With the continuous development of social economy, the scale of oil & gas storage and transportation industry in China increases year by year, and the technological and managerial levels are improved continuously. In this paper, the development history of oil & gas pipelines at home and abroad was reviewed, and current technological achievements of domestic oil & gas storage and transportation industry were summarized from the aspects of high-pour-point and high viscosity crude oil transportation, centralized control of oil & gas pipeline network, material and equipment localization, pipeline engineering and construction, and operation management. Then, the changes of energy consumption structure and the development of related technologies resulting from global energy revolution and technological revolution were analyzed, and the profound influence and great challenge to the oil & gas storage and transportation industry caused by these changes were discussed. Finally, the development direction of oil & gas storage and transportation industry was prospected in terms of facility safety, system reliability and big data application.

China-Russia Eastern Gas Pipeline Project, as an important livelihood project and a major achievement in the development of the China-Russia comprehensive strategic partnership of coordination in the new era, is of great significance in ensuring the national energy security, optimizing the energy consumption structure and accelerating the regional economic development. With global leading comprehensive design indexes and information and intelligence level, China-Russia Eastern Gas Pipeline Project represents the highest level of construction and operation of the current oil and gas pipeline. Facing to the construction challenges such as extremely low temperature of －40 ℃ in winter, vast marsh wetland in summer, limited social support and pressed effective construction period, management innovation and technological innovation have been vigorously implemented in the project. On the one hand, with the means such as “Internet Plus”, the management mode and operation mechanism have been improved and optimized, and the construction period, quality, safety, environmental protection and investment have been fully controlled under the guidance of the Party construction. On the other hand, the “intelligent construction site” and the “intelligent pipeline model project” have been innovatively built by highlighting the intelligence, and the core technologies and key equipment have been upgraded and fully localized, thus effectively ensuring the high-quality completion and high-level service of the China-Russia Eastern Gas Pipeline. Experience has been summarized and achievements have been reviewed so as to provide reference and guidance for future construction of oil and gas pipelines.

For the oil and gas pipeline operating in the permafrost regions, buckling deformation is usually caused by frost heaving and thaw settlement of the foundation soil, which affects the safety and stability of pipeline seriously. With 4 typical types of pipeline foundation soil along China–Russia Eastern Gas Pipeline located in the permafrost region of Greater Khingan Range as the object of study, the relationship of the coefficient of thaw settlement and frost heaving ratio with other influencing factors of various soil samples was analyzed through the frost heaving test and thaw settlement test, and the sensitivity of the influencing factors of the coefficient of thaw settlement and frost heaving ratio was also analyzed with gray correlation method. The results indicate that the coefficient of thaw settlement and frost-heaving ratio of the soil samples are greatly influenced by water content and dry density. In addition, superplastic water content, mud content and loss on ignition also have significant effect on the silty soil, sandy soil and peat soil. According to the grey correlation analysis, water content is the main influencing factor of frost heaving and thaw settlement, but it is not absolute. For some soil, the mud content and superplastic water content may play a major role in frost heaving and thaw settlement, to which great attention shall be paid during design and construction. The study results can provide scientific support and theoretical reference to the design, construction, operation, maintenance and prevention and control of frost damage of buried pipelines in the permafrost regions. (10 Figures, 7 Tables, 23 References)

Pipeline defects have always been the dominant factor leading to pipeline failure. Using in-line inspection technology to inspect and identify various pipeline defects has become a widely acknowledged practice in China and abroad. In order to further promote the development of in-line inspection technology and the improvement of management level, the technology capability and development history of typical in-line inspection technology service companies in China and abroad were systematically combed, the technical limitations of in-line inspection technologies were analyzed for the inspection of girth weld defects, crack defects, pinhole corrosion defects and the stress state of pipelines, and the existing problems in the management of in-line inspection technology were summarized from three aspects of government supervision, pipeline enterprise management and in-line inspection technology service providers. The multi-dimensional strategy was proposed for solving the limitation of inline inspection technology and expected to provide reference for the development of inline inspection technology and the improvement of management level in future. (1 Figure, 25 References)

The phenomenon of oil stealing from long-distance oil and gas pipelines in China is increasing. Once the pipeline fails, it will bring huge safety risks to the operation of the enterprise and the personal property of the people. As the most effective detection method for hot-tap of pipeline, traditional magnetic flux leakage in-line inspection has disadvantages such as high cost and long detection period. Therefore, a low-cost and rapid inspection tool for hot-tap based on the principle of permanent magnet disturbance has been developed. This article introduces the basic principles and characteristics of pipeline hot-tap inspection technology, focusing on the mechanical structure and electronic system of the in-line inspection tool. Site application shows that the pipeline hot-tap in-line inspection tool could effectively inspect typical metal loss, pipeline hot-tap with diameter over 5 mm, internal pipeline deformation and other defects. The inspection tool has active effect on guaranteeing the safe operation of pipelines and is worth popularizing. (10 Figures, 1 Table, 22 References)

Underground gas storage, which serves as the auxiliary facility of the nature gas pipeline network, is very important to maintain the stability of gas supply. In recent years, the construction of underground gas storage develops rapidly in China. However, due to the late construction, the underground gas storage cannot satisfy the growing demand of nature gas, and gas shortage has happened occasionally in winter. In view of the large investment and long construction time required for gas storage construction, generally 4 years required from mining to put into service, an accelerated mining method is put forward herein. Definitely, it is to inject gas while mining and to take the injected gas as the protective blanket of the cavity roof. In this way, not only the cost of blanket material can be reduced, but also the construction time can be shortened significantly. As shown in the simulation analysis, it is feasible to store gas while the underground storage is constructed. (9 Figures, 4 Tables, 20 References)

At present, the multiphase flow technology is applied increasingly in oil and gas mixed transportation system. However, the safety problems of multiphase pipeline are much more complicated than that of single-phase pipeline. Acoustic sensing technology has the advantages of wide frequency range, long propagation distance and easy identification, and it is applied to the two-phase flow pipeline with multiphase medium. Based on the variation of the maximum mean value and the maximum mean square value of the dynamic pressure signal before and after the leakage, the influence of the flow pattern, flow rate, leakage direction and leakage aperture on the leakage signal can be judged. Further, through theoretical analysis, the model of the relationship between the fluctuation amplitude of dynamic pressure and the gas-liquid flow during the stable flow of smooth stratified flow, wavy stratified flow and slug flow was established, which could be used to determine the background noise amplitude fluctuation of steady flow under each flow pattern, laying a foundation for the realization of acoustic leakage detection technology for gas-liquid two-phase flow pipeline. (4 Figures, 3 Tables, 28 References)

To construct intelligent pipeline network, it is essential to solve the problem about the understanding and unification of basic concepts and general ideas. The basic concepts related to intelligent pipeline network should be interpreted based on the development status of artificial intelligence technology, and the connotation and denotation of the concept of intelligent pipeline network should be corrected according to the actual engineering application. In this study, the concept of industrial intelligence was put forward. It was also pointed out that the essence of intelligent industry was the digital application of industrial intelligence, i.e., machines could recognize and apply human knowledge, and intelligent pipeline network was a category of intelligent industry. Based on the characteristics of human intelligence, the definition, capabilities, characteristics and construction objectives of intelligent pipeline network were proposed, the concept of industrial knowledge was redefined, the concept that the intelligent pipeline network was driven by knowledge was put forward, and the technical route of intelligent decision-making for operation of pipeline network based on the industrial knowledge base was clarified. The general idea was proposed, which was to construct Digital Twin pipeline network system and artificial intelligence brain and to realize the intelligent operation of pipeline network based on the cloud platform of intelligent pipeline network. It is clear that the main role of people in the entire architecture of intelligent pipeline network is to create and supply knowledge for the intelligent pipeline network. The research results could provide reference for the construction of intelligent pipeline network. (4 Figures, 26 References)

The construction and operation management of mountainous pipelines in Southwest China faces the “two major risks” of complicated geological changes and frequent human activities, and the “three problems” of poor applicability of laws, regulations and standards, low estimation for construction and management costs and lack of mountainous oil and gas pipeline technology, resulting in high systematic risk in pipeline management and great difficulty in its safety management and control. By analyzing the engineering characteristics and the difficulty of management and control of mountainous oil and gas pipeline, the idea was proposed to balance the two constraints of the unknown and uncontrollable risks and the inefficient management and control system relying on the digitalization and intelligence. Moreover, the general idea of digital transformation with “five longitudinal + two transverse pipelines and two systems” was put forward based on the actual business condition of the mountainous pipeline company, forming the complete technical route of intelligent operation of mountainous pipeline from data perception, transmission, storage, standardization, application and decision optimization to intelligent logic control, and further improving the capability and efficiency of risk management and control of mountainous pipeline. Here, the practice and achievements of intelligent construction of mountainous pipeline in basic support layer (two systems), specific application layer (five longitudinal pipelines) and platform integration layer (two transverse pipelines) were illustrated systematically, and the suggestions on future development were also proposed. (1 Figure, 4 Tables, 20 References)

With the continuous growing demand for natural gas, China’s high-grade oil and gas pipeline construction has developed rapidly and ranked in the international leaders. In the application process of high-grade oil and gas transmission pipes, the technical support system for product development and engineering application has performed an important function. The technical support system is composed of four parts: quality supervision and evaluation, standardization, scientific research and failure analysis. Each part was elaborated from connotation, development history and current situation. The technical support system has played an important role in the development and engineering application of China’s oil and gas pipeline industry, as well as in the development and engineering construction of X80 pipe products for China-Russia Eastern Gas Pipeline Project. The system will continuously provide technical support for construction of intrinsically safe pipeline engineering.

On the 50th anniversary of the “8·3” Pipeline Project, the 50-year development process of China’s oil pipeline technology was reviewed, the scientific research and engineering application results of several technologies were sorted out, i.e. the closed operation and water hammer control & protection technology of oil pipeline, transportation technology of high pour-point and viscous crude oil, batch transportation and optimized operation technology of oil products, design, commissioning and operation technology of hilly pipelines, and operation simulation technology of oil pipeline, and the future development goal of oil pipeline transportation technology was summarized. The future development of intelligent oil pipeline was prospected and the relevant suggestions put forward were as follows: determining a mode of uniform data platform to be built for national pipeline network system, forming professional industrial software suitable for oil and gas pipelines, developing an intelligent decision-making system based on massive data + AI algorithm, establishing the construction principles, targets and application evaluation methods for the digital body and consciousness body of the oil pipeline system, establishing national pipeline and equipment failure database and release platform, developing self-controllable online and offline analysis and prediction software of large-scale oil pipeline network based on data and mechanism model, studying the coordinated operation of the domestic and foreign SCADA systems and the large-scale application technology of domestic softwares, and developing the energy-saving and efficiency-increasing technologies of large-scale oil and gas pipeline networks under precise management. All of the above suggestions are expected to provide a reference for the construction of a large intelligent interconnected pipeline network.

With the development of pipeline business and technology, more and more pipeline-related terms, such as long-distance pipeline, pipeline and pipeline system, appear in the codes, standards, scientific reports and papers. However, arbitrary terms using and inconsistent definitions are very common, which may lead to statistical data deviation, difficulty in comparison and non-uniform terms in standards and regulations. To settle this issue, the current codes and standards in China and overseas were collected and analyzed. Based on the comparative study of the classification of pipelines, the definition and coverage of the terms in relation to the pipeline, pipeline system and long-distance pipeline were compared and studied. The differences of these terms were indicated, and suggestions on the definition and English expressions for pipeline-related series terms uniformly defined in the oil and gas energy industry were proposed.

With the development of digital and intelligent technologies, the operation and management mode of oil and gas pipelines are expected to be substantially changed, and the development concept centered on intelligent pipeline and intelligent pipeline network will be formed. The basis and realization conditions of China’s intelligent pipeline construction were analyzed from the perspective of pipeline operation process. Firstly, the basis and functions of intelligent pipeline construction were discussed from three aspects: the definition of intelligent pipeline, the development status of domestic and foreign intelligent pipeline, and the Internet of Things basis and technical preparation for intelligent operation of oil and gas pipelines, indicating that the application of intelligent pipeline in oil and gas production is the essential issue of intelligent pipeline construction. Secondly, the source of complexity in data, modeling and calculation of natural gas pipeline network was discussed, and the construction ideas of intelligent pipeline and intelligent pipeline network were specified. Thirdly, China-Russia Eastern Gas Pipeline was taken as an example to expound the goal, basis and intelligent composition of the process operation of the China-Russia Eastern Gas Pipeline. The intelligent composition of the process operation is composed of the construction of the pipeline process simulation system, the construction of the Digital Twin based on the pipeline data, and the comprehensive operation scheduling and reliability assessment. Finally, some understanding and suggestions were given against the situation and challenges faced by the development and application of intelligent pipeline technology.

With the development of natural gas industry, the market progress speeds up continuously, global supply and demand of natural gas increase sustainably and the overall supply-demand pattern changes greatly. LNG is advantageous with safe storage and convenient transportation, and it further facilitates the development of global natural gas trading. In this paper, the status and prospect of global natural gas and LNG supply and demand were analyzed, and the development direction of global natural gas market was summarized. Then, combined with the development status of domestic natural gas industry, the basic idea that China shall speed up the overall market development and the related industry construction was put forward to provide the long-term mechanism for national energy supply security.

China-Russia Eastern Gas Pipeline Project is a major strategic project that is attached with great importance and personally promoted by both of the top leaders of China and Russia, and is considered to be another significant outcome in strengthening the comprehensive energy cooperation partnership between the two countries and deepening the comprehensive strategic cooperation partnership, as well as a major project serving the Belt and Road Initiative and constructing China’s four major energy transportation channels. Major achievements made by PetroChina in equipment localization in recent years were summarized, including highstrength line pipes, natural gas power-driven compressor units, oil transfer pump sets, key valves and actuators, flow meters, etc. The latest localization progress in the application of key equipment in China-Russia Eastern Gas Pipeline was introduced, such as 20 MW level powerdriven centrifugal compressor units with one-key start-stop function, complete set of SCADA software and hardware for the core control system of pipeline that satisfies the information safety requirements, 56 in Class900 all-welded ball valves and associated electric, pneumatic and hydraulic actuators, 24 in Class900 safety shut-off valves and working regulators in the main line pressure regulating device, etc. The independence and controllability of the key equipment can ensure the national energy security, promote the development of national equipment manufacturing industry, and facilitate the cost reduction and efficiency increase of pipeline operating enterprises.

Failure of girth welds in high-grade steel pipelines is common. With the surge in mileages of high-grade steel pipeline, the failure of girth weld in high-grade steel pipelines has drawn an increasing attention from domestic and foreign pipeline industries. The typical cases in China and abroad were classified and analyzed. Based on the fracture mechanics theory of girth weld fracture failure, the failure causes were analyzed for the key links that affect the safety of girth weld, and the safety improvement measures were hereby proposed, involving the pipeline welding technology, steel control, welding materials, strength matching of welded joints, internal groove types for unequal wall thickness, nondestructive testing, intelligent inspection, stress and strain, construction management, etc. These measures have been widely applied to the China-Russia Eastern Gas Pipeline Project, and are planned to be used in the middle section of the Line 3 and the Line 4 of West-to-East Gas Pipeline Projects which are to be built. Their practices are anticipated to provide support for improving the service reliability of girth weld in high-grade steel pipelines.

