ML18270A091
| ML18270A091 | |
| Person / Time | |
|---|---|
| Issue date: | 09/24/2018 |
| From: | Benson M L Office of Nuclear Regulatory Research |
| To: | |
| Michael Benson | |
| Shared Package | |
| ML18270A088 | List: |
| References | |
| NUREG-2228 | |
| Download: ML18270A091 (29) | |
Text
Overview of Draft NUREG
-2228Michael L. BensonOffice of Nuclear Regulatory ResearchU.S. Nuclear Regulatory CommissionPublic Meeting to Discuss Draft NUREG
-2228 on Weld Residual Stress Validation and NRC Research Program on Extended Finite Element AnalysisRockville, MDSeptember 24, 2018 Public Release of Draft NUREG
-2228*This meeting allows open discussion of the issues addressed in the NUREG, making the public comment period more productive
- Introduces a validation method for finite element prediction of weld residual stress
- Published in ADAMS on August 31, 2018 (ML18242A007
)*Public comment period formally announced in the Federal Register on September 13, 2018
-
Reference:
83 FR 46524 (ML18239A171) day public comment period
-Submit comments by November 13, 2018
- NRC posed four questions for the public
-Hardening law recommendation
-Choice of benchmark
-Choice of metrics
-Feasibility of implementationPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 2
Outline of Draft NUREG
-2228 1.Introduction
-Brief background on WRS research program
-Report scope 2.Phase 2b Round Robin Study
-Mockup fabrication
-Round robin modeling study
-Overview of measurement techniques
-Overview of measurement and modeling results 3.Uncertainty Quantification Methodology
-Overview of the Sandia method
-Outliers-Results: bootstrapped confidence bounds and tolerance boundsPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 3
Outline of NUREG
-2228 4.WRS Impact on Flaw Growth Calculations
-Superposition of operating stress
-Identification of important features of the stress profile (e.g., 0
-stress points)
-Relation of flaw growth behavior to stress profile features 5.Validation Procedure and Finite Element Guidelines
-Model-measurement comparisons: difference in means and root mean square error functions
-Judgements about hardening law
-Proposed guidelines: based upon commonly
-accepted practice
-Proposed validation scheme: benchmark, metrics, and acceptance measuresPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 4
Chapter 2: Phase 2b Round Robin StudyPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 5Overview Public Meeting to Discuss Draft NUREG
-2228 and xFEM 6Deep Hole DrillingContourVector, Ltd.Hill Engineering, LLCChapter 2: Phase 2b Round Robin StudyMeasurements Public Meeting to Discuss Draft NUREG
-2228 and xFEM 7Axial Residual StressHoop Residual StressChapter 2: Phase 2b Round Robin StudyMeasurement Results Public Meeting to Discuss Draft NUREG
-2228 and xFEM 8Isotropic HardeningNonlinear Kinematic HardeningChapter 2: Phase 2b Round Robin StudyModeling Results Chapter 3: Uncertainty Quantification Methodology
- Uncertainty quantification scheme was developed at Sandia National Laboratory
- The prime information source is a publicly
-available Sandia report (ML16301A055
)*Draft NUREG
-2228 only summarizes the details of the method
- Sandia implemented the method via the R programming languagePublic Meeting to Discuss Draft NUREG
-2228 and xFEM 9Sandia Report Chapter 3: Uncertainty Quantification Methodology
- Recognize WRS as functional data, -i.e., the stress magnitude depends upon the location
-Apply established mathematical methods for functional data
-See references in Sandia Report and draft NUREG
- Outlier screening
-Three round robin submissions screened out of the uncertainty quantification process
-Justification: modeling guidance was not followed
-One hoop stress profile that passed initial screening will be discussed further (slide 14)
- Data smoothing
-Cubic spline routine (see Sandia report)
-Data smoothing for WRS may be worth consideration by the industry
-More sophisticated than a least
-squares polynomial fitPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 10Analysis Concepts=Axial Weld Residual Stress [MPa]
Chapter 3: Uncertainty Quantification Methodology
- Amplitude and phase variability
-Both forms of variability are present in the Phase 2b dataset-Need methods to quantify these forms of uncertainty
- Registration
-Aligns the stress profiles
-Quantifies phase variability
- Functional Principal Components Analysis
-Quantifies amplitude variability
- Bootstrap sampling from the statistical model
-Amplitude and phase variability in the samples reflects that of the original dataset
-Enables determination of confidence bounds and tolerance bounds
- No assumptions on distribution typePublic Meeting to Discuss Draft NUREG
-2228 and xFEM 11Analysis Concepts Chapter 3: Uncertainty Quantification Methodology
- Bootstrapping applied to entire prediction dataset, the hole drilling measurement dataset, and the contour measurement hoop stress data
- Path data was extracted from the contour measurement axial stress data
-Extracted 500 stress profiles
-Confidence bounds and tolerance bounds calculated from the path data, not bootstrappingPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 12Analysis Concepts Chapter 3: Uncertainty Quantification MethodologyPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 13Example ResultsConfidence Bounds on the Mean 95-95 Tolerance Bounds Chapter 3: Uncertainty Quantification MethodologyPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 14Outlier Hoop Stress Prediction?
