Jianbin Hao

Analysis and Numerical Simulation on Dynamic Response of Buried Pipeline Caused by Rock Fall Impaction

Theoretical analysis methods are discussed to estimate additional stresses of shallow buried oil and gas pipeline caused by rock fall impaction. The process of impaction is simulated using finite elements software, in the model a 1 m3 square shape falling hard rock impacts soil ground upright of pipe with a vertical velocity, and dynamic response of pipeline is analyzed. The impact force, soil additional stresses, pipe displacement and additional stresses in the impaction process are studied. The effect of pipeline buried depth and rock velocity to the impaction also discussed. Results show that the impaction process is very short and the duration is about 10−3∼10−2s. The maximum impact force has approximately direct ratio with the velocity of rock. The additional vertical stress in soil caused by impaction load has a stress concentration region near the surface of pipe, and its distribution has the similar pattern with that in static load, but has a faster attenuation from the impaction center to sidewall. The most dangerous pipe cross-section appears in the underside of impaction center, and the maximum additional equivalent stress appears in the top of the cross-section, and has an approximately direct ratio with the velocity of rock if other impaction conditions are confirmed. The buried depth of pipeline has major influence to impaction. Large thickness of soil cover has marked effect on improve the protection of pipeline. According the study, shallow buried pipeline has weak defense to rock fall. The additional internal force and stress of pipeline caused by impaction of rock fall can be approximately estimated using theoretical methods or numerical simulation.Copyright

Deformation Characteristics of Pipeline in Mining Subsidence Areas Based on Strain

The mechanical model of oil and gas pipeline in mining subsidence areas is proposed according to the characteristics of mining areas and properties of pipe material, and the effects of subsidence imposed on pipeline are divided into soil creeping, local pipe span, free pipe span, and sudden soil subsidence respectively. The mechanical equations of four states are provided based on strain and Ramberg-Osgoods’ stress-strain relationship, and the direct search method with Newton-Raphson method is used for the solution. Under the condition of different wall thickness (WT), outside diameter (OD) and buried depth, numerical calculation analyzes the deformation characteristics of the strain subject to the change in length of the span or subsidence. It shows that WT of pipe exerts the greatest impact than others, and the influence of buried depth is larger than OD except the state of soil creeping. In addition, a conclusion can be drawn that the application of strain-based design gives full play to the advantage of self-bearing ability, and the allowable length of subsidence imposed on pipeline is increased.Copyright

A Fiber Bragg Grating Sensing System and Its Application to Monitoring Landslides and Associated Pipelines

The integrity of oil and gas pipelines is seriously threatened by landslides and other geohazards in tough terrain in western China. Monitoring the landslides with slow, continual movements and the strain build up in pipelines due to landslides is an effective way to maintain the serviceability of pipelines. In this paper, a monitoring system based on Fiber Bragg Grating (FBG) sensors is developed and applied. The system is made up of four related parts: the pipeline strain measurement of the with FBG strain sensors, the soil-pipeline contact pressure detecting with FBG soil pressure cells, the landslide inner deformation monitoring with pipe strain gages and the landslide surface monitoring with a special buried concrete beam with FBG sensors. The system is used to monitor a huge, slow moving landslide and the pipeline affected by it. The monitoring results are analyzed and the pipeline integrity is assessed basing the monitoring results. The FBG system has been proved to be suitable to monitor landslides and pipelines automatically and real-timely.Copyright

Study on Buried Pipeline Security and Early-Warning System in Landslide Area Based on Fiber Bragg Grating Sensors

Compared with electric sensors, Fiber Bragg Grating (FBG) sensors are immune to electromagnetic interference, corrosion resistant, small in size and light in weight. Therefore, FBG sensors are easy to bury into geotechnical soil mass, measuring strain and temperature simultaneously. Focused on buried pipeline integrity, a type of sensing network made up of FBG sensors is introduced in this paper, monitoring pipeline strain, landslide surface displacement and inner displacement. An application of the sensing network to a huge landslide affecting a gas mainline is also introduced. The field experimental data show that, the FBG sensors have many advantages such as good real-time monitoring ability, flexible to develop sensing network, convenient to realize long-term monitoring. Moreover, the FBG sensors give reliable long-term monitoring data of pipeline strain and surface and inner displacement of the landslide, which provide the basis to evaluate pipelines integrity affected by landslides.© 2008 ASME