Flaw indications have been found in some dissimilar metal (DM) nozzle to stainless steel piping welds and reactor pressure vessel heads (RPVH) in pressurized water reactors (PWR) throughout the world. The nozzle welds usually involve welding ferritic (often A508) nozzles to 304/316 stainless steel pipe) using Alloy 182/82 weld metal. The welds may become susceptible to a form of corrosion cracking referred to as primary water stress corrosion cracking (PWSCC). It can occur if the temperature is high enough (usually greater than 300°C) and the water chemistry in the PWR is typical of operating plants. The weld residual stresses (WRS) induced by the welds are a main driver of PWSCC.
The purpose of this paper is to determine the weld residual stresses in a double-vee groove welded nozzle and then to model the natural crack growth in the weld. The double vee groove geometry has not been modeled much to date especially in such a large nozzle. This leads to a rather unique weld residual stress pattern which changes as the throat of the double vee is approached. Axial crack growth is modeled using a natural crack growth procedure. This was challenging since the crack shape necked down in the region where the tips of the vee grooves meet making the mesh development during this process challenging. This analysis provides information regarding crack growth evolution versus time. In addition, some comments regarding idealized growth are presented.