Dynamic Response Analysis Of Pipelines Under The Impact Of Debris Flow

Long-distance oil and gas pipelines may be destroyed under the impact of debris flow disasters,which in turn affect residents' personal and property safety and pipeline safety operations.The debris flow activity area is widely distributed in China,and the pipeline crossing area is intricate and complex.It is particularly important to analyze the dynamic response of the pipeline under the action of the debris flow and ensure the safe and reliable operation of the pipeline.In this paper,firstly,a large number of literatures at home and abroad were investigated,and the research status of debris flow impacted on pipelines at home and abroad was analyzed.The calculation method used in this paper was determined by summarizing the impact force of debris flow and the calculation formula of the velocity of large stones,and a simplified model of debris flow impacting pipeline mechanics was established.Secondly,for the non-defective pipelines,the finite element model of the pipeline under debris flow impact was established using ABAQUS finite element software.Based on the validity of the model,the variation rules of pipeline stress and displacement under different influencing parameters were obtained.Thirdly,according to the numerical simulation of corrosion-defective pipelines by the same finite element method,the mechanical response of pipelines with different corrosion parameters under the action of debris flow is obtained,and multiple regression analysis is performed on the corrosion parameters.Then,the numerical simulation data were statistically analyzed,and the limit state equation of the pipeline under the impact of debris flow was established.The reliability of the pipeline was solved through calculation examples.Finally,a casing pipe protection device was designed and verified by finite element modeling method to verify the device's effectiveness.The main conclusions of the above research process are as follows:(1)For buried non-defective pipelines:the pipeline stress is symmetrically distributed along the axial and radial directions,and the maximum stress occurs at the top of the tube in the impacted section;The maximum stress and displacement of pipeline increase with the increase of debris flow velocity;The stress of pressurized pipeline is larger than that of non-pressure pipeline under the same debris flow velocity,while the displacement is slightly less than that of non-pressure pipeline;The maximum stress and displacement of the pipeline increase with the increase of the impact angle;the effect of the large rock block on the pipeline is not significant;For Zhonggui Natural Gas Pipeline,the maximum flow rate of debris flow that the pressurized pipeline can withstand is 15m/s,and the maximum flow rate of the debris flow that the pressureless pipeline can withstand is 16m/s.(2)For exposed and non-defective pipelines:the pipeline stress is symmetrically distributed along the radial direction,and the maximum stress and displacement occurs at the impact part of the pipeline at the inflow plane;When the debris flow width is certain,the exposed length has little effect on the maximum stress of the pipeline;The maximum stress of the pipeline decreases with the increase of the impact angle;For Zhonggui Natural Gas Pipeline,the pipeline stress increases with the increase of the diameter of the large stone,and the stones with a diameter larger than 0.6m may cause damage to the pressureless pipeline,and the particle size is greater than 0.5m stones may cause damage to pressurized pipelines;The pressure pipelines can withstand a maximum flow rate of debris flow of 8m/s,and pressure-free pipelines can withstand a mdflow flow rate of 10m/s.(3)For buried corrosion defective pipelines:the maximum stress occurs at the position of the corrosion pit.Under the same impact velocity,the maximum stress increases with the depth and length of the corrosion pits,and it is not significantly affected by the corrosion width.When the depth of the corrosion pits reaches 0.5,8m/s impact flow rate can make the pipe maximum stress close to yield limit.A multi-variable regression model for different parameters of corrosion defects was established,multiple regression equations were obtained,and the accuracy of regression equations was verified.(5)In light of the debris flow impinging on the elastic limit state of the pipeline,the Zhonggui Natural Gas Pipeline is taken as the specific research object,and the limit state equation of non-defective and corrosion-defective pipelines under the impact of debris flow is established.Several common reliability calculation methods are summarized,and the reliability of the pipeline is solved based on the Monte Carlo method.(6)According to the debris flow disaster,a casing pipe protection device was designed.For buried pressure pipelines,the maximum stress of pipelines with protective devices is 510.4 MPa after being impacted by debris flows with a flow rate of 15 m/s,which is 39.4 MPa lower than that of unprotected pipelines;The maximum stress of the protective device after the semi-exposed pipeline is impacted by the debris flow of 8m/s is 409.4MPa,which is 131.7MPa less than that of the unprotected device,and the protective effect is obvious.