Buried Gas Research Articles

Effect of excavation blasting vibration on adjacent buried gas pipeline in a metro tunnel

To ensure the safety of gas pipeline during tunnel blasting excavation, it is crucial to investigate the dynamic response of gas pipeline to blast vibration under tunnel excavation. In this paper, the blasting excavation of Beijing metro line 16 was selected as a case, and the blasting vibrations in the field were monitored. Based on the field monitoring data, a mathematical model was established and proposed to describe the attenuation of peak particle velocity (PPV) of ground surface soils with respect to the depth of tunnel blasting. Next, a 3D numerical model was established to analyze the response characteristics of burial gas pipeline subjected to blasting vibration and its reliability was verified using the field monitoring data. The effects of metro tunnel blasting vibration on gas pipeline under different tunnel blasting conditions were further calculated, and the dynamic response characteristics of soil, pipe and pipe surrounding soil were discussed. At last, to better and more conveniently assess and predict the influence of blasting vibration, a PPV prediction model of gas pipeline under metro tunnel excavation blasting for this project was proposed.

Intergranular stress corrosion cracking of steel gas pipelines in weak alkaline soil electrolytes

Abstract The paper presents an overview of the main types of stress corrosion cracking (SCC) of pipeline steels under operating conditions of high-pressure buried gas pipelines. Up to the present time, there have been cases of transgranular cracking in gas pipelines in near-neutral pH soil electrolytes in Russian territory. The present work studies fragments of pipes containing cracks as well as soil samples at the excavation sites of gas pipelines running through the territory of the Astrakhan region. It was found that the cracks formed as a result of SCC of pipe metal and are of intergranular character of propagation. It is also established that the chemical composition of the soil along the gas pipeline differs from the previously studied compositions of corrosive environments that encourage the development of intergranular SCC of pipeline steels.

Application of the finite element method for evaluating the stress distribution in buried damaged polyethylene gas pipes

During the loading process, buried gas pipes can experience severe stresses due to soil- structure interaction, the presence of traffic load, the soil’s column weight, daily and/or seasonal temperature changes and uniform internal pressure. In this research, the finite element method is employed to evaluate the behavior of buried Medium Density Polyethylene (MDPE) pipes which have been subjected to damage at the pipe crown. The modeled pipe damage ranges from a very small circular hole to a large circular hole and elliptic holes with various minor to major diameter ratios, a/b, to simulate circular to crack-shaped defects. The computer simulation and stress analyses were performed using the ANSYS software finite element package. The stress distribution around the defect was determined under the aforementioned mechanical and thermal loading conditions. Then, the maximum values of Von Mises stresses in the damaged buried PE pipes, which were evaluated by finite element solution, were compared with their corresponding reduced strength for safe operation with a life expectancy of fifty years. Based on the results, the maximum Von Mises stress values in the defective buried polyethylene gas pipeline are significantly above the pipe strength limit at 35 °C. The previously mentioned stress values increase with the following factors: temperature increase, increase in circular hole diameter and decrease in elliptic hole diameter ratio (a/b). The maximum stress in the damaged PE pipe is due to the simultaneous loading effects of soil column weight, internal pressure, vehicle wheel load and pipe temperature increase. Additionally, the novel finite element models and stress plots for the buried damaged pipe and the pipe material allowable strength will be used to investigate the correct repair method for the damaged gas pipeline and to choose the best patch arrangement which will assure a safe repair.

Structural performance monitoring of buried pipelines using distributed fiber optic sensors

In this study, a method involving the use of distributed fiber optic temperature and strain sensors is presented to quantitatively assess the structural performance for buried pipelines by considering both longitudinal bending load and axial thermal load. The monitoring scheme of distributed strain and temperature sensors is proposed based on the pipeline structural analysis, and the assessment approach is formulated using the distributed monitoring data. The time-spatial variation in the bending strain and temperature of the burial pipelines are monitored using distributed fiber optic sensors. The structural performance of the pipeline is then assessed with the monitored data in conjunction with the pipe parameters and internal pressure. A field application was performed on a buried gas pipeline to investigate the availability of the proposed method and the results from the site application demonstrate that the proposed method effectively assesses the structural performance of the burial pipelines with the distributed strain and temperature data.

