Pipeline Pigging Research Articles

Experimental and numerical investigation on hyperelastic sealing disc contact behavior in pipeline, a comparison between fluid-driven and pull-through approaches

Pipelines are widely recognized as the safest and most efficient means of fluid transportation. Pipeline pigging, a secure and reliable technique, is employed for both cleaning and sealing pipelines to optimize efficiency. Since pigging operation requires differential pressure (ΔP) to facilitate pig movement, this pressure must correspond to the pipeline's operational conditions. Consequently, studying the required ΔP for sealing discs, which serve as primary sealing elements of pigs, is crucial. The primary focus of this study is to examine the difference between pulling the pig using a cable and propelling it with fluid. Furthermore, the main novelty of this research is to experimentally investigate a single sealing disc and conduct fluid-driven tests on it. To study more precisely, three sealing discs with various thicknesses and the same hardness have been launched into a 6-inch spool test, containing five pipes with different wall thicknesses, resulting in multiple oversize ratios (%OSz). In the experimental study, both fluid-driven and pull-through tests were conducted. The range of discrepancy between two methods varies from 15% to 26% for different oversize ratios which is considerable. Additionally, A 2-D axisymmetric nonlinear numerical simulation was conducted in a finite element software ABAQUS in order to study the behavior of sealing discs. Using a pressure-dependent friction coefficient with the proper hyperelastic model was key to achieving simulations that have good agreements with experimental results, with discrepancy of less than 10 percent in all extracted pressures.

Enhanced Speed Control of Pipeline Pigs with Adjustable Bypass Using Quantitative Feedback Theory and Cascade PID Algorithm

During pipeline pigging operations, precise control of the pig's running speed is crucial. However, external speed disturbances often occur during these operations. In response to this challenge, adjustments are made to the flow rate through the pig body, thereby modifying the pressure difference and achieving a targeted speed range of 1 m/s to 3 m/s. Since a pig with an adjustable bypass port operates in a dynamically changing state, conventional control algorithms face difficulties in providing effective control. Moreover, there is limited research on speed control algorithms for pigs with adjustable bypass ports. To address these challenges, this paper introduces a control system based on Quantitative Feedback Theory (QFT), coupled with cascaded Proportional-Integral-Derivative (PID) tuning, for the precise speed control of a bypass pig. The state equation is derived from the pig's operational state, and the QFT Toolbox is employed to design a pre-filter and controller. This integration of QFT with cascaded PID not only facilitates both speed control and disturbance rejection but also demonstrates significantly improved control stability under variable operational conditions. The model, implemented using the Simulink Toolbox, shows that this approach can quickly stabilize the pig's speed, effectively managing continuous variations and enhancing the efficiency and safety of pipeline pigging.

PIV Experimental Research and Numerical Simulation of the Pigging Process

The initial running speed of the pig during gas–liquid two-phase pipeline pigging can significantly influence the velocities of both gas and liquid phases within the pipeline. However, due to the complexity and limited understanding of these velocity variations, developing an effective operational plan for pigging becomes challenging. To enhance pigging efficiency and effectively seal the pig, it is crucial to monitor the velocity variations in the gas–liquid phase within the pipeline. In this study, an experimental platform was established to facilitate precise observation of these variations. Particle image velocimetry (PIV) technology was employed for a comprehensive understanding of gas–liquid two-phase velocities during pig operation in the pipeline. The experimental results demonstrated that increasing both the velocity and the initial liquid level height of the pig resulted in a corresponding augmentation of velocity fluctuation range. Specifically, at a holdup rate of 30%, there was a 10% reduction in the maximum liquid-phase velocity, while at a holdup rate of 25%, this reduction amounted to 16% compared to the pigging velocity.

Localizing and tracking of in-pipe inspection robots based on distributed optical fiber sensing

