Failure Of Buried Pipelines Research Articles

Failure analysis of buried pipelines under the action of oblique slip faults

Oil and gas are often transported by long-distance buried pipelines. When the pipeline is subjected to faulting, the pipeline is highly susceptible to failure under axial loading. However, there is a lack of understanding of the effect of inertial loads on pipeline failure in the analysis of influencing factors under the action of faults. Most of the current studies mainly use static or quasi-static methods to analyze the performance of buried pipelines, often ignoring inertial loads, which may also have an impact on pipeline failure. Therefore, this paper proposes a three-dimensional numerical model considering the dynamic response, and adopts ABAQUS explicit dynamics module to analyze the failure of pipelines under the action of sudden oblique slip faults. Firstly, the deformation features and strain development of the pipeline under the action of oblique slip faults were obtained using response analyses, and three key parameters indicating pipeline failure (local buckling, ovalization and the range of failure) were discussed. Then, the influence of fault velocity, internal pipeline pressure and pipeline wall thickness on pipeline failure were discussed. The results show that with the increase of the failure velocity, the higher the inertia, the smaller the strain and ovalization of the pipeline, the local buckling and ovalization failure are reduced, and the failure fault displacement of the pipeline will increase while the effect on the failure range of the pipeline is small. Therefore, designers and pipeline operators should consider the effects of inertia when analyzing the failure of buried pipelines under fault action.

Source location and anomaly detection for damage identification of buried pipelines using kurtosis-based transfer function

The failure of buried pipelines can lead to serious consequences such as explosions, environmental pollution, settlement, as well as economic loss. To prevent these outcomes, it is crucial to identify the causes of failure and monitor their signs. One of the main causes of failure is unexpected third-party interference (TPI), which is particularly challenging to detect. Regarding to this issue, this study proposes a new algorithm for monitoring impact damage, which can be used for prompt response and damage prevention. The algorithm is integrated into the system using two approaches. The first approach focuses on detecting the location of the damage (referred to as source location). A kurtosis-based transfer function was newly proposed to selecting the optimal frequency band for time-difference-of-arrival based source location, resulting in accurate pinpointing of damage, even in a noisy environment. The second approach is used to determine whether impact damage has actually occurred by observing newly suggested features in both the time and frequency domains (referred to as anomaly detection). These features evaluate the presence of damage and the similarity between signals. As a result, it was evaluated that the field applicability was higher than that of conventional methods, and the superiority of the proposed method was also verified through field experiments. The method proposed in this study is expected to enable immediate response when the integrity of the buried pipelines is on the line of failure due to TPI.

A critical review on performance of buried pipeline subjected to pipe bursting and earthquake induced permanent ground deformation

The primary means of transportation for various substances including water, oil and natural gas are the nation’s pipelines. From the geotechnical perspective, one of the prime reasons for buried pipeline failure is the impact of ground deformation either resulting from the earthquake (viz. landslide, lateral spreading, fault movement), or from nearby pipe bursting operation. Failure of a pipeline can lead to an explosion, environmental contamination, fire, financial loss, and risk to living beings. Hence, it is crucial to design the buried pipeline considering the impact of potential earth movement. In this regard, the current review article highlighted the impact of seismic landslide and other possible patterns of ground deformation on buried pipeline along with the effect of pipe bursting induced ground movement on surrounding pipeline particularly focusing on analytical works. In addition, a statistical sensitivity analysis is also performed to identify the most influencing pipe-soil input design parameters.

Modal Analysis and Flow through Sectionalized Pipeline Gate Valve Using FEA and CFD Technique

Sectionalized gate valves can reduce the volume of product released in the event of a buried pipeline failure or rupture. The risk of pipeline failure is a constant and common occurrence, and many factors can lead to pipeline incidents. In this paper, the free undamped vibration of the pipeline, sectionalized gate valve structure, and the dynamics of the fluid passing through the system are investigated. First and foremost, a modal analysis based on finite element analysis (FEA) is introduced as a fundamental linear dynamics analysis to provide insight into how a pipeline sectionalized gate valve structure may respond to different types of dynamic loading. Secondly, an implicit numerical analysis using computational fluid dynamics (CFD) is employed to describe physical quantities such as the flow velocity profiles at different stream positions and pressure fields at different points in a control volume. Through modal analysis, the effective mass factor shows the mass involved in each mode and helps identify modes with high potential to cause damage and prioritize efforts to address them. The CFD suggests that the sectionalized design of the gate valve leads to a strong vorticity of the fluid in the transversal direction of the flow and a decrease in efficiency due to pressure drop.