Dynamic response of buried gas pipeline under excavator loading: Experimental/numerical study

Abstract Recently, the ongoing mining risk and damage quantitative assessment methods for buried gas pipelines are mostly implemented on the static test data. Naturally, dynamic experimental results may help to enhance the fidelity of the evaluation strategy. The excavator-pipeline-soil test system in this paper is designed to detect the impact digging force, which is derived from the liquid pressure oscillation of hydro-cylinders and the inertial force of mining equipment. The dynamic loading coefficient and impact force under various mining modes are evaluated by experimental and multibody dynamics software, and the results are subsequently verified by comparison with a series of LS-DYNA modeling responses. It should be stressed that the obvious growth of dynamic digging force is as important as the critical resistant analysis to the buried gas pipeline. Thus, one can establish more confident judgments with regard to ground mining protection and damage assessment.

Location estimation of coating defects and mitigation of induced AC voltages along buried gas pipeline

In this study, determining the location of coating defects and severities is evaluated using measurements along the Jordanian buried gas pipeline. Induced alternating current (AC) voltages and current densities along the pipeline are investigated using analytical and practical data under normal operation of the overhead transmission line. Since the induced AC voltages depend on the load currents, it is worthy to determine the actual load current during the lifetime of the pipeline. Accordingly, the forecasting of pipeline-induced AC voltages is investigated using the least square method. The investigation is carried out in order to expect the future effects on the gas pipeline. The mitigation of induced AC voltage based on inserting polarisation cells (PCs) along the pipeline is evaluated. The results show that an agreement between the measured and calculated induced AC voltages is achieved with and without PCs. Based on the forecasting of induced AC voltages and current density along the pipeline, determining the number of PCs and allocations is suggested for the future years. This study increases the lifetime of the pipeline as well as decreases the maintenance cost.

Dynamic response and limit analysis of buried gas pipeline under ground consolidation load

Currently, the significant dynamic plastic deformation of a buried gas pipeline frequently occurs due to the ground construction process that acts as a direct threat to the operation security of a buried gas transmission system. In this study, the pipe-soil interaction structure under a dynamic consolidation load, such as high energy dynamic compaction load, was considered as a non-conservative system in the work. Two parts of structure dissipation energy were introduced into the Lagrange function, and the elastoplastic dynamic equations of a non-conservative system based on the Hamilton Variation Principle (HVP) and the finite element (FE) theory were established. Implicit solution schemes were proposed based on the dynamic equations, and a steel weight-soil-buried pipeline finite element model was developed by performing a dynamic analysis in the LS-DYNA software with an explicit format. Vivid impact responses of an underground pipeline associated with the buried depth, wall thickness, and tamping energy were simulated. The plastic failure criterion of high toughness pipeline steel indicates that treated pipeline buried depth, wall thickness, and tamping energy corresponded to the generalized loads, and limit state of a specific case. So, they were recognized via the relationship of generalized load in relation to the total strain of pipelines. This was performed by using tangent intersection criteria, two elastic slope criteria, and zero curvature criteria. Additionally, the von Mises yield stress criterion was also applied as a traditional approach. The study potentially offers significant references on the quantitative pre-evaluation of a buried gas pipeline that poses as a threat due to the occurrence of third-party damage such as extreme strong ground interference.

Failure probability analysis of the urban buried gas pipelines using Bayesian networks

Abstract Failures of urban buried gas pipelines have caused significant fire and explosion accidents with tremendous losses. This work presents an advanced two-step approach to analyze failure probabilities of the urban buried gas pipeline. First, a logical failure model is developed with the operational, material and environmental parameters contributing to the failure (Fault Tree Analysis). Second, the logical model is transformed into a network model (Bayesian Network). This novel approach can better reveal the relationships among failure causal factors and can also update the failure probabilities as operational and environmental conditions evolve. The Bayesian network failure model is subsequently applied to a case study. The results indicate that this approach is feasible and reasonable which can assist in identifying safety critical factors. Improving reliability of these safety critical factors can be of great help in enhancing the safety of urban buried gas pipelines.

