Studies On Lateral Buckling Of Deep-sea Sandwich Pipe Under Non-uniform Temperature Field

Submarine pipelines are an important part of offshore oil and gas gathering and transportation equipment.With the advancement of offshore oil and gas exploration and development to deep and ultra-deep-water areas,the deep-sea high pressure and low temperature environment make the overall buckling phenomenon of submarine pipelines increasingly prominent.The sandwich pipe composite structure has a broad application prospect in the development of deep-sea oil and gas fields due to its better pressure-bearing capacity and thermal insulation performance.Compared with traditional steel pipes,the buckling process of composite pipes is more complicated,and there is currently a lack of research on the overall buckling of deep-sea sandwich pipes.In terms of buckling control,the buckling control method of deep-sea pipelines has gradually transitioned from passive restriction methods such as pipe trench burial to active control methods such as sleeper method and distributed buoyancy method.The above-mentioned problems have brought new challenges to the buckling analysis and buckling control design of submarine pipelines.This paper will take the deep-sea sandwich pipe as the research object,consider the non-uniform temperature distribution of the pipeline and the deep-sea high pressure environment,carry out the calculation and analysis of the lateral buckling of the sandwich pipe with initial imperfections,and further carry out the active control method research on the basis.The main work is as follows:Use FLUENT software to calculate and analyze the two-dimensional heat transfer model of the sandwich pipe under laminar flow and turbulent flow.Obtain the axial and radial temperature fields of the pipe under two working conditions.Combine theoretical analysis to verify the numerical model and calculate them separately.The influence of parameters such as crude oil inlet flow rate,thickness of the sandwich layer and inner pipe diameter on the temperature field of the pipeline is discussed.Based on the calculation results of the temperature field,compile the ABAQUS subroutine UTEMP to establish the overall buckling analysis model of the sandwich pipe under the non-uniform temperature field and the active control model of the sleeper-buoyancy method to solve and analyze the displacement configuration and each layer of the sandwich pipe during the lateral buckling process.The state of force and the control effect of different control methods.The influence of flow pattern,imperfection parameters and pipe-soil friction on the buckling characteristics of the pipe is further discussed,as well as the influence of the height of the sleeper,the friction coefficient of the sleeper,the length of the buoyancy device,and the buoyancy coefficient on the buckling control effect of the pipe.The calculation results show,compared with the turbulent flow condition,the temperature drop of the sandwich pipe structure in laminar flow state is more obvious;during the buckling process of the sandwich pipe,the stress state of each layer of the pipe is different,among which the inner pipe and the sandwich layer Due to thermal expansion and axial compression,the outer pipe is forced to deform and axially tension;Under turbulent flow conditions,the overall stress of the sandwich pipe is greater than that under laminar flow conditions.The lateral displacement and axial displacement of the pipe first increase and then decrease with the increase of the imperfection amplitude and wavelength,and decrease with the increase of lateral and axial friction coefficient;The critical buckling temperature of the pipeline decreases with the increase of the imperfection amplitude,and increases with the increase of the imperfection wavelength and pipe-soil friction;The maximum stress of the pipeline increases with the increase of the imperfection amplitude,and decreases with the increase of the imperfection wavelength and the pipe-soil friction coefficient;Compared with the sleeper method and the distributed buoyancy method,the sleeper-buoyancy method can better control the buckling characteristics of the pipeline;The maximum stress and critical buckling temperature of the pipeline decrease with the height of the sleeper,the length of the buoyancy device and the increase of the buoyancy coefficient,and it increases with the increase of the friction coefficient of the sleepers.