Buried Natural Gas Pipelines Research Articles

Method for identifying the leakage of buried natural gas pipeline by soil vibration signals

Method for identifying the leakage of buried natural gas pipeline by soil vibration signals

Research on damage assessment of buried pipelines with circular dent defects subjected to blast loading

In order to evaluate the damage characteristics of buried natural gas pipelines with circular dent defects subjected to blast loading, based on pressure–impulse damage theory, explosion experiment and numerical simulations were implemented to evaluate the damage of a natural gas with circular dent defects buried in soil under blast loading in this research. The ALE method was used to develop a coupled pipeline-soil simulation model using LS-DYNA software, and the validity of the established model was verified correctly compared with experimental results and empirical theory equations calculations. Furthermore, according to regulations in the Assessment and Management of Pipeline Dents (American Petroleum Institute Recommended Practice 1183), the effect with different circular dent defect diameter on the mechanical properties of natural gas was also investigated and analysed. The results showed that, under the blast loading, plastic deformation happened on the surfaces of the pipeline facing the explosive, and the high-stress zone appeared in the circumferential direction with 32.27°. The range of the high-stress zone firstly expanded along the axial direction of the pipelines and then along the circumferential direction. The larger diameter of the circular dent defects had, which resulted in a failure at the defects under the condition of the depth of the defects keeping constant. The effect of the size of defect diameter on the amount of pipeline deformation was further investigated, and the mathematical formula described the maximum plastic deformation with different defect diameter was established. Meanwhile, a finite element model of pipeline with a diameter of 457 mm was established for numerical analysis, which implied that the larger diameter of pipeline with the same defect had, the lower risk of pipeline in failure subjected to blast loading had. And through mathematical analysis and considering the feasibility of the actual situation, the curve described the maximum plastic deformation of the natural gas pipeline with three different defects varying in diameter were established respectively. In addition, a formula to express the relationship between pipeline defect diameter and maximum plastic deformation was established, which can effectively predict the critical plastic dent deformation of pipelines with different defect diameter subjected to blast loading. Besides, based on the pressure-pulse damage theory and with the damage assessment criterion of dent depth–dent length ratio of 0.072, the pressure–impulse diagrams of buried natural gas pipelines with defect diameters of 30 mm, 40 mm and 50 mm were defined, which can be used to predict the damage of pipelines with different defect diameters. Moreover, with the pressure–impulse damage evaluation curves, mathematical formula for the buried natural gas pipeline with the circular defects were established. Furthermore, the critical circular defect diameters with 30 mm was confirmed and the unique formula was also established, which could be effectively used to evaluate the safety of buried natural gas pipelines with the critical circular defects.

Quantitative study on dynamic response of buried natural gas pipeline under vehicle load

With the intersections of buried pipelines and highways increasing, the pipelines are under the threat of heavy loads. In this article, a full-section dynamic stress testing system is designed and constructed. A transient vehicle–road-soil-pipeline numerical model based on ADAMS and ABAQUS is established. On this basis, the influence of the vehicle rolling position on the stress distribution is analyzed. The influence of seven important factors, such as vehicle load and pipeline internal pressure, on the maximum stress of the pipeline is investigated. It is found that the maximum stress point always appears in the 12o'clock of the pipeline and the vehicle load most significantly affects the maximum stress of the pipeline. Furthermore, based on the simulation results and the GA-BP neural network, a maximum stress prediction model for the buried pipeline is established. The prediction model shows a high accuracy with a maximum relative error of 11.1%. Through this prediction model, an ultimate bearing capacity method for buried pipelines under vehicle loads is established and applied in three in-service buried pipelines.

Root cause analysis of cracking in buried X80 natural gas pipelines

In 2021, cracks formed in an onshore buried X80 natural gas pipeline with a diameter of 1219 mm. The present study investigated the cause of this failure through environmental and operational assessment, metallurgical evaluation, mechanical testing, material testing, stress analysis, and hydrogen embrittlement (HE) sensitivity testing. The results indicated that the failure was primarily attributable to hydrogen-induced cracking (HIC). The main factors contributing to this failure were identified as excessive material hardness and strength, which resulted in a high sensitivity to HE, even within the normal cathodic protection range. In addition, the mechanical damage that occurred during the construction process resulted in the destruction of the coating, causing stress concentration on the pipe body and further facilitating HIC.

