EVALUATION OF CLADDING RESIDUAL-STRESSES IN CLAD BLOCKS BY MEASUREMENTS AND NUMERICAL SIMULATIONS

Reactor pressure vessels are internally clad with austenitic stainless steel. This welding operation generates residual stresses which can h ave an important role in integrity assessments. In order to evaluate t hese stresses, an experimental and numerical programme has been conduc ted. The experiments includes cladding operations, macrographic analys es, temperature and residual stresses measurements with different meth ods. According to these measurements, transversal stresses (perpendicu lar to the welding direction) and longitudinal stresses (parallel to t he welding direction) are highly tensile in stainless steel and they a re compressive in the HAZ. Finite element calculations were used to si mulate both welding operations acid post weld heat treatment. These ca lculations coupled the thermal, metallurgical and mechanical aspects i n a 2D representation. Different models were studied including effect of generalised plane strain, transformation plasticity, creep and temp ering. The transversal stresses calculated are similar to the measured ones, but the longitudinal stresses showed to be very sensitive to th e model used. As expected because of the two-dimension model, the long itudinal stresses can't be well estimated. More work is needed to impr ove measurements of stresses in depth (important differences appeared between the different methods). A predictive model would be also very useful to determine the thermal loading which is at present dependant on measurements. A 3D calculation appears to be necessary to evaluate longitudinal stresses.