Residual Strength Of Damaged Tubular Members Of Jacket Platforms After Collision

As the most common platforms in shallow and medium-deep sea areas,jacket platforms play an important role in the exploration and development of offshore petroleum resources.However,it is impossible to avoid collision damages caused by supply vessels and dropped objects during the installation and operation of jacket platforms,which threaten their safety and service life.Therefore,it is critical to study the residual strength of the damaged tubular members of jacket platforms.In this paper,the collision damage modes,the residual strength of the tubular pipes after impact and the mechanical mechanism are investigated based on the experimental,numerical and theoretical study.Three groups of specimens with different geometries are selected,and the lateral impact experiments with different impact energies are conducted to imitate the formation process of collision damages.The maximum deformation of the upper and lower surfaces of the pipes and the deformation profile of the section are measured,and the maximum deformation of the upper surface is defined as the damage depth.Besides,the longitude-sectional and cross-sectional deformation modes are established.After impact-process,the quasi-static axial compressive tests are performed on the MTS hydraulic actuator to obtain the residual strength of the damaged pipes.When the axial loading force reaches a peak,the rate of the axial strain at the reverse side of the impact position suddenly increases.Based on the measurement results of two processes,it is found that there is a certain exponential correlation between the dimensionless residual strength and the damage depth of different tubular members.The finite element software ABAQUS is employed to simulate the collision damage and calculate the residual strength of damaged pipes.The simulation results and the experimental results of the two processes are in good agreement,which verifies the reliability of the simulation method.Considering the effects of fixed and simply supported boundary conditions,the finite element calculation results show that the residual strengths obtained under these two boundaries provide the upper and lower values for the evaluation of the residual strength of the damaged tubular members.In addition,referred to the actual sizes of the tubular member of the jacket platform,the effects of geometrical dimensions,damage widths and damage locations on residual strength of the damaged tubular members are investigated,and a formula to calculate the residual strength is proposed.The moment-thrust-curvature relationship of the tubular cross-section and the correlation between the residual bending moment of the cross-section with local deformation is analyzed.Based on the method proposed by Ellinas,an improved reduction factor method to calculate the residual strength of damage pipes is proposed considering the influence of local and global deformation.This method can provide a good prediction for the residual strength of the damaged pipes when the global and local deformation are given.