Simulation and experimental study of buried natural gas pipeline leak detection based on sound source characteristics

Buried pipe-line leakage will affect the thermal characteristics of the soil environment, leading to a poor soil environment. In addition, leakage of natural gas possibly produces an explosion and subsequent fire, which has fatal harm. Sustainable detection of underground gas pipe-line leaks is a significant part of current research. In this study, a method for leak detection of buried natural gas polyethylene pipe-lines based on sound source characteristics is investigated. The simulation software was applied in analyzing the variation of leakage rate and sound source in buried pipes under different leakage conditions including mainly different leakage apertures and pipe pressures. Also, an experiment platform was built to verify the simulation results. These results can provide help for gas pipe-line leakage detection and safety protection.

Enhancing the integrity of a buried gas pipelines: Investigating ruptures, explosions, and strengthening solutions

The present paper presents findings from a case study of a buried gas pipeline that ruptured, causing a gas cloud explosion and subsequent fire. The study aimed to identify the incident's cause and improve the pipeline's strength under specific conditions. The study measured the pipe's actual wall thickness and conducted stress analysis using analytical and finite element methods to assess its integrity under corrosion. It evaluated if the 20-inch pipeline near road crossings could withstand external forces.In conclusion, the research underscores the importance of accurately assessing the structural integrity of buried pipelines, especially under conditions of corrosion. It highlights the utility of finite element analysis in providing a more precise understanding of stress distribution and can aid in designing pipelines that are better equipped to withstand various external pressures.The investigation illustrates the importance of increasing the strength of buried natural gas pipelines, in the crossing road area and, for this purpose, it was proposed (in terms of novelty associated with the study) a solution consisting in introduction of the pipeline in protective sleeves fitted with spacer rings.

Mechanical Properties of Buried Gas Pipeline under Traffic Loads

Dynamic loads generated by heavy vehicles are among the loads resisted by pipelines buried under road surfaces. Most recent analyses are based on static assumptions; however, in practice, vehicle loads change dynamically. In this study, the finite element model of the pipe–soil interaction of a buried pipeline was established using the ABAQUS 2020 finite element software, and dynamic loads were applied above the model soil to simulate the influence of vehicles above the highway on the buried X80 pipeline. The mechanical responses of different influencing factors to buried pipelines were analyzed. Increasing the pipe diameter and burial depth decreases the effect of vehicle rolling on the buried pipeline. The mass of the vehicle is the most significant factor that influences the stress and strain on the pipeline. The stress increase of the conventional vehicle load on the X80 gas pipeline does not exceed 10 MPa, and the maximum shape variable of the pipeline is within 13 mm. This study provides a data reference and a risk warning regarding the rolling of buried natural gas pipelines under a single vehicle load.

Laboratory investigation on the pipeline-soil interaction under different freezing conditions

Designing buried natural gas pipelines in frozen ground requires a comprehensive evaluation of the interaction between pipelines and soil, considering the effects of temperature and water supply conditions. One-dimensional freezing experiments are conducted to investigate soil frost heave characteristics and pipelines strain at three cooling modes, namely, constant cooling mode, linear cooling mode, and stepwise cooling mode. The impacts of cooling modes and water supply conditions on freezing rate, frost heave, and pipeline strain are analyzed. The results indicate that the largest soil frost heave occurs at an ambient temperature of −10 °C, irrespective of water supply presence. Both the linear and stepwise cooling modes enhance the flatness of the overlying soil, as opposed to the constant cooling mode. The stepwise cooling mode reduces freezing rate, yet leads to a higher tensile strain in the pipeline structure compared to the linear cooling mode. The relative incremental strain is the greatest when the freezing depth ranges from one to two times the diameter of pipelines. The test results could provide a reference for the design of buried natural gas pipelines in cold regions.

Study on the Pipe–soil Interaction under Instability of Slope Based on Flume Experiment

To study the landslide of buried gas pipeline caused by rainfall, based on the flume experiment the laboratory model of rainfall-induced pipe–soil interaction of slope instability was established. By monitoring the cross-section strain of the pipeline under the slope instability induced by rainfall infiltration, the effect of soil on the pipeline is analyzed and calculated. The results show that the pipeline is located at different failure surfaces of the slope, which is affected by slope instability to different degrees. In the slope toe of apertures, ultimate cross-section strain is the largest, calculation of soil force and maximum limit 1515.535 N/m, and that of slope top pipe is 216.169 N/m, attenuation trend from toe to the top. Resultant force directions are distributed in soil and the horizontal angle is 68°. The results can provide reference and technical reserve for the study of pipe-soil interaction of buried natural gas pipelines under the action of landslide and the further improvement of pipeline safety.

Experimental and Numerical Prediction Model for the Dangerous Radius of Natural Gas Leakage in Soil.