The distributed fiber optic sensor can sensitively monitor the local temperature changes caused by the leakage at any position of the pipeline. The mass monitoring data has obvious spatial-time nonstationary properties, so it is difficult to diagnose the leakage directly from the monitoring data. In this paper, a spatial-time big data analysis method based on movingwindow outlier analysis was developed in the framework of statistical pattern recognition. By virtue of this method, the intelligent identification of pipeline leakage is realized only based on the intrinsic characteristic of the distributed temperature sensing data. Then, the method to determine the lengths of the moving window and the abnormal state diagnosis window was proposed. Finally, the physical simulation was performed on the leakage detection of prototype pre-insulated steel pipe. It is indicated that the method developed in this paper can never make the false alarm when the pipeline is in the intact state, and it can quickly identify the leakage event and accurately locate the leakage once a leakage happens. In conclusion, this method is an unsupervised artificial intelligence approach of big data analysis, and its application prospect in the leakage detection of buried pipelines is promising.

Regular internal and external detection on oil and gas pipelines is helpful for timely and accurate detection of pipeline corrosion defects, and to take appropriate maintenance and replacement measures and effectively reduce the occurrence probability of corrosion accidents. Focusing on the problems of external corrosion, internal corrosion, stress corrosion cracking, and external corrosion of crossing sections, the development status of corrosion detection technology and related standards for oil and gas pipelines was elaborated, the principles and engineering applications of trenchless detection technologies such as transient electromagnetic detection, ultrasonic guided wave detection, and magnetic stress detection were introduced, the problems existing in the application and management of corrosion detection technology for oil and gas pipelines in China were summarized, and the demands for future development were discussed from the aspects of management improvement and technology upgrading. In terms of management improvement, it was proposed to build a unified technical specification, data management platform and professional corrosion detection efficiency evaluation team. As for technology upgrading, it was suggested to continuously carry out research on stress corrosion cracking detection and assessment technology, initiate research on microbial corrosion mechanism and detection technology, carry out research on pinhole corrosion defect detection and verification technology, and develop combined internal and external detection tools.

Intelligent pipeline is a comprehensive management system covering the full life cycle of long-distance oil and gas pipelines. It is also the continuation and development of SCADA system, electronic pipeline, digital pipeline and smart pipeline in the era of Internet of Things, cloud computing and artificial intelligence. This paper analyzed the connotation and extension of intelligent pipeline in oil and gas pipeline industry, combed the historical development of intelligent pipeline technology, and revealed the essence and application status of Digital Twin technology. On that basis, it is suggested that the principles of demand-driven, problemoriented, priorities-highlighted, unique characteristics, open and integration, data sharing, rolling development and continuous improvement should be adhered to in the construction process of China’s intelligent pipeline, so as to provide reference for the healthy and sustainable development of China’s intelligent pipeline.

The investment, construction and operation management of gas storage have been highly valued by all levels of government departments and related enterprises in China since the 12th Five-Year Plan. Recently, the investment and construction of gas storage have been rapidly developed. As the system and mechanism reform of natural gas industry steps into a critical period, it is necessary to sort out and summarize the relevant policies and regulations on gas storage issued by China in recent years and the research results of Chinese scholars. The time series logic of policy items was clarified according to the investment, construction and operation management policies and evolution of China’s underground gas storage since 12th Five-Year Plan. The research progress and main achievements of Chinese scholars on the working gas capacity, operation mode, unit investment and operation cost, gas storage pricing, economic assessment methods and parameters of underground gas storage at home and abroad were comprehensively summarized. In such special development period when the “three period superimposed” occurs in China’s natural gas industry, in order to further improve the investment decision-making level, stimulate the motivation to invest and construct the underground gas storage, and improve the operation and management capability of gas storage, the main directions for subsequent policy setting, research and consultation works were put forward.

Aiming at the safety problems of pipelines with corrosion defects caused by ground load occupation, a three- dimensional foundation-pipe-load finite element model was developed by means of ABAQUS software. The stress and deformation of buried pipeline subjected to ground load and corrosion defect were investigated. And the effects of pipeline burial depth, pipeline internal pressure, ground load and corrosion defect location on the mechanical properties of buried pipeline were studied. It is indicated that with the increase of pipeline burial depth, the stress distribution on the pipeline can be effectively alleviated, but the amount of excavation works will be increased. When the internal pressure of buried pipeline reaches a certain value, the maximum stress of the pipeline with corrosion defect is mainly dominated by the internal pressure and less affected by the ground load. The effect of pipe-soil tangential friction coefficient on the mechanical properties of buried pipeline is significant. The pipeline stress increases linearly with the increase of the pipe-soil tangential friction coefficient. And the stress of the buried pipeline with corrosion defect is maximum when its corrosion defect is located in the direction of a quarter past five to the pipeline section.

With the rapid development of oil and gas pipeline construction, X80 pipeline steel and steel pipe have been applied on large scale. The research and application history and main progress of X80 high-grade pipeline steel and steel pipe in China were reviewed, the challenges faced were pointed out, and the suggestions for development were put forward. After nearly 20 years of development, about 17 000 km of X80 oil and gas transmission pipelines have been constructed, with the single pipeline capacity up to 380×108 m3/a. China’s X80 pipe manufacturing and pipeline construction technology have also ascended to the ranks of international leaders. Key technologies such as microstructure analysis, identification and assessment, strength test and yield to tensile ratio control, fracture and deformation control of X80 pipeline steel and steel pipe have been formed, as well as manufacturing technologies related to the X80 hot-rolled coiled sheet and large diameter thick wall spiral submerged arc welding pipe, wide and thick plate and large-diameter thick-wall longitudinal submerged arc welding pipe, high strain pipeline steel and steel pipe, and the design and manufacturing of induction bends and fittings. These technologies have strongly supported the construction of major pipeline projects like Line 2 of West-to-East Gas Pipeline Project and the China-Russia Eastern Gas Pipeline Project. For future development, the following suggestions were put forward. It was suggested to strengthen the weldability assessment and control of coiled sheet or steel plate, deepen the research on field welding technology and quality performance control, promote the application of high-grade pipeline steel and steel pipes in the construction of largecapacity pipelines, and improve the research and application of theory and technology on failure control and integrity of oil and gas pipeline.

In consideration of the structural characteristics of high-grade steel pipes and the great influence of weld failure on the safety of pipelines, the bearing capacity of girth welds of pipelines has become a research hotspot in the pipeline industry. The full-automatic joint in the China- Russia Eastern Gas Pipeline was taken as the research object, and the differences of material constitutive relations in the four zones of root welding, heat affected zone, base metal and fill welding in girth welding joint were accurately considered. The numerical simulation model based on finite element method was established for analyzing the strain capacity of pipeline girth welding joints. Quantitative analysis was made on the influence of the matching ratio of toughness and other factors on the driving force of crack growth in pipeline girth welds under combined operating conditions of base metal yield ratio, operating internal pressure and load type. The failure determination method of static crack initiation was adopted. The apparent fracture toughness value was taken as the critical criterion. In combination with the actual variation range of the material characteristic parameters of pipes and girth welding joints of the China-Russia Eastern Gas Pipeline, the strain capacity of the China-Russia Eastern Gas Pipeline girth welding joints under the most unfavorable conditions within the design operating conditions was calculated. The results show that improving the strength matching of weld zone is conducive to reduce the driving force of crack growth in the joint effectively. Increasing the internal pressure of the pipeline or raising the yield ratio of the base metal will cause the driving force of crack growth larger under the same strength matching condition, and the driving force of crack growth under tensile load is greater than that under bending load. This method can be used not only to guide the determination of welding parameters according to the performance requirements of welded joints, but also for the applicability assessment of defective welded joints in service pipelines.

In order to evaluate the operational safety risk of municipal pipeline networks rapidly and scientifically, the operational safety accidents of pipeline networks were collected and analyzed by means of online survey and field investigations. Then, the accident impact mechanisms of key risk elements were studied, including third-party damage, corrosion, aging and temperature change. Based on this, the risk evaluation index system for operational safety of municipal pipeline networks was established. In the system, the index scores are determined by semiquantitative method and the index weights are computed by analytic hierarchy process. Finally, test was conducted on a certain industrial park and the risk of gas pipeline network was assessed. It is shown that the scoring criteria of each index can be determined easily and operated conveniently, and its evaluation results are in accordance with the survey results, so this risk evaluation index system is applicable to the fast risk evaluation of municipal pipe networks.

In order to study the stability of the salt-cavern gas storage with mudstone interbeds subject to the explosion of combustible gas, a numerical model for the deep salt-cavern gas storage was established using the finite differencesoftware FLAC3D. And the dynamic response of salt-cavern gas storage with mudstone interbeds to the explosion loads wasinvestigated, including the change of the stress state, the seismic dynamic amplitude and the stability of the surroundingrocks of the salt-cavern gas storage. It is shown that under the explosion effect of combustible gas, the change of the stressin mudstone interbeds is basically accordant with that in the salt rocks and there are no obvious weak parts. The impactof artificial fitted explosion shock wave to the surrounding rock is severer than that of the triangle explosion wave. Thedamage of the explosion of combustible gas to the surrounding rock of the cavern is limited and it attenuates rapidly with theincrease of the depth. The anti-explosion capability of the deep salt-cavern gas storages is much stronger than that of shallowcaverns, which is favorable for the stability of gas storage caverns.

The backbone network of oil and gas pipelines in China has begun to take shape, and the construction of intelligent pipeline network becomes possible on the base of increasingly perfect operation and maintenance system and the application of Big Data, artificial intelligence, and technologies of the Internet of Things. The construction of intelligent pipeline network undertaken by China National Petroleum Corporation was exemplified to introduce and summarize the construction progress of intelligent pipeline network at the present stage in terms of science and technology, information, and the Internet of Things based on the existing design scheme of intelligent pipeline network. Then the latest achievements were introduced from the pilot projects on China–Russia Eastern Gas Pipeline and China–Myanmar oil and gas pipelines, and the problems to be solved were set forth for the construction of intelligent pipeline network. The targets of the intelligent pipeline operation will be realized, including comprehensive and uniform data, interactive and visual perception, integrated and interconnected system, precise and matched supply, intelligent and efficient operation, and controllable prediction and prewarning, by defining the principles and objectives of pipeline network construction and developing an effective method for the construction of intelligent pipeline network by practical research.

China-Russia Eastern Gas Pipeline, as a landmark project of China’s third generation of longdistance and large-capacity gas pipeline, is the largest single gas pipeline in the world and holds many new records in the history of pipeline construction, both in China and abroad. As a pilot project, the pipeline was built to be China’s first intelligent pipeline model project. The basic connotation and key technologies of intelligent pipeline and intelligent pipeline network were systematically explained, and the key technologies and phased achievements supporting the “full digital handover, full intelligent operation and full life cycle management“ of the pipeline were combed, so as to provide important guidance for continuously promoting the pipeline intelligent construction in China and assisting to build the large intelligent interconnected pipeline network. Furthermore, from the aspects of knowledge and technology, further thinking and suggestions were given on the technical essence of pipeline intelligence, digital infrastructure of pipeline, breakthrough of pipeline bottleneck technologies, intelligent brain of pipeline network, etc.

Following the construction and operation requirement of “one network nationwide”, the grid management objectives are proposed, namely, to focus on safe, efficient and high-quality development, to highlight the "process-oriented" and "refined service" concepts, to transversely sort out and integrate production activities, to vertically compress management levels, to build information support systems, and to seek collaborative optimization schemes for resource sharing and business. With reference to foreign advanced experience, it was proposed to take regional management achievements as part of grid management solutions. With gridding, flattening and specialization as the goal, risk management and control as the core, automation, informationization and intelligence as the support, standardization as the effective approach, and improvement of staff quality and initiative as the foundation, the regional management can be continuously promoted in a closed-loop process. The implementation idea of grid management has been raised, that is, to construct the “grid ＋ flat" organizational form, to set up the integrated and interconnected information center system, to establish the comprehensive and unified standard system, to form the intelligent technical support and professional operation & maintenance support system, and to build a high-quality workforce. At present, it is urgent to develop a scientific grid management implementation plan at the level of “one network nationwide” for better serving the company’s strategic development goals.

Injection-production gas capacity, storage capacity and working gas volume are important indexes for measuring the capacity of underground gas storage (UGS). Dynamic characteristics analysis is an important means to evaluate the capacity of UGS. Based on the multi-cycle injection-production performance of a certain UGS rebuilt from the carbonate sour gas reservoir with bottom water, the injection-production capacity of horizontal well was evaluated by analyzing the dynamic characteristics of UGS during its operation. Then, the storage capacity of UGS was checked by using two methods. Finally, the change of the mass concentration of H2S in the gas reservoir was analyzed, and the operation mode of desulfurization was evaluated. It is indicated that this UGS is high in single well productivity, storage capacity implementing degree and efficient development potential, but its operation mode of desulfurization still needs exploring. What’s more, the water flooding mechanism of Well AH1 leading to its off production was studied, and the specific technological measures for restoring the production capacity of gas well were put forward and successfully applied on site. The research results play an important role in guiding the production, operation and gas storage capacity evaluation of UGSs rebuilt from carbonate gas reservoirs with bottom water in China.

Underground gas storage (UGS) is one important part of natural gas supply chain, and it plays an important role in the peak shaving, security and supply support of natural gas in China. In this paper, the 20 years’ development history of China’s UGSs from zero to large-scale industry was reviewed with the overall construction of the Dazhangtuo UGS of the Dagang Oilfield in 1999 as a mark. In this period, 27 UGSs were built up with the peak shaving capacity more than 100×108 m3, over 100 invention patents and over 20 software copyrights were authorized, 15 standards were formulated and over 20 monographs were issued. Then, the technological innovation achievements obtained in the UGS construction in China were mainly described, including 10 typical technological achievements, e.g. the UGS site selection mode and evaluation technology in the situations with complex fault block, complex fluid, complex lithology and strong-heterogeneity deep reservoir, the evaluation technology for the dynamic sealing performance of UGS trap with complex geological conditions, the drilling and completion technology with the ultralow-pressure lost circulation control and reservoir protection and the wellbore sealing under alternating stress as the core, the key technology and equipment for the surface injection and production at high pressure and large flow rate, and the “three-in-one” risk control system of UGS formation-wellbore-surface. Finally, based on China’s 20 years of UGS construction experience and China’s current industry policies, the opportunities and challenges of the future UGS development in China were clarified.