Chapter 4: WRS Impact on Flaw Growth CalculationsPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 15Flaw Growth Study Chapter 4: WRS Impact on Flaw Growth CalculationsPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 16Evaluation Period
- Uncertainty decreases under shortened evaluation period (20 years vs. 60 years)
Chapter 4: WRS Impact on Flaw Growth CalculationsPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 17Area under the Curve
- Simplified method to understand flaw growth sensitivity to residual stress through
-wall trends
- Identified salient features of the residual stress curve that may have impacts on flaw growth
-ID stress magnitude
-Stress magnitude at initial flaw depth
-Location through the wall thickness where compressive zone begins
-Slope of the curve in the compressive zone Chapter 5: Validation Procedure and Finite Element GuidelinesPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 18Measurement
-Model Comparisons
- Difference in means and root mean square error functions
- Sample a number of measurement stress profiles
- Sample a number of prediction stress profiles
- Calculate the means of the two samples
- Calculate the difference in the two means
- Calculate square root sum of squares of the difference, averaged over the wall thickness Chapter 5: Validation Procedure and Finite Element GuidelinesPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 19Measurement
-Model Comparisons
- Difference in means and confidence bounds on the difference
- "Good agreement" implies that tolerance bounds encompass zero throughout entire wall thickness
- Areas where confidence bounds do not encompass zero indicate disagreementNonlinear kinematic hardening predictionsHole drilling measurement Chapter 5: Validation Procedure and Finite Element GuidelinesPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 20Measurement
-Model Comparisons
- Best comparison
-Average hardening predictions
-Contour measurementAverage hardening predictionsContour measurement Chapter 5: Validation Procedure and Finite Element GuidelinesPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 21Measurement
-Model Comparisons Chapter 5: Validation Procedure and Finite Element GuidelinesPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 22Hardening Law Recommendations
- Uncertainties are large
- Nonlinear kinematic appears to be the least accurate overall
- The averaging approach is the recommended hardening law Chapter 5: Validation Procedure and Finite Element GuidelinesPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 23Modeling Guidelines
- Weld bead geometry definition
-Modeling precise bead shape is unnecessary
-Weld beads may be approximated as trapezoids
-Total number of beads and layers and beads per layer should accurately reflect the real configuration
- Bead and process sequence
-Analyst should model actual fabrication sequence-Analyst should explicitly model the application of the butter and postweldheat treatment
- Heat input model tuning
-Analyst should confirm that weld bead and surrounding material reaches melting temperature
- Structural and thermal boundary conditions
-Boundary conditions should represent the physical situation and can differ from application
-to-application
-For a typical dissimilar metal butt weld, axial displacement in one node away from the weld should be constrained
-Modeled pipe length should be at least 4 times the inner diameter to avoid edge effects
-Heat convection at the surface can be neglected
- Material properties
-Average of isotropic and nonlinear kinematic is the recommended approach
-Temperature
-dependent material properties provided in NUREG for reference
- Element selection and mesh
-Quadrilateral, linear elements
-Avoid triangular elements
-Fine mesh in weld Chapter 5: Validation Procedure and Finite Element GuidelinesPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 24Overview of Validation Approach
- Three ingredients required for a validation approach
-Benchmark-Set of metrics
-Acceptance measures
- Section 5.4 of the draft NUREG develops and justifies NRC's recommendations
- Development of metrics and acceptance measures is tied to flaw growth argument*Analyst creates a finite element model of the Phase 2b mockup, calculates the metrics, and compares the results to the acceptance measures Chapter 5: Validation Procedure and Finite Element GuidelinesPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 25Benchmark*Four choices of benchmark
-DHD measurement data
-Contour measurement data
-Average of DHD and contour results
-Mean of the Phase 2b models (assuming a given hardening approach)
- Benchmark based upon measurement data
-Perhaps the natural choice
-Complicating factors: not a pure measurement, independent techniques may not agree, differences are significant from a flaw growth perspective
-Averaging all the measurements may not be rigorously correct
-Not possible to say which measurement is more correct
- NRC recommended mean of the average hardening predictions
-A qualitative sense that the measurements and models agree
-The "mean" is derived from the uncertainty quantification scheme Chapter 5: Validation Procedure and Finite Element GuidelinesPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 26Proposed MetricsDerivative estimated by slope of secant line
-average sense of agreement
-related to slopes and concavity
-related to importance of the inner surface k k-1k+1 h 2 Chapter 5: Validation Procedure and Finite Element GuidelinesPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 27Proposed Acceptance MeasuresAxial Stress Acceptance MeasuresHoop Stress Acceptance Measures
- See P. Raynaud's presentation for additional background on metrics and acceptance measures Chapter 5: Validation Procedure and Finite Element GuidelinesPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 28Scope and Applicability
- Representativeness
-Excavate and weld repair given as an example
-The general principles in the draft NUREG could be applied to developing a validation approach for applications that are not well represented by the Phase 2b mockup
- Welding process
-High heat inputs and/or large weld beads may not be represented by Phase 2b mockup
- Hardening law
-Hardening law recommendations should be more
-or-less universal
-Additional study of the mixed hardening law may be worthwhile ClosingPublic Meeting to Discuss Draft NUREG
-2228 and xFEM 29*Summarized the contents of the draft NUREG
-2228-Phase 2b round robin
-Uncertainty quantification method
-WRS impacts on flaw growth calculations
-Proposed guidelines and validation scheme
- P. Raynaud will discuss the metrics and acceptance measures in detail
- NRC has initiated the formal public comment process on this NUREG
- This meeting: seeking initial feedback and discussion on the NUREG, in order to facilitate the public comment process