ML21319A390
| ML21319A390 | |
| Person / Time | |
|---|---|
| Issue date: | 10/29/2021 |
| From: | Michael Benson, Patrick Raynaud, Robert Tregoning NRC/NRR/DNRL/NVIB, NRC/RES/DE, NRC/RES/DE/CIB |
| To: | |
| Raynaud P | |
| References | |
| ASTM-E08-04 | |
| Download: ML21319A390 (51) | |
Text
NRC Perspectives on WRS Uncertainty, Predictions, and Use in Regulated Nuclear Applications Patrick Raynaud, Michael Benson, Rob Tregoning U.S. Nuclear Regulatory Commission ASTM-E08.04 Workshop on Incorporating Residual Stress Into Structural Design and Sustainment
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 paper are not necessarily those of the U.S. Nuclear Regulatory Commission.
10/29/2021 ASTM E08.04 Workshop on WRS 2
Outline
- History of WRS research at the NRC
- WRS uncertainty for measurements and predictions
- WRS impact on crack growth predictions
- Exploratory criteria for WRS modeling acceptance
- WRS modeling in nuclear applications
- Conclusions 10/29/2021 ASTM E08.04 Workshop on WRS 3
EPRI/NRC WRS Validation Program
- Scientific Weld Specimens *Fabricated Prototypic Nozzles
- Conducted between 2008-2015 *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
- Identify, quantify, and minimize sources of *Purpose: Develop FE models. conditions. Validate FE models.
model uncertainty
- Develop reliable and consistent modeling procedures *Plant Components *Plant Components
- 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.
WRS models 10/29/2021 ASTM E08.04 Workshop on WRS 4
Phase 1: Scientific Weld Specimens
- Simple, light-weight specimen geometries *Scientific Weld Specimens
- Grooved plate *Phase 1A: Restrained Plates (QTY 4)
Phase 1 - EPRI
- Phase 1B: Small Cylinders (QTY 4)
- Butt-welded cylinders
- Purpose: Develop FE models.
- Objective
- To demonstrate/develop WRS measurement and modeling capabilities 10/29/2021 ASTM E08.04 Workshop on WRS 5
Phase 1 Plate Specimens 203 30o 30o 356 R 0.76 R 0.76 9
Detail A Dimensions in mm 101.5 10 10/29/2021 ASTM E08.04 Workshop on WRS Source: MRP-316, EPRI, 2011 6
Phase 1 Cylindrical Specimens Source: MRP-316, EPRI, 2011 10/29/2021 ASTM E08.04 Workshop on WRS Source: MRP-316, EPRI, 2011 7
Phase 1 Cylindrical Specimens with Weld Repair Source: MRP-316, EPRI, 2011 10/29/2021 ASTM E08.04 Workshop on WRS Source: MRP-316, EPRI, 2011 8
Characterization of Phase 1 Specimens
- Thermocouples were spot welded on the specimens to characterize temperature history at different locations
- Laser profilometer was used to measure individual weld beads 10/29/2021 ASTM E08.04 Workshop on WRS Source: MRP-316, EPRI, 2011 9
Phase 1 WRS Measurement Techniques
- Neutron diffraction - ORNL
- Contour - Hill Engineering
- X-ray diffraction - TEC
- Surface Hole Drilling - LTI
- Deep Hole Drilling - VEQTER
- Ring-Core - LTI
- Slitting - Hill Engineering
- 10/29/2021 ASTM E08.04 Workshop on WRS Source: Veqter, Ltd. 10
Phase 1 Surface WRS Measurements
- Surface hole drilling
- Unrealistically large values: e.g., 1500 MPa
- Independent techniques did not compare well with each other 10/29/2021 ASTM E08.04 Workshop on WRS Source: MRP-316, EPRI, 2011 11
Phase 1 Surface WRS Measurements
- X-ray diffraction showed large fluctuations in the data: e.g., from 950 to -950 MPa
- Data is asymmetric for a similar metal weld 10/29/2021 ASTM E08.04 Workshop on WRS Source: MRP-316, EPRI, 2011 12
Phase 1 Bulk WRS Measurements
- Smooth trends and reasonable magnitudes: e.g., -250 to 200 MPa
- Repair weld significantly affected the hoop stress 10/29/2021 ASTM E08.04 Workshop on WRS Source: MRP-316, EPRI, 2011 13