Girth weld is an indispensable part of long-distance pipelines. Girth weld failure is caused by the interaction of load, defects, local fracture toughness, strength matching, weld geometry and residual stress, and the welding for high steel grade pipelines is particularly difficult which increases the failure possibility of girth welds. In this case, the load, defect and strength matching characteristics of girth weld were analyzed, the strain concentration mechanism of low matching girth welds or softening girth welds in heat affected zone was revealed, and four failure modes including brittle fracture, net section collapse before yield, net section collapse after yield and base metal necking of girth weld were explained. Based on the comparison of the applicability of girth weld safety assessment in GB/T 19624-2019, BS 7910-2015, API 579- 1/ASME FFS-1-2016, API 1104-2013 and other domestic and foreign standards, the strainbased girth weld safety assessment method was proposed, and the influence of crack size, strength matching coefficient and other factors on girth weld crack driving force was discussed. The research demonstrates that the load or displacement of the girth weld should be the premise of the safety assessment, and improving the strain capacity of the girth weld can enhance the adaptability of high grade steel pipelines to adverse geological conditions. It is suggested to carry out the research on the initiation and growth mechanism of the girth weld crack defects, develop the strain-based fracture theory, optimize the strength matching of the girth weld, and quantify the relation between the strain capacity of the girth weld and the geometric and mechanical performance parameters of the weld.

China-Russia Eastern Gas Pipeline has been in the operation stage after commissioning, however, the high steel grade, large diameter, high pressure and large transportation capacity, as well as the cold frozen zone along the pipeline, all pose great challenges to the operation of the pipeline, such as enormous uncertainty, high risks, difficulty in maintenance and security, etc. The problems that may exist in the pipeline technology were elaborated, including optimal operation of the pipeline network, peak shaving in winter, prevention and control of ice blockage, venting and recovery, etc. In the aspect of integrity management, the pipeline was facing problems like in-line inspection of large-diameter pipeline and evaluation of safety status of high-grade steel pipeline. In terms of line risk control, there would be problems such as gas pipeline leakage and safety status monitoring, corrosion, prevention and control of frost heaving and thawing settlement, etc. As for maintenance and repair, a series of technical problems represented by cutting, demagnetization and repair of D 1 422 mm pipeline needed to be solved. The status of related technologies in China and abroad were summarized and technical solutions for the problems were proposed. In addition, some of the technological achievements that have been made in China-Russia Eastern Gas Pipeline were summarized to provide reference for the construction and operation of oil and gas pipeline in the future.

In order to study the flow-pattern transition laws of gas-liquid two-phase flow and establish the gas-liquid hydraulic calculation model with high precision, three flow-pattern-prediction models, i.e. the general model, the modified Taitel-Dukler model and the slug characteristic analysis model, were introduced, and their application effects to predict the flow pattern of gasliquid tow-phase flow were verified based on the experimental data from Shoham and Kokal. Then, based on these three flow-pattern-prediction models, the flow pattern prediction maps were plotted and compared with the experimental data. Finally, the characteristics of the three models were summarized. It is shown that the unified flow-pattern-prediction model and the model via slug characteristic analysis do better in the flow pattern prediction of gas-liquid twophase flow and the unified model is more applicable to different situations. The research results provide the basis for selecting the flow pattern prediction algorithm used for the hydraulic calculation of gas-liquid two-phase flow.

The automatic control level of long-distance oil and gas pipelines has direct relation with the safety and efficiency of production and operation. China–Russia Eastern Gas Pipeline Project put into operation on December 2, 2019 has opened a new chapter in China’s long-distance oil and gas pipeline automatic control technology through innovative practices. Grasping the main line of the technical characteristics of automatic control system and relying on the typical longdistance oil and gas pipeline control system, the development process of key technologies in China’s long-distance oil and gas pipeline control system was reviewed, the development status of automatic control technology for long-distance oil and gas pipelines were introduced, and the development prospect of automatic control technology for long-distance oil and gas pipelines was predicted in combination with intelligent pipeline construction. All design indexes of the northern section of China–Russia Eastern Gas Pipeline Project are in the world’s leading level. From the view of innovative achievements in the composition, structure and function of SCADA system, the automatic control system thereof represents the current highest level of automatic control technology for long-distance oil and gas pipelines in China.

Underground gas storage (UGS) is playing an irreplaceable role in peak shaving and gas supply guarantee. Salt cavern UGS is a kind of cavern-type storage and its construction is characterized by long construction period, high investment and complex engineering technology, but it doesn't need ramp up time and it can be put into production while being constructed. In addition, its ratio of cushion gas is lower and it can be recovered completely. Its operation is characterized by great gas production capacity, flexible gas injection and production, and low coefficient of gas losses. Salt cavern UGSs can not only satisfy the conventional demand of seasonal peak shaving, but also the demand of daily, hourly and emergency peak shaving. In this paper, the construction and operation data of salt cavern UGSs at home and abroad were analyzed, and the important role of Jintan Underground Gas Storage in the actual operation was described. Then, some thoughts on the function orientation of salt cavern UGSs were put forward. The research results provide a reference for the further optimization and reasonable development of salt cavern UGSs.

China-Russia Eastern Gas Pipeline is characterized by ultra-large diameter, high grade steel (X80) and high pressure rating. It is located in the area with geologically active permafrost and semi-permafrost zones in the north, where is prone to geological disasters. Hence, the nondesign load may bring about the overall stress level of the pipeline exceeding the strain capacity of the pipeline, which poses great challenges to the structural integrity and long-term safe operation of the pipeline. Therefore, high-precision measurement of stress value during pipeline operation will be crucial to its safety assessment. According to the actual service conditions of China-Russia Eastern Gas Pipeline, the propagation time of ultrasonic LCR wave in the elastic-plastic deformation of X80 steel was measured, and the propagation rule of ultrasonic LCR wave in the elastic deformation and plastic deformation of X80 steel was explored on the basis of studying the theory and method of detecting pipeline stress by ultrasonic LCR wave. At the initial operation stage of China-Russia Eastern Gas Pipeline, the reliable and applicable pipeline stress measurement technology was formed, serving as a technical reserve for the future safety assessment of the pipeline in its operation and maintenance.

Due to the characteristics, such as massiveness, multi-source, diversity and great difference of value density, of the data of natural gas pipeline network, it is of great difficulty to do data analysis and application. With reference to the study results of big data in power grid, supply chain and internet, a big data analysis framework of natural gas pipeline network based on data processing, data mining and comprehensive analysis of multivariate data is put forward. Definitely, the method and function of data processing is illustrated in terms of data cleaning, feature selection and reconstruction. Based on the specific business and scenarios, it is defined that prediction and early warning, model identification, rule learning and deduction are the basis to construct the data mining method of pipeline network. In addition, the comprehensive application of diversified data of pipeline network is discussed. It is also pointed out that the development of multimode learning and federated learning is the key to break the data barrier and to form data intelligence of pipeline network. Through big data analysis of natural gas pipeline network, the big data “ecology” of pipeline network shall be improved continuously, the machine learning method of knowledge in data fusion shall be deeply researched, and a cross-border interpretable and controllable big data analysis method system of pipeline network shall be established, so as to provide theoretical support for development of intelligent pipeline network technologies.

With the reform of the production management mode of natural gas pipelines, the regional management of the compressor stations has been gradually promoted as an advanced management concept and needs various production and operation technologies to support it, such as regional management, unattended station and remote control. The one-key start and stop technology is the important technical foundation for the regional management of compressor station. In this paper, Gaizhou Compressor Station was taken as a pilot project. The hardware foundation to achieve one-key start-stop station was prepared by taking a series of optimization measures at the compressor station of gas pipeline, e.g. the fully automatic control andtransformation of station and compressor process, the optimization of control system configuration, the in-depth integration ofstation control and compressor control system and the integration of compressor auxiliary system. From the perspective of software function, the one-key start-stop station is divided into one-key start station and one-key stop station. The one-key start is composed of 6 parts, i.e., state feedback and alarming detection, automatically conducting technological processes inside stations, self-startand stop of compressed air system, automatic distribution of air blowers in compressor workshop, one-key start of compressor set, and automatic commission and quit of anti-surge control and load distribution. Based on the 3 stop models of compressor set and their technical requirements, the one-key stop station is divided into 5 automatic stop modes, i.e., normal stop, multi-machine stop, multi-machine pressure maintaining stop, total-station ESD, and multi-machine pressure relief stop. The successful application of the pilot project at Gaizhou Compressor Station reveals the major advancement in the control level of compressor stations in China, and provides the experience and technical base for the construction and reconstruction of the subsequent compressor stations and the reference for the one-key start and stop of long-distance liquid pipelines.

At present, there is still a lack of effective identification methods for oil and gas pipeline surface defects. To solve this problem, based on metal magnetic memory technology, a multicharacteristic statistical identification method for the identification of pipeline corrosion defects and early stress concentration defects was established through the magnetic memory test data obtained from pipeline test pieces with circular-hole corrosion defects and elbow bend stress concentration defects. Under laboratory conditions, the defect types of the three test pieces were identified by this method. Under the site conditions of the oil field, non-blind test and blind test were respectively conducted to verify the defect types of two pipelines. The identification accuracy rate is above 80%, which indicates that the established defect type identification method is effective and has high identification rate for the identification of pipeline corrosion defects and early stress concentration defects, so it can provide certain reference for the research in this field.

Reliability analysis is an effective technical means to reduce the risks in the process of LNG storage and transportation and ensure the safe and efficient operation of LNG supply chain. In this paper, LNG receiving terminal and LNG shipping were combined into an LNG whole transportation system, and the connotation of its reliability was clarified. Then, aiming at the problem of insufficient LNG shipping failure data, a reliability simulation model based on the operation mechanism of whole transportation system was established. Finally, the fault tree model for the system of LNG receiving terminal was established and the minimum cut sets were classified to carry out qualitative and quantitative analysis on the reliability of LNG whole transportation system. And accordingly the weak links of the system were determined. Case application verifies the calculation method for the operation feasibility of LNG whole transportation system is feasible and can provide the reference for the safety management and equipment maintenance in the process of LNG shipping and storage at LNG receiving terminals.

China–Russia Eastern Gas Pipeline Project is the successful model of deepening cooperation between China and Russia under the Belt and Road Initiative. As a representative project of the cross-border gas transmission pipeline, the pipeline project is of great reference value for its characteristics and experience in preliminary works. The background and significance of China–Russia Eastern Gas Pipeline Project were summarized, the preliminary work processes such as commercial negotiation, pre-feasibility study, feasibility study, project application report preparation, etc. were combed, the special research process focusing on the complex technical and economic conditions of China–Russia Eastern Gas Pipeline Project was introduced, and the innovative achievements of the preliminary works of China–Russia Eastern Gas Pipeline Project were highlighted. The research shows that, for large cross-border energy pipeline projects such as China–Russia Eastern Gas Pipeline Project, its preliminary works may involve multi-level issues in the field of diplomacy, commerce, technology, economy, etc. More manpower, research resources and sufficient time may be required for the smooth implementation of the project.

Periodic variation of production pressure in underground gas storages can generate alternating loads acted on skeleton rocks. Under alternating loads of intensive injection and production, rocks will be damaged and their mechanical properties will change. And as a result, the stability of borehole wall and skeleton rock will be impacted and sand production will be induced. In this paper, the sand production law of injection/production wells under the alternating load of intensive injection and production was experimentally simulated. Then, the sand production index formula was modified by using rock damage severity, loading times, loading frequency and other parameters. Finally, the sand production risk of injection/production wells was analyzed and the sand production time was predicted. In this way, the influence law of injection/production cycle on sand production of injection/production wells was figured out. By virtue of the modified sand production index formula, the sand production period and degree of injection/production wells can be predicted. And it also plays an effective role in guiding the selection of early sand control completion mode of injection/production wells in underground gas storages and formulating reasonable production system to control sand production of injection/production wells so as to ensure the smooth operation of underground gas storages.

In order to ensure the safety of a buried pipeline with circumferential surface cracks, it is necessary to accurately figure out the maximum settlement that the buried pipeline can bear. In this paper, the simulation test on the four-point bend settlement of full-size pipeline was carried out under the design pressure to get the ultimate bearing bending moment of the pipeline with circumferential surface cracks. Then, the finite element model for the settlement simulation test was established, and the ultimate bearing bending moment of the pipeline with circumferential surface cracks was calculated and simulated by taking the fracture toughness as the failure indicator. After the finite element model was verified effectively by the simulation test, a series of ultimate bearing bending moments of the pipeline with circumferential surface cracks of different depths could be obtained. Meanwhile, a pipe-soil model for the uneven settlement of the site was established using the software ANSYS, and the influence of pipeline depth on its bearing bending moment was analyzed. It is indicated from the analysis on the ultimate settlement of the pipeline with circumferential surface cracks of different depths that when the pipeline depth is constant, the ultimate settlement of pipeline failure is in an approximate linear negative correlation with the crack depth. And when the crack depth of pipeline is constant, the ultimate settlement corresponding to pipeline failure is in a nonlinear negative correlation with the pipeline depth.

Landslide is one of the geological disasters which threaten the safety of buried pipelines. The mechanical state of the pipeline under the action of landslide is controlled by the pipeline structure and the relationship between the landslide and the extension direction of the pipeline. The stress state of polygonal-shape transverse pipeline is the most complicated. The gas pipeline of Zhongwei-Guiyang tie line K1224 at the slope is a typical polygonal-shape transverse buried pipeline. Due to rainfall and road excavation at the toe of the slope, the slide of this slope leads to pipeline deformation. In this paper, based on numerical modeling and in-situ monitoring, the destruction characteristics of landslide deformation under different operating conditions and the corresponding mechanical response of the pipeline were analyzed by means of the incomplete coupling of pipe-soil separation. It is indicated that the activity of the landslide is intensified by road excavation at the toe of the slope together with rainfall. The horizontal displacement of the pipeline along the sliding direction of the slope is particularly obvious, and the phenomena of sudden displacement increase occur near the turning points of the pipeline. The stress near the turning points of the pipeline is much higher than that in straight sections. Due to the uneven landslide displacement controlled by microtopography and its moment, the stress concentration degree near the turning point in the southern side of the pipeline is the highest. What’s more, the stress near the turning point in the southern side of the pipeline is close to the stress limit of the pipe material, so this part is the most dangerous area of this pipeline section.

As a country rich in oil and gas resources, Turkmenistan’s natural gas industry has become a pillar industry of its national economy. However, Turkmenistan’s natural gas export shows a weak growth trend due to insufficient productivity construction and blocked export channels. At present, Turkmenistan has natural gas export lines from Russia in north, Iran in south and China in east. Whereas China is the only major buyer of its natural gas due to the influence of geopolitical and economic interests. To get rid of such predicament, Turkmenistan actively promoted the diversification of natural gas export. On the one hand, it expanded new export channels, vigorously promoted the implementation of TAPI project to South Asia, and at the same time discussed the Trans-Caspian Natural Gas Pipeline Project with each stakeholder. On the other hand, Turkmenistan fully promoted the resource utilization of natural gas in the country, vigorously developed natural gas chemical industry and power generation, and converted existing natural gas resources into products with high added value for export. Turkmenistan, as a source country of China’s natural gas imports, has an irreplaceable position in China’s natural gas imports from Central Asia. It is the most realistic in the current relations between China and Turkmenistan to tamp down the performance of the China-Turkmenistan natural gas trade contract and to guard against Turkmenistan’s reduction in gas supply. In the future, the possibility of establishing a large natural gas pipeline network from Central Asia to South Asia, covering China, Iran, Turkmenistan, Azerbaijan, Pakistan and India, may be explored based on TAPI and IPI projects.

