expressed as a function of the Reynolds and Weber numbers of the ambient pipe flow, and the Reynolds numbers of both the air and water phases of bubbly jets. The centerline gas void fraction and bubble size increase with distances after bubbles touch the top wall, mainly because bubbles are prone to gathering to the centerline to form larger bubbles. Afterwards, the (horizontal) bubble velocity decreases mainly due to the resistance force from the top wall. Good agreement has been achieved between horizontal bubble velocity and the 1/7th power law for water velocity in the pipe, and a correlation was proposed for predicting bubble rise velocity. Furthermore, turbulence characteristics of bubbles (e.g., root-mean-square of bubble fluctuating velocity, bubble turbulence intensity) were investigated for the bubbly jets.

Experimental study on the rise of aqueous foams in vertical pipes

In this paper we report experiments on the growth of dry foams and their rise in vertical pipes of different circular cross-sectional radii with length over diameter ratios in the interval 25 ≤ h/D ≤ 80 for applications in the study of fracture stimulation in enhanced oil recovery processes. Air injection at the bottom of the pipes is performed at a constant flow rate by means of a single capillary tube. The formation and rising of the foam was investigated for two different cases: 1) when the top cap of the vertical pipes is open and 2) when it is closed. We find that the position and velocity of the foam front as well as the foam dispersivity are both dependent on the pipe diameter and on whether its top end is open or capped. When the top is open, the foam column grows faster compared to the case when it is sealed. In pipes with h/D ≥ 30, the growth rate is non-linear and faster than in pipes with h/D < 30 in which cases the foam rises at an almost constant rate. As the diameter of the pipe increases, the size of the produced bubbles also increases. In closed-top pipes the foams tend to be more homogeneous than in open top pipes. The experimental observations indicate that under foam drainage driven by gravity, the liquid flow velocity across the Plateau borders is indicative of a drainage model based on a plug-like flow in channels with fully mobile interfaces, where viscous dissipation occurs only in the nodes.

Study on the Pipe–soil Interaction under Instability of Slope Based on Flume Experiment

To study the landslide of buried gas pipeline caused by rainfall, based on the flume experiment the laboratory model of rainfall-induced pipe–soil interaction of slope instability was established. By monitoring the cross-section strain of the pipeline under the slope instability induced by rainfall infiltration, the effect of soil on the pipeline is analyzed and calculated. The results show that the pipeline is located at different failure surfaces of the slope, which is affected by slope instability to different degrees. In the slope toe of apertures, ultimate cross-section strain is the largest, calculation of soil force and maximum limit 1515.535 N/m, and that of slope top pipe is 216.169 N/m, attenuation trend from toe to the top. Resultant force directions are distributed in soil and the horizontal angle is 68°. The results can provide reference and technical reserve for the study of pipe-soil interaction of buried natural gas pipelines under the action of landslide and the further improvement of pipeline safety.

All models are wrong, but are they useful? Assessing reliability across multiple sites to build trust in urban drainage modelling

Abstract. Simulation models are widely used in urban drainage engineering and research, but they are known to include errors and uncertainties that are not yet fully realised. Within the herein developed framework, we investigate model adequacy across multiple sites by comparing model results with measurements for three model objectives, namely surcharges (water level rises above defined critical levels related to basement flooding), overflows (water levels rise above a crest level), and everyday events (water levels stay below the top of pipes). We use multi-event hydrological signatures, i.e. metrics that extract specific characteristics of time series events in order to compare model results with the observations for the mentioned objectives through categorical and statistical data analyses. Furthermore, we assess the events with respect to sufficient or insufficient categorical performance and good, acceptable, or poor statistical performance. We also develop a method to reduce the weighting of individual events in the analyses, in order to acknowledge uncertainty in model and/or measurements in cases where the model is not expected to fully replicate the measurements. A case study including several years of water level measurements from 23 sites in two different areas shows that only few sites score a sufficient categorical performance in relation to the objective overflow and that sites do not necessarily obtain good performance scores for all the analysed objectives. The developed framework, however, highlights that it is possible to identify objectives and sites for which the model is reliable, and we also suggest methods for assessing where the model is less reliable and needs further improvement, which may be further refined in the future.

Simulation analysis of the effect of single-chamber double-line pipe jacking through different soil materials on surface uplift and subsidence.

