Research On Mechanical Characteristics And Safety Prevention And Control Measures Of Oil And Gas Pipelines Crossing Rivers

Oil and gas transportation often need to cross the river, so the bottom of oil and gas pipeline is an important part of petroleum engineering production system. However, the bottom of oil and gas pipeline lies in complex geological conditions, and with the effects of water flushing and construction residual stress, it is easy to create suspended span pipeline. In the pipeline suspended span section, due to water flushing action, a vortex release, will change the stress distribution of the pipeline, so that the risk of pipeline transport in the bottom of river would be increasing.Therefore studying the mechanical properties of the oil and gas pipelines'suspended span section, and on the basis of this putting forward the safety prevention and control measures is particularly important.In view of the above content and the theory of pipe soil coupling and finite element theory research the mechanical properties of the level span period about the crossing river pipeline.Using finite element software ABAQUS/CAE set up with single and multi span range (equal span and unequal span) finite element model of the pipeline,and considering the influence of interaction coupling soil pipe and water load.Adopt the method of numerical simulation study the influence that pipeline span length, pipe wall thickness, pipe internal operating pressure, the coupled action of pipe and soil (soil elastic modulus, cohesive force, friction coefficient and friction Angle of soil), flow velocity,the supporting length between soil, unequal span and so on take place on the mechanical properties of pipeline.Single span pipeline mechanical properties research shows that the pipeline's stress and deformation have a positive correlation with suspended span length, the internal pipeline operating pressure and flow velocity,And a negative correlation with the pipe wall thickness,the soil conditions (soil and the elastic modulus of soil cohesive force).Caused by the increase of friction coefficient and friction Angle,pipe stress and displacement change is small,so the impact that friction coefficient and friction Angle place on the model almostly can be neglected. Hydraulic load in span the pipelines, the vertical displacement and the maximum stress in the across region of suspended span pipeline present a periodic changes,besides if the river flow velocity becomes bigger the pipe stress and vertical displacement change more obvious.Researching equal span pipeline mechanical characteristics,we can get the conclusion that the soil coupling effect increased with the increase of the supporting length across the soil pipe, thereby limiting pipeline deformation, so weakening the interaction between two adjacent span section. Researching unequal span pipeline mechanical characteristics shows that with the span length of two cross pipelines becoming closer, the interaction between the two across become more obvious, Increasing the modulus of elasticity of the soil and the cohesion of the soil in the multi cross flow pipeline will weaken the interaction between the two spans.Single span and multi span pipeline analysis contrastly pointing out that The stress of multi span pipeline is less than that of multi span pipeline, and the natural frequency of multi span pipeline is less than the natural frequency of single span pipeline.The determination of the critical span length and the safety control measures are proposed:According to the strength yield theory, the critical span length of the pipe to yield strength can be reached; According to the resonance of oil pipeline draw critical span length of vibration failure; In order to avoid the failure of pipeline, the two length of the minimum is critical span length of the pipeline. At the same time, the critical span length of pipeline at different flow velocity and different wall thickness is obtained, And puts forward the safety control measures for the phenomenon of the suspension span of the pipeline.