The full life cycle data management is the foundation of the full life cycle integrity management of oil and gas pipelines. The research and development status of the full life cycle data management technology for oil and gas pipelines were systematically expounded from the aspects of data model building, digital handover standard, digital handover interface development, data integration maintenance and analysis application. According to the data management requirements of China-Russia Eastern Gas Pipeline, the PIDM data model was optimized and upgraded from two aspects of data content expansion and data organization structure optimization, and the association rules of data in all stages of the full life cycle of the pipeline were added to the PIDM data model. A series of standards and specifications were developed and revised, including Oil and gas pipeline equipment and facilities operation data specification (CDP-G-OGP-IT-148-2019-1), Specification for pipeline integrity management - Part 6: Data collection (Q/SY 05180.6-2019), therein implied the specific service requirements and corresponding data rules of China-Russia Eastern Gas Pipeline. The PIS function of the pipeline integrity management system was optimized: advanced GIS service functions such as vector slicing, WFS, and Web Scene were expanded at the back-end server, while rich data display, analysis, and maintenance functions such as customized drawing, multilingual support, local data display, shared view, roller shutter, timeline, and event editor were developed at the front-end. The above achievements performed well in the practical application of the north section of China-Russia Eastern Gas Pipeline. Finally, the bottleneck problems to be solved urgently in the future life cycle data management of the oil and gas pipeline was put forward.

The full life cycle data management is the foundation of the full life cycle integrity management of oil and gas pipelines. The research and development status of the full life cycle data management technology for oil and gas pipelines were systematically expounded from the aspects of data model building, digital handover standard, digital handover interface development, data integration maintenance and analysis application. According to the data management requirements of China-Russia Eastern Gas Pipeline, the PIDM data model was optimized and upgraded from two aspects of data content expansion and data organization structure optimization, and the association rules of data in all stages of the full life cycle of the pipeline were added to the PIDM data model. A series of standards and specifications were developed and revised, including Oil and gas pipeline equipment and facilities operation data specification (CDP-G-OGP-IT-148-2019-1), Specification for pipeline integrity management - Part 6: Data collection (Q/SY 05180.6-2019), therein implied the specific service requirements and corresponding data rules of China-Russia Eastern Gas Pipeline. The PIS function of the pipeline integrity management system was optimized: advanced GIS service functions such as vector slicing, WFS, and Web Scene were expanded at the back-end server, while rich data display, analysis, and maintenance functions such as customized drawing, multilingual support, local data display, shared view, roller shutter, timeline, and event editor were developed at the front-end. The above achievements performed well in the practical application of the north section of China-Russia Eastern Gas Pipeline. Finally, the bottleneck problems to be solved urgently in the future life cycle data management of the oil and gas pipeline was put forward.

The station temperature of China-Russia Eastern Gas Pipeline Project is designed low to －45 ℃, which poses new challenges to the brittle fracture prevention capability of pipeline facilities, so it is necessary to set up scientific and reasonable toughness index requirements to prevent brittle fracture of in-service components under low temperature conditions. The development process of brittle fracture control technology, from empirical method to fracture analysis diagram method and then to fracture mechanics method, was systematically described. The empirial method based technical status on brittle fracture control of oil and gas pipelines was analyzed with China-Russia Eastern Gas Pipeline as the example. Meanwhile, through the comparison and analysis with the brittle fracture control requirements in ASME Boiling and Pressure Vessel Code (BPVC), the deficiencies of brittle fracture control measures for oil and gas pipeline fittings were pointed out. Analysis shows that the experience-based Charpy impact toughness index may be insufficient to prevent brittle fracture when applied to high toughness pipeline steel. Therefore, it is suggested to ① build a perfect fracture mechanics-based brittle fracture control index system for highgrade high-toughness pipeline steel, ② add Nil-Ductility Transition (NDT) test requirements based on the existing brittle fracture control indexes, ③ and establish brittle fracture control requirements based on fracture mechanics evaluation.

A series of debugging work should be carried out before an LNG tank is put into operation, in which the pre-cooling of LNG tank is the most important part. In this paper, the pre-cooling model of 16×104 m3 ground full-containment LNG storage tank was established by MATLAB, to study the changing rules of LNG spray flow, BOG emission flow, tank pressure and LNG vaporization rate in the process of pre-cooling and the influence of the temperature drop rate on the pre-cooing of LNG storage tank. It is indicated that in the process of pre-cooling, the LNG spray flow increases gradually, the BOG emission flow and the tank pressure increase firstly and then decrease, and the LNG vaporization rate only decreases in the late stage of pre-cooling. As the temperature drop rate increases, the LNG vaporization rate only increases in the late stage of pre-cooling, and the LNG spray flow, the BOG emission flow and the tank pressure increase, but the total amounts of LNG spray and BOG emission decrease. When the temperature drop rate exceeds 3 K/h, its effect on the pre-cooling of LNG storage tank is smaller. Solar radiation shall not be neglected in the analysis on the pre-cooling of LNG storage tank. In order to ensure the smooth commissioning of LNG storage tank, it is recommended to control the temperature drop rate less than 1 K/h in the early stage of pre-cooling, and to increase the temperate drop rate and keep the average temperature drop rate 2-3 K/h in the late stage to increase the utilization rate of LNG cold energy. It is verified by actual case that the simulation error of the pre-cooling model of LNG storage tank is less than 10%, which satisfies the engineering application requirements. The research results can be used as the reference for actual pre-cooling process, pre-cooling plan design and pre-cooling parameter optimization of LNG storage tanks.

Path optimization of natural gas pipeline based on two-dimensional plane can hardly reflect the actual environment. In this paper, high-resolution discrete 3D terrain data was extracted using Global Mapper of GIS software and the Digital Elevation Model (DEM) was established. Based on the DEM, the path optimization model for the pipelines in hilly areas was established with the minimum length of natural gas pipeline as the evaluation index and the curvature radius of elastic installation as the constraint. Then the optimal surface path between two points was solved by the modified Dijkstra algorithm (A* algorithm) in the mode of heuristic search. Finally, it was applied to simulate the actual landform. It is indicated that the DEM based on Global Mapper has the advantages of small workload and high precision and it can be used as the simulated landform effectively. Besides, the A* algorithm is better in global convergence and calculation robustness and applicable to the solution of pipeline path optimization model. By virtue of A* algorithm, the total pipeline length and the path fluctuation degree can be decreased effectively.

In order to solve the technical defects of the conventional inner detector and to meet the actual demands of China-Russia Eastern Gas Pipeline Project, a new type of high density polyurethane inner diameter detector for large diameter pipelines before service was developed. The intelligent diameter measuring device mounted on the main body of high density polyurethane foam can not only find the change of the inner diameter of the pipeline and record the deformation position, but also accurately identify the number of girth welds of the pipeline, so as to verify the girth weld information in combination with the pipeline construction records. The working principle, structural composition and design and implementation of the electronic system of the detector were discussed. The detector has been applied to the site inspection of China-Russia Eastern Gas Pipeline Project. The results show that, compared with the conventional cup-shaped steel skeleton intelligent diameter measuring detector, the required operating thrust of the detector is smaller, the allowable operating speed is higher, the structure is more robust, and the maintenance is simple. While ensuring the detection accuracy and detection rate, the detector brings dramatic decline in use cost and important engineering significance for the geometric deformation detection of large diameter pipelines.

Oil pipeline leakage will cause direct economic losses and even adversely affect the surrounding environment and residents along the pipeline. It is crucial to be aware of the seepage, surface diffusion and evaporation of leaked oil in the surrounding environment for emergency disposal of pipelines and assessment of leakage consequences. Considering the characteristics of onshore oil pipeline leakage accidents, the research results of oil product pipeline leakage were summarized from the aspects of leakage quantity, flow and diffusion rules of the leaked oil under accident conditions and leakage consequences. Additionally, suggestions were proposed for further studying the diffusion process of the leaked oil in surrounding environment, estimating the leakage consequences and developing reasonable emergency disposal schemes.

In order to evaluate the ultimate pressure bearing capacity of high-grade steel pipeline with pure dent defect, finite element analysis was performed for the deformation of steel pipeline during the formation of dent and the hydraulic test. In addition, full-scale hydrostatic burst test and strain test were also conducted for the pipeline with pure dent defect. Based on the full-scale test results, the results of the finite element analysis were verified in terms of burst pressure, rebound behavior and strain of pipeline with pure dent defect. The results show that the finite element analysis results are consistent with the experimental results in both processes of dent formation and hydraulic test, with an error of less than 10%. It indicates that the simulation of the dented pipe is accurate. Besides, the burst pressure of the dented pipe with a depth of 15.9% D (D refers to the outer diameter of pipeline) is 38 MPa, which is higher than the calculated burst pressure, 31.2 MPa, of the non-defective steel pipe, indicating that the tested dent has no adverse effect on the pressure bearing capacity of pipeline. The research findings provide technical support to the theoretical analysis of high-grade steel pipeline with dent defect.

Secondary distribution of product oil is an important part of the oil product supply chain. Different distribution schemes will directly affect the profit of product oil sales enterprises. It is particularly necessary to formulate an appropriate route planning schemes for oil tank trucks. Taking the shortest total distribution route as the objective function, and the actual oil tank truck quality and the oil demand of gas station as constraint conditions, considering the time window of oil product unloading, an optimization model of secondary distribution of product oil is established, and a solution method based on hybrid genetic simulated annealing algorithm is proposed. The model and algorithm are tested using an example with and without a time window. The results show that: Compared with the product oil secondary distribution scheme before optimization, the example without time window shortens the total distance by 3.66%; the example with time window only takes 9.54 s to solve, which is fast in calculation and can meet the distribution requirements. The optimization model of the secondary distribution route of product oil based on hybrid genetic simulated annealing algorithm can not only improve the calculation efficiency, but also search more comprehensively and obtain better solution.

To achieve the construction goal of “full digital handover, full intelligent operation and full life cycle management” of the China-Russia Eastern Gas Pipeline Project, the basic process and working mechanism of digital handover were proposed, and the significance to pipeline construction and operation management was pointed out. The data docking channel was unblocked by unifying the data acquisition standard. With the full life cycle database as the carrier, the association, storage and sharing of data were realized. Hence, the digital handover was promoted in order to meet the demand of simultaneous delivery of entity pipelines and digital pipelines and ensure the traceability of data history. By establishing an interface with the data warehouse for data calls, the orderly transfer of data from the construction phase to the operation phase was ensured, and the docking application of the digital handover data and the pipeline integrity management system was realized. All of these not only present the value of data to the greatest extent, but also provide data guarantee for intelligent pipeline construction and integrity management.

The storage and transportation of natural gas in the form of hydrate has the advantages of low storage pressure, safety and reliability, but the application of hydrate in the field of natural gas storage and transportation technology is hindered by low gas storage, low formation rate and other factors. In this paper, methane hydrate was taken as the research object. The effecting laws of pressure, temperature of constant temperature bath, mass concentration of surfactant SDS and intake time of methane on the bubbling formation of methane hydrate in ice slurry were studied by experiment. The pressure of the experiment is in the range of 4-6 MPa, the temperature of the constant temperature bath is between －1 ℃ and 1 ℃, and the mass concentration of surfactant SDS is in the range of 100-800 mg/L. It is shown that the pressure change has little effect on the ultimate gas storage molar volumetric concentration, the temperature of the constant temperature bath rises from －1 ℃ to 1 ℃, the reaction duration is shortened by 11.5%-17.4%, and the molar volumetric concentration of gas storage is reduced by 7.4%-8.5%. In addition, extending the intake time appropriately is conducive to shortening the induction time and increasing the formation rate and ultimate gas storage molar volumetric concentration.

When the unheated gathering and transportation technology is adopted in oil fields at high water cut stage, the phenomenon of congealable oil adhering to the wall often occurs inside the pipeline due to the low transportation temperature, and this may lead to the reduced pipeline flow area, the back pressure rise at the wellhead and the increased energy consumption of gathering and transportation. On the basis of the traditional cold finger device, an experimental device was designed to realize the circulation of test medium. With this device, the effects of oil temperature, oil wall temperature difference, water cut, shear strength and test time, on the oilwall- adhering behavior of high water-cut waxy oil-were investigated. The results show that the congealable oil wall-adhering and the multiphase wax deposition are not the same deposition behavior. Serious wall-adhering occurs when the temperature of oil-water mixture is lower than the initial wall-adhering temperature. The wall-adhering temperature of high water-cut waxy crude oil is lower than the pour point of pure oil. The higher the water cut is, the lower the initial wall-adhering temperature will be. The effects of oil-wall temperature difference and oil temperature on the wall-adhering behavior are distinguished from temperature intervals. The wall-adhering behavior below the crude pour point is mainly controlled by the oil temperature, while the wall-adhering behavior above the pour point is more affected by the temperature difference. For the unemulsified oil-water mixture, the presence of water phase weakens the wall-adhering behavior. On the contrary, the presence of water phase enhances the wall-adhering behavior. Stirring or pipeline fluid flow mainly exerts shear stripping effect on wall-adhering congealable oil. The thickness of congealable oil adhering to the wall will definitely reach the limit value with time, instead of increasing indefinitely.

The severe slug flow occurred in the multiphase pipelines among 8-3A platform, 14- 3A platform and 116FPSO of Wenchang oilfield group was theoretically analyzed and experimentally studied. The flow state in 14-3A sea pipe was theoretically analyzed according to the judging criterion of severe slug flow. The experimental platform for pipeline S-shaped riser with severe slug flow was designed and reconstructed based on the size of the sea pipe, and the flow patterns of oil, gas and water in the sea pipe and their transformation processes were simulated. A set of automatic control program of throttle valve based on pressure signals along the pipeline was put forward according to slug flow elimination theory and classical PID control theory, and it effectively eliminated the severe slug flow in the experiment. After the transformation of 116FPSO is conducted, this technology is applied in Wenchang oilfield group. And owing to its application, the fluctuation amplitudes of lower sea pipe pressure and upper FPSO pressure are reduced significantly, and oil and gas production is improved.

In the China-Russia Eastern Gas Pipeline Project, large diameter (OD 1 422 mm), high pressure (12 MPa) and high grade steel (X80) pipelines were used to transport huge amounts of natural gas, so as to meet the needs of energy strategy. However, with the increase of pipe diameter, transmission pressure, steel grade and design coefficient, and the reduction in ambient temperature, the design and manufacturing difficulties of monolithic insulation joints have become the focus of the research. A series of technical innovation have been made and filled the domestic blank, e.g., the development of the monolithic insulating joints on the OD 1 422 mm X80 pipeline, the research on the key technologies for monolithic insulating joints in cold regions, the construction of large hydraulic pressure and bending test device. Therefore, a complete set of technology and equipment has been formed for the design and manufacture of monolithic insulation joints on OD 1 422 mm X80 pipeline, having great significance to the construction of natural gas pipeline in the China-Russia Eastern Gas Pipeline Project.

