Numerical Simulation Research On Post-Weld Induction Hreatment Of Girth Welds Of Large Diameter And Thick Wall Cylinder

The MIG welded joints of austenitic stainless steel large vessels need to undergo desensitization heat treatment after welding to eliminate grain boundary segregation and residual stress in the joint structure.This paper proposes a local induction heating process to perform post-weld desensitization heat treatment on the welded joint of TP347 stainless steel cylinder.First,the ANSYS simulation software is used to establish the magnetic-thermal coupling model of the induction desensitization heat treatment of the TP347 stainless steel cylinder after welding,and the coupling analysis of the magnetic field and temperature field is carried out based on electromagnetics and heat transfer.The magnetic field and temperature field distribution of the tube under the induction parameters of a current of 650 A,a frequency of 10 k Hz,a coil with 13 turns,and a distance between the tube and the coil of 70 mm are studied.Through the distribution of magnetic field and eddy current,the distribution of magnetic field intensity and eddy current density in the three-dimensional space of the cylinder in the process of induction heating is studied.The lines of magnetic force pass through the inside of the coil and return along the outside to form a closed loop;the magnetic field on the outer wall of the cylinder has the highest intensity,the eddy current density is concentrated,and the eddy current loss is large.The three data are consistent and all depend on the structure of the induction coil.Taking the temperature field of the post-welded desensitization heat treatment process of the thick-walled large-diameter cylinder as the research object,we design different induction heating parameters to simulate and analyze the temperature uniformity of the cylinder.The results show that the greater the coil current and frequency,the higher the temperature;when the distance between the cylinder and the coil decreases,the final temperature reached is higher,and the temperature difference between the inner and outer walls is not obvious;as the number of coil turns increases,the heating temperature becomes higher.The uniformity of temperature is also better.It is finally determined that when the current is 515 A,the frequency is 7k Hz,the coil is 23 turns,and the heating distance is 70 mm,the temperature of the weld area of the cylinder body can reach 860-906℃,which is out of the sensitization temperature range and meets the process requirements of post-weld stabilization heat treatment.We carried out the experimental verification of the electromagnetic induction heating post-welding heat treatment on the optimized simulation results,set up an electromagnetic induction heating experimental platform,and collected temperature data during the heating process with thermometers and thermocouples.The results show that the temperature of the outer wall of the intermediate frequency induction heating cylinder is 900±10℃,and the temperature of the inner wall exceeds 850℃;the temperature difference between the inner and outer walls is 30-40℃;the outer circumferential temperature difference is about 10℃,and the inner circumferential temperature difference is about 20-40℃;the temperature of the inner wall during the heat preservation process of stabilization heat treatment is greater than 850℃,which has been out of the sensitization temperature range,and the temperature difference in the heat treatment process is within 30℃.Within a reasonable error range,the experiment and simulation results are consistent.Aiming at the radial and circumferential temperature differences in the post-weld heat treatment of large cylinders in actual working conditions,the optimal design of the induction device is carried out.An insulation blanket with a thickness of 50 mm is laid on the inner wall,and the radial temperature difference is reduced from 34℃ to 24℃ to improve the uniformity of the radial temperature distribution;when the cylinder is placed horizontally,the coil is raised by 10 mm at the highest temperature point,and the opening angle is 15°,reduce the circumferential temperature difference of 6℃,and meet the requirements of post-weld heat treatment at the same time.