Prediction of the dangerous radius of natural gas plays an important role in reducing the hazards of a buried natural gas pipeline after leakage. The factors affecting the diffusion law of natural gas in soil after leakage are mainly divided into the pipe, soil, and environmental sides. Previous studies focused on the effects of leakage pressure, leakage aperture, and leakage direction on the pipe side and porosity and water content on the soil side. In this paper, experiments and numerical simulations are conducted for further investigating the effects on the diffusion of natural gas in soil of the soil type (porosity and granule diameter) and layered structure among the soil side factors and soil temperature as environmental side factors. The contour radius corresponding to 5% volume concentration (the lower limit of natural gas explosion in soil) is defined as the natural gas dangerous radius for analysis. Based on comprehensive analysis of the effects of the factors, a prediction model is proposed for the dangerous radius of natural gas in soil with leakage pressure, leakage aperture, porosity, and granule diameter as the dominant influencing factors, which is of great significance for locating the source of the leakage.

Real scenario analysis of buried natural gas pipeline leakage based on soil-atmosphere coupling

Buried pipeline is the most common mode of natural gas transportation. The analysis of methane diffusion characteristics in leakage accident is of great significance for accident detection and secondary explosion accident prevention. The existing numerical simulation and experimental studies focused on the diffusion of methane in the soil from the leakage of buried natural gas pipeline, and the coupling process of methane passing through the soil and entering the atmosphere was rarely mentioned. However, the surface atmosphere is the main area of human activities, which increases the possibility of fire and other risk factors. In this paper, the coupling process of methane leakage passing through soil and entering the atmosphere was studied by numerical simulation, and the effects of various factors on the methane concentration in the first danger zone (FDZ) and the second danger zone (SDZ) were analyzed. Based on the least square method and multiple regression theory, combined with MATLAB mathematical calculation software, a methane concentration prediction model on the high-risk side of the FDZ was established. The results showed that after methane entered the atmosphere, the diffusion velocity increased significantly. The downstream building surface of the FDZ was the high-risk side of methane distribution, and the upstream building surface of the SDZ was the high-risk side. The average calculation error of the methane concentration prediction equation on the high-risk side of the FDZ was 9.97%, which can effectively evaluate the methane concentration under any leakage working condition. When the buildings floors were different, the high building surface between high building and low building was the high-risk side of methane distribution. This study provides guidance for the design of buried natural gas pipelines in residential buildings, and supplies basis for improving detector installation and gas leakage maintenance specifications.

CFD analysis and calculation models establishment of leakage of natural gas pipeline considering real buried environment

Different from the above ground pipeline, the soil characteristics and ground conditions have a great impact on the risk of leakage accident for buried natural gas pipeline. In this paper, the effects of ground conditions and soil characteristics on methane leakage and diffusion were studied by using numerical simulation. The two processes of methane leakage and diffusion, the methane leakage rate and the methane diffusion Early Warning Boundary (EWB) were investigated. Finally, based on the least square method and multiple regression theory, the calculation models of methane leakage rate and EWB were established. The results showed that: Compared with Unhardened Surface Ground (UHSG) condition, Hardened Surface Ground (HSG) increased the distribution of pressure, velocity and methane concentration in soil. The viscous resistance coefficient and inertial resistance coefficient of soil had a great influence on the methane leakage rate, while the ground conditions did not. Both ground conditions and soil characteristics had a certain impact on the EWB of methane diffusion. The average error of methane leakage rate direct calculation model was 4.48%, and the average error of EWB calculation model under HSG and UHSG condition was 3.59% and 7.77% respectively. The methane leakage rate and the EWB calculation models suggest the soil characteristics as independent variables and can provide the rapid calculation of leakage rate and EWB under any soil characteristics without the help of computer iterative solution. The methane leakage rate direct calculation model makes up for the vacancy of calculation method of leakage rate of buried pipeline under different soil characteristics.

Evaluation of Land Subsidence Hazard on Steel Natural Gas Pipelines in California

Buried infrastructure like natural gas pipelines may be impacted by soil movement due to landslides, flood scours, fault ruptures, liquefaction, and subsidence. Subsidence induced settlement is an identified hazard for natural gas pipelines in Central California and has two components: vertical and horizontal. In the past, investigations have revealed that the horizontal displacement is more destructive than the vertical settlement since it may cause pipe ruptures. With the increase in droughts and groundwater pumping due to climate change, more land subsidence has been attributed to these factors. This study discusses the maximum impact of land subsidence on natural gas pipelines and provides design recommendations. The maximum subsidence induced settlement recorded in Central California has been applied to a buried pipeline using non-linear finite element analysis. To capture the most accurate results, 2-miles of steel pipe located in the subsidence zone is included in the finite element model and a simplified soil-pipe interaction modeling technique is used to determine the soil stiffness around the buried pipeline. Based on the results, buckling forces due to the horizontal movement of the soil on the underground pipe are more critical than the bending stress caused by the vertical soil settlement. Although the risk of failure ascribed to buckling is high, the buried steel natural gas pipeline is resilient enough to accommodate the internal forces due to subsidence.

