Study On The Collapse Pressure Resistance Of Offshore Pipelines Under The Influence Of Multiple Factors

In the process of marine resources development,various structural forms of steel pipes and flexible pipes are the main equipment to transport oil and gas resources.In the face of complex and harsh marine environment,the performance of pipes against various loads is very important,and the performance of pipelines against external pressure has increasingly become an important evaluation index for various types of oil and gas pipelines.External pressure resistance is affected by many factors,including material and structure,and other complex combined loads,which brings great inconvenience to the design of offshore oil and gas pipelines.In this paper,seamless steel pipe and steel strip reinforced flexible pipe are taken as research objects to analyze the collapse resistance of marine pipes under the influence of multiple factors.The research is carried out by combining theory,experiment and finite element method.The collapse mechanism is analyzed on the basis of theory.The correctness of theoretical analysis and finite element model is verified by experimental results.The main research method is finite element analysis.The influences of various factors on collapse resistance of pipes is studied through a large number of simulation calculations.Firstly,various collapse theories are summarized,including classical elastic collapse theory,plastic collapse theory and DNV code,and their applicability is discussed.Subsequently,the influence of initial ellipticity and bending load is studied by design experiments.Based on the experimental results,the finite element analysis is carried out.The results show that the initial ellipticity and bending load are the important factors affecting the collapse performance.The increase of initial ellipticity or bending load will significantly reduce the ultimate collapse pressure.The yield strength of materials and the tensile load on pipes have some influence on the collapse performance,but the influence is very small.In the collapse design,the steel with lower strength can be selected to meet the requirement of external compressive performance and save economic cost.In the case of combined action of ellipticity and bending load,the angle?between bending load and initial ellipticity direction is a major factor affecting the collapse resistance of pipes.The ultimate collapse pressure gradually increases with the increase of?.The minimum is at 0°and the maximum is at 90°,and the ultimate collapse pressure p and angle?coincide with exponential function p=e^A+B?+C?2.In the installation of pipes,the collapse resistance of pipes can be improved by reasonable control of angle?,and the greater the initial ellipticity,the greater the space for improving the collapse resistance of pipes.The experimental and finite element methods are used to study the collapse resistance of steel strip reinforced flexible pipes.The results show that the collapse pressure can be increased with the increase of friction coefficient between layers.When the yield limit of steel strip is less than 100 MPa,the collapse resistance of flexible pipe reduces.The increase of yield limit of steel strip after 200 MPa has little effect on the collapse resistance of steel strip reinforced flexible pipes.So the steel strip structure with lower strength can be selected based on the principle of economy.