One-dimensional models for multiphase flow in pipelines are commonly discretised using first-order Finite Volume (FV) schemes, often combined with implicit time-integration methods. While robust, these methods introduce much numerical diffusion depending on the number of grid points. In this paper we propose a high-order, space-time Discontinuous Galerkin (DG) Finite Element method with h-adaptivity to improve the efficiency of one-dimensional multiphase flow simulations. For smooth initial boundary value problems we show that the DG method converges with the theoretical rate and that the growth rate and phase shift of small, harmonic perturbations exhibit superconvergence. We employ two techniques to accurately and efficiently represent discontinuities. Firstly artificial diffusion in the neighbourhood of a discontinuity suppresses spurious oscillations. Secondly local mesh refinement allows for a sharper representation of the discontinuity while keeping the amount of work required to obtain a solution relatively low. The proposed DG method is shown to be superior to FV.@en

A building block strategy for modelling the pressure loss coefficient of flow through a complex geometry is presented. The approach relies on decomposing a complex flow geometry into geometrical building blocks of which the pressure loss coefficients are characterized individually. The different contributions are subsequently combined to describe the pressure loss of the geometry as a whole. This approach is applied and tested to an industrially relevant application: a by-pass pig (Pipeline Inspection Gauge). This is a cylindrical device that travels inside a pipeline and is commonly used in the oil and gas industry for pipeline maintenance. An important factor in determining the ultimate velocity of the device is the pressure drop over the by-pass pig, which is characterized by a pressure loss coefficient due to the by-passing fluids. In this study the pressure loss coefficient of three frequently used by-pass pig geometries in a single phase pipeline is investigated with Computational Fluid Dynamics (CFD). The CFD results are used to validate the simple building block approach for systematic modelling of the pressure loss through the by-pass pigs, which takes the geometry and size of the by-pass opening into account. It is shown that the pressure loss models can capture the CFD results for each of the three pig geometries. The pressure loss models can be combined with pig/pipe-wall friction models to predict the velocity of a by-pass pig in a single phase pipeline, which is important for a safe and effective pigging operation. The applied building block approach may also be suitable to characterize pressure loss coefficients of complex geometries in general.@en

A building block strategy for modelling the pressure loss coefficient of flow through a complex geometry is presented. The approach relies on decomposing a complex flow geometry into geometrical building blocks of which the pressure loss coefficients are characterized individually. The different contributions are subsequently combined to describe the pressure loss of the geometry as a whole. This approach is applied and tested to an industrially relevant application: a by-pass pig (Pipeline Inspection Gauge). This is a cylindrical device that travels inside a pipeline and is commonly used in the oil and gas industry for pipeline maintenance. An important factor in determining the ultimate velocity of the device is the pressure drop over the by-pass pig, which is characterized by a pressure loss coefficient due to the by-passing fluids. In this study the pressure loss coefficient of three frequently used by-pass pig geometries in a single phase pipeline is investigated with Computational Fluid Dynamics (CFD). The CFD results are used to validate the simple building block approach for systematic modelling of the pressure loss through the by-pass pigs, which takes the geometry and size of the by-pass opening into account. It is shown that the pressure loss models can capture the CFD results for each of the three pig geometries. The pressure loss models can be combined with pig/pipe-wall friction models to predict the velocity of a by-pass pig in a single phase pipeline, which is important for a safe and effective pigging operation. The applied building block approach may also be suitable to characterize pressure loss coefficients of complex geometries in general.@en

We present experimental and numerical results for by-pass pigging under low-pressure conditions which aided the design of a speed-controlled pig (Pipeline Inspection Gauge). Our study was carried out using air as working fluid at atmospheric pressure in a 52 mm diameter pipe of 62 m length. The experimental results have been used to validate simplified 1D models commonly used in the oil and gas industry to model transient pig behaviour. Due to the low pressure conditions oscillatory behavior is observed in the pig speed, which results in high pig velocity excursions. The oscillatory motion is described with a simplified model which is used to design a simple controller aimed at minimizing these oscillations. The controller relies on dynamically adjusting the by-pass area, which allows to release part of the excess pressure which builds up in the gas pocket upstream of the pig when the motion of the pig is arrested. Subsequently, the control algorithm is tested by a 1D transient numerical model and it was shown to successfully reduce the pig velocity excursions.@en

We investigate the frictional force which is acting on a pipeline pig. Two complementary experimental setups have been designed and used to study the sealing disc of a pig, which is responsible for the frictional force between the pig and the pipe wall. Six 12’’ off the shelf sealing discs from two different vendors have been used. The first setup is a static setup in which the sealing disc is subjected to a normal wall force and a tangential friction force. A unique feature of the setup is that the ratio between the friction force and the wall force can be readily adjusted. This allows to experimentally determine the force ratio which is directly related to the Coulomb friction coefficient, which is often a difficult parameter to predict. Furthermore, the static setup is used to systematically study the effect of oversize, thickness, and Young's modulus of the sealing disc on the frictional force. A direct comparison with Finite Element (FE) calculations is made. The second experimental facility consist of a dynamic setup in which a sealing disc is pulled through a vertical 1.7 m long pipe. The effect of possible lubrication on the frictional force is studied by applying water to the sliding contact and comparing the results with dry pull tests for different sliding velocities. The corresponding difference in the Coulomb friction coefficient was quantified using FE calculations which were successfully verified with the static setup. The sensitivity of possible wear of the sealing disc on the frictional force is discussed.@en

