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Considering the difficulty in evaluating pipeline safety in permafrost region, the pipeline disaster safety evaluation index system in permafrost region is analyzed and established. A comprehensive weight determination method based on improved fuzzy analytic hierarchy process, entropy weight method and Lagrange algorithm is proposed, and a fuzzy comprehensive evaluation model of permafrost pipeline safety is established. Taking the disaster safety evaluation of pipeline in the China-Russia crude oil permafrost region as an example, the proposed method is used to determine the comprehensive weight of disaster safety index of permafrost pipeline and carry out comprehensive safety evaluation. The rationality of the comprehensive weight determination method is verified by comparing with the performance of the traditional AHP evaluation method. [ABSTRACT FROM AUTHOR]

In-situ monitoring system is absolutely necessary for a long-distance linear pipeline infrastructure in permafrost regions due to the complicated interaction between buried pipeline and its harsh permafrost environment. To study this complex problem, a comprehensive in-situ monitoring system has been designed and established along the China–Russia Crude Oil Pipeline (CRCOP), which is one of vital energy channels for importing crude oil from Russia to China. This monitoring system can record the meteorological data, ground temperature and water content within the permafrost foundation, vertical settlement of the oil pipe, ground surface deformation on the pipeline right-of-way (on-ROW), as well as the thaw bulb around the pipeline at four sites with different engineering geological conditions. In this paper, the layout and instrumentation of the whole monitoring system and monitoring methods are described in detail, and then the thermal regime of permafrost on-ROW and off-ROW and cooling performance of the mitigative measures on foundation soils are evaluated. Results show that heat dissipated from the CRCOP lead to the rapid degradation of permafrost on-ROW and produce different sizes of thaw bulb around the oil pipelines. The mitigative measures, including insulation layer, two-phase closed thermosyphon and U-shaped air-ventilated pipes, are effective to minimize permafrost degradation and ensure the thermal stability of permafrost foundation along the CRCOP. Some recommendations are proposed for future research and for the monitoring system to be improved. This monitoring system can provide multi-field data to clarify the interaction between pipeline and permafrost degradation under different geological conditions, and guide the design and maintenance of the buried warm pipeline in permafrost regions. • An in-situ monitoring system is set up along the CRCOP in permafrost regions. • The geological characteristics and layout of instrumentation at four monitoring sites are reported. • The integrated monitoring method for pipeline-permafrost interaction are presented. • Thermal effect of buried warm oil pipe on underlying permafrost is observed. • Cooling performance of the insulation layer, thermosyphon and U-shaped air-ventilated pipes is evaluated. [ABSTRACT FROM AUTHOR]

The China–Russia crude oil pipeline (CRCOP) traverses rivers, forests, and mountains over permafrost regions in northeastern China. Water accumulates beside the pipe embankment, which disturbs the hydrothermal balance of permafrost underlying the pipeline. Ground surface flows along the pipeline erode the pipe embankment, which threatens the CRCOP's operational safety. Additionally, frost heave and thaw settlement can induce differential deformation of the pipes. Therefore, it is necessary to acquire the spatial distribution of water features along the CRCOP, and analyze the various hazard probabilities and their controlling factors. In this paper, information regarding the permafrost type, buried depth of the pipe, soil type, landforms, and vegetation were collected along the CRCOP every 2 km. Ponding and erosive damage caused by surface flows were measured via field investigations and remote sensing images. Two hundred and sixty-four pond sites were extracted from Landsat 8 images, in which the areas of 46.8% of the ponds were larger than 500 m2. Several influential factors related to freeze–thaw hazards and erosive damage were selected and put into a logistic regression model to determine their corresponding risk probabilities. The results reflected the distributions, and forecasted the occurrences, of freeze–thaw hazards and erosive damage. The sections of pipe with the highest risks of freeze–thaw and erosive damage accounted for 2.4% and 6.7%, respectively, of the pipeline. Permafrost type and the position where runoff encounters the pipeline were the dominant influences on the freeze–thaw hazards, while the runoff–pipe position, buried depth of the pipe, and landform types played a dominant role in erosive damage along the CRCOP. Combined with the geographic information system (GIS), field surveys, image interpretation and model calculations are effective methods for assessing the various hazards along the CRCOP in permafrost regions. [ABSTRACT FROM AUTHOR]

The thermal state of permafrost in the present and future is fundamental to ecosystem evolution, hydrological processes, carbon release and infrastructure integrity in cold regions. In 2011, we initiated a permafrost monitoring network along the China–Russia crude oil pipeline (CRCOP) route at the eastern flank of the northern Da Xing'anling Mountains in Northeast China. We compiled an integrated dataset of the ground thermal state along the CRCOP route consisting of meteorological data near the southern limit of latitudinal permafrost, ground temperature (GT) data in 20 boreholes with depths of 10.0–60.6 m, soil volumetric liquid water contents (VWCs) and 2D electrical resistivity tomography (ERT) data at different sites. Results demonstrate a permafrost warming during 2011–2020 in the vicinity of the southern limit of latitudinal permafrost, as manifested by rising GTs at almost all depths in response to climate warming. Local thermal disturbances triggered by the construction and operation of CRCOPs have resulted in significant permafrost warming and subsequent thawing on the right-of-way (ROW) of the pipelines. This permafrost thaw will persist, but it can be alleviated by adopting mitigative measures, such as an insulation layer and thermosyphons. The in situ observational dataset is of great value for assessing the variability of permafrost under the linear disturbances of the CRCOPs and related environmental effects, for understanding hydro–thermal–mechanical interactions between the buried pipelines and permafrost foundation soils, and for evaluating the operational and structural integrity of the pipeline systems in the future. The dataset is available at the National Tibetan Plateau/Third Pole Environment Data Center (10.11888/Cryos.tpdc.272357; Li, 2022). [ABSTRACT FROM AUTHOR]

In permafrost regions, the soil settlement disaster owing to permafrost degradation has become one of the important reasons for buried warm-oil pipelines failure. In this paper, the 3D sequential thermo-mechanical coupled model is carried out to investigate the interaction between buried warm-oil pipeline and surrounding permafrost. The effects of parameters, including thaw-settlement coefficient, length of transition zone, diameter-thickness ratio and internal pressure, on the pipeline mechanical behavior are numerically investigated. Among them, the thaw-settlement coefficient and length of transition zone present more significant effects on the peak strain of the pipeline. In addition, the effects of insulation layer and two-phase closed thermosyphon (TPCT) on pipeline–soil interaction are investigated in thermal and mechanical fields. With no protective measure, the permafrost layer under pipeline will completely degrade in about 20 years with 0.33m/a. The pipeline is considered to reach failure limitation even within 10 years. However, under the influence of combined measure, the permafrost degradation rate is only about 1/10 of that without protective measure. The peak compressive strain is significantly lower than the critical compressive strain, and the pipeline remains safe for 50 years. Therefore, the combined measure is an ideal method for ensuring pipeline safety in permafrost regions. • Permafrost layer is well protected by the combined measure. • The TSC and the LTZ show significant effects on the peak strain of pipeline. • Pipeline remains safe for 50 years under the influence of combined measure. [ABSTRACT FROM AUTHOR]

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