Stress Analysis And Fatigue Simulation Of Marine Diesel SCR Pressure Vessel

Along with the implementation of the TIERIII stage in Annex IV of The MARPOL73/78 Convention issued by the International Maritime Organization(IMO)in2016,countries must strictly control the emissions for ship diesel engine exhausting NOx.Therefore,how to economically and effectively reduce the content of NOx in marine diesel exhaust has become a problem that marine diesel manufacturers must face and solve.At present,the SCR system of marine diesel engine is one of the most effective means to reduce the NO_X content of exhaust gas.But the SCR system of the marine diesel engine is more complex because of the condition of the reactor pressure vessel.If the high temperature corrosive gas of the reactor pressure vessel of the SCR system leaks in the working process,the result will be very serious.Therefore,the correct stress analysis and stress assessment of marine diesel SCR pressure vessels are very important.In this paper,the structural stress analysis and stress assessment are carried out by the classical mechanics and finite element method.Then,the influence of saddle structure on the stress distribution of marine SCR pressure vessel is studied.Finally,the crack fatigue failure of the SCR pressure vessel which is the common failure mode of the SCR pressure vessel is studied.The contents of the specific research work are as follows:(1)The stress conditions of the head and cylinder of the pressure vessel under the mechanical load and the heat temperature load are analyzed and the theoretical analytical solution is given.The numerical method is used to calculate the thermal mechanical stress coupling of a certain type SCR pressure vessel and evaluate the stress.It is proved that the analysis design method is more superior than conventional design.(2)The stress condition of SCR pressure vessel under double support and multi support is studied.Through formula deduction,it is proved that the multi support form is not suitable for marine pressure vessel.Based on the dual support form of SCR pressure vessel,the effect of the height of saddle and the deviation angle of gravity acceleration on the stress distribution of the SCR pressure vessel is analyzed by the ABAQUS software.The increasing of saddle height can effectively improve the force condition of the cylinder.When the direction of gravity acceleration deviates,additional stress will be added to the F saddle and its corresponding cylinder part.(3)Finite element modeling of the SCR pressure vessel submodel with different crack parameters is carried out to analyze the stress condition at each crack.And the ODB file of the stress result is obtained.Then,the result file is used as the input data of the fatigue life analysis software of FEMFAT and the fatigue life of the submodel is calculated.Through the comparative analysis between the models,the crack parameters having great influence on fatigue life are obtained which is of guiding significance for correctly judging the harmfulness of cracks in the future.