Overview of Stage 1b Stress Corrosion Crack Initiation and Growth of Pipeline Steels

Stress corrosion cracking (SCC) can cause catastrophic failure of buried pipelines for oil and gas transmission. The life cycle of pipeline steels experiencing SCC consists of five stages: incubation stage, stage 1a (crack initiation), stage 1b (early-stage crack growth), stage 2 (sustainable crack growth caused by mechanical driving force), and stage 3 (rapid crack propagation to rupture). Stage 1b encompasses a large portion of the pipeline’s lifespan, which is of great significance to pipeline integrity management aimed at service life extension. However, this stage is less studied so far. This invited paper provides a brief review of the recent progress on stage 1b stress corrosion crack initiation and growth for buried pipeline steels. Emphasis is placed on the effects of loading conditions and their interactions on stage 1b growth of high pH SCC, while some progress of near-neutral pH SCC is included for the purpose of comparison. It first introduces SCC in pipeline steels which is followed by a definition of stage 1b and its significance in terms of the service life of pipeline steels. Then the most recent advancements in understanding early-stage crack growth in stage 1b are reviewed and discussed. In summary, stage 1b growth can be self-induced by existing cracks (the so-called mother-daughter analogy), involving crack initiation in the plastic zone ahead of the surface tip of a surface crack, which is quite different from the stochastic process of coalescence of randomly formed individual cracks. Stage 1b growth extends crack length and increases the stress intensity factor at the depth tip without a physical increase in crack depth, serving as a bridge to stage 2. Further, the need for future research on stage 1b SCC initiation and growth of pipeline steels is discussed.

A method for leak detection in buried pipelines based on soil heat and moisture

Leakages in urban heating pipeline networks are mostly caused by underground corrosion, external environment interference and construction. The fluid leaking from pipes accumulates in surrounding soil for a long time, resulting in changes in soil machinery and hydraulic structure, and potential accidents threaten people's daily life and property safety. A preliminary judgment was made to determine whether the pipeline failed according to the infrared images of underground heating pipeline taken from the actual engineering. By comparing the soil moisture around the faulty pipe, we subsequently proposed a fault detection method for buried pipelines which coupled infrared thermography and the variation characteristics of surrounding soil moisture. In order to verify the effectiveness of this method, the numerical simulation was carried out on a leaking buried pipe, and the variation characteristics of soil heat and moisture in the direction of the failure point and its driving mechanism were analyzed. The results showed that the difference between the internal and external pressures at the failure point of the leaking buried pipeline enhanced the effect of soil pressure potential, resulting in significant heat and moisture transfer in soil, which contributed to detecting the buried pipeline failure and identifying the failure types of buried pipelines.

Coupling Interaction of Surrounding Soil-Buried Pipeline and Additional Stress in Subsidence Soil

In the process of underground resource exploitation, the induced surface subsidence easily leads to the deformation and failure of buried pipeline. And in the process of soil subsidence, the complex interaction between buried pipeline and surrounding soil occurs, which leads to deformation and additional stress in buried pipeline. In this paper, a laboratory test system is designed and developed to analyze the influence of buried depth, cohesion of soil, and angle of internal friction on stress, in order to obtain the deformation mechanism of pipe-soil and the pressure around the pipe and the distribution of additional axial stress along the pipeline. The research results show that in the process of subsidence, the synergistic deformation between the pipe and soil at both ends of the subsidence area is maintained, while there is a compressive nonsynergistic deformation zone in the soil at the top of the pipe, and the deformation zone in the cohesion-less soil and the cohesive soil presents a spire shape and an arch shape, respectively. Areas of maximum additional tensile and compressive stresses occur in the area of maximum curvature and the central position. In addition, the smaller the burial depth, the earlier the unloading phenomenon occurs; and the additional stress in buried pipe in cohesion-less soil is significantly less than that in cohesive soil, and the unloading phenomenon occurs earlier. The research results provide the basis for disaster prevention of buried petroleum transmission pipeline in subsidence process.