With the outbreak of the epidemic of COVID-19, traffic control, setting of check posts and other control measures have been implemented and posed challenges to the routine inspection of the pipeline. Regarding the issue that pipeline inspection personnel cannot complete the onsite inspection and maintenance under epidemic prevention and control situation, the spaceair- ground integrated pipeline intelligent perception technology system was proposed through analyzing the deficiencies of the existing pipeline perception technology. According to the principles of comprehensive perception, unmanned perception, real-time accurate perception and full life cycle perception, the technical route integrating artificial intelligence technology and pipeline perception technology was established. The intelligent interpretation method for satellite remote perception images of pipelines at space level, the unmanned aerial vehicle intelligent inspection method based on automatic airport in air, as well as the intelligent video method for key pipeline areas aboveground and the comprehensive intelligent perception method of underground optical fibers at ground level were designed. The field application of unmanned aerial vehicle（UAV） intelligent inspection technology based on automatic airport was explored. Field tests and applications show that the unmanned aerial vehicle intelligent inspection system based on automatic airport enables the automatic take-off, landing, charging and other operations without the human participation, and the operations following the set inspection path and inspection time. Besides, it can intelligently recognize threat events such as mechanical excavation and personnel gathering. During the epidemic of COVID-19, the UAV flew for more than 80 sorties and recognized more than 20 threats. This shows that it can provide strong technical support for pipeline inspection personnel to master the safety status of pipelines.

In order to improve the economic benefit of oilfield united stations and reach the target of further energy saving, a series of studies were carried out in this paper to adopt the scientific energy utilization and saving method of distributed energy system and allocate the equipment and operation strategy of distributed energy system rationally, so that its energy output could match the energy demand of united stations. Then, the Mixed Integer Linear Programming (MILP) model for the distributed energy system of united stations was established and solved with the minimization of annual average total expenditure as the objective function and the energy balance and the safe equipment operation as the constraints. The case calculation results show that compared with the traditional centralized energy and combined cooling heating and power system, the scheme based on the solution of this MILP model is more advantageous with remarkable economic benefit, high energy efficiency and efficient energy saving and environmental protection.

Study on the law of oil vapor leakage and diffusion in inner floating roof tanks is of great significance for strengthening environmental pollution control and ensuring tank farm safety. The wind tunnel test platform was established to test the effects of wind speed and floating plate position on evaporation loss rate of small inner floating roof tank, and the distribution laws of wind field and concentration field were investigated. Based on CFD numerical simulation, the UDF was used to introduce environmental wind, the numerical model of oil vapor leakage and diffusion from inner floating roof tank was established, and the feasibility of the simulation was verified by wind tunnel experimental data. The distribution law of wind field and wind pressure outside the inner floating roof tank, as well as the influence of wind speed on the flow field distribution and the diffusion concentration of oil vapor in the inner floating roof tank, was emphatically discussed. The results show that the lower the floating plate position and the higher the wind speed, the faster the evaporation rate will be. The static pressure distributed on the tank wall is as follows: highest on windward wall, medium on leeward wall and lowest on the two side walls. Under different wind speeds, the distribution of oil vapor on the tank is symmetrical. The lower the wind speed, the higher the oil vapor mass concentration will be. The oil vapor concentration at the gap between floating plates is the highest, leaving hidden dangers of safety and environmental pollution. The research results are of reference value for the design, operation and maintenance of the inner floating roof tank and environmental protection and safety management.

To solve the problems of insufficient power, high speed impact, high energy consumption, etc. of the detectors applied to large-diameter pipelines before the conventional cup-type pipelines are put into production, the self-driven inner detector suitable for large-diameter pipelines was developed. As the detector is capable of travelling autonomously inside the pipeline, detecting the geometric deformation of the pipeline and shooting the internal video of the pipeline, it can be used for pipeline inspection before putting into operation or during the shutdown maintenance period. The overall structure and body design of the detector were introduced, the influence of travelling attitude on driving force was analyzed, the design and function of the detection unit were systematically expounded, and the motion characteristics and detection performance of the detector were verified through field application tests. After being applied to the pipelines under construction in China-Russia Eastern Gas Pipeline Project, the application results show that the endurance mileage of the detector reaches more than 50 km, and the synchronous visual inspection on geometric deformations of the pipeline, internal surface defects of the pipe wall, foreign matters such as water film inside the pipeline is realized, thus demonstrating its excellent usability and advancement in practice.

To solve the problems of insufficient power, high speed impact, high energy consumption, etc. of the detectors applied to large-diameter pipelines before the conventional cup-type pipelines are put into production, the self-driven inner detector suitable for large-diameter pipelines was developed. As the detector is capable of travelling autonomously inside the pipeline, detecting the geometric deformation of the pipeline and shooting the internal video of the pipeline, it can be used for pipeline inspection before putting into operation or during the shutdown maintenance period. The overall structure and body design of the detector were introduced, the influence of travelling attitude on driving force was analyzed, the design and function of the detection unit were systematically expounded, and the motion characteristics and detection performance of the detector were verified through field application tests. After being applied to the pipelines under construction in China-Russia Eastern Gas Pipeline Project, the application results show that the endurance mileage of the detector reaches more than 50 km, and the synchronous visual inspection on geometric deformations of the pipeline, internal surface defects of the pipe wall, foreign matters such as water film inside the pipeline is realized, thus demonstrating its excellent usability and advancement in practice.

The use of high pressure, large diameter and high steel grade pipelines for long-distance natural gas transportation have become an important development tendency in the pipeline industry. The application of X90 pipeline steel pipe can raise the pipeline transmission capacity, lower the effective wall thickness of the steel pipe and save the pipeline construction cost. The X90 hot rolled coil, with a wall thickness of 20.3 mm and mainly composed of granular bainite, has been developed by adopting the design of alloying components with low C, high [Mn+Nb] and high [Mo+Cr], as well as technologies such as pure steel smelting and controlled rolling and cooling. The welding technology for X90 pipeline steel pipe with a wall thickness of 20.3 mm was optimized through experimental research on welding technology, and the low residual stress of high strength and large diameter submerged-arc helical welded pipe was controlled by optimizing design of pipe forming parameters. The test results show that all performance indexes of the trial-manufactured X90 submerged-arc helical welded pipe with a wall thickness of 20.3 mm and the diameter of 1 524 mm meet the requirements of relevant technical specifications, and it would make technical reserves for the construction and application of X90 high strength and large diameter steel pipes in China. high strength and large diameter steel pipes in China.

To investigate the formation process and blockage of hydrates in deepwater oil-gas multiphase pipelines, the formation process of hydrates in subsea risers and subsea horizontal transportation pipelines was numerically simulated by OLGA, based on the phase equilibrium curve of hydrate formation from condensate gas and the hydrate kinetic model (CSMHyKv2.0). It is shown that under the process parameters of one certain subsea pipeline, a large amount of hydrates are formed in both risers and horizontal transportation pipelines, and the viscosity of hydrate slurry increases 10 times in risers and 18 times in horizontal transportation pipelines. The formation rate of hydrate in risers decreases from the sea floor to the sea level and finally approaches to zero, while that in horizontal transportation pipelines remains unchanged. The area of hydrate formation and the viscosity of hydrate slurry decrease with the decline of pipeline outlet pressure. When the outlet pressure of risers and horizontal transportation pipelines are controlled at 3 MPa and 2 MPa, respectively, the formation of hydrates can be avoided and the smooth flow of pipelines can be ensured.

Heilongjiang crossing section in the dominant engineering project of the transit section of China-Russia Eastern Gas Pipeline crosses the border between China and Russia. Its longitudinal submerged arc welded (LSAW) pipes and induction bends are supplied by Russia, but according to the negotiation results of two sides, the key pipe performance indicators shall comply with the stricter requirements of China or Russia. In order to reasonably determine the pipe performance indicators of Heilongjiang crossing section and ensure the safety of the pipeline, this paper comparatively analyzed Chinese and Russian pipe standards and investigated the key performance indicators of LSAW pipe and induction bend. It is shown that compared with Chinese standards, Russian standards are stricter, focus more on low yield ratio, high fracture ductility and harsh low-temperature toughness of pipe and have close relation with construction sites. Combined with comparison results and actual project situations, it is finally determined to implement Russian standards in the pipe performance indicators of Heilongjiang crossing section.

In order to research the maintenance problems of the submarine pipelines with pitting corrosion, this paper put forward a method for calculating the variation of pipeline failure probability and reliability index over the time for different pipe materials and surrounding environments. By virtue of this method, the ultimate failure probability and reliability index under the constraint of reliability were calculated. Then, the incomplete preventive maintenance model for the submarine pipelines with pitting corrosion was established. In this model, the effect of each pipeline maintenance is characterized using virtual age and improvement factor, and the sensitivity analysis is carried out on the improvement factor, so that it can accurately reflect the effect of pipeline maintenance. Finally, the method for calculating pipeline life and cost was put forward. In addition, the above mentioned methods were applied to a case calculation of one certain submarine pipeline which had been in operation for many years, and the pipeline life and maintenance cost under different maintenance cycles were compared. It is indicated that the model can provide the best preventive maintenance cycle at a more reasonable cost while reflecting the pipeline maintenance effect accurately. The applicability and correctness of this method is verified.

Active fault is a major geological hazard threat to submarine pipelines, which may subject to excessive axial deformation and fail from the faulting. Thus an improved analytical method for strain of submarine pipeline under strike-slip faulting was proposed in this paper. The nonlinear constitutive relation of pipeline materials was considered based on the linear strengthening model, and the influence of soil nonlinear constraint on the response of the pipe structure was accurately calculated through the nonlinear soil spring model with ideal elastic-plastic constitutive relation. From the differential control equation of the pipeline stress, analytical results of the axial strain in the pipeline were derived and the expression of the pipe elongation was obtained. Based on the equilibrium equation and iterative calculation, the stress and strain of the pipeline can finally be accurately calculated. Compared with the finite element calculation results, the improved analytical method for pipe strain has higher calculation accuracy than the existing recommended method (i.e. Newmark method).

In order to investigate the factors influencing the cross-sectional distortion of small-radius dieless hot-bending bend and grasp the influential laws of technological parameters on the size of the cross section, so as to optimize and control the geometric deformation of the cross-section of small-radius pipe bend and reduce the distortion, the relationships between the processing technological parameters (heating temperature, advance speed and bending radius) and the cross-sectional distortion parameters (wall thinning ratio, wall thickening ratio and ovality) of L415M small-radius (3 D) pipe bend ( pipe diameter is 610 mm, wall thickness is 11 mm) were analyzed to reveal their correlation. It is showed that the bending radius of pipe bend has the remarkable effect on the cross-sectional distortion, and the shorter the bending radius is, the more serious the cross-sectional distortion is. As the advance speed increases, the wall thinning ratio and ovality of the pipe bend decrease, and the wall thickening ratio increases. With the increase of the heating temperature of pipe bend, the wall thinning ratio and ovality of the pipe bend increase, and the wall thickening ratio decreases. The research results can provide technical reference for the design and processing of small-radius hot-bending bend.

With the development of intelligent pipeline construction and regional management, higher requirement is put forward to intelligence of oil and gas stations. The intelligent inspection system for oil and gas station was designed to solve the problem that the current oil and gas stations were dominated by manual inspection and the monitoring systems were independent of each other. The 3D model of the real scene of the station was established by 3D modeling technology, and the video real-time monitoring images of the station were stitched and fused into the 3D model to panoramically monitor the oil and gas station in one picture. The intelligent video recognition algorithm was developed by combing the inspection requirements of the station, thus realizing the intelligent recognition of the unsafe events in the station. Modules such as route setting and historical video backtracking were set up to realize automatic inspection of station panorama. The system has been applied to Heihe Initial Station of China– Russia Eastern Gas Pipeline Project. The test results show that the system can be used to automatically inspect along the inspection route, and intelligently recognize and alarm typical threat events. The application of the system improves the intelligence level of the station and provides technical support for the construction of the intelligent pipelines.

According to the requirements for corrosion detection of tank bottom plate, the identification principle of corrosion defect and the countermeasures to different influencing factors were analyzed based on the principle of ultrasonic pulse reflection method and common types of corrosion defects of tank bottom, and thereby, an immersion ultrasonic defect detection system with ARM and FPGA chips as the core was developed. As a defect detection unit of the inservice tank bottom inspection robot, the system comprises 16 5 MHz immersion probes, an ultrasonic signal processing board and an industrial computer. Therein, the ultrasonic probes and the ultrasonic signal processing board are connected by the 100 m long coaxial cables, which simplifies the explosion-proof requirements of the robotic circuits. The test results of mockup defect plates show that the system could find the defects with a diameter of not less than 5 mm and a corrosion depth of 10% or more of the original wall thickness, satisfying the requirements of practical applications.