Ensuring the safe transportation of energy relies heavily on the timely safety inspection and pigging of energy pipelines using in-pipe inspection robots known as Smart/Intelligent PIGs. Addressing the potential risks of PIG block incidents and the limitations of excessive speed in the maintenance, real-time localization and tracking of these inspection robots has become imperative. However, traditional localization and tracking methods present a challenge due to their resource-intensive nature, requiring significant manpower and resources. To overcome this limitation and enhance the intelligence of the robot operation monitoring, this paper proposes an innovative artificial intelligence (AI) integration algorithm framework based on distributed optical fiber sensing (DOFS) for real-time localization and tracking of robots. It adopts noise reduction and reconstruction techniques in signal processing, effectively enhancing the quality of optic fiber vibration signals. Notably, the integration of two distinct features that complement each other enables dual verification of tracking detection, ultimately bolstering the system’s effectiveness and trustworthiness. Besides, a logical reasoning-based localization decision strategy further enhances the system’s capabilities, allowing for controlled tracking intervals and step sizes that can be tailored to meet the task requirements under diverse working conditions. The collaboration of three modules makes it feasible to monitor dynamic changes of the detection robot in the pipeline along the direction of operation. The experimental results convincingly demonstrate that the integrated framework possesses several key advantages of remarkable robustness, real-time performance, and minimal error. It underscores the system’s potential to ensure energy pipeline safety efficiently and effectively.

Tracking and Localization Method of Pipeline Pigs Based on a Noise Reduction Autoencoder

In the pigging operation of an oil pipeline, the traditional pigging localization method can only achieve fixed-point detection and cannot track continuously. To ensure the normal operation of the pigging operation and track and locate the pig in a timely manner, a tracking and localization method of an oil pipeline pig based on a noise reduction autoencoder is proposed. First, using the advantages of U-Net (U-shaped Convolutional Neural Network) multi-scale feature extraction, combined with coding and residual-dense blocks, U-Net combined with Residual Dense Block U-shaped Network (RDBU) was proposed for noise reduction, and then real-time localization was calculated out based on the negative pressure wave localization formula of pigs. The experimental results show that, compared with the traditional method, the SNR of the RDBU is increased by 0.9dB and the root mean square error is reduced by 14.92%. The denoising algorithm in this paper can effectively eliminate the noise of the negative pressure wave signal of pigs.

A Novel Speed-Sensorless Wireless Universal Motor With Bidirectional Movement

This paper proposes a novel wireless universal motor. By eliminating the motor controller and position sensor, the secondary side is very simple and robust. Besides, bidirectional movement can be achieved. The key is to employ a self-driving circuit at the secondary side. Also, the advantages of the small size and large starting torque of universal motors can be retained. Hence, the proposed wireless universal motor is very suitable to be sealed and employed in isolated environments, such as pipeline pigging. A series of simulations and experiments have been conducted, which confirms that the secondary side can be self-driven, and the motor speed can be detected at the primary side.

Multilayer Feature Boosting Framework for Pipeline Inspection Using an Intelligent Pig System

As pipelines take an increasingly important role in energy transportation, their health management is necessary. In-pipe inspection is a common pipeline life maintenance method. The signal obtained through internal inspection contains strong noise and interference where the internal environment of the pipeline is extremely complicated. Thus, it is challenging to accurately identify the defect signal. In this paper, a defect detection framework based on feature boosting is proposed by using the multi sensing pipeline pig as the detection signals. Through boosting construction of features and hierarchical classification, the framework can not only correctly classify various signals in the internal detection signals but also realize the accurate identification of defect signals. Concurrently, in order to demonstrate the high flexibility and robustness of the detection framework, experiments and verifications have been carried out on specimens in three different environments i.e., laboratory environment, simulated environment and actual environment. In the classification of actual environmental detection signals, quantitative evaluation with different algorithms have been undertaken using the F-score to demonstrate the effectiveness of the proposed framework.

Application of Superparamagnetic Nanoparticle (SPM-NP) Heating in Wax Removal during Crude Oil Pipeline Pigging

Mechanical pigging is a major wax removal technique in crude oil pipeline transportation. To lower the risk of pig stalling accidents in pigging, a superparamagnetic nanoparticle (SPM-NP) pigging system that consists of an electromagnetic pig and nanopaint is designed to soften the wax deposit and reduce the wax resistive force. During pigging, the induction coil on the pig generates an alternating magnetic field, which induces heat production of the nanopaint on the pipe wall. The COMSOL software is used to simulate the temperature distribution of the wax layer. Yield stress measurements reveal that the wax layer yield stress is nearly linearly correlated to temperature. Compared with a regular pig, the SPM-NP pigging system reduces the wax resistive force by up to 20~40%, with an acceptable electrical current intensity of about 20 A in the given cases. Multiple factors affecting the wax layer temperature were analyzed. SPM-NP heating could be a promising technique for wax remediation and hydrate prevention.