Effect of weld geometry parameters on dynamic behavior of buried X70 steel pipeline under subsurface detonation

Although a significant amount of research has been conducted to investigate the deformation and failure of buried pipelines subjected to load disturbance, scarce information is available about the effect of weld geometry parameters on the dynamic behavior of buried pipelines under blast loads. In the present study, numerical method and range analysis method were conducted to investigate the effect of weld geometry parameters including bevel angle, residual weld height, weld root opening, and thickness of root face on the dynamic performance of welded X70 steel pipelines under subsurface detonation. The results showed that the deformation of explosion-front surface is larger than that of explosion-back surface of the buried pipeline. The bevel angle, residual weld height, and thickness of root face have different effects on the dynamic comparison index of the welded pipes including peak vibration velocity, peak equivalent stress, peak equivalent strain, and peak displacement. Reasonable configuration should be adopted to properly select the geometry and dimensions of welding groove due to the complex influence of the weld geometry parameters. Combined the present results with the designing practice and current standards, the suggested weld geometry parameters to decrease their effects on the dynamic behavior of the welded X70 steel pipeline are as follows: the bevel angle (25 ± 5°), residual weld height (less than 1 mm), weld root opening (3.5 ± 0.5 mm), and thickness of root face (1.6 ± 0.6 mm).

Recommendations for determining nonlinear Winkler spring parameters for buried steel pipe stress analysis applications

Permanent ground movements due to seismic fault rupture, ground subsidence or liquefaction-induced lateral spreading may result to failure of buried pipelines crossing the affected areas, due to the development of excessive bending and axial pipe strains. Verification of pipe integrity against such actions and design of mitigation measures is based on analyses with nonlinear beam-on-non-linear Winkler foundation models, where the soil reaction developing on a pipe as result of differential ground movements is modelled by means of elastoplastic springs. This note presents a new set of guidelines and expressions for determining the parameters of Winkler springs applicable to the analysis of steel pipes backfilled with sand and subjected to differential movement with a lateral, vertical-upwards and/or vertical-downwards component. The guidelines, collectively referred to as UoN recommendations, are accordingly employed in the parametric stress analysis of a buried steel pipe crossing an oblique seismic fault. Results of this parametric analysis demonstrate that adoption of the UoN recommendations in the analysis workflow results in considerably lower pipe axial and bending strains, compared to analyses based on current conservative methods, and thus more realistic and economical design solutions.

Studies on ablation failure on pipeline related to lightning strikes

The phenomena lightning causes failure of buried pipelines, in the form of ablation pits on pipe wall, have been reported several times in the past, and there are only few studies focusing on the formation of such failure and the impact to structural integrity in service. To study factors causing the formation of ablation pits on pipelines, lightning strike simulation experiments were conducted on pipeline steel specimens by means of an impulse current generator facility. With the obtained steel specimens from the simulation experiments, combined with the failure samples obtained in the field, metallographic examination and mechanical property tests were carried out for further fitness-for-service analysis. The results showed that the field failure samples had consistent properties with the laboratory specimens. The microstructure of the damage part transitioned in the order of, from the ablation zone inward to the matrix, a remelting zone, an HAZ surface layer, an HAZ subsurface layer, an HAZ innermost layer, and the matrix. The field and laboratory ablation failure samples showed similar changing trend of hardness, i.e., gradually decreasing from the remelting zone to the matrix. These observations demonstrate that the damage parts have distinct mechanical properties from the normal matrix. In conclusion, the ablation failure caused by lightning strike had severe impacts to the pipeline material itself, which necessitated thorough repair of the HAZ by grinding or other measures.

Modelling and testing of optimum soil moisture levels in the corrosion of underground pipelines

Corrosion is one of the major factors leading to the failure of buried pipelines. Soil properties such as aeration, moisture content and level of compaction are known to cause variations in the level of corrosion of buried metallic structures. It is known that, at a particular soil moisture content, the corrosion rate reaches a maximum value. While this phenomenon is generally understood, an explanation from a soil mechanics perspective with mechanisms for soil water continuity and mass transport processes is currently lacking. This work fills this void by modelling the moisture-controlled diffusion transport and electrical conductivity in soil coupled to the electrochemical activity on the buried metal surface. Variations in the electrical conductivity and oxygen diffusion in sand at different degrees of saturation were determined experimentally. The results were used as input parameters in a finite element model. Results from the coupled finite element model were compared with experimental results from electrochemical corrosion tests. The tests were conducted on cast iron specimen buried in sand and the corrosion behaviour under various aeration regimes were studied. The presence of an optimum moisture/aeration regime, where the corrosion rate becomes a maximum was demonstrated and the mechanisms behind this phenomenological behaviour are discussed in this paper. The modelling and experimental results are expected to be useful in developing non-intrusive testing methods for underground corrosion.

