| With the gradual depletion of land oil resources and the continuous improvement of the oil equipment in China,the oil exploitation has gradually shifted from land to sea.As the key large-scale transportation equipment for oil exploration and development,the offshore platform crane is mainly responsible for transporting the personnel and the goods,so the personnel attaches great importance to the safety and reliability during its service life of the platform.Offshore platform crane is located in the worse working environment than that in the land,and during the service is often subject to a variety of load,and thus it is prone to be damaged.At present,the mainstream safety detection targeted at offshore platform crane remains to be traditional non-destructive detection.However,this detection method is found to have some limitations.As a new-type non-destructive detection technology that emerges and develops in recent few years,metal magnetic memory detection could detect the metal components in stress concentration area.Moreover,in view of its simple detection programs and functions in early diagnosis and prevention,metal magnetic memory detection has been gradually applied in the petrochemical industry.In order to test whether metal magnetic memory detection technology could be applied in offshore platform crane detection,this thesis has conducted considerable research work.First of all,the ANSYS finite element software is used to determine the maximum stress area in Bohai Sea platform crane and make overall stress analysis under the complex and variable load conditions so as to find out the weak points of the crane of the cradle in the cradle base and hydraulic cylinder connected to the lower ear plate,and provide follow-up site guidance for the magnetic memory test of the offshore platform crane.In order to better study the magnetic memory signal distribution rule at the weak point of the crane and the magnetic field characteristic criterion in stress concentration state,this thesis adopts finite element simulation technique to simulate metal magnetic memory values in static tensile load conditions based on magnetic theory and the magneto-magnetic coupling model and subsequently regards E36 specimen material applied in platform crane as the research target to carry out the theoretical study on the distribution law of the magnetic memory signal in the elastic and plastic stages.The simulation results show that the E36 steel component has a zero-point characteristic value of the critical magnetic field strength during the elastic-plastic transition phase and the corresponding magnetic field strength gradient is 2.667A/mm~2;Next,based on E36specimen material applied in platform crane,this thesis conducts indoor stretching and fatigue test on the load condition of offshore platform crane during service time and uses metal magnetic memory detector to test leakage magnetic field signal of E36 metal specimen.Through analyzing superficial leakage magnetic field distribution law,the thesis determines the eigenalue of magnetic field intensity in stress concentration area and provides basic data for on-site crane magnetic memory detection in comparison with simulation results.The results show that the corresponding magnetic field strength gradient value of the component under yield stress is 2.696A/mm~2 under tensile conditions,which is only 1.07%compared with the finite element simulation.Corresponding magnetic field strength eigenvalues show zero-crossing phenomenon,so to a certain extent,the feasibility of finite element simulation is verified,and also provide basic data for on-site metal magnetic memory testing. |
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