A method for identifying support conditions of buried subsea gas pipelines based on forced vibration signal analysis

Subsea pipeline is crucial for oil and gas transportation. It is advantageous to be able to identify the free-spanning segments of a long subsea pipeline. The existing technologies for detecting the support condition of buried subsea pipelines are constantly affected by complex external environment since they are outer pipeline detecting methods. An inner pipeline method for detecting the support conditions of buried gas subsea pipelines based on forced vibration signal analysis is proposed in this study. Two evaluation indicators, frequency response function and natural frequency change ratio, are used to identify the free-spanning segments. A free span–detecting device and a test rig are built to verify the applicability of the method by forced vibration tests. Gray contour plots of frequency response functions and natural frequency change ratio bar charts are generated to analyze the experimental results. The experimental results show that two evaluation indicators are sensitive to the support condition. The appearance of the free span and its length can be identified by the gray contour plots of frequency response functions and natural frequency change ratio bar chart.

Stress analysis on large-diameter buried gas pipelines under catastrophic landslides

This paper presents a method for analysis of stress and strain of gas pipelines under the effect of horizontal catastrophic landslides. A soil spring model was used to analyze the nonlinear characteristics concerning the mutual effects between the pipeline and the soil. The Ramberg–Osgood model was used to describe the constitutive relations of pipeline materials. This paper also constructed a finite element analysis model using ABAQUS finite element software and studied the distribution of the maximum stress and strain of the pipeline and the axial stress and strain along the pipeline by referencing some typical accident cases. The calculation results indicated that the maximum stress and strain increased gradually with the displacement of landslide. The limit values of pipeline axial stress strain appeared at the junction of the landslide area and non-landslide area. The stress failure criterion was relatively more conservative than the strain failure criterion. The research results of this paper may be used as a technical reference concerning the design and safety management of large-diameter gas pipelines under the effects of catastrophic landslides.

Dynamic response and limit analysis of buried high-pressure gas pipeline under blasting load based on the Hamilton principle

For non-conservative systems consisting of elastic-plastic material, dissipative damping of a system in a dynamic environment involves two parts: (1) the dissipative energy related to the velocity of the mass point and (2) the dissipative energy associated with the strain rate. In this paper, the dynamic response of buried high-pressure gas pipeline under blasting load is studied, where, dissipation of energy is explicitly considered. The dissipative work was introduced into the Lagrange function. According to the Hamilton principle and finite element theory, a non-conservative explosion model composed of elastic and plastic materials was established to identify the dynamic response and the propagation characteristics of a detonation wave in the earth medium, where the explosion cavity with a triangle pressure time history on internal wall was used to describe the explosive stress from blasting buried gas pipeline. In the scheme of modeling, 15 cases of different explosive payloads, different distances from the explosion center and different wall thicknesses of the pipe were regarded as the generalized load were carried out. Then the specific dynamic responses of pipeline under blasting load were shown in the post processing, as well as the relationship between peak particle vibration velocity and explosion distance and payload. Using three types of limit analysis methods, the critical explosive loading, critical blasting center distance and critical wall thickness of a buried high-pressure gas pipeline under blasting loading were determined. The computational method and results in this paper could be referenced for security operation of a buried pipeline and blasting construction scheme.

裂缝型潜山油气藏地质导向建模方法与应用

裂缝型潜山油气藏地质导向建模方法与应用

An acoustic emission based multi-level approach to buried gas pipeline leakage localization

Precisely localizing a leakage source in a buried pipeline is of great importance for decision making on emergence response of gas leakage accident. As an effective leakage localization method, acoustic emission (AE) has received much attention in recent years. However, the application of AE for leakage localization in long-range or buried pipeline is greatly limited due to the conflict between the accuracy of testing results and the efficiency of testing works. To further improve the applicability of AE technique for long-range pipeline, a novel leakage localization approach is proposed based on the multi-level framework. The approach is consisted of two steps: regional localization and precise localization. The regional localization is to determine the region of the leakage source based on the signal attenuation characteristics, and then the precise localization results are obtained by the cross-correlation analysis of wavelet packet decomposition (WPD) components based on the region of leakage source. Experiments were conducted on a buried pipeline with a continuous leakage source and a linear array of two sensors was positioned in two sides of the leakage source. To study the feasibility of the proposed approach, a series of in-situ tests were carried out by changing the source-sensor distance. The results indicate that the accuracy of regional localization is 100% and the maximum error percentage of precise localization is 5.3% under varying sensors distances from 10 to 33 m. The proposed leakage localization method provides a promising way to locate the leakage source in long-range pipeline by using AE technique because it can achieve a better balance between accuracy and efficiency.

