Horizontal Pipeline Research Articles

A visualization study on characteristics of severe slugging in the S-shaped riser with a kilometer-scale pipeline

Severe slugging is a hazardous multiphase flow phenomenon in the process of offshore oil and gas transportation. Few visualization image data are obtained in experimental riser systems with kilometer-scale pipelines. Therefore, the interface distribution characteristics of severe slugging are visually investigated in a 29.1 m high S-shaped riser connecting a 1657 m long horizontal pipeline. Based on the image data of the gas–liquid interface structure and the pressure fluctuation of the riser, the flow pattern map is plotted. The high riser increases the accumulation space of severe slugging and prolongs the cycle period. A new prediction correlation of the slugging period suitable for experimental systems with different pipeline lengths is proposed. The long pipeline provides sufficient gas compression space and intensifies the blowouts of liquid slugs. The maximum velocity of the slug blowout in the riser reaches 23 times the gas–liquid mixed velocity. The gas expands sharply during the gas blowdown stage of severe slugging, which causes the instability of the gas–liquid interface in the horizontal pipeline and induces a large number of liquid slugs to flow into the riser; thus, the continuity blowdown of slugs appears in the riser.

Effects of riser height and pipeline length on the transition boundary and frequency of severe slugging in offshore pipelines

Investigating the transition boundary and frequency characteristics of severe slugging under different riser heights and pipeline lengths provides important support for the expansion of offshore oil and gas to deeper waters. The visualization research on air-water two-phase flow is carried out in a system with a horizontal pipeline length of 1687 m and riser heights of 16 m, 22 m, and 29 m, and flow pattern maps are plotted. Based on existing experimental data, the database of the flow pattern and slugging frequency in pipeline-riser systems with riser heights of 3–29 m, pipeline lengths of 10–1687 m, and pipe diameters of 25.4–50.8 mm is established. The long pipeline makes the gas pressure growth rate slower than that of the liquid pressure in the riser, which causes severe slugging occurring at higher superficial gas velocity. On the contrary, increasing the riser height causes the boundary of severe slugging to shift to a lower superficial gas velocity. The severe slugging length is greater in the higher riser and longer pipeline system, causing a smaller severe slugging frequency. A correlation for predicting severe slugging frequency at various riser heights, pipe lengths, and pipe diameters is established by employing gas and liquid Froude numbers.

Development of artificial neural networks for the prediction of the pressure field along a horizontal pipe conveying high-viscosity two-phase flow

Pressure fluctuations are one of the primary concerns regarding the safety of two-phase flows in pipelines. Therefore, it is crucial to closely monitor pressure variations and predict their spatiotemporal behavior to the greatest extent possible. In this article, we present the development of a set of models based on artificial neural networks (ANN) to predict the time-dependent behavior of the pressures produced by high-viscosity gas-liquid flows at predetermined locations along a horizontal pipeline. Different volume fractions of glycerin and air constitute the mixtures of interest. The models use the measured values of the mass-flow rates of both fluids at the pipe’s inlet, together with the pressures measured at other locations further downstream. In order to determine the optimal architecture for the artificial neural network, we tested the following four transfer functions for the hidden layer: logsig, tansig, softplus, and swish. Additionally, we utilized the linear function purelin for the output layer. We employed the Levenberg–Marquardt algorithm to train the ANN models and the experimental data set to test their performance.

The CPFD approach was used to investigate the particle flow characteristics and auxiliary air inlet in an ash transfer pipe

Numerical simulations for the air-solid two-phase flow in a horizontal pipe with a diameter of 125 mm and a length of 10 m were carried out using the Computational Particle Fluid Dynamics (CPFD) method. The deposition characteristics of particles in the pipe were investigated at various inlet flow rates and velocities, and the effect of the auxiliary inlet with different structural parameters on the evacuation of particles in the pipe after the auxiliary inlet was added to the horizontal pipe was compared. The results show that when the volume fraction of particles in the tube is less than 0.6, the flow of particles is relatively stable, and when the volume fraction of particles is greater than 0.8, the particles are seriously deposited and easily form a blockage; the auxiliary air inlet speed is proportional to the effect at the same tilt angle; when the air inlet speed is constant, the auxiliary air inlet angle increases from 35° to 55°, the effect of auxiliary air inlet increases and then decreases, and the effect of auxiliary air inlet reaches its peak at around 45°. The study's findings have implications for long-distance particle transport in horizontal pipelines.