Phase 1 Bulk WRS Measurements 10/29/2021 ASTM E08.04 Workshop on WRS Source: MRP-316, EPRI, 2011 14
Phase 1 Bulk WRS Measurements 10/29/2021 ASTM E08.04 Workshop on WRS Source: MRP-316, EPRI, 2011 15
Phase 1 Model-Measurement Comparison 10/29/2021 ASTM E08.04 Workshop on WRS Source: MRP-316, EPRI, 2011 16
Phase 1 Summary and Conclusions
- Simple weld geometries in order to develop measurement and modeling techniques
- Near-surface stress measurement is uncertain
- In general, mechanical strain relief techniques seemed most reliable
- Agreement between models and experiment seems feasible 10/29/2021 ASTM E08.04 Workshop on WRS 17
Phase 2: Fabricated Prototype Nozzles
- Full-scale mockups
- Two mockups: Phase 2a and Phase 2b
- Fabricated under controlled conditions
- Finite Element Round Robin *Fabricated Prototypic Nozzles
- Type 8 Surge Nozzles (QTY 2)
Phase 2 - NRC
- Double-blind: i.e., modelers did not have access
- Purpose: Prototypic scale under controlled to the measurement data and vice-versa conditions. Validate FE models.
- Obtain modeling results from a community of independent modelers
- Objectives
- To validate WRS modeling with experiment
- To assess WRS modeling uncertainty 10/29/2021 ASTM E08.04 Workshop on WRS 18
Phase 2a Mockup Fabrication DM weld with fill-in weld F316L Safe End
- Pressurizer surge nozzle
- Welding performed by automated gas tungsten arc welding
- Thermocouple and laser profilometry readings
- Rough dimensions: 31 overall length, 11 inner diameter Buttering TP 308 Stainless TP 316 Stainless Steel Steel Weld Pipe 14-in Sch 160 SA-105 Fabricated Nozzle 10/29/2021 ASTM E08.04 Workshop on WRS 19
Phase 2a WRS Measurement
- Incremental deep hole and deep hole drilling - bulk 2 DHD/iDHD Before SS Weld 2 DHD/iDHD After SS Weld
- Measurements taken before and after safe end to pipe weld was complete
- Safe end to pipe weld can affect the stress field at the dissimilar metal weld 10/29/2021 ASTM E08.04 Workshop on WRS 20
Phase 2a Deep Hole Drilling
- Axial stresses shown here
- Safe end to pipe weld can potentially have a beneficial affect on inner diameter stress
- Safe end length can be an important parameter 10/29/2021 ASTM E08.04 Workshop on WRS 21
Phase 2a Finite Element Round Robin Study
- ANSTO (Australia)
- AREVA (USA and EU)
- Battelle (USA)
- Dominion Engineering (USA)
- Goldak Technologies (Canada)
- EMC2 (USA)
- Inspecta Technology (EU)
- Institute of Nuclear Safety System (Japan)
- Osaka University (Japan)
- Rolls Royce (UK)
- Structural Integrity Associates (USA)
Phase 2a Example Model Alloy 82 Alloy 82 Butter Weld SA-105 SS Safe End SS Weld SS Cladding SS Pipe Fill-In Weld Boundary Conditions:
- Fixed axially on left end and free on right end
- Equivalent convective cooling on both outer and inner diameter surfaces 10/29/2021 ASTM E08.04 Workshop on WRS 23
Phase 2a Example Model 10/29/2021 ASTM E08.04 Workshop on WRS 24
Phase 2a Round Robin Study Philosophy
- Postulated sources of uncertainty: welding heat input and material properties
- Three analysis stages Alloy 82 Alloy 82 Butter Weld SA-105 SS Safe
- No thermocouple data or material property data End SS Weld supplied
- Thermocouple data only supplied
- Thermocouple and material property data SS Cladding SS Pipe supplied Fill-In Weld
- Models completed before and after the Boundary Conditions:
stainless-steel closure weld
- Fixed axially on left end and free on right end
- Equivalent convective cooling on both outer and inner diameter surfaces 10/29/2021 ASTM E08.04 Workshop on WRS 25
Phase II: Fabricated Prototype Nozzles