차량을 이용한 원격전위 측정방법 개발에 관한 연구

도시가스사업법령에 따라 지하에 매설된 도시가스 배관에는 전기부식 방지조치를 하도록 하고 있으며, 테스트 박스에서 배관의 방식전위를 1년마다 측정하도록 하고 있다. 그런데, 도심에 설치된 테스트 박스(T/B)의 경우 대부분 차량이 통행하는 도로위에 설치되어 있어 전위를 측정할 때 어려움이 있다. 즉, 전위를 측정하기 위해서는 차량을 통제하거나, 교통량이 적은 심야에 실시해야 하는 등 어려움이 있다. 본 연구에서는 이러한 방식전위 측정의 문제점을 해결하기 위하여 차량을 타고 이동하면서 테스트박스의 전위를 측정하는 방법을 연구하였다. 도로위에 설치된 테스트박스 하부에 기준전극과 데이터로거를 설치하고, 차량이 이동하면서 데이터로거로부터 방식 전위를 수신하는 방법으로 시험 연구를 진행하였다. 테스트 박스가 도로위에 설치되어 있어 전파를 송수신하는 데 어려움이 있어 안테나 방식을 변경해 가면서 가장 효과적인 방법을 채택하기로 하였다. 개발한 방법을 도시가스사의 실제 테스트박스에 적용한 결과 이 방법은 기존의 측정방법보다 20배 이상 시간을 절약할 수 있었다. According to the urban gas business law, electrical corrosion prevention measures shall be installed to the buried gas pipelines and the pipe-to-soil potentials should be measured at the test box at least once a year. Most of the test boxes installed in urban area are usually located on the road where the vehicle travels, therefore, it is difficult to measure the CP potentials at the test boxes. That is, we need traffic control when carrying out the measurement of the CP potentials on daytime when the traffic is heavy, or we have to measure the potentials in the late night when the traffic is light. To solve these difficulties, we have studied remotely CP potential measuring method by using the patrol car. We have installed solid reference electrodes and data loggers under the test boxes on the site and received the CP potentials from the data loggers when the vehicle moves. It was difficult to send and receive the data because the data logger was located under the ground. We have applied 3 different method including 2 antenna systems to achieve best effective way in receiving the data. We have found the remote CP measuring method by using a car can save more 20 times of measuring time than conventional measuring methods.

외면부식직접평가 장비 개발 및 실증 시험에 관한 연구

매설된 강관의 피복이 손상되는 경우에는 부식이 발생할 수 있고, 부식으로 인한 핀홀이 발생하여 가스누출사고가 발생할 수도 있다. 미국과 영국 등 국외에서는 이를 방지하기 위하여 DCVG 또는 ACVG 등을 이용하여 매설된 배관의 피복손상을 탐측하고 이상부위에 대하여 직접 굴착을 통해 배관외면부식여부 등을 확인하고 필요시에는 보수를 하고 있다. 이를 외면부식 직접평가법(ECDA)이라 하며, NACE 기준 등에서 ECDA에 대한 기준을 규정하고 있다. 국내의 경우에는 2014년 중압배관의 정밀안전진단 제도를 도입하면서 KGS 코드에 외면 부식직접평가에 대한 내용을 포함하여 규정하고 있다. 본 연구에서는 매설배관의 외면부식을 탐측할 수 있는 장비를 개발하고, 개발된 장비의 실증시험을 위한 배관시험장을 구축하였다. 또한, 개발된 장비의 성능을 입증하기 위하여 배관 시험장에서 현장 실증시험을 실시하였다. 현장 실증 시험은 개발된 장비와 국내에 도입되어 사용중인 국외 장비와의 피복결함 탐측 성능 비교시험으로 실시하였다. 개발한 장비를 이용하여 매설배관 탐측 시험을 실시한 결과, 개발한 장비는 미국이나 영국에서 개발되어 국내에 보급되어 사용중인 장비에 비해 훨씬 사용이 편리하고 성능이 우수함을 확인할 수 있었다. When the coatings of buried steel pipelines are damaged, corrosion could be occurred on the surface of the damaged areas. Moreover the pinhole occurred by corrosion of pipelines may cause accidents due to gas leakage. To prevent these accidents, foreign countries including UK and USA have carried out coating defect detection on the buried gas pipelines by using a DCVG or a ACVG and have conducted direct assessment of pipelines through digging the ground, and if necessary, have repaired the pipelines. That is called ECDA i.e External Corrosion Direct Assessment which is regulated by NACE standards(SP 0502) and etc. In Korea, the ECDA provisions were included in KGS FS551 in 2014 when the regulations of Safety Validation in Detail for the medium-pressure piping were introduced. We have developed the equipment which can be used to detect external corrosion of the buried gas pipelines. We have also constructed pipeline test bed for empirical test of the developed equipment. In addition, we have carried out the verification experiments of the developed equipment on the test bed to demonstrate the performance of the equipment. The experiments were conducted by comparison tests of the developed equipment and other equipments which have been introduced and used in Korea. As the result, we have found the developed equipment is easier to use and has far superior performance compared to other equipment being used in Korea.