In order to improve the calculation accuracy of the inertial measurement coordinate data of in-service pipelines and thereby promote the pipeline digitization process with high quality, a calculation model of dead reckoning error of a small-caliber inertial measurement unit was proposed on the basis of the information of the inertial measurement unit and the odometer with reference to the smooth filtering algorithm. Through the filter recursive calculation with the established state equation and the measurement equation, the optimal estimated value of the system error can be obtained, and the data accuracy can be guaranteed by solving the ambiguity of the whole cycle with the smoothing filter algorithm. According to the verification of the pipeline inertial measurement results, the pipeline centerline coordinates calculated by the dead reckoning error calculation model are consistent with those collected by GNSS-RTK, and the error can be controlled at the meter level. As the result shows, the calculation model, which is special for reducing dead reckoning error of the smallcaliber inertial measurement unit based on the information of the inertial measurement unit and the odometer in combination with the smooth filtering algorithm, can effectively reduce the influence of the pure inertial navigation error accumulation over time on the accuracy of measurement results, and thus it has good application value. (3 Figures, 21 References)

Salt cavern gas storage is an important facility for storage and peak-load sheaving of natural gas. In order to analyze the effects of pillar width on the stability of double-cavity salt cavern storage, by taking Jintan Underground Salt Cavern Storage as an example, a numerical model of double-cavity storage was established with the finite element analysis method on the FLAC 3D software platform based on the deformation stability theory under the precondition of ensuring the cavity safety, improving the solution mining efficiency and maximizing the utilization ratio of salt bed. Besides, simulation analysis was conducted for the stability of the double-cavity salt cavern storage with different pillar widths, the reasonable pillar width of the double-cavity salt cavern storage was identified, and further, the change law of the maximum damage length, damage volume, nondestructive width and volumetric shrinkage of the double cavities with reasonable pillar width was studied. The results show that the reasonable pillar width of the double-cavity storage was 1.5-2.5 times of the cavity diameter in the study area. In case of reasonable pillar width, the pillar width is proportional to the maximum damage length, has little relation to the damage volume and is inversely proportional to the nondestructive width and volumetric shrinkage. Additionally, the maximum damage length, damage volume and volumetric shrinkage increase gradually, while the nondestructive width decreases with the creep time increasing. The average design pillar width is 2.0 times of the cavity diameter for Jintan Salt Cavern Gas Storage, which is within the reasonable range, and the field applications indicate that the stability model of double-cavity storage is good in reliability and accuracy. (13 Figures, 1 Table, 20 References)

In order to effectively guarantee the safe operation of oilfield gathering pipelines, reduce the failure probability and avoid the major safety accidents, a safety risk assessment method was proposed on the base of the membership of information entropy. With this method, the particularity of the failure of gathering pipelines was defined by analyzing the failure data, and a calculation model for the risk assessment factor weights of gathering pipelines was established with the information entropy membership method. Moreover, based on the failure particularity and the weight calculation model, a relatively perfect risk assessment index system of gathering pipelines was developed. Additionally, a risk calculation model for gathering pipelines was established with Kent method, realizing the quantitative risk analysis of gathering pipelines. With the gathering pipelines in Xinjiang Oilfield as the object of study, a safety risk analysis was performed with the gathering pipeline safety risk assessment method based on the membership of information entropy. The analysis results show that the proposed method can more accurately assess the risk of gathering pipelines, and the assessment results are consistent with the actual conditions of gathering pipelines in Xinjiang Oilfield. Meanwhile, it can be a reference for the formation of risk assessment standards of gathering pipelines. (4 Figures, 3 Tables, 23 References)

Since the salt cavern gas storage was constructed in China, diesel blanket has always been used to control the cavern shape, which is costly and polluting. Therefore, nitrogen blanket is proposed for the leaching of cavern. However, as the nitrogen is easy to leak and has strong compressibility, and it is difficult to control the gas-water interface, the solutionmining-under-nitrogen technology was developed by reforming the flow of wellhead, developing the associated field nitrogen injection equipment and establishing the monitoring and control system of gas-water interface, and for the technology, field tests were carried out. As indicated in the tests, nitrogen can be used as the blanket material for solution mining of salt-cavern gas storage, with good effects and the gas-water interface can be controlled effectively. Further, the control method of gaswater interface with nitrogen blanket was developed for cavity roofs with different opening, and valuable field experience was accumulated for the solution-mining-under-nitrogen technology. (8 Figures, 3 Tables, 20 References)

The traditional two-curve crack arrest control model based on Charpy impact toughness is no longer suitable for the high-grade steel pipelines, which poses a great threat to the safety of energy transportation. The Crack Tip Opening Angle (CTOA), as a promising crack arrest toughness parameter, is expected to replace the Charpy impact toughness and form a new crack arrest control method. However, there has been no adequate progress and verification in the relevant research by now. Therefore, the latest research progress home and abroad was comprehensively reviewed and discussed from three aspects, which are the standard test of CTOA with laboratory specimens, the transferability of CTOA test results, and the CTOA based crack arrest control method. Meanwhile, the disputes and deficiencies in the current research were pointed out, and the future working direction of the researches was analyzed. It is expected to promote the research process in the field of crack arrest control of pipelines, as well as the development of pipeline construction in China. (2 Figures, 1 Table, 45 References)

The number of samples for detecting corrosion characteristic value is difficult to reach a large enough size in practical engineering, which leads to the pipeline corrosion evaluation results tend to be aggressive. For this reason, the influence of sample size on the inference results was analyzed, and based on the Bayesian theory and the uncertainty of measurement, the Bayesian inference method for the pipeline corrosion depth under the condition of small sample size was proposed. Then, the correlation between the corrosion depth and the length was considered, and the prediction method of corrosion depth based on the correlation and Bayesian inference was developed. Thereby, the corrosion depths under different defect lengths was inferred with the pipeline corrosion detection data, and further the effectiveness of the method was verified. The results indicate that: the new method could better reflect the influence of sample size on the inference results, the prediction results are more conservative and consistent with the engineering experience, and so it is safer and more favorable to the engineering application. The research results could provide more accurate information to the prediction of pipeline corrosion depth, as well as theoretical reference to the prediction of the characteristic value of other corroded pipelines with consideration given to the correlation of random variables. (1 Figure, 4 Tables, 25 References)

Foundation settlement often leads to large deformation of the tank wall, which seriously affects the safe operation of the tank. In order to study the deformation response state of crude oil storage tanks under harmonic settlement, a numerical simulation model of large crude oil storage tanks under harmonic settlement was established with the finite element analysis software ABAQUS. The model, considering the effect of the foundation comprehensively, is capable of accurately simulating the true service state of the storage tanks. In addition, the influence law of wall diameter-thickness ratio, height-diameter ratio, harmonic number, harmonic amplitude and liquid level of the tanks on the radial deformation of the tank wall was studied quantitatively based on the established numerical simulation model. The results indicate that, the wall diameter-thickness ratio and the liquid level of the tanks have little effect on the radial deformation on top of the tank wall, which can be ignored from the perspective of engineering. Besides, the radial deformation on top of the tank wall increases approximately linearly with the increase of the height-diameter ratio of the tank wall and the harmonic amplitude. Moreover, the radial deformation of the tank wall increases at first and then decreases as the harmonic number increases. (14 Figures, 4 Tables, 22 References)

Flood scouring the river bed where the directional drilling crossing pipeline is located may lead to pipeline exposure above the riverbed, as well as pipeline suspension and failure. The failure mechanism of pipeline during the whole process from initial exposure to fatigue failure under the action of hydrodynamic force was studied and the safety assessment method of the exposed pipeline due to scouring was proposed through the lateral stability, strength failure and suspended span fatigue analysis. In addition, safety assessment was performed for two actual pipelines with the solution was developed. The results indicate that the pipeline in Example 1 is in safe state for the maximum equivalent stress of the exposed pipeline is 176 MPa, which is less than the minimum yield strength of the pipeline, and there is no suspension. However, the pipeline in Example 2 cannot operate any more for the scouring time of flood on the pipeline exceeds its fatigue life during exposure. Thus, the research results provide theoretical support and basis for the safety assessment and the development of the replacement scheme of scoured pipelines. (8 Figures, 4 Tables, 28 References)

During the 13th Five-year Plan, the domestic oil and gas storage and transportation business developed rapidly, which promoted the progress of oil and gas storage and transportation technologies. In terms of engineering design and construction, a series of research results concerning high-grade steel pipeline design and mechanized construction have been achieved, and the design and construction technologies of LNG receiving terminals and storages become mature gradually. In terms of material and equipment, the key technical problems of the third generation large-capacity natural gas pipeline project were solved, the X70/X80 steel pipes were successfully developed with the key equipment such as the compressors, oil pumps and key valves localized basically. In addition, the localized SCADA software was also developed. In terms of the transportation technologies, the optimization technology of pipeline network operation with the centralized control as the core has been formed, and the transportation technology system of the high pour-point and high viscosity crude oils and product oils has been established. As for the operation and maintenance, the supporting technologies of pipeline integrity management, inspection and evaluation, geological hazard protection, monitoring and early warning, corrosion protection and emergency repairing have been developed, and many international and national standards have been prepared and published. During the 14th Five-year Plan, the oil and gas storage and transportation industry will face new opportunities and challenges in technology development, and the oil and gas storage and transportation technology will develop towards safe operation, efficient transportation and intelligent pipeline network, which will provide scientific support and guarantee for the rapid development of oil and gas storage and transportation businessess. (2 Tables, 57 References)

As the “decision-making brain” of a pipeline network system, the control centre is a comprehensive decisionmaking control centre that integrates large amounts of data, rules and expert experience. It is very similar to the development idea and evolution direction of a new generation of artificial intelligence characterized by data driving. Herein, the intelligent and digital transformation plans for the control business of the pipeline companies and the power grid companies at home and abroad were analyzed, and the latest research results were summarized. Then, combined with the latest development of artificial intelligence technology, the basic concepts and functional characteristics of intelligent control were preliminarily put forward based on the demand of natural gas pipeline networks for the control business, namely, to achieve the intelligent perception, prediction and early warning, optimal decision-making, and intelligent control, and ultimately to realize the intelligent control mode based on black screen. Subsequently, the architecture of intelligent control was designed, and the key technologies of the intelligent control layer and the intelligent decision layer, as well as their potential application scenarios, were analyzed. Finally, the research results are expected to provide reference for the development and application of artificial intelligence in the control of pipeline networks in the future. (3 Figures, 20 References)

In order to verify the applicability of epoxy-filled steel sleeves for reinforcement of the girth weld defects in X80 steel pipelines, X80 pipe fittings with 1 016 mm diameter were selected as the specimens and on the specimens two girth welds with same defects were set by manual welding. Definitely, one of the welds was reinforced with an epoxy-filled steel sleeve, while the other was not. Then, the full-scale mechanical tests were performed under the internal pressure, fluctuation pressure and the coupling effect of internal pressure and bending moment for the above two defective girth welds with/ without reinforcement. In addition, the failure mode, bearing capacity and deformation performance of the two specimens were compared and analyzed. The results show that the hoop and axial stresses of the girth weld defects reinforced by the epoxy-filled steel sleeve under the operating pressure is reduced, and the sleeve shares 47% of the internal pressure. The stress of the girth weld defects reinforced by the epoxy-filled steel sleeves under the cyclic fluctuating pressure is kept unchanged, which indicates that the stress level of the sleeve reinforced girth weld defects is stable, without changing with the fluctuation of the pressures. In addition, under the coupling effect of the internal pressure and the bending moments, the failure mode of the unreinforced pipeline is overall fracture of the weld section, while the failure mode of the reinforced pipeline is local buckling failure in the pressure region after the yield of the steel in the tensile region, which indicates that the epoxy-filled steel sleeves increase the bending capacity of the pipelines and reduce the bending deflection. In brief, the research results can provide a reference to the engineering application of reinforcing the defective girth welds of X80 pipelines with epoxy-filled steel sleeves. (16 Figures, 24 References)

The actual strength under-matching of pipeline girth welds is a principal cause for the fracture failure of welds. The current Failure Assessment Diagram (FAD) method for the applicability assessment of pipeline welds cannot accurately consider the influence of weld strength matching. Thus, accurate inclusion of strength matching becomes critical to broaden the FAD method to apply to the crack defect assessment for the girth welds of high-grade steel pipelines. Based on the nonlinear finite element method, a numerical simulation model of the crack driving forces for the girth welds of high-grade steel pipelines was established, and the general failure assessment curve of girth weld cracks was plotted with the equivalent stress-strain relationship method. Then, a series of finite element assessment points under different load levels were determined with the finite element calculation results of the crack driving forces in combination with the recommended methods in Guide to methods for assessing the acceptability of flaws in metallic structures (BS 7910-2019). Further, the assessment accuracy of BS 7910- 2019 to the crack defects of girth welds was determined, and the critical causes affecting the accuracy of the assessment results were investigated. On this basis, the optimized ultimate load calculation model of the pipeline girth welds and the improved FAD method were put forward with the crack depth, the crack length and the weld strength matching coefficient considered, and the weld strength matching was accurately included into the FAD method. Thereby, the assessment accuracy of the girth weld crack defects of the high-grade steel pipelines was further enhanced. Generally, the method could provide reference for the applicability assessment of the girth weld cracks of in-service high-grade steel pipelines. (11 Figures, 24 References)

Formation collapse is one of the common geological hazards for the buried long-distance pipelines. In order to study the mechanical response law of the buried steel pipelines under continuous collapse, experiments and numerical simulations of buried steel pipelines under continuous collapse were carried out, the deformation and stress changes of the buried steel pipelines during continuous collapse were analyzed, and the theoretical calculation results of pipeline mechanics under the collapse geological hazards were checked. The research results show that, in the case of collapse in a small area, the deformation and stress of pipelines increase continuously with the collapse area enlarged, and the displacement and stress in the middle of the pipelines are maximized. When the collapse area is expanded to a certain extent, the soil collapses completely, the pipelines are suspended, the displacement of the pipeline is reduced, the stress of the pipe is released greatly, and the maximum stress position of the pipelines changes from the middle to the point near the collapse boundary of the pipelines. The calculation results of the pipeline stress under the collapse geological hazards are greater than the experimental and simulation values if the friction or cohesion are considered based on the gravity, which are of more guiding significance. Further, the reasearch results could provide effective guidance to pipeline protection. (19 Figures, 4 Tables, 25 References)

Once a supercritical CO2 pipeline fractures, decompression wave will appear at both end of the crack. Hence, the calculation of the decompression wave velocity during the pipeline fracturing is critical for the prediction and control of pipeline fracture. Based on the GERG-2008 equation of state, a decompression wave velocity prediction model for the supercritical CO2 pipelines containing impurities was established with reference to the homogeneous flow model and the sound velocity calculation model for gas-liquid two-phase flow, and a calculation procedure thereof was developed. In addition, the effects of single-component non-polar impurities, single-component polar impurities and multi-component mixed impurities on the decompression wave curve of the supercritical CO2 pipelines were studied. The results show that the addition of non-polar impurities increases the plateau pressure of the decompression wave curve, and thus the decompression wave is more likely to intersect with the pipeline fracture curve, increasing the risk of pipeline fracture. However, the presence of polar impurities can slightly reduce the plateau pressure of the decompression wave curve of the supercritical CO2 pipelines, further reducing the risk of pipeline fracture. Therefore, this model could provide a theoretical basis for pipeline crack arrest and impurity composition control. (4 Figures, 2 Tables, 25 References)

In the middle and late production stages of natural gas condensate pipelines, the problems of increased liquid accumulation and friction usually occur in the pipelines. Therefore, regular pigging operations are essential to ensure the safety and efficiency of the oil and gas pipelines. However, the traditional pigs often go out of control as a result of their same velocity with the driving gas during the operation, which brings about a series of problems. Thereby, a new type of bypass pig was designed and developed, and a matching experimental system of horizontal-vertical pipelines was built to analyze the movement characteristics of the bypass pigs in different structures. Herein, air and water were used as the flow media, and the data of flow, pressure and terminal liquid level during pigging were collected by the LabView data collection system in real time. By changing the parameters such as the bypass rate, the driving gas velocity, the liquid velocity, etc., the movement characteristics of the bypass pig were explored, and the abnormal movement process of the pig and the internal mechanism of eliminating pig slug were analyzed. As shown in the results, the movement velocity of pigs can be slowed, the pressure fluctuation in the pipelines can be mitigated and the liquid holdup in the slugs before the pigs can be reduced with the bypass pigs for the purpose of effectively controlling the volume of slugs. The research results could provide references for in-depth understanding of mechanism of bypass pigging technology and promoting its engineering application. (14 Figures, 2 Tables, 39 References)