This article is based on the relocation project of the 330 kV overhead line in Xi’an, China. In this paper, the soil settlement under different jacking depths was calculated by using the modified Peck’s formula. Meanwhile, by modeling in ABAQUS, the jacking process of a single-chamber double-line large diameter pipeline under different soil conditions was simulated, and the ground deformation data under the different simulated working conditions were obtained. The results of the two methods were compared with the construction monitoring results, and it was found that the finite element simulation results were closer to the actual results. The control variable method was used in the analysis of the surface soil deformation law to analyze the effect of different soil parameters and pipe jacking depths on surface soil deformation. Finally, the best soil conditions applicable to single-chamber double-line large diameter pipe jacking construction were obtained through comparative analysis. The results show that (1) when using double-line construction, the maximum surface settlement under different soil conditions is located 11–15 m from the centerline of the soil above the pipeline, the minimum settlement location is inside the isolation pile, and with the increase in jacking distance, the settlement at the same section of the surface will gradually decrease and finally produce a small uplift. (2) In the first jacking, the settlement of powder clay is the largest, and the maximum settlement points in the surface section are more distributed. The maximum settlement value is approximately 11.66 mm. The settlement of powder soil is the smallest but produces a certain uplift deformation, and its maximum settlement is more concentrated in the surface section. After the comparison of deformation and soil parameters, loess-like soil is more suitable for single-compartment double-line large diameter pipe jacking construction. (3) When the top pipe burial depth changes, the greater the burial depth is, the smaller the settlement but the greater the lateral influence range. In the soil parameters, the modulus of elasticity only changes 3 MPa, and the settlement change value is approximately 5 mm. By changing the parameters, it can be obtained that the larger the modulus of elasticity of the soil is, the smaller its deformation. The larger the internal friction angle of the soil is, the smaller its deformation, but the maximum value of settlement change is only 1.7 mm, which means that the change in the internal friction angle has little effect on the soil deformation.

Numerical Simulation on Backfilling of Buried Pipes Using Controlled Low Strength Materials

The backfill quality of a pipeline has an important influence on pipeline operation. When loose backfill is used, the pipeline may be damaged after short term operation. In this study, the numerical simulation analysis of buried pipes was carried out under three conditions: loose backfill around the pipe, dense backfill, and controlled low strength materials (CLSM) backfill. The effects of narrow trench backfilling using CLSM on the force and deformation of pipelines were studied. The results showed that When CLSM was used for buried pipe backfilling, the pressure on the top of the pipe and on the side of the pipe was significantly reduced. When the surface pressure was 200 kPa, the radial displacement at the top of the pipe was only 0.6 mm. Compared with the dense backfill of the pipe, the radial displacement of the pipe top was reduced by 82.9%, which greatly reduced the deformation of the pipe. CLSM backfilling is a good way to protect the pipeline. The pressure is uniformly applied around the pipe, and the circumferential strain around the pipe is greatly reduced. Pipelines backfilling with CLSM for buried flexible pipes has good mechanical properties and it is expected to be applied to engineering practice.

The experimental investigation of pipes system array inside the pressurized cylindrical container in various orientations

The experimental investigation of natural convection analysis in pressurized containers has been successfully addressed fusing four identical circular rectangle pipes. The pressurized tank of 0.3 m diameter and 0.45 m height within 0.43 m height and 0.025 m side length interior square pipes are used to obtain the present investigation. Various parameters are used such as gauge pressure (0.5-1 bar), pipes Ra configurations and enclosure orientations. The results are Nusselt number for cold and hot sides. Both sides has reverse response, the parametric analysis shows the ordinary behavior according to gravity and pressure forces interaction. The optimum conditions is observed when horizontal enclosure of top pipe in one bar is applied where the heat transfer improvement is 24 % approximately.

Research into the physical and chemical properties of fire-retardant materials of structural elements of trucks running on gas engine fuel with the aim of increasing their fire-retardant efficiency

The fire load is an integral part of the fire hazard definition. Reducing this load is one of directions to fight fires in transport. To study the physicochemical processes and thermal effects occurring as a result of thermal decomposition of wood fire-proofed by retardants like BAN, OK-GF, OK-DS (OK-GFM), SPAD-0 and their chemical compositions, we used the methods of differential thermal analysis, thermogravimetry, and derivative thermogravimetry. In addition, to study the intensity of physicochemical combustion processes, tests to control changes in woodwork masses and temperature at the top of pipe depending on the duration of combustion of the samples and the consumption of fire retardants were conducted. Fire retardant compositions like OK-GF, OK-DS, Pirilax biopyrene at the consumption of 0.1 kg / m2 ensure flame and combustion resistance of the wood. The analysis of the research results confirmed the possibility of assigning to wood structures of a lorry’s body of the group 1 of flame and combustion resistance. Using the above fire retardants and their compositions in the treatment of lodgment elements and runners significantly affects the possibility and duration of the combustion process of a lorry. This was tested by means of an artificial fire source method (without chemical treatment, the burning time does not exceed 50 minutes). This significantly improves post-collision safety of vehicles with an increased fire load in terms of fire resistance because of using the natural gas as a motor fuel.

