Safety Evaluation Of Overage Service Offshore Platform Structures Under Super Typhoon

Offshore platform is the basic equipment of offshore oil development,and its security is related to national energy security.Nearly 30% of CNOOC’s offshore platforms are already past their design life,raising the risk of overextended service.It is one of the key issues that the Marine engineering is concerned about whether the overage service offshore platform can continue to serve safely.It is of great practical significance and engineering application value to evaluate the safety of the overage service offshore platform.At present,researches on safety evaluation of offshore platforms at home and abroad mainly consider the effects of earthquake,ice load,corrosion behavior,etc.,while literatures on safety evaluation of over-aged offshore platforms that consider the effects of super typhoon and fluctuating wind are still relatively rare.In view of this,based on the finite element analysis and ultimate bearing capacity theory,this paper uses the ABAQUS finite element analysis software to establish the finite element model of the offshore platform,obtain the ultimate bearing capacity of the offshore platform,use the strength coefficient of the structure to estimate the safety situation of the offshore platform,and realize the safety evaluation of the over-aged service platform.Firstly,the analysis steps and types of environmental load and ultimate bearing capacity of the offshore platform are analyzed to verify the effectiveness and reliability of ABAQUS analysis of the offshore platform.The finite element model of the offshore platform is established in ABAQUS software to calculate the static and dynamic analysis of the jacket offshore platform under the once-in-a-century wind load in the South China Sea.The study finds that: At 0°,45° and 90°,the maximum displacements on the windward side of the platform are 5.13 mm,5.92 mm and 6.62 mm,respectively.The maximum displacements of 0°,45° and 90° are 11.64 mm,12.34 mm and 12.23 mm,respectively.The maximum stresses in 0°,45° and 90° directions are 42.49 MPa,47.20 MPa and 45.43 MPa,respectively.When only the wind load is considered,only the displacement safety is considered,and the 90° direction wind load is more vulnerable to damage.Considering the safety from both the stress and displacement,the wind load in 45° direction is more vulnerable to damage.Under the condition of dynamic load of fluctuating wind,the maximum displacement of the windward side increases by about 100% compared with the static wind load.The maximum total displacement is increased by about 20%;The maximum stress increased by about 10%.Secondly,on the basis of the super typhoon load action,the analysis results and safety evaluation of the jacket offshore platform under the action of wave and ocean current load are studied.The maximum displacements in 0°,45° and 90° directions are 35.58 mm,33.66 mm and 35.84 mm,respectively,when wind,wave and current loads are taken into account.The maximum stresses at 0°,45° and 90° directions are 179.1MPa,179.4MPa and 187.2MPa,respectively.When the phase Angle is 200°,the displacement and stress of the jacket platform are the largest.For the same environmental load,jacket offshore platform is more vulnerable to damage under 90° wind load.Although the safety of the jacket offshore platform under the simultaneous action of wind,wave and current load is decreased compared with that under the action of wind load only,it is still within the safety range and the structure is still reliable.Finally,the study considered overage service platform of offshore platform structure corrosion,sea creatures to external factors,such as to modify jacket offshore platform jacket offshore platform serving for overage model,considering of wind,wave and flow load per100 and their combination as the environmental load,after the pushover analysis for the ultimate bearing capacity of the corresponding,Then the strength reserve coefficient,residual strength coefficient and residual reserve strength coefficient of the over-age service offshore platform are obtained.The results show that the ultimate bearing capacity and amplification coefficient under 45° direction load are larger,which indicates that the working condition is safer under the same wind wave and current load,which is far beyond the design load.Since the overage service offshore platform has accumulated damage in the service process,according to the residual reserve strength coefficient and the service time curve,when the residual strength coefficient is 1.5,the service time is 48.7 years.The research results provide theoretical basis and technical support for safety evaluation,structural reinforcement and life prediction of over-aged offshore platforms.