Failure Mechanism And Safety Evaluation Of Deep-sea Pipelines With Complex Dent Defects

Offshore pipelines plays an irreplaceable role in the transportation of offshore oil and gas,which is known as the "lifeline" of offshore oil and gas fields.Once damaged,the consequences will be disastrous.As one of the common defects of offshore pipelines,dents will directly affect the residual strength of pipelines and cause the pipelines to easily buckle under external forces.Therefore,it is of practical significance to study the failure mechanism of deep-sea pipelines with dents and develop corresponding safety evaluation methods to protect the integrity of offshore pipelines.Numerical simulation via ABAQUS is used to study the failure rules of deep-sea pipelines under complex loads and complex defect forms.The main contents are as follows:The numerical simulation model of deep-sea pipeline collapse with different shapes of dents is established,and the influence of dent depth and diameter-to-thickness ratio on the failure mode of the pipeline is explored.Based on this,a method for predicting the collapse pressure of deep-sea pipelines with different dent shapes is proposed.Then,the axial force of the pipelines caused by the temperature difference,the displacement of the soil,and the laying of the pipeline are further considered,and the collapse failure rule of deep-sea pipelines with dent under the action of axial compressive force or axial tensile force was investigated.Finally,a method for predicting the collapse pressure of deep-sea pipelines with dent under the combined action of external pressure and axial force was proposed.Using strain-based design and evaluation ideas,the compressive buckling failure rules of internal pressure pipelines(internal pressure > external pressure)and external pressure pipelines(external pressure > internal pressure)under displacement-controlled bending loads are investigated.The influence of internal pressure,external pressure,dent depth,and diameter-to-thickness ratio on the failure mode and compressive strain capacity(CSC)of the pipelines is analyzed.Based on this,a CSC prediction formula is proposed for the pipelines with dent under the combined action of internal pressure,external pressure and bending.A three-dimensional numerical simulation model of deep-sea pipeline collapse with corrosion-dent coupling defect is established,and the effects of corrosion length,corrosion width,corrosion depth,and dent depth on the collapse mode and collapse pressure of the pipeline is investigated.Based on the results of finite element calculations,a prediction formula for the collapse pressure of deep-sea pipelines with corrosion-dent coupling defects is obtained through nonlinear regression.