Modelling of soil–structure interaction behaviour: geometric nonlinearity of buried structures combined to spatial variability of soil

In the analysis of non-linear behaviour of buried structures, the soil–structure interaction is the most important cause of buried pipeline failure, especially when the soil is modelled as a random elastic medium. In order to design safe and economical means of transporting energy and fluid, it is necessary to predict realistic behaviour of buried pipeline. In this work, the influence of spatially random soil properties on the geometric non-linear behaviour of pipeline is investigated. However, a numerical model has been developed, by modelling the pipeline as a geometric non-linear long beam resting on linear elastic random soil. Due to large deflections and moderate rotations of pipeline, the von Kàrmàn-type non-linearity based on the finite element formulation of non-linear pipeline response is adopted and then combined with random field theory of soil based on Monte Carlo simulations. The equation of motion is obtained using the principal of virtual works and solved using the Newton–Raphson incremental iterative method. A MATLAB program has been developed to implement the numerical method applied to the non-linear analysis of the buried structure. When the pipeline undergoes large deflection, the spatial variability of soil properties significantly affect the pipeline’s response and in this case, the obtained results allow a more reliable design of pipeline.

Multiresolution Change Analysis Framework for Postdisaster Assessment of Natural Gas Pipeline Risk

Natural disasters, such as hurricanes and floods, pose significant threats to the integrity of natural gas pipelines. In an emergency situation following a disaster, thorough pipeline safety assessments must be performed to avoid costly postdisaster damage and to ensure the safe and reliable delivery of energy resources. This paper presents a multiresolution change analysis approach for detecting emerging threats to natural gas pipeline systems after a natural disaster. For aboveground pipeline facilities, the change analysis focuses on displacement of buildings as an indicator of whether a pipeline segment or gas meter needs repair or replacement. For underground pipeline facilities, the change analysis focuses on detecting soil movement and storm surges, all of which cause additional stress on the pipeline facilities. This approach can also be applied to estimate the likelihood of failure of buried pipelines by measuring terrain change and soil movement.

EFFECT OF SOIL CORROSION IN FAILURES OF BURIED PIPELINES

Over the last few years, several failures in transmission and distribution water/gas pipelines have been reported around the world. The failure of buried pipeline is controlled by several factors, such as pipe material, soil corrosion, internal and external loading, etc. Among these, soil corrosion makes a significant contribution towards failure mode and mechanisms in buried pipes, yet few studies have been done. Although a number of corrosion models have been developed over the years, the applicability of the model predominantly depends on the type of soil and its moisture change over time at the pipe depth. By incorporating a corrosion model, the remaining life of the pipe can be estimated on the basis of applied traffic and pressure loads, which determine the stresses in the pipe segment. Depending on the model, the estimation can show significant variability, and consequently affect the pipe renewal and rehabilitation plans that ultimately have economic impacts. Therefore, it is important for the pipeline asset owners to understand the effect of corrosion models in the remaining life calculation. This paper reviews briefly the available corrosion models and the sensitivity of each parameter in pipe corrosion pit properties and in the remaining life estimation. Finally, a comparison among the corrosion models on the basis of the remaining life estimation is provided to improve the renewal plan.

Failure Analysis and Numerical Simulation of the Buried Steel Pipeline in Rock Layer Under Strike-Slip Fault

Fault movement is one of the threats for the structural integrity of buried pipelines. Failure of buried pipeline will cause explosion, environment pollution, fluid leakage, and other accidents. Buckling behavior of buried pipeline in rock layer under strike-slip fault displacement was investigated by finite element method. Effects of internal pressure and fault displacement on buckling mode and strain of buried pipeline were discussed. The results show that buckling modes of high pressure and low pressure pipeline are different. There are three buckling locations of the pipeline under strike-slip fault when u = 1.8 m; the buckling modes in the fault plane are different with the modes on both sides. The maximum von Mises stress appears on the buckling location. Buckling modes on both sides change from collapse to wrinkle gradually with the internal pressure increases, and the wrinkle amplitude increases. Axial strain and plastic strain increase first and then decrease with the internal pressure increases. Buckling locations of the low pressure pipeline increase from two to three with the fault displacement increases. But for high pressure pipeline, buckling locations increase from two to three, and then increase to five. Those results can provide a basis for the safety assessment and construction design of buried pipelines.

Excavation-Induced Buried Pipeline Failure – A Case Study

This paper presents a case history involving a failure of water pipeline due to a deep excavation. The case history was analyzed using both the simplified method and more sophisticated finite element modeling. Also presented are the fundamentals of damage assessment of buried pipelines associated with deep excavation-induced ground movements. A number of ground displacement profiles pertinent to the damage assessment are introduced. The results of the analysis indicated that the excessive ground movement was the major cause for the failure. These results were partly supported by the finite element analysis which takes the soil-pipe interaction effect account. It is demonstrated that although conservative, the simplified approach presented in this paper can be effectively used as a first-order method for excavation-induced pipeline damage.