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.

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.

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.

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.