Estimates on thermal effects of the China-Russia crude oil pipeline in permafrost regions

Using the finite element method, thermal effects of the Chinese-Russian crude oil pipeline in permafrost regions were estimated under two construction modes (conventional burial and aboveground embankment), two thermal control techniques (bare and insulated pipe), and three climate conditions along the route (marked under the natural mean ground surface temperatures of − 0.5, − 1.0, − 1.5 °C, respectively). The results show that with the silt embankment on gravel berm and the insulated pipe, the thaw of permafrost under the pipeline could be prevented during its service life. However, thawing of the permafrost under the conventionally buried pipeline cannot be prevented regardless of climate conditions or thermal insulation around the pipe. So it is strongly recommended that over-excavation and/or thermosyphons be applied for the conventional burial construction mode, especially in the warm and ice-rich permafrost sections to mitigate frost heave and thaw settlement in the subsoil.     

Development of freezing-thawing processes of foundation soils surrounding the China-Russia Crude Oil Pipeline in the permafrost areas under a warming climate

The proposed China-Russia Crude Oil Pipeline (CRCOP) will be subjected to strong frost heave and thaw settlement of the surrounding soil as it traverses permafrost and seasonally frozen ground areas in Northeastern China. The freezing-thawing processes, the development of the maximum frozen cylinder in taliks and thawed cylinder in permafrost areas, and the variations in the maximum freezing depths under the pipeline in taliks and thawing depths in different permafrost regions near Mo'he station, the first pumping station in China, were studied in detail using numerical methods in this paper. The inlet oil temperature at Mo'he station was assumed to vary from 10 to − 6 °C in a sine wave form during the preliminary design phase. Research results showed that the freezing-thawing processes of soils surrounding the buried pipeline had distinct differences from those in the undisturbed ground profile in permafrost areas. In summer, there was downward thawing from the ground surface and upward and downward thawing from the pipeline's surface once the temperature of the oil rose above 0 °C. In winter, downward freezing began from the ground surface but upward and downward cooling of the cylinder around the pipeline didn't begin until the temperature of the oil dropped below 0 °C. However, in the undisturbed ground profile, downward thawing from the ground surface occurred in summer and downward freezing from the ground surface and upward freezing from the permafrost table occurred in winter. The maximum thawing depths and thawed cylinder around the pipeline in warm permafrost enlarged with elapsing time and decreasing water content of the soils. In taliks, the maximum freezing depths and frozen cylinder around the pipeline kept shrinking with elapsing time and increasing water content of the soils. The freezing-thawing processes and development of the thawed and frozen cylinders around the pipeline were muted by any insulation layer surrounding the pipeline. Insulation had better thermal moderating on the heat exchange between the pipeline and the surrounding soils during the early operating period. But its role slowly weakened after a long-term operating. Research results will provide the basis for assessment and forecasting of engineering geological conditions, analysis of mechanical stability of the pipeline, foundation design, and pipeline construction and maintenance.     

Forecasting the oil temperatures along the proposed China-Russia Crude Oil Pipeline using quasi 3-D transient heat conduction model