Study on leak localization for buried gas pipelines based on an acoustic method

As an important part of a city’s “lifeline,” an urban underground natural gas pipeline network is an integral part of the infrastructure, facilitating energy transmission. If the source of a leak is not located accurately, explosive incidents may occur owing to the highly flammable nature of natural gas, causing casualties and property damage. Thus, this study presents a new method of leak identification in buried natural gas pipelines. The proposed method achieves this goal through leak noise in the soil, and this is verified through experiments conducted as part of this research. The surrounding soil of the buried pipeline was considered as the propagation medium of the noise associated with leaks. For four microphones, placed in detection holes, were used to capture leak noise within the soil. Multi-layer wavelet packet decomposition was performed on the collected time domain signal of leak noise and was reconstructed on the characteristic frequency band of 0–200 Hz. Leak localization was completed by estimating the time difference of arrival between each pair of microphones on the buried natural gas pipeline. In the experimental scenario, the leak location error of the buried gas pipeline was 8 %–12 %. Therefore, the proposed method can successfully be applied to realize leak localization for buried natural gas pipelines.

Analysis and Prediction of Methane Invasion Distance Considering Real Ground Boundary.

Natural gas has become a global energy consumption hotspot because of its large reserves and clean combustion. Due to soil corrosion, construction damage, and natural disasters, leakage accidents of buried natural gas pipelines often occur. In this paper, the steady simulation method was used to study the methane invasion limit state (MILS) and the methane invasion limit distance (MILD) under the conditions of hardened surface ground (HSG), unhardened surface ground (UHSG), and semihardened surface ground (SHSG), and the transient simulation of methane invasion distance (MID) under the condition of HSG with the largest MILD was carried out. The results showed that regardless of ground conditions, with the increase of leakage time, the diffusion range of methane in soil will not increase all the time, and there was a limit state (MILS). The distribution range and concentration of methane in the soil under HSG condition were the largest, followed by the SHSG condition, and the UHSG condition was the smallest. When the ground condition changed from UHSG to HSG, the MILD increased from 3.41 to 9.32 m. The HSG condition will increase the MILD and the range of dangerous areas. The buried depth of the pipeline had a serious impact on the MILD. When the buried depth of the pipeline increased from 0.3 to 1.5 m, the MILD increased from 1.75 to 3.49 m under the condition of UHSG and exceeded 10 m under the condition of HSG. The average error of the MID prediction model was 2.37% under the condition of HSG, which can accurately predict the leakage of buried pipeline. The MID provides a reference for the layout of urban underground gas leakage monitoring points. The MILD can provide guidance for the safe distance between natural gas pipeline and structures in the design code of natural gas pipeline.

Numerical and experimental study on leakage detection for buried gas pipelines based on distributed optical fiber acoustic wave

Buried natural gas pipeline leakage can cause severe environmental pollution and human casualties. The currently used fiber optic temperature sensors cannot detect pipeline leakage in all directions, and there are monitoring blind spots. Besides, there is a lack of field tests and verification of the acoustic characteristics caused by leakage. In this work, a sound wave attenuation model considering gas flow in viscous porous media is established based on the Φ-optical time-domain reflectometry (Φ-OTDR) principle, combined with fluid dynamics and acoustic wave propagation mode in porous media (soil). The attenuation characteristics of acoustic wave propagation in soil are studied by varying the leakage hole size and leakage pressure. It is found that the acoustic source of buried natural gas pipeline leakage belongs to broadband noise. The acoustic signals detected by optical fiber acoustic sensors are vary with different leakage holes and leakage pressures. In particular, the leaked acoustic wave’s energy is prominent in the low-frequency band of 15 kHz, and the sound pressure level (SPL) oscillates and attenuates with the increase in frequency. With the increase in the transmission distance, the amplitude of the pipeline leakage signal gradually attenuates. Eventually, the acoustic wave decays to the point where the fiber-optic acoustic sensor cannot detect it. The optimum frequency of acoustic wave propagation in soil is obtained through experimental research. The propagation characteristics of acoustic waves in the soil are not a fixed value. The simulation results are in good agreement with the experimental results, indicating that the SPL in the low-frequency band is significant for pipeline leakage monitoring. The above research results can provide valuable guidance for field optical fiber installation.

