Periodic Reporting for period 3 - ATLASplus (Advanced Structural Integrity Assessment Tools for Safe Long Term Operation)
Période du rapport: 2020-06-01 au 2021-11-30
The European Horizon 2020 project ATLAS+ (Advanced Structural Integrity Assessment Tools for Safe Long Term Operation) focuses on developing:
• innovative quantitative methodologies to transfer laboratory material properties to assess the structural integrity of large piping components,
• enhanced methods for treatment of weld residual stresses when subjected to long term operation,
• advanced simulation tools based on fracture mechanics methods using physically based mechanistic models,
• improved engineering methods to assess components under long term operation taking into account specific operational demands,
• integrated probabilistic assessment methods to reveal uncertainties and justify safety margins.
The actions to achieve the objectives were completed. This includes;
1) The tearing resistance curves (J-R curves) were determined with compact tension (C(T)) and single-edge notched tension (SE(T)) specimens. The pipes were tested in four-point bending with elliptical cracks on the outside of the pipe, and through wall cracks. The testing was mostly done in room temperature, but for the last test the testing was done in 100 °C since unsuspected mechanisms were observed at lower temperature. The increase in temperature guaranteed sufficient ductile tearing of the pipe. Overall, the fracture mechanical testing was successful and served the modelling tasks.
2) Weld residual stresses were modelled and measured. Despite careful planning of the welding processes some minor mistakes were made which made the assessment of the results more challenging, but this problem was solved. Both the residual stress measurements and tearing resistance measurements were delayed due to COVID. Thus, the project was extended with 6 months.
3) Benchmarking of selected Local Approach (LA) models on WP 1 experimental data dealing with the transferability of ductile fracture toughness properties from a specimen to a component. Most of the participating organisations were able to develop a reasonable approach for prediction of ductile fracture in large and mid-scale mock-ups that are representative of real nuclear components. Together with the methods developed for the residual stress characterisation, these developed and validated tools cover most of the project objectives. Some of the critical tasks were completed later than planned (due to COVID) and there was not that much time to post-process, and disseminate and exploit to the best quality, but that work continues still after the project.
4) Understand how different assumptions and parameters influence a probabilistic assessment. These tasks progressed well through-out the project and were not that much influenced by the experimental work. Several virtual meetings were held to reach agreement on the applied parameters and discuss differences in the models and the results. This task fulfilled the project objective related to integrated probabilistic assessment.
• innovative quantitative methodologies to transfer laboratory material properties to assess the structural integrity of large piping components,
• enhanced methods for treatment of weld residual stresses when subjected to long term operation,
• advanced simulation tools based on fracture mechanics methods using physically based mechanistic models,
• improved engineering methods to assess components under long term operation taking into account specific operational demands,
• integrated probabilistic assessment methods to reveal uncertainties and justify safety margins.
The actions to achieve the objectives were completed. This includes;
1) The tearing resistance curves (J-R curves) were determined with compact tension (C(T)) and single-edge notched tension (SE(T)) specimens. The pipes were tested in four-point bending with elliptical cracks on the outside of the pipe, and through wall cracks. The testing was mostly done in room temperature, but for the last test the testing was done in 100 °C since unsuspected mechanisms were observed at lower temperature. The increase in temperature guaranteed sufficient ductile tearing of the pipe. Overall, the fracture mechanical testing was successful and served the modelling tasks.
2) Weld residual stresses were modelled and measured. Despite careful planning of the welding processes some minor mistakes were made which made the assessment of the results more challenging, but this problem was solved. Both the residual stress measurements and tearing resistance measurements were delayed due to COVID. Thus, the project was extended with 6 months.
3) Benchmarking of selected Local Approach (LA) models on WP 1 experimental data dealing with the transferability of ductile fracture toughness properties from a specimen to a component. Most of the participating organisations were able to develop a reasonable approach for prediction of ductile fracture in large and mid-scale mock-ups that are representative of real nuclear components. Together with the methods developed for the residual stress characterisation, these developed and validated tools cover most of the project objectives. Some of the critical tasks were completed later than planned (due to COVID) and there was not that much time to post-process, and disseminate and exploit to the best quality, but that work continues still after the project.
4) Understand how different assumptions and parameters influence a probabilistic assessment. These tasks progressed well through-out the project and were not that much influenced by the experimental work. Several virtual meetings were held to reach agreement on the applied parameters and discuss differences in the models and the results. This task fulfilled the project objective related to integrated probabilistic assessment.
The work was divided into four technical work packages. WP1 focuses on materials characterisation of ferritic and austenitic pipes, and dissimilar metal welds (DMW). The tearing resistance curves (J-R curves) were determined with compact tension (C(T)) and single-edge notched tension (SE(T)) specimens. The tensile properties were characterised with smooth round bar specimens and notched tension specimens. The pipes were tested in four-point bending with elliptical cracks on the outside of the pipe, and through wall cracks. The testing was mostly done in room temperature, but for one case the testing was carried out in 100 °C. The data was applied in WP3 for development of numerical models.