The China-Russia Crude Oil Pipeline (CRCOP) faces significant challenges due to differential frost heaving and thaw settlement resulting from significant variations of oil temperatures along the pipeline. Oil temperature distribution along the pipeline during the long-term operation period is a very important factor in pipeline foundation design under future climate warming and various frozen soil conditions. It is important for the assessment and prediction of differential frost heave and thaw settlement of the pipeline foundations soils, forecasting the development of the seasonal and inter-annual frozen and thawed cylinders around the operating pipeline, stress-strain analysis of the pipeline, and mitigation of subsequent frost hazards. A quasi three-dimensional computational model was developed to predict the oil temperature along the pipeline. It was verified by analytic solutions of the minimum oil temperatures along the route provided by the Daqing Oilfield Engineering (DOE) Co. The oil temperatures were predicted and analyzed for two proposed annual oil flow rates of 15 million tons (0.3 mbpd) and 30 million tons (0.6 mbpd) with and without mitigative measures (only pipe insulation was considered here) during the operation period. Also, the inter-annual variations of oil temperature at key typical locations were investigated to understand the impact of climate warming. The results indicated that the maximum oil temperature cools southwards, but the minimum oil temperature warms southwards (with the inlet oil temperatures from − 6 to +10 °C). However, the average annual oil temperature decreases southwards in the northern part of the pipeline, then it starts to slowly increase. The amplitudes of oil temperature change will decrease southwards. Oil temperatures will slightly increase with elapsing time due to the imposed boundary conditions of climate warming. The oil temperatures with a lower flow rate vary more significantly than that with a higher flow rate because the oil temperature with a low flow rate is more affected by the thermal regime of the surrounding soils and the external environments. Insulation around the pipeline tends to reduce the oil temperature variations along the pipeline during pipeline operation period. Therefore, pipe insulation can effectively reduce the development of frozen and thawed cylinders in the permafrost zone. The phase change of water in soils around the pipeline has a distinct influence on the oil temperature during the freeze-thaw transition periods. The oil temperature tends to be equal to the ambient ground temperature around the pipeline with southward distance and with elapsing operation time. The pipeline oil temperature is controlled by the incoming oil temperature and the surrounding ground temperature before the equalization. It would be mainly controlled by the ground temperature around the pipeline afterwards.     

Development of freezing–thawing processes of foundation soils surrounding the China–Russia Crude Oil Pipeline in the permafrost areas under a warming climate

The proposed China–Russia Crude Oil Pipeline (CRCOP) will be subjected to strong frost heave and thaw settlement of the surrounding soil as it traverses permafrost and seasonally frozen ground areas in Northeastern China. The freezing–thawing processes, the development of the maximum frozen cylinder in taliks and thawed cylinder in permafrost areas, and the variations in the maximum freezing depths under the pipeline in taliks and thawing depths in different permafrost regions near Mo'he station, the first pumping station in China, were studied in detail using numerical methods in this paper. The inlet oil temperature at Mo'he station was assumed to vary from 10 to − 6 °C in a sine wave form during the preliminary design phase. Research results showed that the freezing–thawing processes of soils surrounding the buried pipeline had distinct differences from those in the undisturbed ground profile in permafrost areas. In summer, there was downward thawing from the ground surface and upward and downward thawing from the pipeline's surface once the temperature of the oil rose above 0 °C. In winter, downward freezing began from the ground surface but upward and downward cooling of the cylinder around the pipeline didn't begin until the temperature of the oil dropped below 0 °C. However, in the undisturbed ground profile, downward thawing from the ground surface occurred in summer and downward freezing from the ground surface and upward freezing from the permafrost table occurred in winter. The maximum thawing depths and thawed cylinder around the pipeline in warm permafrost enlarged with elapsing time and decreasing water content of the soils. In taliks, the maximum freezing depths and frozen cylinder around the pipeline kept shrinking with elapsing time and increasing water content of the soils. The freezing–thawing processes and development of the thawed and frozen cylinders around the pipeline were muted by any insulation layer surrounding the pipeline. Insulation had better thermal moderating on the heat exchange between the pipeline and the surrounding soils during the early operating period. But its role slowly weakened after a long-term operating. Research results will provide the basis for assessment and forecasting of engineering geological conditions, analysis of mechanical stability of the pipeline, foundation design, and pipeline construction and maintenance.     