In the high pressure and low temperature conditions during the production and transportation of deep-sea oil and gas, hydrate is formed easily, which could cause pipeline blockage. Herein, for gas-liquid-solid flow system of hydrate slurry, the hydrate particles are classified according to the particle size based on the characteristics of the dispersed phase. In combination with the kinetics model of hydrate formation/decomposition, the number, size and movement laws of the hydrate particles were simulated, the two-fluid model and the temperature equation were coupled, and a multiphase transient flow mechanism model of hydrate slurry applicable to the oil-dominated flowlines was established. The governing equations were discretized by a staggered grid, and the coupled solution of multi-physics fields covering the multi-phase flow, the dynamic change of hydrate particle formation/decomposition and the movement of hydrate particles was realized on the basis of the pressure-based algorithm. By applying the model to a multiphase transportation pipeline, the change of the hydrate volume fraction were obtained, which could provide theoretical basis to the quantitative analysis on the blockage risk of hydrate slurry transportation. (12 Figures, 5 Tables, 37 References)

For the failure of oil storage and transportation facilities may endanger the surrounding public safety, it is necessary to conduct quantitative assessment for the derived disasters under multiple scenarios so as to effectively control the adverse impact resulted from the accidents of oil storage and transportation facilities. Meanwhile, research should also be performed for the consequence assessment system of derived disasters. Herein, the differences between the common and the serious accidents were analyzed, and the derived disasters of oil and gas storage and transportation facilities were defined to comprehensively identify the probability and consequences of disasters. In addition, an assessment model of derived disasters based on the sensibility of the disaster-inducing environment was put forward from the three aspects of the derived disaster system, the disaster-causing mechanism and the disaster-inducing environment. A case study was carried out to a disaster occurred in the densely-populated and environmental sensitive areas. Specifically, the failure probability of the oil storage and transportation facilities and the sensitivity of the disaster-inducing environment in the areas after the fire caused by the pipeline leakage were calculated with the Bayesian network using the derived disaster assessment model. The results show that the derived disaster assessment system with comprehensive consideration to the disaster frequency and consequences can not only characterize the degree of loss as a result of multi-scenario disasters, but also reflect the disaster characteristics of accidents of the storage and transportation facilities, which further provides reference to the development of safety measures of the pipelines and facilities for oil storage and transportation, as well as the emergency management and the planning of emergent resources. (7 Figures, 6 Tables, 21 References)

Soft matter is something between the ideal solid and liquid. For the gelled waxy crude oil has the specific and complicated mechanical behavior of the soft matters, learning from the rheological research methods for soft matters is an efficient approach to further investigate the rheological behaviors of waxy crude oil. Herein, the specific mechanical behavior of soft matters was introduced with reference to the rheological behaviors of the waxy crude oils. The controversies in present studies for the yielding behaviors were systematically demonstrated in terms of the concept of yield stress, its measurement, the matter of yield strain, and the viscoelastic response prior to macroflow arising. The rheological behavior during the viscoelasticity-to-yielding transition process after loading was also analyzed. In addition, considering that the rheological measurement is the main means to investigate the complicated structural characteristics of the soft matters, the main research methods of the rheological behaviors of soft matters were illustrated, including the steady shear, creep and large amplitude oscillatory shear, and the appropriate data analysis methods were also summarized, further providing guidance to the in-depth study of the rheological behavior of the waxy crude oil. (9 Figures, 83 References)

Geohazard is one of the major factors threating the safe operation of oil and gas pipelines. However, due to the inspection accuracy of equipment and the discreteness of inspection data, the pipeline safety cannot be analyzed quantitatively with a single monitoring and inspection technology. Thus, it is urgent to study the Digital Twin mechanism model for the structural safety of pipelines in combination with the multi-source monitoring and inspection data, so as to realize the intelligent perception and prediction of pipeline safety in geohazard areas. Herein, the process to establish a Digital Twin mechanism model for the structural safety of pipelines in geohazard areas was put forward. Meanwhile, by building a parameterized finite element model of pipelines in geohazard areas, a stress-strain database of the pipeline was established with consideration to the range of the variable parameters affecting the stress-strain distribution of pipelines, and then the highly nonlinear relationship between the variable parameters and the stress-strain state of the pipelines was fitted by BP neural network. In addition, combined with the real monitoring data of pipeline stress and strain, a mechanism model capable of accurately inverting the real stress and strain distribution along the pipeline was constructed with the particle swarm optimization algorithm. Moreover, the accuracy of the model was verified by an application case. Therefore, the research results could be applied to the quantitative safety assessment of the pipelines in geohazard areas, and core support could be provided for the construction of Digital Twin of pipelines. (8 Figures, 1 Table, 20 References)

In order to improve the accuracy of thermodynamic modeling for centrifugal compressors, an adaptive modeling method for thermodynamic model and characteristic curve of centrifugal compressors based on field test data was proposed. During the modeling, the field installation errors and the degeneration during operation were considered, and the accuracy of thermodynamic calculation was improved by the modified similarity conversion method. For the inaccurate general characteristic curve, a neural network prediction model based on multi-layer perception was established to generate new characteristic curve, and the characteristics was adjusted with the particle swarm optimization algorithm, so that the output at the design points and the off-design points under variable working conditions met the matching accuracy with the field test data. With this adaptive method, a thermodynamic model was established for PCL803 centrifugal compressors from Italy GE Company. The results show that the calculation error of the design points and the off-design points under variable working conditions after performance adaptation is reduced significantly compared with that before adaptation when the general characteristic curve is used. The research results could provide basis for the condition monitoring, performance prediction and fault diagnosis of centrifugal compressors. (6 Figures, 4 Tables, 21 References)

CO2 corrosion is one of the important threats to the safe operation of oil and gas pipelines. Generally, the pitting often has a greater depth than that of the uniform corrosion and it is likely to be concealed, bringing about particularly serious hazards. In order to study the ion concentration distribution within the corrosion pits and verify the existing corrosion prediction models, the relative integral intensity was defined based on the characteristic peak of the bicarbonate in Raman spectroscopy and that of the background solution water with the internal standard method, and the quantitative relationship between the relative integrated intensity and the bicarbonate molar concentration was established in the range of 0.04-0.6 mol/L. Meanwhile, a set of flow cell system based on the in-situ laser Raman spectroscopy was designed, and the bicarbonate molar concentration was determined at different depths of artificial pits on the X65 pipeline steel in the flow environment. The experimental results show that: the bicarbonate molar concentration in the pit decreases gradually within 500 μm from the pit bottom to approach the bulk solution concentration as the distance increases, and it is basically constant when the distance is greater than 500 μm. The experimental method for determining the distribution of bicarbonate molar concentration in the pits could provide important reference for the development of pitting theory and the verification of corrosion calculation models. (8 Figures, 2 Tables, 28 References)

For the problem that the conventional oil pipeline detection system cannot effectively detect the leakage of the two-phase flow pipelines, a leakage identification method based on the acoustic emission signal was proposed for the gasliquid two-phase flow pipelines. According to the basic principles of acoustic emission detection technology, the leakage detection tests were carried out for the three flow patterns of laminar flow, slug flow and annular flow at a gas pressure of 0.1 to 0.4 MPa in three different orientations of leak holes with two different diameters. The main signal components extracted by wavelet packet decomposition combined with local mean decomposition were taken as the input of pattern recognition, and the BP artificial neural network pattern recognition was also performed. The test results show that the average accuracy of the leakage identification of the three two-phase flow pipelines of laminar flow, slug flow and annular flow is 83.5%, which is high in accuracy. Further, the proposed method has a reference value for the leakage detection of gas-liquid twophase flow pipelines. (7 Figures, 4 Tables, 26 References)

Affected by the extreme geological hazards such as the fault and uneven ground settlement, pipelines are prone to produce large deformations. However, the large strain monitoring cannot be achieved with the existing strain sensing technology due to its insufficient measuring range. Thus, the method of monitoring the large strain of crossing-fault pipelines with Coaxial Cable Fabry-Perot Interferometer (CCFPI) sensors was proposed herein. Definitely, the sensing principle and manufacturing method of CCFPI sensors were briefly introduced, and with the help of a self-made buried crossing-fault pipeline test device, the packaging and deployment methods of CCFPI sensors to match the buried pipelines were studied. Additionally, the rationality and effectiveness of applying CCFPI sensors to the large strain monitoring of buried crossingfault pipelines was verified through the simulation test. The research results show that the measured strain value of the CCFPI sensor and the optical fiber sensor agrees well when the fault displacement is less than 165 mm. However, when the fault displacement is greater than 165 mm, the fiber breaks due to out-of-range, but the CCFPI sensor can monitor the strain of the pipeline continuously, and a strain of 0.081 36 is measured by the CCFPI sensor at a fault displacement of 300 mm, which verifies the rationality and reliability of applying the CCFPI sensors to large strain monitoring of buried crossing-fault pipelines. (17 Figures, 21 References)

Modification of crude oil is a basic method to improve the safety and economy of pipeline transportation. Definitely, high-voltage electric field treatment is a new approach to modify the crude oil based on its electrorheological effect. Herein, the progress of research on electric field treatment for modification of crude oil was summarized systematically, and the law of the electrorheological effect of crude oil was also concluded. The research results indicate that: applying an electric field (with an intensity of 0.2-5 kV/mm) to crude oil for several seconds can obtain the significant immediate modification effect. Specifically, the viscosity and yield stress can be reduced at a rate of 80% or higher, but the energy consumption is only 1% of that required for the same viscosity reduction rate by heating. After the removal of electric field, the viscosity and yield stress will recover gradually. The effect of viscosity reduction will disappear after about one day of placement. But the yield stress recovers slowly (at 90% of the reduction rate of yield stress two days later). The modification effect of electric field treatment is closely related to the composition of crude oil, and the presence of wax crystal, resin and asphaltene in the crude oil is essential for electric field treatment. In addition, the existing issues of the current research on electric field treatment technology were analyzed, and the development direction of the technology in the future was also proposed. (16 Figures, 50 References)

The marine oil spill accidents will not only result in the waste of energy, but also the unrecoverable destruction of the ecological environment. The superhydrophobic-superoleophilic 3D elastic porous materials are the most efficient oil adsorbents for the marine oil spill treatment, due to its low density, high porosity, strong elasticity, large oil adsorbing capacity and the convenient recovery of the materials and oil. Herein, based on the theoretical basis and the construction principles of the superhydrophobic-superoleophilic surface, the latest research progress was reviewed for three types of the superhydrophobic-superoleophilic 3D elastic porous materials respectively, i.e. the polymer-based, the carbon-based and the organism-based materials, in terms of the specific materials, the preparation method, and the application performance. Finally, the merits, defects and the faced challenges of the three types of the superhydrophobic-superoleophilic 3D elastic porous materials during their preparation and application were summarized, and the prospect was made for the development in future. (4 Figures, 67 References)

Long-distance oil and gas pipelines passing through the areas with serious geological hazards are prone to bending deformation due to the external soil loads, which will threaten the safe operation of pipelines. The inline inspection technology based on the inertial measurement unit (IMU) is the main means to inspect the local deformation of pipelines at present. Herein, the characteristics of IMU data of the four typical locally-deformed pipeline sections, i.e. the buried pipeline elbows, the dented pipelines, the pipelines with bending deformation and the abnormal girth welds, were provided. Meanwhile, a IMU data pre-processing method based on wavelet denoising was put forward, a deep neural network model was established to identify the IMU data thermal map of the 4 types of typical locally-deformed pipeline sections, and a set of method was developed to identify the pipeline sections with bending deformation based on IMU data. By analyzing the 6-year IMU data of China-Russia Crude Oil Pipeline with the new method, totally 33 177 data of sample pipeline sections were formed, and an IMU bending strain database was set in China. The results of application example show that: the accuracy of the deep neural network model established based on the database to identify the pipeline sections with bending deformation is more than 90%, and the identification efficiency is up to 0.02 min/km. Hence, the method for identification of pipeline sections with bending deformation based on IMU data provides an effective technical means to identify the deformed pipeline sections with bending strain greater than 0.125% in the integrity assessment of pipelines. (9 Figures, 26 References)

As an important part of pipeline integrity management, the alignment of the external and internal pipeline inspection data is to align the external inspection points to the internal inspection centerline, so as to fully mine the value of internal and external inspection data. Herein, from the perspective of the relationship between the surface marking points and the mileage piles of the pipelines, a relation model of internal inspection points and external inspection mileages was constructed using the machine learning algorithm based on the external and internal inspection data from the pipeline integrity management system of a long-distance pipeline company, and the mileage information of the internal inspection points in the external inspection was predicted to increase the mapping between the internal inspection points and the external inspection mileage, further realizing the data enhancement. In addition, the pipelines were segmented by the surface marking points and mileage piles, and the external inspection points were aligned to the internal inspection centerline with the linear stretching algorithm, so as to realize the alignment of the external and internal inspection data. The results show that the average absolute percent error is less than 0.10% and the determination coefficient is 99.99% for the internal inspection point based external inspection mileage prediction model established with the machine learning algorithm. Moreover, the model could capture the relationship between the internal inspection points and the external inspection mileages, so as to support the automatic alignment of the external and internal inspection data of the pipelines. (5 Figures, 1 Table, 21 References)

To accurately obtain the true constitutive relationship of each material area in the girth welds of high-strength pipeline steel. Definitely, two kinds of notched round bar specimens were obtained by setting notches on the base metal and in the weld area of X80 steel respectively, and the tensile tests were carried out on the specimens, with the real-time images of specimen notches captured by the high-speed cameras during the tensile process. Then, based on the change law of gray value at the notch edge, an automatic measurement method, i.e. the minimum diameter tracing method, was proposed to measure the minimum sectional diameter of the notch area in real time. In addition, the true constitutive relationship between the base metal and the weld material can be obtained based on the minimum diameter tracing method and the modifier formula, and by fitting the curve obtained with the power law hardening model, the constitutive relationship parameters of corresponding materials can be gained. Finally, the test results were verified with the finite element method. The results show that both of the test method and the results are reliable and effective. The studied test method and the process are of great practical significance for obtaining the constitutive relationship between the base metal and the weld area and realizing the accurate test of the mechanical performance of the pipeline girth welds. (11 Figures, 5 Tables, 20 References)

Liquid holdup is one of the most important parameters of gas-liquid two-phase flow. Affected by the image noise, the traditional liquid holdup measurement method based on image processing is difficult to accurately extract the gas-liquid interface, resulting in the great error of the liquid holdup measurement. Hence, a network model based on Deeplab V3+ was established with the semantic segmentation algorithm of deep learning, which was also trained by the image data set obtained from the slug flow pattern acquisition experiment, and then the interface of the gas and liquid flow area in the slug flow was identified and extracted to realize the measurement of the liquid holdup of the gas-liquid two-phase slug flow. The results show that the semantic segmentation model can extract the images of the gas-liquid two-phase flow online, and accurately divide the gas zone, liquid zone and background zone. In addition, the liquid holdup obtained by the top interface extraction is relatively high, while that obtained by the bottom interface extraction is relatively low, but the liquid holdup obtained by the average liquid film thickness is the closest to the true value measured by WMS （Wire-mesh Sensors） grid imaging sensors, with the maximum error less than 10%. The research results provide a new way for real-time monitoring of liquid holdup. (12 Figures, 18 References)