Comparative Analysis of Longitudinal and Transverse Vibration Characteristics of Ocean Mining Pipe

In this paper, the 5000 m mining pipe is taken as the research object, and the transverse and longitudinal vibration laws of the pipe under different working conditions are analyzed. Based on the finite element method (FEM), the pipe is discretized and calculated by the Wilson-θ Wilson - θ integral method; finally, the corresponding vibration laws of the mining pipe are obtained. The research shows that the mining pipe vibration responses are irregular motion, with the obvious oscillation phenomenon, and the overall vibration trend decreases first and then increases from the top to the bottom; the maximum vibration response occurs at the pipe top. Under the same working conditions, increasing the towing velocity will decrease the overall longitudinal vibration amplitude and increase the overall transverse vibration amplitude. While the ore bin weight will increase the longitudinal vibration amplitude and decrease the transverse vibration amplitude, increasing the mining pipe large diameter stepped section length and damping will decrease the longitudinal and transverse vibration simultaneously. When the towing velocity is between 0–2.8 m/s, the longitudinal vibration intensity is large, which is the main vibration mode. When the towing velocity is 2.8 m/s, the critical point is reached, and the longitudinal and transverse vibrations have the same intensity. When the towing velocity is greater than 2.8 m/s, the transverse vibration intensity is gradually greater than the longitudinal vibration intensity; at this time, the control of the transverse vibration should be appropriately increased.

Numerical investigation on effect of internal flow on vortex-induced vibration dynamics of a full-scale mining riser

The dynamics of a full-scale pipe conveying fluid inside is investigated based on the finite element method (FEM). During the numerical simulation, the Euler–Bernoulli beam equations are used to model the motion of the full-scale pipe while the effect of internal flow is considered. And the semi-empirical time-domain model is applied to simulate the external hydrodynamic forces exerted on the pipe. Then the typical vortex-induced vibration (VIV) characteristics of the full-scale pipe considering both internal and external flows are analyzed. The results show that with the increase of the internal flow velocity, the natural frequencies of the full-scale pipe decrease and the in-line (IL) and cross-flow (CF) dominating modes are increased. Furthermore, the dominating frequencies in both IL and CF directions are not notably changed. And the IL and CF root-mean-square (RMS) values of amplitudes fluctuate at around the stable values due to the stable external hydrodynamic forces. It should be noticed that the IL and CF RMS strain values of the full-scale pipe are increased, especially for high external and internal flow velocities. The maximal RMS strain values in both IL and CF directions appear next to the pipe top, which could have an influence on the motion of the ship on the sea surface.

Measured Deformation of Pipe-Roof during Box Culvert Jacking in Soft Ground

RBJ method is suitable for shallow covering and micro-disturbed underpassing project. In this paper, the pipe deformation induced by box culvert jacking is analyzed. The research shows that: (1) The closed pipe-roof frame presented a phenomenon of expanding outward, namely the uplift of top pipe and the settlement of bottom pipe. (2) Along the jacking direction, the deformation of pipes was positioned over the box culvert structure and about 10m in front of the excavation face. (3) Due to the bounded constraint of diagram wall, it’s prone to be a reverse deformation at joint between pipe and diagram wall, and resulting in a wave-type deformation pattern.

Jacking precision control of pipe roof and large box culvert below urban expressway-a case study of a large underpass in Shanghai

Pipe roof-culvert box method is an effective way for shallow buried tunnel passing beneath important facilities. In soft ground, the culvert can be jacked under the pre-reinforcement of pipe roof. This paper presents an investigation on the precision analysis and control of a large- scale pipe roof jacking (the scale of this structure is 21.648m*8.148m) of an underpass, which passes beneath the Mid-Ring expressway in Shanghai. The conclusions drawn from this paper show that: (1) In this project, more than 70 percent of the deflection values of jacking machines and pipes are controlled within 20mm. (2) During the process of pipe jacking, the deflections of pipes tend to lag behind the machines’ about 3~10m. 68 percent of the rangeability of pipes’ deflection are 50%~100% of the corresponding machines’ deflection. (3) Due to Stiffness effect of pipeline, posture of pipe is difficulty to be rectified during the stages of pipe starting and receiving. A compelling rectification will result in overlarge deviation and increase the difficulty of subsequent operation. (4) For two adjacent pipes, the posture of latter pipe is positively related by the stiffness of prior pipe. The Pearson correlation coefficient of horizontal pipes and vertical pipes can be 0.46 and 0.68 respectively. (5) Considering the interspace between top pipes and box culvert, the control criterion of vertical deviation of box culvert is recommended as 5cm.