A review of mechanical model, structure, and prospect for long-distance pipeline pig and robot

AbstractThe safety and reliability of robots are very important for the inspection in a long-distance pipeline used for the oil and gas transportation. In this paper, the long-distance pipeline pig and robots (LDPPRs) are classified into two categories, which are velocity-uncontrollable type and velocity-controllable type. Among them, the velocity control of velocity-controllable LDPPR has three ways, which are friction resistance, driving force, and self-running. Meanwhile, the mechanical models of the motion of the LDPPRs are classified into the dynamic model of the velocity-uncontrollable LDPPRs, velocity-controllable LDPPRs, and vibration, and the contact mechanics model between the rubber barrel and the pipe wall. In addition, the anti-stuck technologies, the inspection technologies, and the location technologies are investigated and analyzed. Thus, the purpose of this review is to provide a concise reference for the development and research directions, as well as the design of the LDPPRs.

Experimental investigation on speed excursion of PIG due to friction variation in natural gas pipeline

Natural gas pipeline pigging with speed excursions may lead to potential loss of inspection data and possible dangers due to high acceleration; however, the operation relies heavily on a rule of thumb. Most pigging operations in gas pipelines are performed at normal operating pressures with regular flow rates, and the PIG velocity is generally in the range of 2–5 m/s. However, pigging in low-pressure and low-flowrate gas pipelines is very difficult due to speed excursion, which rapidly increases the PIG velocity. Mitigating speed excursions is an important challenge during the gas pipeline pigging process, but fundamental studies on this phenomenon have not been conducted. This study is the first to conduct a lab-scale experiment on speed excursion due to friction variation during gas pipeline pigging to investigate the mechanism of speed excursion and the relationship between the main variables and speed excursion. Based on the differential pressure results, mechanism of speed excursion was derived as 5 phases of speed excursion process: Stable behavior, build-up phase, pre-speed excursion phase, speed excursion phase, recovery phase. In the results of relationship between main variables and speed excursion, it was found that the flow velocity has a linear relationship with the speed excursion, but the excursion ratio has an exponential fit curve that rapidly increased at low flow velocity. These result means that low-flow pigging produces relatively low-speed excursions, but can be a very risky operation due to the rapid increase in excursion ratio. Both build-up time and recovery time also showed an exponential fit curve that increased rapidly at low flow velocity. These result indicate that pigging behavior is significantly unstable due to the long build up time and recovery time during low-flow pigging. When the linepack length changed, higher speed excursions occurred as the linepack length increases even at same friction conditions. When the wall thickness change ratio increased, the increase in friction led the speed excursion increased from about 46% to 110% showing the same trend of linear fit curve, and the rate of increase was higher as the flowrate decreased, and these results means that PIG behavior is more unstable due to increased friction, especially in the low flowrate. The results indicated that the linepack length is the main factor in pigging behavior. In particular, linepack should also be considered as an important variable that affects speed excursion, and behavior in long-distance pipeline pigging.

Numerical simulation and experiment of the gas-liquid two-phase flow in the pigging process based on bypass state

In the pigging of long-distance gas-liquid pipelines, the sealing disks and the inner wall of the pipeline will inevitably wear out. This may cause the diameter of the pig seal disks to be smaller than the inner diameter of the pipe, resulting in a clearance. The presence of clearance has a significant influence on the liquid flow pattern. Aiming to explore liquid flow characteristics in the pipeline, the paper conducted a series of numeric simulations based on the CFD method to investigate the process. The calculated model and experimental data verified the accuracy of simulations. Our results show that both the front and back of the pig are gas-liquid two-phase flow, and the higher the clearance, the lower the volume fraction of the liquid slug at the front of the pig. The increase in the speed of the pig will increase the length of the liquid slug segment and the front-end speed of the liquid slug. And as the inlet gas velocity gradually increases, the liquid at the front of the pig gradually scatters and becomes chaotic. The time for the liquid to reach the terminal outlet is only related to the pig speed. When increasing the clearance, the residual liquid in the pipeline increases, and the pigging effect worsens. Our results can provide some reference in pigging of gas-liquid pipelines.