(Pipeline Inspection Gauge), which is a cylindrical device that just fits the pipe and propagates through the pipe along with the transport of fluids. While a conventional pig completely seals the pipeline and travels with the same velocity as the production fluids, a by-pass pig has an opening which allows the fluids to partially by-pass the pig. The purpose of the present study is to get a better understanding of the physics of the pigging of a pipeline with multiphase flow transport. The focus is on pigs with by-pass. An important factor in determining the ultimate travel velocity of a by-pass pig is the pressure drop over the by-pass pig, which is characterized by a pressure loss coefficient. We investigate the pressure loss coefficient of three frequently used by-pass pig geometries in a single phase pipeline with Computational Fluid Dynamics (CFD). We present a building block approach for systematic modelling of the pressure loss through the by-pass pigs, which takes the geometry and size of the by-pass opening into account. The CFD results are used to validate the simple building block approach for systematic modelling of the pressure loss through a by-pass pig. It is shown that the models for the pressure loss closely resemble the CFD results for each of the three pig geometries.@en

In this study the frictional force between a pig and the pipe wall is studied by investigating the properties of the sealing disk of the pig. This is done by subjecting the sealing disk to a wall normal force and a frictional force in a lab facility. The experimental results are compared with values obtained by Finite Element Analysis and by a simplified mechanistic model. The obtained results are important for estimating the steady state pig velocity in a pipeline, and thus for the arrival time of the pig. In addition, the results can be used to improve 1D transient pig modelling in a pipeline, where the frictional force is an input parameter.@en

In this study we investigate the development of a speed controlled pig in a low pressure pipeline. This is known to be a challenge due to the compressibility of the gas which can induce velocity surges of the pig. In order to reduce these velocity surges, a speed controlled pig with active by-pass control has been designed, fabricated and subsequently tested on a laboratory scale. The experimental setup consists of a 52 mm diameter pipe with a length of 62 meter. The working fluid is air. The speed controlled pig has an adjustable by-pass valve which can provide the right amount of by-pass to regulate the by-passing fluid force. First test runs show that the velocity surges can indeed be reduced, which demonstrate the feasibility of realizing fully autonomous control for bypass pigs in low pressure pipelines.@en

In this study we investigate the development of a speed controlled pig in a low pressure pipeline. This is known to be a challenge due to the compressibility of the gas which can induce velocity surges of the pig. In order to reduce these velocity surges, a speed controlled pig with active by-pass control has been designed, fabricated and subsequently tested on a laboratory scale. The experimental setup consists of a 52 mm diameter pipe with a length of 62 meter. The working fluid is air. The speed controlled pig has an adjustable by-pass valve which can provide the right amount of by-pass to regulate the by-passing fluid force. First test runs show that the velocity surges can indeed be reduced, which demonstrate the feasibility of realizing fully autonomous control for bypass pigs in low pressure pipelines.@en

In the oil and gas industry, bypass pigs are used to allow part of the production fluids to bypass the pig (Pipeline Inspection Gauge) during a pigging operation as compared to a conventional pig. This has been proven to be beneficial for both cleaning of the pipe and inspection of the pipe wall in both single and multiphase systems. To monitor the propagation of the bypass pig in a pipeline with a ID transient tool (such as OLGA or LedaFlow), the pressure loss coefficient between the bypassing fluid and the pig and the friction coefficient between the pig and the wall needs to be known in advance. The pressure loss coefficient in these tools typically ranges from 1-1.5, and is modelled without taking into account the specific geometry that is used to create the bypass area of the pig. The present CFD study is focused on finding an appropriate value for the pressure loss coefficient. For many bypass pig configurations a deflector plate is attached at the exit of the orifice of the bypass pig. This deflector plate constitutes of a circular disk which is mounted at a specified distance from the bypass pig opening which ensures that the pig gets into motion in the launcher and can help in distributing corrosion inhibitors at the top of the pipeline. In fact by changing the space between the deflector plate and the front of the orifice the bypass opening can be set before launching the pig. In this study the effect of the deflector plate on the flow through the bypass pig in a single phase system is investigated using CFD (Fluent version 14.5). An axisymmetric framework is used in which the bypass pig is assumed to move at a constant velocity. It is found that the pressure loss coefficient of the pig can be as high as 4, which is in contrast to a value of 1 - 1.5 that is commonly used in industry for bypass pigs without a deflector plate. This has significant practical implications as the driving force related to the pressure loss coefficient (which is counteracted by wall friction) determines the travel velocity of the pig through the pipeline. With the help of the obtained CFD results for various parameter ranges (such as the Reynolds number and the bypass opening) existing correlations for pressure loss coefficients used for bypass pigs are reviewed and their range of applicability is discussed for bypass pigs with and without a deflector disk. These results can be used to improve ID modelling tools for bypass pigging.@en

The present paper is focused on the development of an accurate 1D numerical model for pig motion in two-phase flow. The focus will be on the liquid slug that is accumulated in front of the pig, the so-called pig-generated slug. Under the assumption of a stratified flow, we first discuss the academic case of liquid slug accumulation where we neglect the viscosity of the fluids. The size of the liquid slug will then effectively be determined by the speed of the hydrostatic wave which runs ahead of the pig. We also consider the more realistic case which includes the viscosity of the fluid. Finally, we discuss the effect of the presence of a by-pass in the pig on the accumulated liquid slug.@en