WP2 primarily focuses on modelling and measuring residual stresses. Thick and thin-walled (manufactured with low and high heat-input) narrow-gap gas tungsten arc-welds (GTAW) (AISI 316L), fully circumferential and 120° patch overlay welds, and thick walled thermally aged NG-GTAW were manufactured, and the residual stress profiles were measured with different techniques vital to minimize uncertainty. The FEM 2D and 3D residual stress predictions agreed with the experimental results. The austenitic pipe girth welds are important new benchmarks for RS simulation of engineering weldments. The austenitic pipe girth welds provide valuable new data for improving the RS profiles used in engineering structural integrity assessments. WP2 focused also on improving the assessment of residual stress profiles, assessing residual stresses in operation conditions and investigating the effect of residual stresses on fracture.
The objective of sub-WP 3.2 is to benchmark selected Local Approach (LA) models on WP 1 experimental data dealing with the transferability of ductile fracture toughness properties from a specimen to a component. Most of the participating organizations were able to develop a reasonable approach for prediction of ductile fracture in large and mid-scale mock-ups that are representative of real nuclear components. The achieved results have potential to improve the qualification of key mechanical components relevant for safety of nuclear power plants. Based on the results of LA analyses the following recommendations are given: 1) develop appropriate optimization tools for material parameter selection. 2) The results indicate that, if possible, it is beneficial to calibrate the material parameters with both low and high constrained fracture mechanical specimens.
In WP4, the results have made it possible to better understand how different assumptions and parameters influence a probabilistic assessment. When evaluating results from probabilistic analyses using a specific tool, it is important to have a good knowledge of how this tool define different limit states, how the deterministic fracture assessment methodology is defined and how the re-characterization of surface breaking defects at “Snap-Through” is defined.
The results have been used for developing the standards/Codes, e.g. the tools developed and results for residual stresses are implemented to the UK codes. Similar thoughts have been presented for the validated and developed ductile tearing models. The results have been disseminated at many public events e.g. NUGENIA, SNETP, FISA, FSI, EC, PVP, SMiRT and national conferences. All together 27 publications were written
WP2 primarily focuses on modelling and measuring residual stresses. Thick and thin-walled (manufactured with low and high heat-input) narrow-gap gas tungsten arc-welds (GTAW) (AISI 316L), fully circumferential and 120° patch overlay welds, and thick walled thermally aged NG-GTAW were manufactured, and the residual stress profiles were measured with different techniques vital to minimize uncertainty. The FEM 2D and 3D residual stress predictions agreed with the experimental results. The austenitic pipe girth welds are important new benchmarks for RS simulation of engineering weldments. The austenitic pipe girth welds provide valuable new data for improving the RS profiles used in engineering structural integrity assessments. WP2 focused also on improving the assessment of residual stress profiles, assessing residual stresses in operation conditions and investigating the effect of residual stresses on fracture.
The objective of sub-WP 3.2 is to benchmark selected Local Approach (LA) models on WP 1 experimental data dealing with the transferability of ductile fracture toughness properties from a specimen to a component. Most of the participating organizations were able to develop a reasonable approach for prediction of ductile fracture in large and mid-scale mock-ups that are representative of real nuclear components. The achieved results have potential to improve the qualification of key mechanical components relevant for safety of nuclear power plants. Based on the results of LA analyses the following recommendations are given: 1) develop appropriate optimization tools for material parameter selection. 2) The results indicate that, if possible, it is beneficial to calibrate the material parameters with both low and high constrained fracture mechanical specimens.
In WP4, the results have made it possible to better understand how different assumptions and parameters influence a probabilistic assessment. When evaluating results from probabilistic analyses using a specific tool, it is important to have a good knowledge of how this tool define different limit states, how the deterministic fracture assessment methodology is defined and how the re-characterization of surface breaking defects at “Snap-Through” is defined.
The results have been used for developing the standards/Codes, e.g. the tools developed and results for residual stresses are implemented to the UK codes. Similar thoughts have been presented for the validated and developed ductile tearing models. The results have been disseminated at many public events e.g. NUGENIA, SNETP, FISA, FSI, EC, PVP, SMiRT and national conferences. All together 27 publications were written
Results obtained from the whole project will lead to a better knowledge of the applicability limits of our experimental and simulation work thus leading to increasing confidence in predictions made for the safe long term operation of power plants. The results specially related to the methods developed and validated based on experimental results to predict large scale tearing and residual stresses have a significant impact. These methods will enable more accurate prediction of the safety of coolant-boundary components of nuclear power plants and the new models showed that the old methods are conservative. Thus, the true margin for safety is larger, meaning that the components can be used for a longer time. This will increase the life-time/cost-efficiency of nuclear power plants, leading on a larger scale to cost-efficient carbon-free energy solutions.