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Abstract PIGs (pipeline inspection gauges) have been the main equipment for pigging, inner inspecting operations in oil and gas pipelines. Due to the insurmountable shortcomings of conventional sealing discs, it is impossible to actively control the PIG when it is running on the pipeline, which leads to no way when the PIG is stuck. In this study, a new type of bio-inspired sealing disc was designed in combination with the webbed foot structure of animals (e.g., bird, frog, duck), soft robot technology and the conventional sealing disc, adding a new way to the mechanical pigging method. And the 3D printing technology was used to print the sample of the bio-inspired sealing disc, taking into account the new direction of manufacturing the PIG. Then, effects of the interference (δ), clamping rate (ζ), webbed foot thickness (t w) and the number of webbed foot (N) of the bio-inspired sealing disc on the contact force and stress were studied using MSC Marc 2016 when the PIG was in pipe. The simulation results show that the contact force and stress on the bio-inspired sealing disc are not uniform, showing a great difference in the uniform contact force and stress on the conventional sealing disc. The effect of interference and clamping rate on the maximum contact force, stress on the bio-inspired sealing disc and the influence on the conventional sealing disc are basically the same, but the impact on the minimum stress and contact force is different. The thickness of the webbed foot has the greatest influence on the contact force, stress on the bio-inspired sealing disc, and the number of the foot has the least influence. Highlights • A bio-inspired sealing disc is designed, adding a new way to the pigging method. • 3D printing technology is applied to the processing of PIGs for the first time. • The contact force of the bio-inspired sealing disc differs from the conventional. • The number of the webbed foot has the least effect on the contact force and stress. • The conclusions indicate the results are important and useful for further research. [ABSTRACT FROM AUTHOR]

Gas well stimulation based on a ball-drop fracturing system is a widely adopted operation in the oil & gas industry. The flow resistance of a multistage fracturing pipe string increases as the number of stages grows, which is a major problem for the traditional graduated ball-drop multistage fracturing system, as it can increase the load of the pump and may ultimately result in a high-cost operation. A new openhole multistage hydraulic fracturing system, which has unlimited multistages, activated by ball plugs is proposed to improve the operation efficiency. In this system, all the downhole sliding sleeves are a single size, and a group of ball plugs activate them to achieve full-inner-diameter pipe access. As a key part of the fracturing system, the approximate cylinder-shaped ball plugs would suffer from a larger resistive force in the horizontal pipe than that of the sphere-shaped fracturing ball. Therefore, a simplified miniature indoor experiment setup is built to investigate the motion of the ball plug. The physical dimensions of the cylinder models and the velocities of the pumping flow vary in the experiment. In addition, the motion in the cylinder models are observed with a high-speed camera. Finally, the experimental data are analysed by a combination of dimensional analysis and the empirical equation method, and the results can help to determine the pumping rate during operations. [ABSTRACT FROM AUTHOR]

Pipeline inspection gauges (PIGs) are essential for regular maintenance in natural gas exploration in cleaning and inspection. Their sealing discs, made of polyurethane rubber (UR), are often found to be worn quickly due to rubbing against steel surfaces. The damage in the UR sealing disc would cause a PIG stuck in operation (pigging). In this research, we investigate the frictional behavior and wear mechanisms of the UR sealing disc. Experimental study was carried out on UR samples against steel pipe materials using a pin-on-disc tribometer. The morphology and wear modes were studied using an optical microscope combined with finite element method (FEM). Results showed the completing mechanisms of abrasion, oxidation, and surface fatigue. The inter-correlation between these three modes and test conditions are discussed here. The understanding obtained in this research is beneficial for the improvement of pipeline design and operation. [ABSTRACT FROM AUTHOR]

The continuous collision between a running PIG (pipeline inspection gauge) and girth welds in a pipeline can induce significant vibrations on the PIG, which can harm its mechanical structure. The vibration response caused by the collision between a running PIG and a girth weld was studied both experimentally and theoretically. A two-dimensional dynamic model of the PIG is introduced to explain and understand the collisional vibration. Our results demonstrate that the girth weld, which can be regarded as an obstacle, can greatly affect the dynamic behaviour of a running PIG. The instantaneous acceleration when the PIG passed over the girth weld is larger than that of the PIG that collided with the girth weld. The distinct and regular vibration response signal of a PIG passing through a girth weld can be used to identify the obstacles inside a pipe to calculate and correct the pigging mileages with the help of a special algorithm based on the function of odometers during the pigging or inspection process. [ABSTRACT FROM AUTHOR]

