Haihao Wu

Hydraulic Transients Induced by Pigging Operation in Pipeline with a Long Slope

Pigging in pipelines basically performs operations for five reasons including cleaning the pipe interior, batching or separating dissimilar products, displacement, measurement, and internal inspection. A model has been proposed for the dynamic simulation of the pigging process after water pressure testing in a long slope pipeline. In this study, an attempt has been made to analyze two serious accidents during pigging operation in 2010 by the model which is developed by the method of characteristic (MOC) by Wylie et al. (1993) and the two-phase homogeneous equilibrium vaporous cavitation model deveoped by Shu (2003) for vaporous cavitation. Moreover, simulation results of the third operation show good agreement with field data from the previous field trial. After investigation, it was showed that the impulse pressures produced during collapse of a vapor cavity result in severe damage of tubes.

Hydrate slurry flow property in W/O emulsion systems

Hydrate risk management strategy has become a promising way of dealing with hydrates in subsea transportation pipelines in recent years. In this way, hydrates are allowed to form in the pipeline and are treated as a slurry flow with the help of anti-agglomerants. This work investigated the effect of hydrate formation on the flow friction factor in water in oil (W/O) emulsion systems. A series of hydrate formation and slurry flow experiments were conducted using a high pressure flow loop. Results show that the friction factor is in direct proportion to the volume fraction of hydrates formed, as it increases significantly after hydrate formation onset and then increases gradually with hydrate growing. A novel method is proposed in this work to amend the effective hydrate volume fraction and take into account the effect of hydrate agglomeration and water occlusion. In addition, it is found that the slurry flow velocity has a significant effect on the friction factor variation. As a larger flow velocity can lift the particles suspension height and cause the particles to be away from the pipe wall surface, so it gives a smaller friction factor by reducing the collisions between hydrate particles and the pipe wall surface. With the modified effective hydrate volume fraction and particle chord length distribution data, a model is proposed to estimate the hydrate caused friction factor in W/O emulsion systems, which shows a good prediction accuracy in 10% and 20% water cut conditions.

Investigation on the Transition Criterion of Smooth Stratified Flow to Other Flow Patterns for Gas-Hydrate Slurry Flow

A stability criterion for gas-hydrate slurry stratified flow was developed. The model was based on one-dimensional gas-liquid two-fluid model and perturbation method, considering unstable factors including shear stress, gravity, and surface tension. In addition, mass transfer between gas and liquid phase caused by hydrate formation was taken into account by implementing an inward and outward natural gas hydrates growth shell model for water-in-oil emulsion. A series of gas-hydrate slurry flow experiments were carried out in a high-pressure (>10 MPa) horizontal flow loop. The transition criterion of smooth stratified flow to other flow patterns for gas-hydrate slurry flow was established and validated and combined with experimental data at different water cuts. Meanwhile, parameters of this stability criterion were defined. This stability criterion was proved to be efficient for predicting the transition from smooth to nonsmooth stratified flow for gas-hydrate slurry.

Experiment Study of Pigging Characteristics in Horizontal Gas-Liquid Flow Pipeline With Different Pig Sizes

During pigging process of long-distance pipeline, pig seals wear due to abrasion on pipe wall, the diameter of seal decreases and even to be smaller than pipe inner diameter as a result. This study has researched the characteristics of pigging processes using pigs different in diameter in horizontal experimental pipe. In the study, mandrel pig with two seals was chosen for experiment. Five pigs different in size were used, and pigging experiments under various flow conditions were carried out in a horizontal air-water flow experimental loop. During experiment, the features of pigging process from pig launcher to trap were observed, the liquid holdup and pressure were detected and collected, pig velocities in different sections of pipe were measured, the velocity of pigging slug front and length of the slug were also measured. The relationship between pig movement and flow conditions was analyzed, the methods to calculate velocity of pigging slug front and length of the slug were obtained and the results calculated were similar to the results measured. Based on the results of experiment, some suggestions were proposed for pigging operation in real pipeline.Copyright