Scaling analysis for the condensation induced water hammer effect in horizontal pipe

In nuclear power engineering, researchers pay significant attention to phenomena related to the condensation process involving direct contact between saturated steam and subcooled water, mainly the phenomenon known as Condensation Induced Water Hammer (CIWH). Within the steam pipes of the pressurized water reactor, when saturated steam comes into direct contact with subcooled water, it may form an isolated steam pocket surrounded by water. The condensation of steam within this pocket results in its subsequent collapse, accelerating the surrounding water column to collide with the pipe wall and causing a substantial pressure peak. In this paper, the scaling analysis was conducted on the CIWH phenomenon in the steam line of a small PWR. The research is rooted in a two-fluid, six-equation framework and employs equation-based analysis to investigate the non-dimensional number of CIWH occurring within horizontal pipelines. By analyzing the conservation equations, suitable non-dimensional criteria for thermohydraulic phenomena were determined. These criteria can be employed to ascertain experimental facilities' geometric dimensions and operating conditions, which can study the risks associated with CIWH phenomenon.

CFD-DEM analysis of hydraulic conveying of non-spherical particles through a vertical-bend-horizontal pipeline

In this study, an in-depth analysis of elbow wear is performed with the assistance of a wear model by combining computational fluid dynamics with the discrete element method. After validation, a vertical–bend–horizontal pipeline is simulated with non-spherical particles: φ = 1, 0.9451, 0.8048, and 0.7433. The simulation results are used to evaluate the effects of sphericity on flows, forces, and wall erosion. The results indicate that the solid particle concentration at the center of the vertical tube increases with decreasing particle sphericity. Moreover, as particle sphericity in the pipeline decreases under the same conveying environment, the conveying velocity increases, the fluid flow rate decreases, and the kinetic energy conversion rate of the liquid and solid phases increases. Accordingly, the pressure drop of the particles in the pipe decreases with decreasing sphericity. Furthermore, the particle shape significantly affects the forces on the particles and walls as well as the wall erosion.

Modeling of stationary mode for pipeline operation during hot oil pumping

The objective of this work is to build and analyze a mathematical model of steady-state operation of a pipeline that conducts hot oil pumping in a particular section. Mathematical modeling of pipeline operation during hot pumping makes it possible to determine the pumping flow rate, temperature and pressure distribution along the length of the pipeline. The object and subject of the study is a horizontal pipeline route between two pumping stations with preheating of oil at the beginning of the section. Within the framework of this work, the dependence of oil viscosity on temperature was determined, and the following graphs were obtained: graph of oil temperature distribution in the considered pipeline section, graph of pressure distribution in the pipeline in the considered section, graph of hydraulic resistance coefficient distribution according to the Leibenzon model, graph of pressure distribution in the pipeline in the considered section according to the combined model of Shukhov and Leibenzon. The graphs obtained allowed us to assert that taking into account the real rheological properties of oil leads to a change in the law of pressure distribution along the pipeline route and to a significant change in the length of the linear section of the pipeline, where a significant pressure drop occurs.

Modeling of stationary mode for pipeline operation during hot oil pumping

The objective of this work is to build and analyze a mathematical model of steady-state operation of a pipeline that conducts hot oil pumping in a particular section. Mathematical modeling of pipeline operation during hot pumping makes it possible to determine the pumping flow rate, temperature and pressure distribution along the length of the pipeline. The object and subject of the study is a horizontal pipeline route between two pumping stations with preheating of oil at the beginning of the section. Within the framework of this work, the dependence of oil viscosity on temperature was determined, and the following graphs were obtained: graph of oil temperature distribution in the considered pipeline section, graph of pressure distribution in the pipeline in the considered section, graph of hydraulic resistance coefficient distribution according to the Leibenzon model, graph of pressure distribution in the pipeline in the considered section according to the combined model of Shukhov and Leibenzon. The graphs obtained allowed us to assert that taking into account the real rheological properties of oil leads to a change in the law of pressure distribution along the pipeline route and to a significant change in the length of the linear section of the pipeline, where a significant pressure drop occurs.