- Axial stresses shown here Axial Stress
- Variety of hardening laws employed
- Modeling uncertainty is the same 10/29/2021 ASTM E08.04 Workshop on WRS 26
Observations from Phase 2a
- While modeling and measurement results show reasonable agreement in magnitude and profile shape, there is significant model-to-model variability
- Providing thermocouple data and material property data did not decrease modeling uncertainty
- Hardening law is a significant modeling parameter 10/29/2021 ASTM E08.04 Workshop on WRS 27
Phases 3 and 4
- Nozzles from a canceled plant
- Phase 4 nozzle had a weld overlay
- Double-Blind Finite Element Round Robin 10/29/2021 ASTM E08.04 Workshop on WRS 28
Phase 3 Results
- Spread in modeling results evident in the Phase III results
- Phase 3 average 3s = 243 MPa, Phase 2a average 3s = 278 MPa 10/29/2021 ASTM E08.04 Workshop on WRS 29
Phase 4 Weld Overlay Study
- Investigation of a mitigation technique: Optimized Weld Overlay (OWOL)
Nozzel, without OWOL Nozzel, with OWOL 10/29/2021 ASTM E08.04 Workshop on WRS 30
Phase 4 Example Model 10/29/2021 ASTM E08.04 Workshop on WRS 31
Phase 4 Example Model 10/29/2021 ASTM E08.04 Workshop on WRS 32
Phase 4 Round Robin Study 10/29/2021 ASTM E08.04 Workshop on WRS 33
Observations from Phases 3 and 4
- The modeling and measurement results showed improvement of the residual stresses at the ID location after OWOL was applied
- Modeling uncertainty still exists, but general agreement between models and measurements 10/29/2021 ASTM E08.04 Workshop on WRS 34
Phase 2b Mockup
- Final mockup chronologically in the EPRI/NRC WRS program
- Last data collection effort before developing modeling and validation recommendations
- Deep hole drilling measurements, contour measurements, finite element round robin 10/29/2021 ASTM E08.04 Workshop on WRS 35
Phase 2b Measurement Results - Deep Hole Drilling 10/29/2021 ASTM E08.04 Workshop on WRS 36
Phase 2b Measurement Results - Contour Method 10/29/2021 ASTM E08.04 Workshop on WRS 37
Phase 2b Round Robin Results 10/29/2021 ASTM E08.04 Workshop on WRS 38
Phase 2b Uncertainty Quantification Project
- Uncertain models and uncertain measurements
- How do we make meaningful comparisons between the two?
- Uncertainty quantification work at Sandia National Laboratory
- Final Report at NRC ADAMS Accession Number ML16301A055
- Pressure Vessels and Piping Conference Proceedings Paper PVP2017-65552
- Chapters 3 and 5 of NUREG-2228 10/29/2021 ASTM E08.04 Workshop on WRS 39
Phase 2b Uncertainty Quantification Project 10/29/2021 ASTM E08.04 Workshop on WRS 40
Phase 2b Uncertainty Quantification Project
- With a similar bootstrapping approach, we can construct a difference in means function (i.e., mean of the measurements -
mean of the models)
- Confidence bounds on the difference function
- Judgment on when a difference between the models and measurements is statistically significant 10/29/2021 ASTM E08.04 Workshop on WRS 41
Recommended Modeling Guidelines
- The round robin data and subsequent statistical analysis was used to justify modeling recommendations
- Much of the guidance is based upon MRP-317, Revision 1, published by the Electric Power Research Institute, e.g.:
- Weld bead geometry
- Bead and process sequence
- Element birth and death methodology for welding process modeling
- Heat input model tuning
- Structural and thermal boundary conditions
- Element selection and mesh
- The NRC developed guidance on hardening law, based upon the statistical analysis (NUREG-2228)
- Average of the isotropic and nonlinear kinematic results