Model test study on influence of freezing and thawing on the crude oil pipeline in cold regions

Buried pipelines are one of most economical and convenient methods for the transportation of large volumes of oil and gas. When a pipeline is buried in cold regions, it may suffer frost damage. Previous studies of pipelines and the surrounding soils in cold regions have tended to concentrate on the theory and practical engineering problems. This paper reports the results of a model test to investigate the stresses and strains on the buried pipeline and surrounding soils in the permafrost and seasonal frost areas based on the Mo'he–Daqing section of the China–Russia Crude Oil Pipeline (CRCOP). The temperature of the soils surrounding the pipeline, displacement and axial strain as well as stress in the pipeline induced by frost heave and thaw settlement are monitored and analyzed. The test results will have some significance in guiding the construction of the CRCOP in cold regions.     

Model test study on influence of freezing and thawing on the crude oil pipeline in cold regions

Buried pipelines are one of most economical and convenient methods for the transportation of large volumes of oil and gas. When a pipeline is buried in cold regions, it may suffer frost damage. Previous studies of pipelines and the surrounding soils in cold regions have tended to concentrate on the theory and practical engineering problems. This paper reports the results of a model test to investigate the stresses and strains on the buried pipeline and surrounding soils in the permafrost and seasonal frost areas based on the Mo'he-Daqing section of the China-Russia Crude Oil Pipeline (CRCOP). The temperature of the soils surrounding the pipeline, displacement and axial strain as well as stress in the pipeline induced by frost heave and thaw settlement are monitored and analyzed. The test results will have some significance in guiding the construction of the CRCOP in cold regions.     

Design and construction of a large-diameter crude oil pipeline in Northeastern China: A special issue on permafrost pipeline

The design and building of a pipeline in permafrost regions challenge engineers and scientists in many regards, and the geohazards resulting from the (differential) frost heaving and thaw settlement of the pipeline foundation soils present one of the most daunting tasks. The China-Russia Crude Oil Pipeline, a spur line from the Siberia-Pacific Pipeline System, presented unique scientific and engineering problems because of: 1) extensive presence of the more ice-rich permafrost in boreal forests and swamps; 2) an insistence on a buried construction mode because of concerns about the potential for frequent forest fires and other safety issues; 3) great uncertainties in the temperatures of oil being transported although the given estimated oil temperature of − 6.4 to + 3.6 °C entering the Mo'he Pump Station, and the estimated oil temperatures could vary from about − 6 to + 10 °C along the southward pipeline route; 4) the limited lead time for detailed surveys on engineering geology along the pipeline routes and for engineering design; 5) very much limited investment and a limited number of engineers experienced in designing and building a major pipeline in an area where about one-half of its length would be impacted by generally warm (− 3 to 0 °C) permafrost. Nevertheless, the pipeline engineers and permafrost scientists strived to economically build and satisfactorily operate the first major crude oil pipeline in the boreal ecosystem in China. The major results on the formation mechanisms and mitigative measures for the (differential) frost heave and thaw settlement were presented in the eight papers in this special issue on permafrost pipeline, and one additional paper on the Golmud-Lhasa Oil Products Pipeline on the Qinghai-Tibet Plateau was also included. They may provide insights to the understanding of pipeline-permafrost interactions and benefit the future design and construction of pipelines in similar northern environments.     

Stresses and deformations in a buried oil pipeline subject to differential frost heave in permafrost regions

Differential frost heave of the buried oil pipelines in permafrost regions can have an adverse effect on the mechanical status of the pipeline, and seriously endanger the pipeline security. In order to reduce the damage to the pipeline during its designed lifetime, it is necessary to analyze the mechanical behavior of oil pipelines taking into consideration the differential frost heave in the design of the pipelines in permafrost regions. In this paper, an elastico-plastic finite element model for the mechanical behaviors of the pipeline–soil system was established. In order to simplify computations, the effects of the temperature and moisture fields on the problem were considered by applying the computed temperature zones of soils surrounding the pipeline from the thermal analysis, and actual frost heaving ratio of the soils was applied to the mechanical model to calculate the stresses and deformations of the pipeline in permafrost regions. These analyses may provide some useful insights into the possible mechanical states of the pipeline–soil system for the design, construction and operation of the buried oil pipelines in permafrost regions.     

