ML18170A221
| ML18170A221 | |
| Person / Time | |
|---|---|
| Issue date: | 07/15/2018 |
| From: | Michael Benson, Patrick Raynaud, Jay Wallace Office of Nuclear Regulatory Research |
| To: | |
| References | |
| Download: ML18170A221 (13) | |
Text
Exploring Finite Element Validation for Weld Residual Stress Prediction PVP2018-84931 Michael L. Benson, Patrick A. C. Raynaud, and Jay S. Wallace Office of Nuclear Regulatory Research U.S. Nuclear Regulatory Commission ASME 2018 Pressure Vessels and Piping Conference Prague, Czech Republic July 15-20, 2018
Disclaimer
- This presentation was prepared as an account of work sponsored by an agency of the U.S.
Government. Neither the U.S. Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third partys use, or the results of such use, of any information, apparatus, product, or process disclosed in this presentation, or represents that its use by such third party would not infringe privately owned rights. The views expressed in this presentation are not necessarily those of the U.S.
Nuclear Regulatory Commission.
ASME 2018 Pressure Vessels and Piping Conference 2
Weld Residual Stress Research (2008-2015)
- Scientific Weld Specimens *Fabricated Prototypic Nozzles
- Phase 1A: Restrained Plates (QTY 4) *Type 8 Surge Nozzles (QTY 2)
Phase 1 - EPRI Phase 2 - NRC
- Phase 1B: Small Cylinders (QTY 4) *Purpose: Prototypic scale under controlled
- Measurements studies
- Modeling studies
- Plant Components *Plant Components
- Range of specimens
- WNP-3 S&R PZR Nozzles (QTY 3) *WNP-3 CL Nozzle (QTY 1)
- Purpose: Validate FE models. *RS Measurements funded by NRC
- Purpose: Effect of overlay on ID.
- NRC/EPRI MOU Draft NUREG on WRS Validation Planned for Public Comment Release ASME 2018 Pressure Vessels and Piping Conference 3
Example Results - Phase 2b Models Measurements ASME 2018 Pressure Vessels and Piping Conference 4
Uncertainty Quantification - PVP2017-65552 Statistical modeling and bootstrapping Comparing measurements to models Axial Residual Stress [MPa]
Axial Residual Stress [MPa]
Normalized Depth from ID Normalized Depth from ID Axial Residual Stress [MPa] Difference [MPa]
Normalized Depth from ID Normalized Depth from ID ASME 2018 Pressure Vessels and Piping Conference 5
Validation and Guidelines
- Potential value in proposing a validation approach
- Increased efficiency in regulatory reviews
- Increased confidence in modeling approaches
- Consensus process agreed to by both industry and regulator
- Guidelines can be based upon industry practice and research experience
- Conclusion to several years of research ASME 2018 Pressure Vessels and Piping Conference 6
Validation
- A validation scheme should have three basic ingredients
- Benchmark
- Set of metrics
- Acceptance measures
- These ingredients should be developed with the end use of the model in mind ASME 2018 Pressure Vessels and Piping Conference 7
Benchmark Axial Residual Stress [MPa]
- Physical measurement data is a natural choice of benchmark, and perhaps a preferred choice
- Complications for WRS
- WRS is not directly measured
- Two independent measurements may not agree
- Averaging the two measurements may not be valid Normalized Depth from ID
- Parsing out which measurement is more correct requires a larger effort and the right partnerships Difference [MPa]
- Benchmark based upon the models may be an option
- Comparisons of predictions to measurements indicate that FE is a reasonable approach
- Demonstrate the concept, final decisions can be made later Normalized Depth from ID ASME 2018 Pressure Vessels and Piping Conference 8
Metrics
- One potential metric is root-mean-square error: an average sense of how well the predicted stress magnitudes compare to the benchmark
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- However, metrics should be designed with end use in mind: stress corrosion crack growth calculations
- Metrics should interrogate features of the residual stress curve that affect flaw growth
- Behavior near the ID
- Slopes and concavity
- Other metrics beyond RMSE may need to be considered ASME 2018 Pressure Vessels and Piping Conference 9
Acceptance Measures
- Each proposed metric should have an acceptance measure
- Like the metrics, acceptance measures should be developed with stress corrosion crack growth in mind
- Conceptually, the acceptance measures will screen out WRS profiles that lead to unreasonable crack growth, as determined by the benchmark ASME 2018 Pressure Vessels and Piping Conference 10
Validation: Conceptual Overview
- Analyst creates a finite element model of the Phase 2b mockup
- Analyst extracts relevant data from the output database
- Analyst calculates a series of metrics and compares results to the acceptance measures
- No flaw growth calculation, but the metrics and acceptance measures were developed with flaw growth in mind ASME 2018 Pressure Vessels and Piping Conference 11
Draft NUREG
- Draft NUREG only introduces the concept of a validation scheme
- Actual implementation will depend upon a number of factors
- Industry-regulator consensus
- Codes and standards
- Other guidance documents?
- Planned release for 60-day public comment period
- May include specific questions about the proposed approach and technical justification, soliciting public feedback on key issues
- NRC will formally respond to all comments received ASME 2018 Pressure Vessels and Piping Conference 12
Conclusions
- Weld residual stress research program at NRC has come to a close
- Latest outcome includes an uncertainty quantification methodology developed by Sandia National Laboratory
- Draft NUREG proposing a validation methodology planned to be released for public comment day public comment period
- Proposed benchmark
- Metrics and acceptance measures rooted in flaw growth
- Modeling guidelines based upon industry and research experience
- Actual implementation of proposed validation scheme, or something similar, depends upon other factors, including industry-regulatory consensus ASME 2018 Pressure Vessels and Piping Conference 13