Safety assessment of buried natural gas pipelines with corrosion defects under the ground settlement

Local corrosion defects of the pipeline and the ground settlement in the geotechnical engineering problem area pose a huge threat to the integrity and safety of the buried steel pipeline. The existing researches mainly focus on the design and construction of new pipelines or the safety evaluation of completed pipelines. However, the impact of pipe segments with anomalies (e.g., corrosion defects) on pipeline integrity has not been clearly and fully considered. The novelty of this study lies in the development of a nonlinear pipe-soil coupling mechanical model considering the coupling effect of the typical ground settlement and local corrosion defects of the buried pipelines. Numerical results show that the developed model is feasible to evaluate the integrity and safety of corroded pipelines under the ground settlement.

The effects of site preparation equal those of seeding at a dryland restoration site: 6 years of plant community development

Dryland ecosystems generally require active restoration to recover from severe land degradation caused by resource and energy extraction operations. While seeding remains one of the most used forms of active restoration, land managers in dryland systems have generally had difficulty re‐establishing desirable plant communities, due in part to alterations in supporting ecosystem processes and the episodic nature of resource availability. In this study, we examined the impacts of site preparation, seeding, and livestock grazing on developing plant communities after the construction of a buried natural gas pipeline corridor in the southwestern United States. We monitored plant species cover and composition beginning with the second season of growth through the sixth. Analysis of each individual year show that conclusions from the initial year of data collection did not well represent the findings in the following years. The site preparation and topsoil treatment had an ongoing positive effect on richness and cover compared to the nearby baseline conditions, while seeding only further increased cover and richness in the first year of monitoring (second season of growth). However, without seeding, the plant communities were driven by ruderal, annual species, whereas the seeded plant communities were driven by desirable seeded perennial grasses and forbs. Grazing and trampling effects were not significant overall, and the effects of livestock may have been confounded with effects of small mammals due to the exclosure configuration. We suggest that the site preparation, topsoil treatment, and configuration linearity of the disturbance corridor allowed for high levels of natural recruitment.

Leakage diffusion characteristics and harmful boundary analysis of buried natural gas pipeline under multiple working conditions

Natural gas transportation heavily relies on buried natural gas network. Unfortunately, natural gas pipeline leakage can cause environmental pollution and resource loss, and even leads to serious risks on human's life and properties due to its flammable and explosive properties. In this study, numerical stimulation methodology was applied to investigate the leakage and diffusion characteristics of buried natural gas pipeline, and the first dangerous time (FDT), farthest dangerous range (FDR) and ground dangerous range (GDR) were utilized to track harmful boundary for gas leakage and diffusion. By exploring thirteen different working conditions and evaluating the impacts of six parameters on harmful boundary, prediction models for harmful boundary was successfully established. The results demonstrated that the effect of soil on the pressure and velocity of the leaking hole occurred within 30 s right after pipeline leaked. Sonic flow was absent at the leaking hole, while reversal flow was present at the pipeline downstream of the leaking hole. Soil types play a critical role on harmful boundary: FDT increased by more than five times, FDR decreased by more than two times and FDR remained zero when soil type switched from sand to clay. Larger leakage diameters and higher pipeline pressures can raise FDR and GDR, but reduce FDT. In this prediction models, the average errors for FDT, FDR and GDR were 8.81%, 1.51%and 3.82% respectively. This is the first study to assess harmful boundary by utilizing prediction models. This work will provide reasonable time estimation for emergency evacuation, but also suggest the location setting of underground gas leakage monitoring points.

Study on acoustic source characteristics of distributed optical fiber acoustic wave monitoring buried natural gas pipeline leakage

In order to study the leakage of buried natural gas pipeline caused serious environmental pollution and human casualties, the acoustic propagation characteristics of buried natural gas pipeline leakage monitored by distributed optical fiber were studied. At present, the research on the leakage of buried pipeline mainly focuses on the propagation of sound waves along the pipe wall, while the study on the propagation of sound waves in the soil is still lacking. The acoustic attenuation of acoustic wave propagation in soil by the size of leakage hole and leakage pressure is studied, and the evolution process of acoustic wave in soil is revealed. The conclusion is that the acoustic source of buried natural gas pipeline leakage belongs to broadband noise, and the acoustic energy of leakage is prominent in the low frequency band of 15kHz. The lower frequency, the higher sound pressure level. The oscillation of the sound pressure level attenuates with the increase of frequency. Fiber optic monitoring of buried natural gas pipeline leakage early warning provides theoretical support for the conclusion. The sound pressure level in low frequency band is of great significance for buried pipeline leakage monitoring.