Mechanical behaviour analysis of buried pressure pipeline crossing ground settlement zone

Numerical simulation model of buried pipeline crossing ground settlement zone was established considering pipeline–soil interaction. Mechanical behaviour of the buried pipeline was investigated, and effects of ground settlement, pipeline parameters and surrounding soil parameters on mechanical behaviour of the buried pipeline were discussed. These results show that there are two high stress areas on both sides of the dividing plane. High stress areas are oval on the top and bottom of the pipeline. Z-shape bending deformation appears under the action of ground settlement. In ground settlement zone, axial strain on the top of the pipeline is compression strain, and axial strain on the bottom of the pipeline is tension strain. On the contrary, they are tension strain and compression strain respectively in no settlement zone. Bending deformation, axial strain and plastic strain of the buried pipeline increase with the increase in ground settlement. Von Mises stress, high stress area, axial strain and plastic strain of the buried pipeline increase with the increasing diameter-thick ratio and internal pressure, but they decrease with the increase in buried depth. Diameter-thick ratio and internal pressure have a small effect on the bending deformation of the buried pipeline. Bending deformation decreases with the increase in buried depth in ground settlement zone. Von Mises stress and high stress area increase with the increasing surrounding soil’s elasticity modulus and cohesion, but they increase first and then decrease with the increase in Poisson’s ratio. Bending deformation of the pipeline in no settlement zone increases with the increase in elasticity modulus and Poisson’s ratio, but it is affected little by the cohesion. Axial strain and plastic strain have a bigger relationship with the elasticity modulus and Poisson’s ratio. Axial strain and plastic strain of the buried pipeline increase with the increase in cohesion, and the change rates increase with the increase in ground settlement.     

Numerical study on the effect of frost heave prevention with different canal lining structures in seasonally frozen ground regions

Frost heave damage problems in canal linings are a common phenomenon in seasonally frozen ground regions. These problems are regarded as interactions between heat transport and moisture flow processes. To research the influence of frost heave prevention in two types of canal structures in the Ningxia irrigation district of China, a two-dimensional coupled heat transport and moisture flow model was used to analyze temperature characteristics in the traditional canal lining structure and a new type of canal lining structure for frost heave prevention. The simulated results from this numerical model are in agreement with in situ temperature measurements for both canal lining structures. The in situ measurement results show that the new canal lining structure exhibits low seepage, low thermal conductivity, quick drainage speed and less uneven deformation. Therefore, this new canal lining structure is a good choice for frost heave prevention in seasonally frozen ground regions.     

Stresses and deformations in a buried oil pipeline subject to differential frost heave in permafrost regions

Differential frost heave of the buried oil pipelines in permafrost regions can have an adverse effect on the mechanical status of the pipeline, and seriously endanger the pipeline security. In order to reduce the damage to the pipeline during its designed lifetime, it is necessary to analyze the mechanical behavior of oil pipelines taking into consideration the differential frost heave in the design of the pipelines in permafrost regions. In this paper, an elastico-plastic finite element model for the mechanical behaviors of the pipeline-soil system was established. In order to simplify computations, the effects of the temperature and moisture fields on the problem were considered by applying the computed temperature zones of soils surrounding the pipeline from the thermal analysis, and actual frost heaving ratio of the soils was applied to the mechanical model to calculate the stresses and deformations of the pipeline in permafrost regions. These analyses may provide some useful insights into the possible mechanical states of the pipeline-soil system for the design, construction and operation of the buried oil pipelines in permafrost regions.     