Impact of geometric pattern corrosion on limit failure pressure of buried gas pipelines

Gas pipelines are types of structures that are highly susceptible to corrosion. Sometimes, the pipes are subjected to a thinning of the wall thickness at the inside or outside wall due to erosion/corrosion. Therefore, it is important to evaluate the strength of the pipes undergoing corrosion to maintain the integrity of the piping systems. The main purpose of this study is to understand failure aspects caused by degradation of metal due to corrosion through. The ASME standard offers a relationship for the yielding pressure of the corroded pipes which was compared with the finite element results. The results demonstrate to obtain accurate results, the ASME relationship is unreliable. Moreover, pitting corrosion must be considered critical more than of other types.

Seismic fragility analysis of a buried gas pipeline based on nonlinear time-history analysis

Seismic fragility analysis was performed for API X65, a type of buried gas pipeline that is widely used in Korea. For this purpose, nonlinear time-history analyses were carried out using 15 different analytical models of the pipeline, which represent variations of modeling parameters. The nonlinear Winkler approach was adopted to simulate the soil-pipeline interaction during an earthquake loading. A set of 12 recorded ground motions were selected for the time-history analyses and scaled to represent a range of earthquake intensity levels. Then, fragility functions were developed with respect to the damage states, which are defined in terms of the maximum axial strain of the pipeline. The parameters under consideration for subsequent seismic fragility analyses are the soil conditions, boundary conditions, burial depth, and type of pipeline. Comparative analyses revealed that the first three parameters, most notably the soil conditions, influence the fragility curves, but the last parameter negligibly affects the fragility curves. It is concluded in short that this study is promising to give a useful insight for a rapid seismic performance evaluation of a buried gas pipeline based on nonlinear and fragility analyses.

Welding residual stress measurement of an urban buried gas pipeline by X-ray diffraction method

Welding residual stress measurement of an urban buried gas pipeline by X-ray diffraction method

Gas leakage consequence modeling for buried gas pipelines

One of conservation transfer methods for such widely-used gases as natural gas and hydrogen is buried pipelines. Safety of these pipelines is of great importance due to potential risks posed by inefficiencies of the pipelines. Therefore, an accurate understanding of release and movement characteristics of the leaked gas, i.e. distribution and speed within soil, the release to the ground surface, the movement of hydrogen gas through the ground, gas underground diffusion, gas dispersion in atmosphere, and following consequences, are very important in order to determine underground dispersion risks. In the present study, consequences of gas leakage within soil were evaluated in two sub-models, i.e. near-field and far-field, and a comprehensive model was proposed in order to ensure safety of buried gas supply pipelines. Near-field model which is related to soil and ground and its output is the gas released at different points and times from ground surface and it was adopted as input of far-field sub-model which is dispersion model in atmosphere or an open space under the surface. Validation of near-field sub-model was performed by the experimental data obtained by Okamoto et al. (2014) on full-scale hydrogen leakage and then, possible scenarios for far-field sub-model were determined.

Numerical Investigation of Factors Influencing Oil and Gas Lifelines Behavior due to Normal Faulting Geo-Hazard

In this study, some factors influencing the response of buried oil and gas lifelines subjected to normal faulting are investigated. Due to such phenomenon, the stress, strain and displacement are induced in pipeline. Finite element code of Abaqus has been employed to model pipe and its surrounding soil considering material nonlinearities, soil-pipe interaction and foot wall and hanging wall interface. The numerical model has been calibrated through some small scale geotechnical centrifuge model tests and based on such calibrated model, some factors influencing the response of buried pipeline has been investigated.