Investigation on gas-liquid two-phase frictional pressure drop in pipeline riser

The pressure drop characteristics of gas-liquid two-phase flow in pipeline-risers are important to the design optimization of marine risers lifting oil and gas. In this study, experimental investigation on single-phase and air-water two-phase flow pressure drop characteristics in vertical and S-shaped risers have been carried out in a long-distance pipeline with the gas superficial velocities ranging from 0.03 to 6.2 m/s and the liquid superficial velocities from 0.02 to 1.3 m/s. The test loop with 50 mm i. d. Consists of a horizontal pipeline with 114 m in length, followed by a 16 m downward inclined section, and ended at a riser. The downward section is adjustable in inclination with various angle of −2°, −3°, −4° and −5° with respect to horizontal. A vertical riser and an S-shaped flexible riser were used in the experiment. The effects of flow and geometry parameters on two-phase frictional pressure drop multiplier are studied. For flow parameters, the two-phase frictional pressure drop multiplier increases with increasing the inlet gas and liquid superficial velocity. For geometric parameters, the two-phase frictional pressure drop multiplier in S-shaped riser is larger compared to that in straight vertical riser. The existing correlations reported in the literature are evaluated. A single-phase friction factor correlation and a two-phase frictional pressure drop multiplier correlation for pipeline-riser system are developed. Comparison of the predicted value and the measured results shows good agreements.

IMPROVEMENT OF METHODS FOR CALCULATION OF GAS-LIQUID SLUG OF FLOW IN PIPELINES

To calculate pressure losses during transportation of gas-liquid fluids in flowlines, it is important to correctly estimate the effective density and viscosity of the mixture, which increases the accuracy of calculating the tangential stresses required to determine hydraulic pressure losses at the liquid-wall boundary. The determining parameter when calculating the effective values of the density and viscosity of the mixture is the coefficient liquid holdup in the cross section of the pipeline. The article analyzes the applicability of empirical methods for modeling two-phase gas-liquid currents when calculating liquid holdup in slug body of a intermittent (slug) flow in horizontal pipelines. A description is given of the mechanistic approach proposed by Zhang to calculate the liquid holdup in the slug body used in one of the most famous modern models of gas-liquid flow — TUFFP Unified model. The results of calculating the actual liquid holdup in the slug body using the TUFFP Unified model hydrodynamic model are presented, showing good consistency of the calculated data with experimental ones for vertically located pipelines, and unsatisfactory consistency for currents in horizontal pipes. The purpose of the article is to improve the methods of calculating the gas-liquid slug structure of the current using the TUFFP Unified model, by improving the accuracy of calculating the liquid holdup in the slug body at the horizontal location of the flowline. The proposal to use in the TUFFP Unified model a new approach to assessing the stable diameter of the gas bubble of the dispersed-bubble flow regime in the body of a liquid slug made it possible to increase the reliability of calculating the liquid holdup in the slug body with a horizontal location of the pipeline.

