Study On Residual Stress Distribution Of J Bevel In Nuclear Reactor Pressure Vessel

Nuclear reactor pressure vessel(RPV) is core piece of equipment in nuclear power plants, the early stress corrosion cracking easily break out on the J bevel in nuclear RPVs. It is the main cause which leads to coolant leakage on the upper head. The residual stress is one of the main driving factor which causes stress corrosion on J bevel weld joint.The J bevel weld joint in the RPV is the study object of this thesis. The material of the upper head is high strength stainless steel. The material of penetration assemblies and welding path is Inconel. The welding process is muti-pass welding.Firstly, the muti-pass welding on the J bevel in RPV was simulated by the SYSWELD. After, it calculates the temperature distribution data on the 14 different weld paths by heat load. After setting the heat transfer clamping model and other limiting conditions, the stress distribution data with former temperature date was calculated. There is a risk to have a crack in the axial or circumferential direction. By analyzing the residual stress at different paths on the inside and outside surface of the J bevel, the following information was obtained: the axial tensile stress is much higher than the hoop tensile stress on the internal surface of penetration assemblies, the stress of maximum point at the weld toe is 330.5MPa. There is a tendency for more cracking in the circular than axial; the hoop tensile stress is larger then the axial tensile stress on the outer surface of the J bevel. The maximum hoop tensile stress at the weld toe on the B path.-It is 498.5MPa, and may form an axial crack.Secondly, experiments conduct on the special points in different paths on the surface of the J bevel by drilling hole according to the ASTM-E837 standard. The axial and hoop stress on the surface of the J bevel was measured. Experimental results shows: the maximum axial stress of the inside face of the J bevel is 265.8MPa on the weld toe HAZ on C path. On the outside surface of the J bevel, the maximum hoop stress is 407.1MPa on the down weld toe of the A path.Finally, the simulation results was compared with experimental data. The following distributions were formed: the residual stress of the outside face is higher on the up and bottom weld toe than on the HAZ or weld center, showing a “M” distribution. The residual stress of the inside face keep increase from the up weld toe to the bottom weld toe, the maximum tensile stress is on the bottom toe. The experimental results were consistent with the simulation results; therefore the experimental data verifies the simulation results. It is meaningful to get a reliable stress distribution for the life prediction of the RPV to improve the welding process.