Experimental investigation on sphere pig movement in multiple thickness pipe

In the petroleum industry, using pipelines is the safest and most reliable method for crude oil or product transportation. Pipeline pigging is crucial for safe and reliable pipeline operation. The driver pressure of a pig is an important parameter of this operation. Thus, it should be known in advance. In the present survey, an experimental setup has been built to investigate the driver pressure for sphere pig motion for various material hardness as well as oversize ratios. Three spheres have been produced from 55, 65, and 75 Shore-A hardness polyurethane and they have been launched into a six-inch test spool, containing four pipes with different wall thicknesses, equipped with a reciprocating pump as well as a digital pressure measurement system. Then the driver pressures have been measured for all test cases. The uniaxial tension test results of each material along with the test spool and sphere geometries were imported into the simulation software, ABAQUS. The predicted pressure difference values by the simulation had no similar manner to the experimental results when a fixed friction coefficient has been employed. A modification of the simulation scheme is presented here, which is the use of contact pressure dependent frictional behavior in finite element simulations, as the main novelty of the work. This correction leads to close matching of the experimental and numerical results with less than 10% deviation which is an acceptable estimation in the pigging operation. Thus, the pressure-dependent coefficient of friction along with the proper hyperelastic material model can successfully evaluate the differential pressure needed for ball pig motion in a pipe. As the experimental tests are time consuming and expensive for larger pipeline pigs, this method provides a fast and economic tool for driver pressure prediction in larger pipes, based on FEM simulation.

Experimental study on the wax removal physics of foam pig in crude oil pipeline pigging

Mechanical pigging is the most conventional method to mitigate the wax deposition in the field pipeline. However, wax removal physics of foam pig is still poorly understood. In this work, wax removal physics of foam pig is experimentally investigated in the pigging facility. Furthermore, wax removal physics of foam pig is proposed and further evaluated. Due to the energy absorption of foam pig during its elastic buckling, the wax resistive force of foam pig presents five phases including the build-up phase, pre-plug phase, damping phase, plug phase, and production phase. In the five-phase pigging process, the initial wax breaking force has a high risk of the pig stuck in the field compared to the steady wax breaking force. It is also noted that the wax removal physics changes when the wax yield stress and the wax layer thickness are increased. The effects of foam pig density, wax yield stress, and wax layer thickness on the wax breaking force and the wax removal efficiency are discussed. Furthermore, force analysis physical models and the energy absorption of foam pig are proposed to illustrate the experimental results. The effect of foam pig density on the wax breaking force is different for the wax layers with different strength. The wax removal efficiency of the low-density foam pig is significantly reduced for high strength wax layer.

Planning pipeline pigging operations with predictive maintenance

Deposition of waxes, asphaltenes, scales or hydrates is one of the most challenging operational problems in the oil and gas industry, both during production and transportation. Direct inspection procedures, such as employing a closed-circuit television system, allow visual assessment of the blockage, yet discretely in time and, consequently, of low value for the purpose of ensuring production over time. Therefore, an indirect predictive maintenance method for systematic evaluation of the internal pipe section is herein developed, adding a much needed solution to the current body of knowledge. Using continuous field measurements, it is now possible to predict when pigging should be performed to avoid significant blockages. Moreover, evaluating the maintenance plan risk is another major achievement. Finally, the proposed methodology and model were applied to a real case-study yielding good results compared to the current scheduled maintenance approaches.

Advances and Future Challenges of Wax Removal in Pipeline Pigging Operations on Crude Oil Transportation Systems

Wax deposition is a severe flow assurance challenge that threatens waxy crude oil production and transportation. For wax remediation, pipeline pigging is the most widely used technique. However, the elusiveness of wax removal mechanism and the lack of reliable methods to evaluate wax breaking force and wax removal efficiency easily trigger pig stalling and wax blockage in field pigging operations. Modeling wax breaking force and wax removal efficiency, therefore, promotes the pigging confidence. This Review seeks to clarify the current picture of wax removal research in crude oil pipeline pigging. Relevant wax deposit properties including wax layer thickness and strength are discussed. Wax removal mechanisms are summarized from perspectives of wax–pig interaction, macroscopic force response, and scenarios with oil flow. Prediction models of wax breaking force and wax removal efficiency are analyzed comprehensively. Pig geometry optimization using this model is given. In addition, the key roles of wax deposit strength, viscoelasticity and thixotropy, foam pig investigation, and wax plug prediction are highlighted for guiding future endeavors in this area.

