Mechanical stress improvement process

摘要

A process for reducing residual tensile stresses in high nickel-chromium alloy nozzle safe-end welds of pressurized water reactor nuclear pressure vessels such as are found at the reactor vessel inlet and outlet nozzles and the pressurizes surge, spray, safety and relief nozzles. The process involves the application of radial compression on the outside surface of the nozzle's safe-end and/or connecting coolant piping, to reduce the outside diameter at the mid-point of the piping element to which the load is applied to between about 0.2% and about 3%. The radially compressive load applied by this process is imparted using a mechanical device that can be employed at the vessel manufacturer's facility or at a nuclear power plant after welding of the nozzle safe-end to the coolant piping or before either after plant commissioning of operation.