- An engineering approach to hardening law, rather than physics-based
- The analysis indicated that the averaging approach provided improved predictions over isotropic or nonlinear kinematic alone 10/29/2021 ASTM E08.04 Workshop on WRS 42
NUREG-2228 Proposal on WRS Validation Criteria
- Proposed Quality Metrics
- Axial WRS criteria in WRS NUREG
- Root mean square error on WRS: RMSEWRS Quality Metric Acceptance Criteria
- Average difference up to the initial crack depth RMSEWRS 55 MPa of interest: diffavg diffavg -15 MPa 15 MPa
- Developed based upon flaw growth studies
- Hoop WRS criteria in WRS NUREG Quality Metric Acceptance Criteria RMSEWRS 70 MPa 0 MPa diffavg 65 MPa 10/29/2021 ASTM E08.04 Workshop on WRS 43
Other Metrics Investigated
- D1
- Looking at first derivative as a test for slope
- Did not improve differentiation between good and bad RMSE D1 =
1 K 1 K 2 k =2 (D1k D1mean k ) D1k =
dWRS dxnorm 1
2h
( WRS k 1 + WRS k +1 )
predictions k
- D2
- Looking at second derivative as a test for concavity/convexity RMSE D 2 =
1 K 2
(
D2 k D2 mean ) D2 k =
dD1 1
(WRS k + 2 2WRS k + WRS k 2 )
- Did not improve differentiation between good and bad K 4 k =3 k
dx norm k 4h 2 predictions
- Truncated RMSEs (WRS )
KT 1
- Calculate RMSE up to x/t = T, with 0.01<T<0.99 = WRS kmean T
RMSEWRS k KT k =1
- Calculation performed for T=0.1, 0.2, , 0.9
- No improvement RMSEDT 1 =
1 KT KT 1 k =2 (D1k D1meank ) RMSEDT 2 =
1 KT K T 2 k =3 (D 2 k D 2 mean k )
- Weighted RMSEs
- Apply a weight function on the error to give more (1 x t ) (WRS )
K 1 W RMSEWRS W
= WRS kmean importance to low x/t values K k =1 k
- Calculation performed for W=1, 2, 5, 10 RMSEDW1 =
1 K 1
(
1 x t ) (D1 D1 )
W mean RMSEDW2 =
1 K 2
(
1 x t ) (D2 W
D 2 mean )
- No improvement K 2 k =2 K 4 k =3 k k k k 10/29/2021 ASTM E08.04 Workshop on WRS 44
Thoughts on a Flaw Growth Validation Approach (1/2)
- Current proposed approach:
- Metrics are based on WRS predictions
- Acceptance criteria are based on results of flaw growth calculations performed by RES with FES
- Could there be predictions that do not pass all WRS acceptance criteria but do result in adequate prediction of flaw growth?
- Could there be predictions that do pass all WRS acceptance criteria but do not result in adequate prediction of flaw growth?
- Flaw growth behavior is ultimately what matters, and is strongly influenced by WRS
- Could potentially use flaw growth predictions as a metric and define acceptance criteria
- BUT
- Flaw growth calculations can be performed in many ways, which introduces source of variability
- Flaw growth analysis could be offered as option when WRS acceptance criteria cannot all be met, but licensees WRS predictions looks close to the correct result (example: within 10% or 25% or proposed acceptance limits, TBD)
- Let licensee use their preferred flaw growth method on both the mean prediction in the NUREG and their prediction, for equal comparison
- Harder to validate licensee calculations, potential disagreements with methods or constants employed
- OR
- Impose that licensee use FES to perform flaw growth calculation based on their predicted WRS
- Easy to validate, less potential variation, can fix loads and other crack growth constants 10/29/2021 ASTM E08.04 Workshop on WRS 45
Thoughts on a Flaw Growth Validation Approach (2/2)
Licensee WRS Validation Metrics and Criteria Calculation per RMSEWRS diffavg WRS NUREG Pass all Criteria Pass at Least 1 Criterion and Within X% of Criterion for Other(s)
Flaw Evaluation Licensee WRS Software Flaw Growth Prediction Flaw Growth Similar ?