Методика определения технологических параметров ремонта трубопровода с ненормативной кривизной

Pipe sections with curvatures exceeding the required specified values are often found during the pigging of major pipelines. Process parameters for repairs have to be defined in order to develop a maintenance project that also includes works to restore the specified status of the section found. A corresponding method is known for cases of relocation of an initially straight pipeline. The authors developed a method for determining process parameters for repairing pipelines with out-of-project axis curvature. The method is based on modeling the deformation of a pipeline with initial axis curvature; it takes into account the actual operating conditions of the pipeline and in-line inspection data. Examples of calculating process parameters for repairs and stress-deformed state of pipeline sections with out-of-specs curvature have been presented. The modeling results confirm the possibility of using the method for evaluating the repair process parameters, the length of the required trench exposure, and the magnitude and boundaries of additional digging-in or the need to lift the pipeline in order to determine the stress–strain state of the pipeline section to be repaired during execution and after the completion of repairs.

Estimating Wax Plug Transportation Force in Crude Oil Pipeline Pigging

Wax plug growth in pipeline pigging significantly impacts the crude oil transportation, even resulting in a wax blockage accident of pipeline. A pigging facility was constructed to conduct the pigg...

Tribological Exploration on Pigging System using Computational Simulation

Pipeline inspection gauge or known as PIG basically a device which is inserted into a pipeline with the purpose of cleaning or inspecting the pipeline for example in oil and gas industry. Pipeline pigging enhances the flow rate and corrosion control in the pipeline. During operation, the PIG is subjected to frictions and wear that occur between the sealing disc and the pipeline wall. The objective of this study is to simulate the contact pressure between the PIG sealing disc and the inner pipeline during pigging process. Other than that, the study is conducted to calculate the wear volume on the PIG sealing disc as the distance of pigging operation increase. The simulation is performed using COMSOL Multiphysics 5.3. The analytical calculation implemented Archard’s law formula. The result showed the higher the normal load applied to the PIG sealing disc, the higher the contact pressure between the sealing disc and the pipeline. Next, when the PIG travel through a pipeline with normal load applied, the volume loss of PIG sealing disc is increasing. As a conclusion, when the PIG is travel through a pipeline during pigging, the PIG is subjected to various conditions such as friction and wears which can affect the pigging performance.

Study on wax precipitation characteristics of wax deposit in pipes

AbstractWax deposit properties are a significant concern in pipeline pigging during waxy crude oil transportation. In the present work, the impacts of flow conditions and oil properties on the wax precipitation characteristics of wax deposits are investigated. A flow loop apparatus was developed to conduct wax deposition experiments using four crude oils collected from different field pipes. The differential scanning calorimetry (DSC) technique was employed to observe the wax precipitation characteristics of crude oil and wax deposit. The results show that the wax content and the wax appearance temperature (WAT) of the deposits increase with shear stress and radial temperature gradient, and decrease with radial wax molecule concentration gradient near the pipe wall. The DSC tests on the wax deposits revealed that the deposit wax content is strongly correlated to the oil wax content. Furthermore, an empirical correlation was developed to predict the wax content and the WAT of the wax deposit. Verification of the empirical correlation using the different oils indicated that the average relative error of the wax content prediction and average absolute error of WAT prediction were 13.2% and 3.6°C, respectively.

A new model for predicting oil-wax gel strength as a function of wax crystal precipitation and structural characteristics

Wax deposit strength is a determinant parameter for scheduling crude oil pipeline pigging program. However, previous oil-wax gel strength models only take into account wax precipitation amount (WPA) and ignore other influential parameters, like wax crystal structure. In addition, wax deposit strength measurement remains difficult because its structure would be damaged when using conventional rotational rheometer. In response, this paper develops an oil-wax gel strength model with wax crystal precipitation and structural characteristics incorporated, and proposes an indirect approach to measure the yield stress of real wax deposit. The impacts of WPA, wax crystal roundness, boundary fractal dimension, area fraction and aspect ratio are investigated. Grey relational analysis method shows that WPA, wax crystal boundary fractal dimension and area fraction are highly relevant factors. It is also revealed that a typical pigging process on real wax deposit can be divided into four stages, and wax breaking force is the wax removal force in the second phase. Moreover, it is found that high oil temperature increases WPA, wax crystal boundary fractal dimension and area fraction, and decreases wax layer thickness, accordingly, wax breaking force increases. For model validation, an indirect approach involving wax deposition and pipeline pigging is proposed. It overcomes the uncertainty of rotational rheometer in real wax deposit yield stress measurement. The average and maximum relative errors between predicted and inversely calculated yield stresses are 15.89% and 37.32% respectively, which proves the feasibility of this model to real wax deposit.