ML23145A156

Presentation on Weld Residual Stress Validation

ML23145A156
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Issue date:	06/11/2023
From:	Michael Benson NRC/NRR/DNRL/NVIB
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Validation of Weld Residual Stress Finite Element Predictions for Use in Nuclear Regulatory Applications Michael Benson, Patrick Raynaud, Rob Tregoning U.S. Nuclear Regulatory Commission 15th International Conference on Fracture (ICF15)

June 11-16, 2023, Atlanta, GA USA

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.

11-16 June 2023 ICF-15 2

WRS Modeling in Nuclear Applications:

NRCs Regulatory Evaluations

• Evaluate acceptability of industry proposals.

- Use of NUREG-2228 validation scheme is a condition to accepting ASME CC N-847, Evacuate and Weld Repair Technique for SCC Mitigation.

- NUREG-2228 incorporated by reference in 10 CFR 50.55a

• Evaluate industry fitness for service evaluations 11-16 June 2023 ICF-15 3

Background:

EPRI/NRC WRS Validation Program

• Scientific Weld Specimens *Fabricated Prototypic Nozzles

• Phase 1A: Restrained Plates (QTY 4) *Type 8 Surge Nozzles (QTY 2)

Phase 1 - EPRI Phase 2 - NRC

• Conducted between 2008-2015 *Phase 1B: Small Cylinders (QTY 4)

• Purpose: Develop FE models.

• Purpose: Prototypic scale under controlled conditions. Validate FE models.

• Identify, quantify, and minimize sources of model uncertainty

• Develop reliable and consistent modeling *Plant Components *Plant Components procedures *WNP-3 S&R PZR Nozzles (QTY 3) *WNP-3 CL Nozzle (QTY 1)

Phase 3 - EPRI Phase 4 - EPRI

• Purpose: Validate FE models. *RS Measurements funded by NRC

• Develop recommendations for validation of *Purpose: Effect of overlay on ID.

WRS models 11-16 June 2023 ICF-15 4

Phase 1: Scientific Weld Specimens

• Simple, light-weight specimen geometries

- Grooved plate

- Butt-welded cylinders

• Objective

- To demonstrate/develop WRS measurement and modeling capabilities

• 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 11-16 June 2023 ICF-15 5

Phase 2: Fabricated Prototype Nozzles DM weld with fill-in weld

• Full-scale mockups: Phase 2a and Phase 2b F316L Safe End

• Finite Element Round Robin

- Double-blind: i.e., modelers did not have access to the measurement data and vice-versa

- Community of independent modelers

• Objectives Buttering TP 308 Stainless TP 316 Stainless Steel Steel Weld Pipe 14-in Sch 160 SA-105 Fabricated Nozzle

- To validate WRS modeling with experiment

- To assess WRS modeling uncertainty

• Observations

- Reasonable agreement in magnitude and profile shape, but significant model-to-model variability

- Providing thermocouple data and material property data did not decrease modeling uncertainty

- Hardening law is a significant modeling parameter 11-16 June 2023 ICF-15 6

Phases 3 and 4

• Scope

- Nozzles from a canceled plant

- Phase 4 nozzle had a weld overlay

- Double-Blind Finite Element Round Robin

• Observations

- 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 11-16 June 2023 ICF-15 7

WRS Validation Data: 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 11-16 June 2023 ICF-15 8

Phase 2b Measurement Results

• Deep Hole Drilling

• Contour Method 11-16 June 2023 ICF-15 9

Phase 2b Modeling Round Robin Results 11-16 June 2023 ICF-15 10

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 11-16 June 2023 ICF-15 11

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 11-16 June 2023 ICF-15 12

Model Validation Philosophy

• Three ingredients: benchmark, metrics, and acceptance criteria

• Relate the metrics and acceptance criteria to the end use of the model

• Developed an example validation scheme

- Assumed end use case: stress corrosion crack growth in a dissimilar metal butt weld

- Benchmark: mean of the Phase 2b models (controversial)

- Metrics and acceptance criteria: next slide 11-16 June 2023 ICF-15 13

NUREG-2228 Proposal on WRS Validation Criteria

• Proposed Quality Metrics

- Root mean square error on WRS: RMSEWRS

- Average difference up to the initial crack depth of interest: diffavg

- Developed based upon flaw growth studies 11-16 June 2023 ICF-15 14

Thoughts on Implementation

• NUREG-2228 is not a one-size-fits-all approach

• Demonstrates the principles of developing a model validation scheme

• Validation steps

- Choose a benchmark based upon available data

- Develop metrics and acceptance criteria relevant to the end use of the model

- Validate both the analyst and the modeling process

- NUREG-2228 provides an example 11-16 June 2023 ICF-15 15

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

- Two quality metrics with acceptance criteria

- Developed with the end use of the model in mind

• Implement and refine proposed guidance as experience is gained 11-16 June 2023 ICF-15 16