Calculation of horizontal collective drainage pipelines of reclamation systems in the presence of a ground water level slope

The purpose of this work is to develop a methodology for calculating the parameters of pressure horizontal collective drainage pipelines of reclamation systems that operate in the presence of a ground water level slope.
 The presented materials are based on the results of personal analytical studies of the main mathematical dependencies, which describe the pressure liquid flow in horizontal collective perforated pipelines, which operate in the presence of the ground water level slope.
 System of two differential equations, which describe the liquid motion in a drainage pipeline with variable flow rate and the conditions of liquid entry from the surrounding soil through the walls of the pipe in filtration mode, is considered. The explored pipeline is laid in the presence of the ground water level slope. By introducing new variables, the original system and its solution is presented in a dimensionless form.
 In this case the solution of the system depends on the value of three main factors: the resistance factor of the collecting drainage pipeline "ζl"; the generalized parameter "A", which comprehensively takes into account the structural and filtering characteristics of the stream; the ground water level slope «І». The analysis used the concept of an infinitely long drainage pipeline, which operates in the presence of the ground water level slope, or, what is the same, an inclined pipeline with an infinite filtering capacity of the side surface walls. Relatively simple and easy-to-use analytical dependencies were obtained on the basis of the conducted analysis. They allow to calculate the nature of the flow rate variations and pressure drop along the length.
 Corresponding graphic dependencies were constructed to simplify the calculations. It is shown that the value of the geometric slope of the ground water level, along with the resistance factor and the generalized parameter, significantly affects the calculated parameters of such pipelines.

Optimization effect of propylene oxide (PO) on evaporation, combustion, and pollutant emissions of high-energy–density JP-10 fuel

JP-10 is a high-energy–density fuel that is widely used in aerospace propulsion systems due to its wide range of synthetic raw materials and low production costs. However, it faces challenges related to difficult ignition, low combustion efficiency and high pollutant emissions. To address this, blending JP-10 with propylene oxide (PO), a highly volatile substance, provides a practical solution. This study investigates the propagation and evolution characteristics of JP-10/PO binary fuel in large horizontal pipelines. The results demonstrate a synergistic enhancement effect achieved by the JP-10/PO hybrid fuel. PO, with its lower boiling point, quickly evaporates from the mixed droplets, creating a continuous primary flame. As the droplet temperature increases, JP-10, known for its high combustion heat, starts to evaporate, actively participating in the explosion process and forming a secondary flame that spreads in two directions. The combustion of the JP-10/PO mixed droplets involves both physical and chemical processes, including droplet evaporation and gaseous combustion. A binary droplet evaporation model is developed to quantitatively assess the impact of PO fuel ratio on spray evaporation. Additionally, the study examines steam explosion parameters and reaction product characteristics under different PO fuel ratios. It is observed that the evaporation of JP-10/PO mixed droplets occurs in three stages: transient heating, binary equilibrium evaporation, and single component equilibrium evaporation. Increasing the PO fuel ratio leads to a higher temperature rise rate of the droplets and an increased evaporation reaction rate constant. Moreover, the ignition delay time of JP-10/PO gas-phase mixture fuel decreases, while the adiabatic flame temperature gradually reduces. Furthermore, higher PO fuel ratios help reduce the emissions of unstable products in both mixed fuels due to the inherent oxygen content of PO molecules. The current research results can provide scientific references for the improvement of high-energy density fuels and the development of new propellants.

Analysis and prediction of hydrogen-blended natural gas diffusion from various pipeline leakage sources based on CFD and ANN approach

The influences of pipeline leakage source types on the hazard area distribution caused by accidental hydrogen-blended natural gas leakage are still the focus of gas leakage accidents. Three types of pipeline leakage sources are discussed in this study. Namely, the gas in the vertical pipeline flows from top to bottom, and the leakage orifice is in the pipeline wall; the gas in the vertical pipeline flows from bottom to top, and the leakage orifice is in the pipeline wall; the leakage orifice is in the horizontal pipeline end. The common feature of the above three pipeline leakage sources is that the normal of leakage orifice is parallel to the horizontal plane. The differences in the flow field distribution of hydrogen-blended natural gas released from three pipeline leakage sources are compared through numerical simulation. The effect of various factors on the jet centerline, concentration decay, and maximum horizontal diffusion distance of hydrogen-blended natural gas released from three pipeline leakage sources are analyzed. The predictive models of hydrogen-blended natural gas's maximum horizontal diffusion distance in three pipeline leakage sources under multi-factor coupling are established through a backward propagation neural network (BPNN). Results show that the angle between the gas flow direction in the pipeline and the normal of the leakage orifice, and the background step flow cause differences in the concentration field near the leakage orifice from the three pipeline leakage sources at the same working conditions. In the near-field region, the leakage orifice diameter has the most significant influence on the jet centerline of three hydrogen-blended natural gas jets among three factors. The concentration decay rate of gas released from the horizontal pipeline end is greater than that of gas released from the other two pipeline leakage sources. With the increase of volumetric flow rate, the maximum horizontal diffusion distances of methane released from three pipeline leakage sources all increase, while the maximum horizontal diffusion distances of hydrogen released from three pipeline leakage sources have little change. The predictive models of the maximum horizontal diffusion distance of hydrogen-blended natural gas released from three pipeline leakage sources are established through BPNN. The maximum horizontal hazard distances of the new working conditions are predicted, and the predicted results are in good agreement with the numerical simulation results. This investigation has guiding value for fast and accurate prediction of flammable gas hazard areas.