用能量法确定考虑冻胀力和冻土抗力作用时桩基的临界荷载

借鉴经典欧拉弹性稳定理论,建立了冻土地区自由桩稳定理论的能量方程,再用能量法求解出在冻胀力和冻土抗力作用下桩屈曲临界荷载计算的通用公式。在ANSYS中用离散弹簧单元模拟桩侧冻土的弹性抗力作用,以昆仑山多年冻土地区桩基试验场试验桩为例,进行有限元法求解。两种方法的计算结果吻合较好,最后通过参数分析得出冻土地区影响桩基稳定性的主要因素。     

Mechanical behaviour analysis of a buried steel pipeline under ground overload

Ground overload is one of the most important factors that threaten the safe operations of oil and gas pipelines. The mechanical behaviour of a buried pipeline under ground overload was investigated using the finite element method in this paper. The effects of the overload parameters, pipeline parameters and surrounding soil parameters on the stress–strain response of the buried pipeline were discussed. The results show that the maximum von Mises stress appears on the top of the buried pipeline under the loading area when the ground load is small, and the stress distribution is oval. As the ground load increases, the maximum stress increases, and the high stress area extends. The von Mises stress, plastic strain, plastic area size, settlement and ovality of the buried pipeline increase as the ground load and loading area increase. The buckling phenomenon of the no-pressure buried pipeline is more serious than the pressure pipeline. As the internal pressure increases, the high stress area and the maximum plastic strain of the buried pipeline first decrease and then increase, the settlement of the buried pipeline increases, and the ovality decreases. The von Mises stress, maximum plastic strain, settlement and ovality of the buried pipeline decrease with increasing buried depth, the surrounding soil's elasticity modulus, Poisson's ratio and cohesion. The maximum von Mises stress, high stress area, the maximum plastic strain, plastic area and ovality increase as the diameter–thickness ratio increases. The critical diameter–thickness ratio is 60, and the settlement of the buried pipeline first increases and then decreases as the diameter–thickness ratio increases. Finally, a protective device of the buried pipeline is designed for preventing ground overload. It can be repaired in a timely manner without stopping the transmission of oil and gas and widely used in different locations because of its simple structure and convenient installation.     

Frost heave control of a chilled gas pipeline

This paper concerns the investigation of a possibility of controlling frost heave of a buried, chilled gas pipeline by heating cables. Experimental and numerical approaches were used to determine the influence of two heat sources placed underneath slab insulation. Saturated sand and highly frost-susceptible Niagara silt were chosen to represent two soil condition extremes regarding frost heave. Laboratory and mathematical models showed good agreement in predicting the size and shape of the frost bulb with variation of heat output from the cables. Experiments on Niagara silt demonstrated the engineering practicability of this system to control frost heaving of a pipeline.     

Mechanical Response of a Buried Pipeline to Explosion Loading

In order to study the stress-strain response of a buried pipeline with internal pressure under the ground explosive, a numerical calculation model of the buried pipeline with internal pressure was established. The dynamic process of the buried pipeline was simulated after the explosion on the ground. Effects of internal pressure, magnitude of TNT, wall thickness, and buried depth on the stress-strain of pipeline were studied. The results showed that the region of high stress and plastic strain presented to the upper pipeline and extended toward axial direction, and then extended toward circumferential direction under the ground explosion. With the increasing of internal pressure, the high-stress zone fades away, the plastic strain zone and deformation of pipeline decrease. The stress and deformation of buried pipeline increase with the magnitude of TNT increases, but they decrease with the increasing of buried depth and wall thickness. Those results can provide theoretical basis and reference for pipe laying of oil-gas pipeline, safety evaluation, and maintenance, etc.     

埋地管道爆炸地冲击作用的试验研究

利用DASP采集分析系统对常规武器或TNT药柱土中爆炸地冲击作用下引起埋地管道上的动应力进行了测试分析,得出了常规武器钻地爆炸地冲击作用下,正对爆心的埋地管段背面部分因弯曲易受到轴向拉应力破坏,且受力过程是瞬态受力过程的结论。利用LS-DYNA3D有限元程序对埋地管道爆炸地冲击作用影响进行了数值模拟分析,并与测试结果进行了比较,效果较好。     

