The Impact of Key Simulation Variables on Predicted Residual Stresses in Pressuriser Nozzle Dissimilar Metal Weld Mock-Ups: Part 2—Comparison of Simulation and Measurements

Abstract

British Energy (BE) has funded a large work programme to assess the possible impact of primary water stress corrosion cracking on dissimilar metal welds in the primary circuit of the Sizewell ‘B’ pressurised water reactor. This effort has included the design and manufacture of representative pressuriser safety/relief valve (SRV) nozzle welds both with and without a full structural weld overlay, multiple residual stress measurements on both mock-ups using the deep hole and incremental deep hole methods, and a number of finite element weld residual stress simulations of both the mock-ups and equivalent plant welds. Three organisations have performed simulations of the safety/relief valve nozzle configuration: Westinghouse, Engineering Mechanics Corporation of Columbus (EMC2) and the Australian Nuclear Science and Technology Organisation (ANSTO). The simulations employ different welding heat input idealisations, make different assumptions about manufacturing history, and use a variety of different material constitutive models, ranging from simple bilinear kinematic hardening to a full mixed isotropic-kinematic formulation. The availability of both high quality measurements from well characterised mock-ups, and a large matrix of simulations, offers the opportunity for a “mini-round-robin” examining both the accuracy and key solution variables of dissimilar metal weld finite element simulations. This paper is one of a series at this conference that examine various aspects of the BE work programme. It draws together residual stress measurement results and the results of all three simulation campaigns (described in detail in other papers at this conference) to examine the impact of manufacturing history, thermal modelling assumptions, material constitutive models and other key solution variables on the accuracy of residual stress predictions in this dissimilar metal weld geometry.

Calculation of a lower bound ratchet limit part 2 – Application to a pipe intersection with dissimilar material join

“…The intersecting pipe was chosen to be from low alloy steel SA508 and the weld material is Inconel 82/182. Recently the UK nuclear industry has been analysing the residual stresses present in this dissimilar weld with a view to investigating stress corrosion cracking (Brust et al, 2010;Smith et al, 2010aSmith et al, , 2010b.…”

Deep Hole Drilling

“…The first case study is based on major investigations in Japan, [31][32][33] and in the USA, [34,35]. In each case a series of full-scale mock-ups of safe-end nozzles for pressurized water reactors (PWR) were manufactured.…”

“…In the USA research [34,35] full-scale dissimilar-metal welds were examined with additional structural weld overlays introduced. Weld overlay is used extensively as a repair and mitigation technique for SCC in pressurizer nozzle dissimilar-metal welds.…”

“…Predictions of residual stresses were made also using a thermo-mechanical finite element analysis assuming an axisymmetric model of the nozzle. Further details can be found in [35]. A comparison between predictions and measurements of the axial and hoop stresses in the nozzle are shown in Figure 3.12.…”

“…In both mock-ups the axial measured stresses were slightly more tensile than the predicted stresses. This is thought [35] to be due to through-wall bending that was not accounted for in the FE analysis. Conspicuously, the addition of the weld overlay did not make the inner wall more compressive but did make the zone of compression expand deeper from the inner surface towards the outer surface.…”