Alternative NUREG Mean Custom Flaw WRS Flaw Growth Evaluation Prediction 10/29/2021 ASTM E08.04 Workshop on WRS 46
WRS Modeling in Nuclear Applications:
NRC Evaluation Tools Fracture Analysis of Vessels, Oak Ridge (FAVOR)
Flaw Evaluation Software (FES) PFM RPV code that assesses crack initiation and through wall cracking Deterministic code that analyzes time frequencies to leak or rupture for SCC piping flaws Residual stresses from RPV cladding WRS added to operating stresses incorporated deterministically Internal NRC Code More information: Theory and User manuals Extremely Low Probability of Rupture (xLPR)
PFM piping code that assesses leakage and rupture probabilities for SCC and fatigue cracks WRS distributions used in analysis More information: NUREG-2247 10/29/2021 ASTM E08.04 Workshop on WRS 47
WRS Modeling in Nuclear Applications:
NRCs Regulatory Evaluations
- Evaluate acceptability of proposed ASME Code modifications related to repair, inspection, and other mitigation techniques for safety significant systems, structures, and components.
- Use NUREG-2228 acceptance criteria proposed as a condition to accepting ASME CC N-847, Evacuate and Weld Repair Technique for SCC Mitigation.
- Confirm appropriateness of requests for regulatory relief of existing requirements (e.g., inspection periodicity, coverage, or acceptance criteria).
- Evaluate significance of emergent issues, usually related to service-induced degradation found during required inspections.
- NUREG-2228 incorporated by reference in 10 CFR 50.55a 10/29/2021 ASTM E08.04 Workshop on WRS 48
WRS Modeling in Nuclear Applications:
ASME Code
- Code Case (CC) N-899: WRS for Ni-based Alloy Butt Welds
- Scope
- Full penetration, single-V dissimilar metal welds (DMWs)
- Weld thickness between 32 and 102 mm
- No outside surface weld repairs
- Level I: Yield level, constant through-wall hoop and axial stresses
- Level II: Predetermined WRS distributions for applicable welds (with and without safe ends)
- Machined surface
- Back gouged and rewelded
- Inside surface repair
- Level III: WRS calculation using FEA
- Methodology used to calculate WRS distribution should be verified and validated
- NUREG-2228 methodology could be considered for V&V acceptance criteria
- Examples of other relevant CCs (not inclusive)
- N-694-2: Evaluation procedure and acceptance criteria for PWR RPV penetration nozzles
- N-770: Alternate examination requirements for DM butt weld
- N-881: Exempting SA-508 Grade 1A from PWHT based on WRS measurement
- N-897: Analytical evaluation procedures for axial flaws in partial penetration nozzle welds 10/29/2021 ASTM E08.04 Workshop on WRS 49
WRS Modeling in Nuclear Applications:
Possible Future Directions
- Continue to monitor and evaluate best practices in other industries and throughout relevant codes and standards Photo by Drew Beamer on Unsplash
- Implement and refine acceptance criteria in relevant applications
- Consider incorporating best practices
- Gather stakeholder feedback
- Pilot guidance in hypothetical or actual nuclear applications
- Continue sensitivity analyses to examine significance of deviations on crack growth rate
- Expand technical basis beyond initial DMW scope
- Evaluate different weld joint configurations
- Consider other safety-significant nuclear piping systems
- Expand to other common weld and base materials (e.g., carbon, LAS, stainless steel) 10/29/2021 ASTM E08.04 Workshop on WRS 50
Conclusions
- NRC, in conjunction with nuclear industry and other partners, conducted extensive, decade-long WRS measurement and modeling program
- Representative nuclear-specific dissimilar metal weld joint configurations
- Phase I: Experimental measurement
- Phase 2: Validate modeling approaches and assess modeling uncertainties
- Phases 3 & 4: Validate using plant components and assess mitigation effects
- Modeling guidance developed based on results from WRS program
- Modeling best practices for inputs, boundary conditions, mesh refinement and weld bead geometry
- Guidance for material properties, specifically material hardening law
- Proposed guidance for verification and validation of weld-specific WRS models
- Three unique acceptance criteria or quality metrics
- Considering coupling with flow growth evaluations to assess sensitivity of metrics for specific applications
- Implement and refine proposed guidance as experience is gained and additional best practices are evaluated 10/29/2021 ASTM E08.04 Workshop on WRS 51