Stress–Strain Assessments for Buried Oil Pipelines Under Freeze-Thaw Cyclic Conditions

Abstract In this study, outdoor freeze-thaw cyclic tests on the Q345 steel pipeline portion were conducted to analyze the buried oil pipeline stress evolution in a seasonally frozen soil area, namely, the Mohe–Daqing portion of China–Russia crude oil pipeline. The results obtained show that under the freeze-thaw cycle, the variation trend of soil temperature around the pipeline exhibited a hysteresis pattern, which was similar to that of atmospheric temperatures. The soil frost heaving force was shown to drop with depth, and its value at the pipe top was higher than that at the pipe bottom. With the number of freeze-thaw cycles, the frost heaving force of the soil first increased and finally stabilized, while the principal stress of the pipeline increased gradually, and its extreme value tended to be stable after 7–8 cycles, which was consistent with the “ratchet effect” theory. The above findings made it possible to elaborate on a more efficient freeze-thaw cyclic test setup for clarifying the mechanism of frozen soil/pipeline interactions.

Simulation of cut off characteristics of 2.45 GHz microwave inside the open-ended conductor cylindrical pipe

For a realtime measurement of moisture contents and temperature profiles of a sample inside a microwave oven, Sensors and open-ended pipes are equipped to the microwave system, allowing to measure those parameters from other ends of the pipes. The main role of the pipes is to reduce the microwave wave from leaking out to the environment and the interference with measuring equipment. In this research, a model of a microwave system with five installed pipes is simulated using COMSOL Multiphysics. The microwave cavity is modelled to be a cube with equal lengths of 33 cm. A pipe with diameter of 1.5 cm is installed on the top of the microwave and the other four pipes with diameter of 2.5 cm are installed at the bottom. The system is designed so that an infrared sensor can be attached to one end of the top pipe to measure temperature and a load cell is equipped under the bottom four pipes to measure the moisture content. The simulation result shows an exponential decay of electric field norm along the pipes away from the microwave chamber. For the pipes with diameters of 1.5 cm and 2.5 cm, the microwave wave is reduced to virtually zero at the distance of 3 cm and 4 cm away from the chamber, respectively.

Gradient heat flux measurement in study of condensation at inner surface of the tube

To study heat transfer during water steam condensation in the pipe, experiments were carried out with a steam supply from the top pipe edge with the gradient heatmetry. The results which allowed us to apply the new method for non-classical problem have shown compliance with literature data. When the pipe is inclined, the distribution of heat flux per unit area on the inner surface becomes asymmetric, that’s why it is necessary to measure local heat flux in some points there. The distribution of local heat transfer coefficients on the inner surface of the pipe at different angles of inclination is obtained. The heat flux decreases in the lower part of the pipe section, which corresponds to increasing of the condensate film thickness in this area.

Earth pressure and deformation of cut-and-cover and trenchless flexible pipes under different soil properties and groundwater conditions

A field case was first studied to verify the reliability of PLAXIS 2D and the accuracy of the modeling and calculation methods, in terms of calculating the radial earth pressure and vertical deformation on the cut-and-cover and trenchless pipes. Then, four types of classical soils were considered to compare the effects of cut-and-cover and trenchless construction methods on the installed flexible pipes. Besides, groundwater conditions and main physical properties of soils were also considered. Results demonstrate that deviations among the simulation calculated and the field measured value on earth pressure and deformation are all within 5%, showing a high accuracy and reliability. The maximum earth pressure and deformation on the cut-and-cover flexible pipe are 2.66–11.65 times and 3.96–11.95 times larger than that on the trenchless pipe, which is mainly due to the passive earth pressure caused by the deformation of the trenchless pipe. As the groundwater level increases from the bottom to 5.5 m above the top of pipes, the maximum earth pressure and deformation of the cut-and-cover pipe increase by 18.74% and 13.38%, while that on the trenchless pipe increased by 6 times and 3 times, because of the difference of reduction in effective stress. Density, cohesion, and friction angle are positively related to the earth pressure and deformation on the cut-and-cover pipe, and Poisson’s ratio and density are positively related to that on the trenchless pipe, while the others are the opposite. Density and cohesion are respectively the most significant factors affecting the cut-and-cover pipe and trenchless pipes.