Xiaoxiao Zhu

Experimental Research on the Frictional Resistance of Fluid-Driven Pipeline Robot with Small Size in Gas Pipeline

Pipeline inspection gauge (pig), as a kind of pipeline robot, is commonly used in oil and gas pipelines during different stages of operation to perform functions such as dewatering, cleaning and inspecting. Predicting the motion of a pig to estimate its velocity, position and required driving pressure is essential before pigging. A precise evaluation can greatly help the operator to control the motion of the pig and reduce the pigging risks. The frictional resistance between a pig and the pipeline is a key determinant of the prediction accuracy, and research on the contact behaviour of sealing disc can help to understand the frictional resistance well. As a result, in this paper, an experimental rig for measuring the frictional resistance of the bidirectional pig with high accuracy was developed, and the effects of the sealing disc’s interference, thickness and clamping rate on the sliding friction of the pig were experimentally studied. The corresponding normal force between the sealing disc and the pipeline was obtained by a 2D axisymmetric nonlinear finite element model, and the frictional coefficient with the variation of the sealing disc’s size was presented. Research results show different effects of the sealing disc’s sizes on the frictional force, normal force and the frictional coefficient. In addition, different contact behaviours can be observed by the indication of the frictional coefficient curve. The contact behaviour can be grouped into several conditions, depending on the size of the sealing disc.

Synchronous clamping control of marine umbilical cable tensioner

The umbilical cable tensioner is a core component of deep-water oil and gas development, and it can lay and recover the umbilical cables to ensure the transmission of communication signals, electric signals or liquid injection. The displacements of tensioner’s clamping hydraulic cylinders, which are not synchronized as the nonlinear electro-hydraulic control system, results in the occurrence of the crawler mechanism’s stuck phenomenon or cause umbilical cable deformation or even cause damage by the extrusion in the umbilical cable’s clamping process. To ensure synchronous clamping, the structure scheme of umbilical cable tensioner, crawler mechanism, clamping mechanism and the hydraulic system of synchronous clamping control is designed in this study. This article also analyzes the function of structure parameters and hydraulic cylinders’ displacement, speed and acceleration, and builds the synchronous clamping mechanical model to reveal crawler mechanism’ clamping law. The study proposes the control strategy including the fast moving stage, the working stage and the pressuring stage based on proportional–integral–derivative control, and analyzes the characteristics of synchronous clamping control by building the synchronous clamping experimental platform in the lab environment. The experimental data shows that the tensioner’s hydraulic cylinders have excellent synchronous clamping performance and the theoretical analysis is feasible. The research has important guiding significance for the tensioner design, and provides theoretical support for the laying of the deep-sea umbilical cables.

Pose overshoot analysis of the marine spherical double plugging in twisting process

Marine spherical double plugging is a novel plugging device, which can achieve the initiative plugging in the oil and gas pipeline. In order to ensure that the plugging head will not collide with the pipeline wall and not be scratched by the drill cuttings, the analysis of twisting process is necessary to assure reliable operation. In this article, we designed the overall scheme of marine spherical double plugging and established the mathematic model of spherical double plugging. Through studying the twisting algorithm of plugging head and trajectory algorithm of plugging head contour, four dangerous points were obtained. The multi-body dynamic of the structure was built using ADAMS, and the twisting process and motion analysis of four points were analyzed. The twisting error of the plugging head between the four points and the inner wall of the pipeline was analyzed in overshoot states to obtain the maximum allowable overshoot of inserting hydraulic cylinder and twisting hydraulic cylinder. Simulation results show that overshoot of inserting hydraulic cylinder needs to be controlled within 11.5 mm and overshoot of twisting hydraulic cylinder needs to be controlled within 5.3 mm to avoid the unpredictable danger. This article will provide theoretical and technical support for the optimization design of control system and the plugging head.

Research on pressure fluctuation phenomenon using the smart isolation tool in subsea pipeline maintenance operation

A new isolation technology in subsea pipeline maintenance has been gradually developed in recent years. During the operation, the smart isolation tool is desired to decelerate and stop in the accurate position, which will cause a pressure surge in pipe, it was named “pressure fluctuation phenomenon” in this article. For control precision and sealing reliability, avoiding or reducing the fluctuation phenomenon has been necessary. The characteristics of this phenomenon and the effects of parameters have been investigated using numerical methodologies. The results indicated that this phenomenon mainly affected by deceleration time, flow velocity and aspect ratio, and the optimal parameters are t = 1.5 s, v = 1 m/s and γ = 1.2, respectively. The identical results could be achieved from the sensitivity analysis. It can be concluded that the peak value is more sensitive to deceleration time, less sensitive to flow velocity and least sensitive to aspect ratio. All the studies in this article will provide a reference to improve the control precision and seal reliability using smart isolation tool in subsea pipeline maintenance.

The impact of pipeline bend on bi-directional pig and the theories for the optimal pig design

As a kind of pipeline robot, pig is needed to perform operations such as dewatering, cleaning and internal inspecting to improve the efficiency and ensure the safety of oil and gas pipeline. A pig with improper geometry will easily get stuck in the pipeline and the attached electrical equipments may also be damaged by the crash, especially when passing through pipeline bends or elbows. This is not only harmful for the pig itself, but also threatens the transportation security of pipeline. In this paper, avoiding getting stuck in the pipeline bend, the detail process when the bi-directional pig passing through pipeline bend is discussed. The proper method for determining the geometry size of the pig body is proposed and displacement of the bi-directional pig when passing the bend is presented after a force analysis of the sealing discs. The related theories for the pig design can provide some references to determine the size of pig body and make an appropriate setup of discs.