Effect of leakage source condition on the unignited hydrogen released issuing through a horizontal realistic pipeline geometry

An unignited gas release experiment system for the schlieren visualization and concentration quantitative measurement is designed and built to investigate the diffusion and concentration distribution features of turbulent hydrogen jets issuing from a realistic pipeline geometry. Helium is used in place of hydrogen for safety reasons. The spatial and temporal evolution of the asymmetry of turbulent helium jets was studied. The influence mechanisms of the volumetric flow rate (Q), the ratio of orifice diameter to the inner diameter of pipeline (R), and the angle between the normal of the leakage orifice and the opposite direction of gravity (θ) on the asymmetric concentration distribution are revealed. The experimental results show that the diffusion angle (α) and the inclination angle (β) of the turbulent helium jet are the largest when Q is 15 SLPM, R is 0.3, and θ is 0°, and the asymmetric feature of the turbulent helium jet is obvious. As the Q increased, the slope k of the inverse helium concentration (1/volume fraction) and a scaled distance L (L = (x/d)·(ρa/ρ0)1/2) became small. The increase of Q aggravated the concentration attenuation caused by the volumetric flow rate and the asymmetry jet. As R increased, the slope k of the inverse helium concentration and a scaled distance L first decreased and then increased. The slope k got the minimum value when R was 0.3. The downward movement of the leakage orifice position increased the turbulent intensity near the leakage orifice. This work can provide theoretical support for accident prevention and emergency treatment of hydrogen leakage accidents in long-distance pipeline low-pressure hydrogen transportation.

Formation Mechanism of CO2 and CH4 Hydrates in Bubbly Flow in a Horizontal Pipeline

Formation Mechanism of CO₂ and CH₄ Hydrates in Bubbly Flow in a Horizontal Pipeline

Numerical simulation of two-phase slug flows in horizontal pipelines: A 3-D smoothed particle hydrodynamics application

A fundamental difficulty of studying gas–liquid pipe flows is the prediction of the occurrence and characteristics of the slug flow regime, which plays a crucial role in the safety design of oil pipelines. Current empirical methods and one-dimensional computational models only achieve limited success. While 3-D numerical simulations are highly recommended, they have been very seldom used. We perform 3-D Lagrangian numerical simulations of gas–liquid pipe flows by adapting an existing multi-phase smoothed particle hydrodynamics (SPH) method based on a Riemann solver to achieve an efficient solver. To realize the high inlet velocities of gas and liquid an in- and outlet boundary condition is presented. The results are validated against existing experimental data, numerical simulations and analytical solutions. Multiple gas–liquid pipe flow patterns are predicted, namely, smooth stratified, stratified wavy, bubble flow, slug flow and bubble flow. Several principle characteristics of slug flows, e.g., pressure gradient, slug development and slug frequency are analyzed in a 3-D fully Lagrangian framework.