At present, the biggest safety risk and accident source of pipeline systems can be attributed to the lack of sensing ability of buried pipelines to a large extent. For this reason, a method of laying pipelines in underground space was put forward, so that the buried pipelines could be observed, monitored and accessed directly with the present detection, monitoring and sensing technologies. The sensing ability of critical pipeline sections can be enhanced fundamentally by the full range data acquisition and intelligent monitoring technology, and further the safety level of the pipelines can be improved greatly. By referring to the laying mode of municipal rainwater and sewage pipelines and urban utility tunnels, the underground space structure of semi-prefabricated reinforced concrete U-shaped pipe culvert with cover plate was proposed, where the pipelines are installed at the bottom of the pipe culvert with the support of metal bracket or concave cement pipe holder. Meanwhile, the intelligent video monitoring, optical fiber sensing, combustible gas sensing, external detection of pipeline defects or stress and other fixed or movable sensing means should be provided in the underground space. In addition, the risk factors of pipeline laying in underground space were analyzed preliminarily, and it was conservatively estimated that the overall risk could be reduced by more than 34%. Moreover, the economy of pipeline laying in underground space was also analyzed. It is expected that the construction cost of pipeline sections laying in underground space will be increased by about 7.5% to 25%, but the pipeline operation and maintenance cost, as well as the accident loss, will be reduced by more than 30%. Therefore, it is suggested that the relevant feasibility study and engineering tests should be performed in the pipeline idustry in future. (5 Figures, 22 References)

The oil and gas pipelines in the oil field are usually equipped with a layer of cladding in certain thickness, and the pulsed eddy current testing technology can be adopted to measure the wall thickness without removing the cladding, which saves a lot of costs for the removal and assembly of the cladding. However, as a result of cladding, distance exists between the pulsed eddy current sensor and the pipeline, which leads to the variation of the equivalent resistance and inductance of the sensor, and further affects the voltage signal of the pulsed eddy current detection, reducing the accuracy of the residual wall thickness inversion. In order to solve this problem, a quantitative inversion model of lift-off, slope of late detection voltage signal and pipe wall thickness was established with a support vector machine (SVM), and inversion test of the residual wall thickness of the step specimen with the wall thickness of 5-21 mm was carried out with this model under the condition of 0-10 cm lift-off, with the error of the inversion result controlled within 7%. Thereby, the inversion model is verified to be valid with high practical value, and certain reference could be provided for the measurement of the residual wall thickness of the pipeline with cladding. (4 Figures, 5 Tables, 20 References)

In order to understand the influence rule of the grounding electrode of HVDC transmission system on the stray current of buried pipeline, the remote potential monitoring system was equipped for 12 pipelines near the 17 grounding electrodes of HVDC transmission system for continuous monitoring of pipeline potential in long time. The interference frequency and time of grounding electrodes, as well as the interference degree and range of pipeline, were analyzed based on the variation of pipeline potential. According to the monitoring results, the interference influence of grounding electrode to pipeline can be judged accurately through the long-time continuous monitoring of pipeline potential. In 2017, the interference frequency of 17 grounding electrodes was 201 times, and the total interference time was 657.31 h, which was slightly shorter than that in 2016. Interference of grounding electrode was monitored on 1 987 km pipelines, and particularly, the interference of grounding electrode to pipeline in South China was greater than that in East China, Central China and Northwest China. By analysis on the distribution rule of interference potential, it is found that the shorter the vertical distance from grounding electrode to pipeline, the shorter the pipeline section with stray current flowing in the end close to the grounding electrode, the greater the interference to the pipeline far away from the grounding electrode, and the larger the interference range is. (7 Figures, 2 Tables, 21 References)

In order to investigate the reason for collapse of a 100 m³ aviation kerosene storage tank in Xinjiang, eigenvalue buckling analysis and nonlinear buckling analysis were conducted with the numerical simulation technology based on the finite element model (FEM) of a high-order shell unit, and the collapse mechanism of small aviation kerosene was discussed in detail. According to the operation parameters of the tank, the bearing capacity of negative pressure was determined for the tank, and through modal analysis, its ultimate bearing capacity of negative pressure was determined for the tank without any defect. The deformation and stress distribution of the tank under various working conditions were compared, and the ultimate bearing capacity of negative pressure for the defective tank was determined. The study shows that only the negative pressure itself could not have led to the collapse of tank, but the initial defect together with the negative pressure caused by unsmooth breathing could result in collapse of tank. Additionally, the ventilation rate of the breathing valve at the moment the tank collapses can be determined based on the critical load. The study results could provide reference for the repair and subsequent safe operation of the tank. (8 Figures, 2 Tables, 20 References)

The construction and operation of long-distance pipelines in China and abroad have entered the digital era. The development and application of a variety of new technologies provide technical support for the advancement of pipeline intelligent management. Meanwhile, there are also challenges posed. Here, the development status of pipeline intelligent technology at China and abroad was investigated, and based on the current application of pipeline intelligent technology in the oil and gas pipeline industry, a core pipeline intelligent management architecture of “data layer-service layer-application layer” was established. Further, the management principles were proposed, including making the pipeline data management throughout the full life cycle of pipeline with top design, grasping the main contradictions under the guidance of problems, and correctly handling the relationship between data, technology, production and management. Finally, through the study of typical pipeline intelligent management cases, the application trend of multi-technology integration was summarized to provide a reference for China’s pipeline intelligent management. (5 Figures, 26 References)

Motor-driven centrifugal compressor unit has been widely installed in the compressor station of natural gas pipeline in recent years. Motor-driven compressor unit industry of China starts late but develops fast. Here, the development and application of domestic motor-driven centrifugal compressor unit in natural gas pipeline was reviewed, and the main technical characteristics of compressor unit were described systematically, including combination mode of the main units, complete mode, electric motor, variable-frequency speed regulation device and control system. Through operation data analysis, typical fault analysis and comparison with imported unit, the advantages and disadvantages of the domestic motor- driven compressor unit were summarized, and suggestions were put forward in terms of design, operation, management and after-sales service. Moreover, prospect was presented from the prospective of development of domestic motor-driven compressor unit above 20 MW, promotion of domestic motor-driven compressor unit, application of high speed variable- frequency asynchronous motors, development of integrated compressor, development of magnetic bearing and its application in domestic split type compressor unit. Generally, it is concluded that the domestic motor-driven compressor unit will become the core power equipment of China’s gas pipeline in future, and it will be safer, more environment-friendly, more reliable and more economic. (2 Figures, 1 Table, 19 References)

Geological hazard is one of the main reasons for the failure of buried oil and gas pipelines. Particularly, the landslide, ground subsidence and surface collapse seriously threaten the safe operation of pipelines. Based on the existing research, several common models for analysis of pipeline-soil coupling were introduced, and the stress calculation methods of buried pipeline under the action of geological hazards were summarized. By means of experimental simulation and numerical simulation, the pipeline-soil interaction experiments and FLAC 3D numerical simulation were conducted under the action of different geological hazards such as collapse, settlement and landslide, and thus the stress distribution of pipeline under 3 types of geological hazards were obtained. By comparing the experimental results, numerical simulation results and the calculation results based on the theoretical model of pipeline, it can be concluded that it is feasible to simulate the pipeline-soil interaction with the finite difference software FLAC 3D, and for the theoretical calculation results only considering the pipeline, transportation medium and soil gravity load are quite different from the experimental and numerical simulation results, the influence of such parameters as soil friction and cohesion should be considered to improve the stress calculation method of pipeline. (12 Figures, 25 References)

The stress state is the key factor for the fitness-for-service assessment of girth weld, and the misalignment causes the discontinuity of girth-welded structure, which changes the stress state of girth weld. In order to explore the mechanical behavior and stress distribution of girth weld with misalignment under the action of external load, the stress concentration of girth weld with misalignment was studied through wide plate tensile test, and verified by establishing a finite element model. Additionally, comparison was made with the calculated values obtained with the recommended method specified in BS 7910-2013 Guide to methods for assessing the acceptability of flaws in metallic structures and GB/T 19624-2014 Safety assessment for in-service pressure vessels containing defects. The research shows that misalignment can lead to obvious stress concentration in weld, the stress concentration coefficient calculated according to BS 7910-2013 is moderately conservative compared with the results obtained through the wide plate tensile test and finite element simulation, and for defect fitness-for-service assessment of girth weld of pipe with misalignment, equivalent stress concentration treatment of misalignment according to BS 7910-2013 is recommended. (13 Figures, 2 Tables, 23 References)

Based on the three-dimensional finite element numerical simulation, an evaluation method of pig cleaning capacity was innovatively proposed from the perspective of the contact friction characteristics of the sealing component. Three-dimensional finite element models were established for two kinds of typical pigs running in horizontal straight pipeline with ANSYS, and the accuracy of the models was verified by field tests. Further, the cleaning capacity of the two kinds of pigs under different friction conditions were compared respectively through analysis on the calculation results. The research results show that the contact friction coefficient can affect the sealing tightness, tangent scraping force and effective cleaning area of running pigs. The scraping force increases with the increasing of friction coefficient while the sealing tightness and the contact area decrease. If the material and interference of the sealing components are identical under the same friction condition, the sealing tightness and the scraping force of the straight plate pig are superior to those of cup pig. However, the effective cleaning area of the cup pig is larger than that of the straight plate pig with same running distance. Appropriate pig should be selected according to the type of impurity in the pipeline to be cleaned, so that the cleaning capacity and efficiency can be improved effectively. (13 Figures, 2 Tables, 27 References)

Construction of high voltage direct current (HVDC) transmission system and long-distance oil and gas pipelines has greatly optimized the allocation of energy resources in China. However, attention should be paid to the strong direct current interference caused by the discharging of the HVDC grounding electrode to the buried pipelines. In order to further strengthen the management and control of the relevant risks, the development history of HVDC transmission grid in China was summarized, the typical characteristics of the influence of HVDC grounding electrode by discharging on the buried pipelines were analyzed, and the development direction of risk management and control was identified according to the actual conditions. The results indicate that the influence of HVDC lines and grounding electrodes on the nearby long-distance oil and gas pipelines in the same route has the characteristics of random time, complex interference mechanism, great interference intensity and difficulty in mitigation, and it is one of the prominent safety risks pipelines face to presently. During the commissioning or fault running of the HVDC transmission grid, discharging of single grounding electrode will accelerate the corrosion of buried pipelines. In the future, the level of inspection, research and governance should be enhanced by strengthening the communication, coordination and joint testing, studying the corrosion mechanism and rules in depth and taking the comprehensive governance measures, so as to guarantee the safety and stability of the national energy corridors in all rounds. (32 References)

With the continuous promotion of urbanization in China in recent years, the surrounding environment of some pipelines is changing constantly, and the scope of the high-consequence areas of the pipeline section is also changing. Accurately and efficiently mastering the data of environment change to update the information of the high-consequence areas is very important for the safety management of the pipeline companies. According to the characteristics of less change of natural features but frequent change of artificial features along the pipeline in short term, a method for detection of the change of the high-consequence areas based on the multi-source remote sensing image with high-resolution orthoimage and multispectral image was put forward. In this method, the change information of multi-source data is extracted with the LBP-HOG fusion feature and spectral gradient difference method based on the super-pixel segmentation. Experiments show that, the change of artificial features along the pipeline can be detected accurately with this method, so that the efficiency for management of high-consequence areas could be improved effectively. (9 Figures, 1 Table, 20 References)

In guided-wave based pipeline non-destructive inspection, it is inevitable that guided waves will interact with multiple defects, which makes damage identification more challenging. In this study, a numerical simulation was conducted to investigate the interaction of longitudinal guided waves with double notches in pipes. Firstly, a three-dimensional finite element model was established to simulate guided wave propagating in a pipe with a single notch. Then the established model was validated by comparing with existing experiments results. Based on the validated model, the guided wave reflection characteristics of two equal-sized notches of various relative positions were discussed systematically. The results show that, the relative circumferential positions of the two notches have little influence on the overall reflection, and the reflection coefficient rarely varies with the circumferential distance. However, the overall reflection of the two notches at the same circumferential location mainly depends on their axial positions, and the reflection coefficient varies periodically with the axial distance of the two notches. Moreover, the reflection coefficients of multiple notches within some axial range follow superposition principle approximately, which is very helpful for group corrosion detection. (10 Figures, 3 Tables, 20 References)

Hydrogen energy is recognized as a clean energy, and mixing hydrogen into natural gas pipeline is an effective way to transport hydrogen on a large scale. However, as the physical properties of hydrogen vary greatly from those of natural gas, the quality of natural gas will change after mixing. Here, summary was made for the research progress of the interchangeability of hydrogen-mixed natural gas, the adaptability of the hydrogen mixing process system of natural gas pipeline, and the safety of pipeline equipment during the transportation of mixed hydrogen in the natural gas pipeline transportation system in the world. Giving consideration to the actual condition of China’s gas pipeline network, it is suggested that: (1) Study should be performed on the requirements of different regions and different types of gas appliances on the interchangeability of hydrogen-mixed natural gas, and evaluation should be organized for the potential impact of hydrogen-mixed natural gas as fuel on civil/industrial users and other end users. (2) The operation parameters of pipelines at different flow rates, seasons, and hydrogen ratios should be analyzed, and the work condition point variations of different compressors and turbines should be researched. (3) The online/offline chromatographic analysis systems of gas components should be improved with consideration of the factors such as hydrogen content and the stratified flow of hydrogen and methane.⑷ The correction of metering equipment should be studied in combination with the CFD simulation and experiment methods. (5) By revealing the leakage and diffusion characteristics of hydrogen-mixed natural gas, the space layout and installation mode of gas leakage detection equipment should be optimized for different leakage scenarios, and a contingency plan should be improved. (6) The adaptability of high-grade steel pipeline to transportation of mixed hydrogen should be analyzed to guarantee the ontological security of pipeline. (1 Figure, 1 Table, 50 References)

Under the context of COVID-19 pandemic and PipeChina establishment, this paper reviews the development of China’s natural gas industry chain in 2020 and explores its development prospect in 2021. In 2020, the apparent consumption of natural gas in China reached 3 238 × 108 m³, with a year-on-year growth of 5.5%, and the reserve and production of domestic gas was well increased, reaching a production of 1 886 × 108 m³ and realizing a year-on-year growth of 8.4%. However, the growth rate of imported natural gas reached an all-time low, with the imported pipeline gas and LNG totaling 1 363 × 108 m³ at a year-on-year growth of 3.1% only, and the external dependence declined continuously. In 2021, with the large-scale vaccination of COVID-19 vaccine, the order of domestic production and living is fully restored. Further, with the drive of favorable environmental policies, the increment and growth of natural gas demand rises significantly compared to that in 2020, and it was predicted that the growth rate of market demand will reach 8.6% in 2021. Finally, in view of the development of China’s natural gas industry chain, the following three suggestions were put forward: (1) speeding up the construction of gas storage facilities, (2) unifying and coordinating the procurement of long-term trade resources of different domestic companies, and (3) implementing a unified floating ratio for the residential and non-residential gas in winter. (2 Figures, 17 References)