Research On Overlay Surfacing Welding Process Of 304 Stainless Pipe Socket Weld

304 austenitic stainless steel is widely used in nuclear power plants because of its excellent corrosion resistance,radiation resistance and high strength.For 304 stainless steel bearing widely distributed in the machine group,its welding joint is prone to crack due to residual tensile stress,which endangers the operation safety of nuclear power plants.In addition,some repair processes need to be carried out under normal operation conditions of nuclear power plants.Therefore,by studying the distribution of temperature and stress fields in the welding process of the support,this paper improves the OVERLAY surfacing repair process to transform the original residual tensile stress into compressive stress,thus inhibiting the crack initiation and expansion.The research content can provide theoretical support and process guidance for OVERLAY surfacing repair of support pipe in domestic nuclear power plants,and has important research significance.Firstly,the heat distribution and residual stress distribution in OVERLAY repair process of 304 stainless steel support with and without water were simulated by finite element numerical simulation method.It was proposed that OVERLAY surfacing repair should be carried out under water-carrying condition of main pipeline.If the pressure difference between inner and outer walls of main pipeline was greater than 1bar,the welding position of pipe wall would be locally deformed and prone to occur.When the pressure difference between the inner and outer wall of the main pipe is less than 1bar,the welding temperature of the pipe wall decreases obviously and there is no deformation basically.Internal pressure relief and water filling welding in main pipe can significantly reduce welding residual stress and welding deformation.Co Mpared with no water and small welding heat input,the effect of internal water filling operation has greater advantages.Secondly,combined with the results of simulation analysis,the single layer surfacing process is studied firstly.The current greater than 125 A should not be used under the condition of water to avoid the consequences of leakage of fluid medium in the original pipeline weld.For the original weld surfacing with water in the pipeline,the maximum penetration reaches 1.08 mm at 105 A and is lower than that without water.OVERLAY surfacing repair is recommended under the condition of 95A-115 A and 2.5mm/s welding speed.Finally,OVERLAY surfacing repair process,structure and properties were studied based on numerical simulation results and single layer surfacing test results.The results show that the thickness of HAZ increases significantly and the ferrite content increases obviously when welding without water,and the volume expansion of HAZ results in the increase of stress due to a large amount of ferrite.When the welding current is 100A-110 A and the welding speed is 2.5mm/s,the welding deformation is the smallest and the solidification structure of the weld is FA solidification structure,and the crack resistance is high.Sensitivity.When OVERLAY is repaired,the first layer is welded from the side of the main pipe to the side of the branch pipe,and the second layer is welded from the side of the branch pipe to the side of the main pipe,and the ideal surfacing joints can be obtained under the process conditions of single weld bead welding 180 degrees in both directions.It is proved that OVERLAY surfacing can promote the formation of compressive stress on the inner wall of pipeline and is beneficial to the implementation of field surfacing.