Numerical Simulation Of Welding Residual Stress Of Pressure Vessel

Pressure vessels are widely used pressure equipment in many industries.In order to meet engineering requirements,they need to be connected with various calibers of nozzles.Residual stress will occur in the welding process of nozzle,which will affect the strength and safety reliability of the structure.In this paper,finite element method is used to simulate the dynamic change of temperature field in pressure vessel welding.On this basis,the distribution characteristics of residual stress field are studied.At the same time,the residual stress field of welded joints with cracks is analyzed and the stress intensity factor is calculated.The main contents of this paper are as follows:(1)Aiming at the welding process of pressure vessel,the "life and death unit" technology is used to simulate the formation of weld pool,and the temperature and time variation process of weld seam is calculated by setting the weld path and related nodes.The results show that the temperature time history curves at each node have similar trends.The heating process of the welding heat source is rapid.After the heat source leaves,the cooling rate is faster.Generally speaking,the heating rate is faster than the cooling rate.(2)The residual stress field of pressure vessel welding was studied by thermal-stress coupling calculation.The characteristics of instantaneous stress variation of welded joints were analyzed,and the distribution of residual stress along the welding direction and cross section was studied.The analysis shows that the residual stress at the weld seam is large,and the peak value of the residual stress appears at the weld toe of the weld seam and the barrel and nozzle of pressure vessel.The residual stress at the inner surface is larger than that at the outer surface.(3)Using the method of killing part of the "element" to simulate welding cracks,the redistribution of welding residual stress field of pressure vessel with cracks is studied,and the stress intensity factors of cracks under residual stress with cracks are calculated,and compared with those under residual stress field without cracks.The results show that the stress intensity factor based on the crack-free residual stress field is lower than that based on the crack-free residual stress field,which is closer to the true stress intensity factor.The geometric size and shape of the crack affect the distribution of residual stress.At the same time,the stress intensity factors of cracks of some sizes are calculated by the extrapolation method of finite element calculation,and the correction coefficients of stress intensity factors of cracks of various sizes are fitted,and the formulas for calculating the stress intensity factors of cracks under internal pressure and residual stress are obtained.The ultimate internal pressure of a pressure vessel with cracks is determined by calculating the crack stress intensity factor.