Measurement of Residual Stresses in the Dissimilar Metal Weld Joint of a Safe-End Nozzle Component

This paper presents results from a programme of residual stress measurements and modelling carried out on a Pressurised Water Reactor Safe-end Nozzle component. The full-scale Safe-end Nozzle component was manufactured to the same specifications as those typically found on Japanese Pressurised Water Reactors. The basic component consisted of a ferritic steel nozzle with a tapered outer diameter (OD) ranging from 883mm to 1192mm, an inner diameter (ID) of 735mm and a length of roughly 1080mm. A stainless steel ring (i.e. the safe-end) of 883mm OD, 735mm ID and length 100mm was attached to the ferritic steel nozzle using a double-V nickel base alloy (i.e. alloy 132) weld with buttering. Later on in manufacturing a stainless steel, main coolant piping section (883mm OD, 735mm ID and 500mm length) was then attached to the safe-end using a single-V stainless steel weld. The residual stresses generated through the centre-line of the double-V weld connecting the stainless steel safe-end to the ferritic steel nozzle were measured using the Deep-Hole Drilling (DHD) and inherent strain techniques. The residual stresses generated by welding were modelled using ABAQUS. Presented here are the DHD measurements from six locations circumferentially around the weld made at three different stages during the manufacture and testing of the component. The DHD measurements are compared against those measured on a similar component using the totally destructive inherent strain technique and those modelled using finite element analysis. Details of the FE modelling carried out for this project are to be presented in another paper at this conference (PVP 2009-77269). The measured and modelled results are also compared against the UK based BS7910 and R6 standards. It is shown that there is excellent agreement between the DHD, inherent strain and modelling results in the as-welded state, showing peak tensile stresses at the inner and outer weld cap surfaces, reducing into compression in the centre at the meeting of the double-V grooves. It is also shown with the DHD measurements that after attaching the main coolant piping, the peak tensile residual stresses present at the inner surface in the hoop and axial directions changed to become compressive. Furthermore, following hydrostatic and operating condition tests, the DHD measured residual stresses at the inner surface were shown to move towards tension again, with the axial residual stresses remaining slightly compressive, but the hoop residual stresses becoming slightly tensile. The residual stresses generated at the outer surface were relatively unchanged by the manufacturing and operating processes carried out.