In this work, the effect of alternating current (AC) interference on the cathodic protection (CP) of API 5L X60 pipeline steel was investigated using electro-chemical and mass-loss methods, as well as surface analysis techniques. The results demonstrate that, the corrosion potential of API 5L X60 steel shifts, and the polarization current density increases, with the AC interference. At a lower AC interference density, the existing standard CP potential (−850 mV (vs. a CSE)) can provide full protection for a buried API 5L X60 steel pipeline. However, at a higher AC interference density, the potential cannot ensure the safety of the pipeline. The results of a CP of −950 mV (vs. a CSE) demonstrate that a more negative CP potential can relieve the AC corrosion risk for buried API 5L X60 pipeline at higher AC interference densities. This finding benefits pipeline safety design and operation and weakens the AC-induced corrosion often observed in buried pipelines. [ABSTRACT FROM AUTHOR]

Pipeline transportation is a safe and reliable way for transporting dangerous and flammable substances, such as oil and gas. In the process of transportation, third-party damage, corrosion destruction, design flaws, misuse of factors and other risk factors can also cause leakage or rupture of pipelines, which has a serious influence on social security and environment. In this paper, a comprehensive risk evaluation method based on a fuzzy Petri net (FPN) model for long-distance oil and gas transportation pipelines is proposed. In the process of the fuzzy reasoning, to tackle the impact of subjective factors and objective factors, the related parameters are optimized. In terms of risk factors weights, the combination weighting method is proposed, which combines AHP model and EM model. To reflect the fuzziness and randomness of risk factors, apply the cloud model to calculate the initial degrees of membership of the risk factors under the different risk grades. Furthermore, the risk evaluation values can be modified via the credibility. It is verified that the risk evaluation method based on the FPN model applies for the long-distance oil and gas transportation pipelines and provides some decision support for the risk management of the oil and gas pipelines. [ABSTRACT FROM AUTHOR]

Odometer wheel system, designed to measure the traveled distance and the instantaneous velocity of the intelligent inspection pig in operation, is an important part of the pig to define the position of pipeline defects. High accuracy positioning of pipeline defects can greatly improve the pipeline maintenance efficiency and highly reduce the costs. However, due to the peculiarity of its construction, the odometer is prone to unbounded accumulative errors and pipeline weld is the main reason. As a result, research on the motion and accuracy of odometer system is essential. In this paper, the motion of the odometer passing over the weld was investigated. Mathematical and simulation models were presented to describe and analyze the errors of the odometer, which was verified by the experiment. Research results indicate that the error of the measured distance can be divided into two conditions. At low velocity, the measured distance is larger than the actual distance, while the measured distance is smaller than the actual distance at high velocity. The results in this paper can provide better understanding of the accumulative errors of the odometer, and contribute to find a way to improve the accuracy of the odometer wheel system. [ABSTRACT FROM AUTHOR]

The safety of natural gas pipelines not only is very important to the economy but also significantly affects social security, considering the flammable property of natural gas. This study proposes a risk assessment method based on cloud inference, with multiple factors such as third-party damage, corrosion damage, misuse of factors, design flaws, biological erosion, aging factors, and so on. First, an assessment index system is established, considering the risk factors that may lead to an accident by using a fault tree analysis (FTA). Second, the index weights and index scores are established via the analytic hierarchy process (AHP) and expert scoring method, respectively. Third, the marking results of experts are transformed into the numerical characteristics of a cloud model by using the backward cloud generator. Finally, the whole assessment cloud droplet distribution of a natural gas pipeline is acquired by using the normal cloud generator and virtual cloud. The risk assessment result of natural gas pipelines using the cloud inference method indicates that the whole risk evaluation level can be clearly shown. Moreover, the cloud inference method can solve the fuzziness and randomness of the quantitative description and qualitative concept transformation in the risk assessment process for natural gas pipelines. [ABSTRACT FROM AUTHOR]

Pipeline inspection gauges (PIGs) are needed for operations such as cleaning and internal inspection of the natural gas pipelines to facilitate improvement in efficiency and safety. There is chatter vibrations appeared in PIGs when they run in the dry pipe with the wear of rubber sealing disc. Dry friction-induced self-excited vibration between sealing disc and pipe is the source of chatter vibration on PIG. In this paper, an experimental setup for measuring chatter vibration response signal of a typical bi-directional PIG running in a real dry steel pipe was implemented. The reason that cause self-excited vibration which manifest as chatter vibration on PIG, was explained through the analysis of classic dry-friction model. A self-excited vibration model based on LuGre friction model was proposed for better understanding of the phenomenon of chatter vibration during the process that PIG running through the natural gas pipeline, and the model was solved by MATLAB/SIMULINK. Our results show that the PIG runs in dry pipe with chatter vibration at a certain period within micro-vibrations in the single ladder period. Dry friction-induced self-excited vibration between sealing disc and pipe is the source of chatter vibration on PIG, and lead to the wear of PIG's sealing disc in natural gas pipeline; the negative damping of system in dry friction contact is the reason that causes self-excited vibration; the simulation of the numerical model can validate the PIG's self-excited phenomenon well. These results provide a better understanding of the complex behavior of PIG motion within natural gas pipelines. [ABSTRACT FROM AUTHOR]