Economic particulate transport performance analysis of k-epsilon models in highly concentrated slurry through pipelines

The paper analyzed the economic transporting performance of k-epsilon turbulence models using the Eulerian two-fluid approach in transporting highly concentrated fine particulate slurry through horizontal pipelines using Kaushal et al. (2005) experimental data of glass beads slurry of 125 μm mean diameter for volumetric concentration ranging 30%–52% and flow velocity ranging 2–5 m/s. The primary components of economical slurry transport are Specific Energy consumption (SEC) and pressure drop; both have been examined in the performance of different κ-ϵ models and are yet to be unlighted on these parameters. The CFD model found the excellent performance of all k-epsilon models with slightly more effectiveness in the case of the Realizable κ-ϵ model. The analyzed and validated CFD model was subsequently used in examining the parameters of slurry flow, such as the secondary phase velocity, concentration distribution, and SEC analysis for the range of fine particles 125, 150, and 212 µm. The plotted contours from CFD are useful in visualizing slurry flow parameters at intermediates inlet values for slurry inlet flow velocity ranging 2–6 m/s and inlet volumetric concentration ranging 30%–55% for fine particles. Analysis revealed that the highly concentrated fine particles slurry transported at optimum volumetric concentration range of 40–45% are economical slurry transport.

Influence of pipeline diameters and fluid properties on slug frequency in horizontal pipelines

The accurate prediction of slug frequency is critical for the construction of multiphase flow models and the flow assurance of oil and gas pipelines. In this paper, the slug frequency data are obtained by visualization method in short (65 mm ID, 215 D) and long (46 mm ID, 35957 D) pipelines. The slug frequency of horizontal pipeline is inversely proportional to pipeline diameter (26–300 mm) and proportional to the liquid viscosity (1.01–7500 mPa·s). The quasi-developed distance for the air–water slug flow at VSG ≤ 1.00 m/s is about 1200 D, and the frequency of the quasi-developed slug flow is less affected by the pipeline length. Based on the gas Strouhal number and the liquid viscosity ratio, the quantitative relation between the slug frequency data at different viscosities is constructed, and a new correlation is developed to predict both the slug frequency of water and viscous liquids.

Experimental investigation of the motion states of coarse particles with sediment-laden flow in a horizontal pipe

This paper investigates coarse particle motion states via physical experiments of coarse particles and sediment-laden water or pure water flowing in a horizontal pipeline. The effects of coarse particle sizes, pipe flow velocities and coarse particle mass rates entering the pipeline are analyzed. The coarse particle motion can be divided into three regimes: plug, layer shift and mobile conveying. Regarding plug conveying, a particle plug is formed and moves as a head-to-tail transformation. Regarding mobile conveying, particles are in discrete contact with each other and move rapidly. The layer shift conveying is a transition stage, a continuous flat particle layer is formed at pipe bottom. The relationships among conveying regimes, instantaneous pressure, time-averaged pressure and fluctuating pressure features are clarified. A parameter is proposed to classify coarse particle motion states. Its accuracy is demonstrated using particle image velocimetry (PIV) and the relationships between conveying regimes and instantaneous pressure features.

Numerical analysis of particle injection effect on gas-liquid two-phase flow in horizontal pipelines using coupled MPPIC-VOF method

Pipeline transport of three-phase (gas, liquid, and solid particles) flows has become increasingly prevalent in various industrial applications. Due to complicated fluid phase interactions, experimental and numerical investigation of this type of flow can be very demanding. In this study, the coupled Eulerian–Lagrangian approach MPPIC-VOF is adopted, which is capable of capturing solid particle motion as well as fluid phase development simultaneously. Prior to three-phase flow simulation, two-phase air–water flow in a specific range of gas and liquid superficial velocities with slug and plug flow patterns is simulated. Then, polypropylene particles are injected as the solid phase into the air–water flow and the effects of particles on pressure drop, void fraction, and flow patterns are studied. The pressure drop and void fraction results are validated for both two-phase and three-phase flows by different correlations and experimental results. As a result of particle injection at the low concentration of 0.5%, void fraction increases by 13.7% and pressure drop changes on average by 18%, respectively. However, there was no significant change in the flow patterns.