Evaluation of Cladding Residual Stresses in Clad Blocks by Measurements and Numerical Simulations

Abstract

Abstract. Reactor pressure vessels are internally clad with austenitic stainless steel. This welding operation generates residual stresses which can have an important role in integrity assessments. In order to evaluate these stresses, an experimental and numerical programme has been conducted. The experiments includes cladding operations, macrographic analyses, temperature and residual stresses measurements with different methods. According to these measurements, transversal stresses (perpendicular to the welding direction) and longitudinal stresses (parallel to the welding direction) are highly tensile in stainless steel and they are compressive in the HAZ. Finite element calculations were used to simulate both welding operations and post weld heat treatment. These calculations coupled the thermal, metallurgical and mechanical aspects in a 2D representation. Different models were studied including effect of generalised plane strain, transformation plasticity, creep and tempering. The transversal stresses calculated are similar to the measured ones, but the longitudinal stresses showed to be very sensitive to the model used. As expected because of the two-dimension model, the longitudinal stresses can't be well estimated. More work is needed to improve measurements of stresses in depth (important differences appeared between the different methods). A predictive model would be also very usehl to determine the thermal loading which is at present dependant on measurements. A 3D calculation appears to be necessary to evaluate longitudinal stresses.

Redistribution of residual stress by thermal shock in reactor pressure vessel steel clad with nickel alloy

“…Accurately assessing the integrity of an RPV subjected to thermal shock requires knowledge of the thermal stress and cladding residual stress, and an understanding of how they combine to cause a defect to propagate. After cladding, RPVs are usually subjected to post-weld heattreatment, whereby the material is maintained at high temperature to partially relax the residual stress by creep [2]. However, the residual stress is not completely erased [2][3][4] because additional stresses are generated upon cooling due to the difference in thermal expansion coefficient between the cladding and parent materials.…”

“…After cladding, RPVs are usually subjected to post-weld heattreatment, whereby the material is maintained at high temperature to partially relax the residual stress by creep [2]. However, the residual stress is not completely erased [2][3][4] because additional stresses are generated upon cooling due to the difference in thermal expansion coefficient between the cladding and parent materials. The residual stress in pressure vessel steel clad with stainless steel has been well characterised in previous work using modelling techniques [2,4] and experimental measurements [2][3][4][5][6][7][8][9][10].…”

Modelling of metal deposition

“…The first threedimensional multipass weld simulations were mentioned in [18][19][20][21][22]. Overlay repair and cladding, consisting of several hundred weld passes, has been studied in a simplified manner [23][24][25][26][27].…”

A Review on Cladding Process to Improve Metal Properties

“…Another process called plasma transferred arc welding was used to produce strong cladding of stainless steel over carbon steel with low dilution by selecting proper parameters [32]. In electroslag cladding with strip electrodes, high deposition rate and low dilution made the process cost-effective for marine applications [33]. GTAW was found to be an effective cladding procedure for stainless steel.…”

“…Pressure vessels used in power plants were reportedly clad to provide anti-corrosive as well as strong surface layer to survive severe working conditions at elevated temperature. Residual stresses developed in clad pressure vessels were evaluated, and these data were used in its designing process [25]. Cladding was also tried to provide for enhanced performance of components in service, or to repair worn or corroded components [26].…”