To predict the motion of a pig to estimate its velocity, position and required driving pressure is essential before pigging. The frictional force between a pig and the pipeline is a key determinant of the prediction accuracy, and a precise evaluation of the frictional force between the pig and the pipeline can enhance the prediction of pig motion. The contact between the pig and the pipeline is a soft interference of rubber and steel, and good performance of nonlinear simulation for evaluating the frictional force has been verified. However, due to some mathematical or technical limitations, the linear elastic behaviour of rubber has sometimes been used to simplify the prediction, greatly affecting the prediction accuracy. To determine the difference between these two cases in this paper, comparisons of linear and nonlinear simulation for predicting the bidirectional pig contact forces are presented. The effects of the elastic module ( E ), interference ( δ ), thickness ( ξ ), and clamping rate ( ζ ) of the sealing disc on the performance of the linear and nonlinear models at different differential pressures are discussed. The results indicate that the contact forces obtained from the linear simulation model are greatly underestimated. The linear simulation model is incapable of predicting the contact force or the frictional force between the pig and the pipeline because the elastic behaviour of the sealing disc is described in the linear approximation. Consequently, the assumption in the pigging simulation that the sealing discs/cups attached on the pig exhibit a linear elastic behaviour lead to improper predictions regarding the pigging time, velocity, driving pressure, and so on. However, the pigging risks and uncertainties can be greatly reduced based on the nonlinear prediction rather than the linear simulation due to the inaccurate simulation results. This study clearly presents the differences between the linear and nonlinear simulations based on the complex behaviour of pig motion in oil and gas pipelines. [ABSTRACT FROM AUTHOR]

Leakages are the major cause of in-service natural gas and oil pipeline accidents, and many factors, such as corrosion, can lead to leakages. The feeler pig is one of the most typical contact-testing tools in oil and gas pipelines. In this paper, the probe dynamic behaviour of the feeler pig in detecting internal corrosion has been investigated using a handmade inspecting system. The dynamic characteristics of the probe are different in the uphill section and the downhill section, and the trajectory of the probe is asymmetric. A bouncing phenomenon was found in the outlet region of the corrosion. The experimental results indicated that both the speed and the spring pre-tightening elastic force are closely related to the inspection precision. The research in this paper provides guidance for studying the inspection precision of the feeler pig. [ABSTRACT FROM AUTHOR]

The offshore platform serves as the infrastructure for offshore mining. In order to guarantee safe operation of the platform and the development of the platform in the direction of intelligence, a natural gas leakage intelligent detection system with fast response is necessary to prevent potential accident when leakage occurs. In this work, a method to locate leaked natural gas is proposed based on the particle swarm optimization algorithm for the multi-robots to achieve. First, the advection diffusion equation is calculated to simulate the leakage gas transmission using finite difference method in different scene layouts. At the same time，a multi-robot collaborative detection strategy for gas detection, gas tracking, and gas source localization is proposed using an improved particle swarm optimization algorithm. After that, the process of multi robots search for leak sources was simulated. In addition, the control algorithm is analyzed, and the results show that the strategy has a high detection rate. Further analysis shows that the number of robots has increased from 2 to 7, the time it takes for the multi-robot system to successfully locate the leak source decreased; when the number of robots is constant, the time it takes for the multi-robot to successfully locate two leak sources is longer than the time to locate a single leak. Finally, search strategies based on particle swarm optimization, ant colony algorithm and cuckoo search algorithm are used to simulate in a single leak source environment. When the number of robots is changed from 3 to 7, compared with the other two algorithms, the accuracy of the search strategy search based on particle swarm is increased by 2%–28%, and the search time is accelerated by 27s–92s.the particle swarm optimization is superior than two others for control of multi-robot system in leakage source location. • Simulating gas diffusion based on advection diffusion equation. • Based on particle swarm optimization, a strategy for multi robot to locate natural gas leakage is proposed. • Through numerical simulation, the feasibility and effectiveness of the method are verified. • This method has great positioning effects in different environments. [ABSTRACT FROM AUTHOR]