Study on the height effect of highway embankments in permafrost regions

Thaw settlement is the main embankments distresses of highway in permafrost regions, according to survey data of the Qinghai–Tibet Highway (QTH). It can be effectively mitigated or even controlled by raising the embankment height. In view of this engineering problem, this study proposes the concept of the Height Effect of Embankment in Permafrost (HEEP). The concept represents the deformation and failure rules of embankment resulting from height variations. A thermal-elastic-plastic thaw settlement computational model is used to simulate the settlement processes of embankment, considering scenarios of different mean annual ground temperatures (MAGTs) and different heights. The model is validated by the field monitored data from a specific embankment section along the QTH. It is found that the total deformation of embankment is of considerable value and comes primarily from the thaw settlement of permafrost. Some special structures are recommended to supplement the built embankment, to ensure the stability of embankment in warm permafrost regions. The research results could provide essential theoretical and technological support for the transversal section design of highway embankments in permafrost regions.     

Stresses in buried conduits caused by freezing front

A laboratory experiment modeling the buried conduit problem was performed to study the stress changes in the conduit as a result of frost penetration in the soil. The model consisted of a large-scale soil container insulated on all sides except the top. The level and temperature of the ground water in the container, and the end restraints of the buried conduit, could be controlled. The model was placed in a cold room where the air temperature could be reduced to ?25°C. The experimental results, supplemented by the available field data, demonstrate the influence of soil freezing on pipe bending stresses. Maximum frost depth, which can vary with the rate of freezing even for comparable air freezing indexes, is a significant soil thermal parameter that correlates with pipe stresses. Availability of ground water significantly increases pipe stresses while pipe-end restraints tend to decrease them slightly. The results suggest that the water expulsion by the advancing freezing front causes loss of soil stiffness due to the increased pore water pressures and decreased effective stresses in the soil.     

Characteristics and mechanisms of embankment deformation along the Qinghai-Tibet Railway in permafrost regions

Based on field monitoring datasets, characteristics of embankment deformation were summarized along the Qinghai-Tibet Railway in four permafrost regions with different mean annual ground temperatures (MAGTs). Then, further analyses were carried out at some typical monitoring profiles to discuss mechanisms of these embankment deformations with consideration of detailed information of thermal and subsurface conditions. The results indicated that in regions with MAGT <− 1.5 °C, embankments only experienced seasonal frost heaves, and of which the magnitudes were not significant. So, the embankments in the regions performed satisfactorily. Whereas in regions with MAGT ≥− 1.5 °C, both traditional embankment and crushed rock embankment experienced settlements, but characteristics and mechanisms of the settlements were different for the two kinds of embankment. For crushed rock embankment, the magnitudes of settlement and differential settlement between right and left embankment shoulders were not significant and increased slowly. In respect that upwards movements of permafrost tables and better thermal stability of permafrost beneath embankment, mechanism of settlements on the embankment was inferred as creep of warm and ice-rich layer often present near permafrost table. While for traditional embankment, particularly in warm and ice-rich permafrost regions, the magnitudes of settlement and differential settlement between right and left embankment shoulders were significant and still increased quickly. Considering underneath permafrost table movements and permafrost temperature rises, mechanisms of settlements on the embankment included not only creep but also thawing consolidation of underlying permafrost. Therefore, some strengthened measures were needed to ensure long-term stability of these traditional embankments, and special attention should be paid on temperature, ice content and applied load within the layer immediately beneath permafrost table since warming and thawing of the layer could give rise to considerable settlement.     

Modelling of coupled heat,moisture and stress field in freezing soil

A model for coupled heat, moisture and stress field in freezing soil is proposed. A numerical simulation for an experiment published by Penner (1986) in saturated soil using this model is carried out. The results of the simulation for temperature field and heave agree well with the experimental results. In addition, the stress field in freezing soil is also given by this model. The model is well adapted for solving practical frost heave problems in which the heave is coupled with deviatoric creep, such as under foundations or around chilled buried pipelines.