Study On The Stress Concentration Factor And Fatigue Life Prediction Of The Structure Of Oblique Nozzle In The Circumferential Direction Of Pressurized Vessel

Due to engineering needs,the nozzle of some parts of pressure-bearing equipment such as pressure vessels and boilers adopts oblique connection structure.The stress distribution in the intersecting area between the oblique nozzle and the container is complex,and there is stress concentration.At present,the research on the stress distribution and stress concentration factor of the circumferential opening oblique nozzle structure is not perfect,and the relevant technical specifications have not yet defined the design requirements of the oblique nozzle.It is of practical engineering significance to explore the change of stress concentration coefficient and fatigue life prediction of circumferential opening oblique structure.In this study,the concentrated stress coefficient of the circumferential oblique nozzle structure model under internal pressure is calculated,and the relationship between the structural parameters,stress state distribution and fatigue life prediction results of the oblique nozzle structure is summarized and analyzed.The finite element numerical simulation is used as the main data acquisition method and combined with theoretical calculation to predict the maximum stress,stress concentration factor and fatigue life of the oblique nozzle structure.The main research contents and research results include the following :1.The finite element model of circumferential oblique nozzle structure was established by using three dimensionless parameters : opening ratio d/D,thickness ratio T/t,and eccentricity ratio representing the opening position parameter.The relationship between the elastic stress concentration coefficient of the oblique nozzle structure and the dimensionless structural parameters was investigated.The results show that the small eccentricity ratio,the large opening ratio and the large thickness ratio of the cylinder to the nozzle will increase the stress concentration of the oblique nozzle structure and adversely affect it.When the opening rate exceeds 0.6,the stress concentration factor increases greatly,which should be avoided in the structural design.2.The possible position of the maximum stress point(dangerous point)of the circumferential oblique nozzle structure was investigated.According to the characteristics of the stress and strain distribution of the oblique nozzle structure,the investigation range was locked on the internal intersecting line,nozzle and cylinder weld toe line of the possible dangerous point in the ideal weld zone.The results show that in the ideal circumferential oblique nozzle structure,the maximum stress area is always inside the junction between the nozzle intersection line and the cylinder.3.Various fatigue life prediction methods commonly used at present are analyzed,and their steps,advantages and disadvantages in the fatigue life prediction of the oblique nozzle structure are compared.The applicable conditions of the prediction method are evaluated,and a feasible research method is selected.4.The BP neural network improved by artificial bee colony optimization algorithm(ABC)is used to establish the fatigue life prediction model of circumferential opening oblique structure,and the influence of structural parameters on it is obtained.The results show that small e value,large opening ratio and large thickness ratio of cylinder to nozzle will reduce the fatigue life prediction results and have adverse effects on them.The prediction results of the improved ABC-BP neural network and the traditional BP neural network are compared.The results show that the ABC-BP neural network has better performance in both prediction accuracy and model stability.Exploring the stress concentration factor of the circumferential oblique nozzle structure and improving the structural fatigue life prediction method provide some references for safety design,thereby increasing the service life in actual work.