12/15/14, U.S. NRC Perspective on Phase 2b Round Robin Study. · 1 U.S. NRC Perspective on Phase 2b Round Robin Study Category 2 NRC Public Meeting and Webinar on the NRC/EPRI Weld

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U.S. NRC Perspective on Phase 2b Round Robin Study

Category 2 NRC Public Meeting and Webinar on the NRC/EPRI Weld Residual Stress Validation Program

December 15, 2014

Michael Benson, Joshua Kusnick, David Rudland RES/DE/CIB

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Feedback

Public Meeting

• Feedback forms available after the meeting

• For those attending in person:

– Fill out paper forms manually, or

– Scan the QR code to access the web form on a smart phone

• For those attending remotely:

– Web-based form

– http://feeback.nrc.gov/pmfs/feedback/form?meetingcode=20141833

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Purpose

Public Meeting

• Acknowledge the contributions of participants

• Publically present results of the latest round robin study for weld residual stress (WRS) prediction

• Discuss future plans for the EPRI/NRC WRS Validation Program

• Explore the challenges in applying the knowledge gained from this work

• Foster technical discussion on implications of the work

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Historical Overview

NRC/EPRI WRS Validation Program

• Overall Goal: Validation of WRS prediction for use in flaw initiation and growth assessment

• Four phases of research – Phase 1: measurement and modeling on scientific specimens

– Phase 2a: international round robin on pressurizer surge nozzle mockup

– Phase 3: measurement and modeling on nozzles from cancelled plant

– Phase 4: measurement and modeling of optimized weld overlay

• References – EPRI: MRP-316 and -317

– NRC: NUREG-2162

•Scientific Weld Specimens•Phase 1A: Restrained Plates (QTY 4)•Phase 1B: Small Cylinders (QTY 4)•Purpose: Develop FE models.

Phas

e 1 -

EPRI

•Fabricated Prototypic Nozzles•Type 8 Surge Nozzles (QTY 2)•Purpose: Prototypic scale under controlled conditions. Validate FE models.

Phas

e 2 -

NRC

•Plant Components•WNP-3 S&R PZR Nozzles (QTY 3)•Purpose: Validate FE models.

Phas

e 3 -

EPRI

•Plant Components•WNP-3 CL Nozzle (QTY 1)•RS Measurements funded by NRC•Purpose: Effect of overlay on ID.

Phas

e 4 -

EPRI

*

* WRS = weld residual stress

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Present Work


• Goals

– Formulate guidance to reduce modeling uncertainty

– Establish acceptance criteria for WRS models

– Judge and account for uncertainty in WRS inputs for fitness-for-service evaluations

– Establish ASME Code guidelines

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Present Work


• Phase 2b

– Second international round robin on a pressurizer surge line mockup

– 10 analysts from different organizations

– 4 hole drilling measurements, contour measurement, near-surface measurements

Pressurizer Surge Line Mockup

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Model Geometry

Finite Element Round Robin Study

CS Nozzle

SS Clad

Alloy 82

Butter

DMW

SS Safe End

SS Closure

Weld Alloy 82 Backweld

SS Pipe

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WRS Measurement Techniques

• Small diameter reference hole is drilled into part

• Diameter of reference hole, at multiple angles, is measured through the part thickness

• Stress is relieved by machining a larger hole (cylindrical core) around the reference hole

• Change in diameter of reference hole is measured and analyzed to calculate the original residual stresses present

• Measures bi-axial residual stresses in plane 90°to axis of hole

Hole Drilling

http://www.veqter.co.uk/residual-stress-measurement/deep-hole-drilling

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WRS Measurement Techniques

• Wire EDM used to cut a free surface in the specimen containing residual stresses

• Stresses released by the creation of a free surface cause distortions

• Coordinate measurement machine measures distortion

• Inverse displacements are applied to the surface of a finite element model to obtain the original residual stresses that were present in the component

• Produced a full field 2D stress map

Contour Method

http://www.lanl.gov/contour/principle.html

Cut

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Experimental Setup

Phase 2b Measurements

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Raw Hole Drilling

Phase 2b Measurement Data

22°location 112°location

202°location 292°location

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Raw Contour – Axial Stress


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Raw Contour – Hoop Stress


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Processed Measurement Data


Axial Residual Stress Hoop Residual Stress

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Modeling Package


• Problem Statement

– Mockup geometry and fabrication details

– Information on measurements (no experimental data!)

– Modeling guidance based on lessons learned

– Material property files

– Submission guidelines

• Participant Questionnaire

– Establish point of contact

– Identify deviations from guidance

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Raw Modeling Data


Axial Isotropic

Hoop Isotropic

Axial Kinematic

Hoop Kinematic

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Processed Modeling Data


Axial Isotropic

Hoop Isotropic

Axial Kinematic

Hoop Kinematic

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Future Work: Analysis and Deliverables

Technical Issues

• Flaw growth calculations (Q1 2015)

• Technical Letter Report (Q1 2015)

• Formal statistical analysis (Q1-Q2 2015)

• NUREG publication (Q4 2015)

• ASME Code guidance (Q4 2015)

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Discussion Topics

Technical Issues

• Uncertainty Characterization – What is the measurement uncertainty? Modeling uncertainty? – Are there outliers? If so, how do we identify and treat them? – Did we decrease uncertainty relative to Phase 2a? – How do we use the distribution in time to leakage?

• Model Validation – What is the proper method to compare the measurements and the models? – What are reasonable validation criteria?

• Modeling Guidance – What is the correct approach to hardening law? – How does this work affect development of ASME Code guidance?

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Thank You!

Questions?

NRC/EPRI Public Meeting December 15th, 2014

Rockville, MD

Michael R. Hill and Minh N. Tran Mech and Aero Engineering, UC Davis

Phase 2b Round Robin Study of Weld Residual Stress in

Pressurizer Surge Nozzle: An Initial Analysis

Analysis and Validation work supported by EPRI Materials Reliability Program

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• Objective of this meeting – Describe Phase 2b round robin measurement and model outputs – Communicate validation analysis of model outputs

• Background on Phase 2b • Summary of submitted results

– Simulation outputs – Measurement data

• Validation: comparisons with benchmarks – Output from validation metrics

• RMS difference • Section forces (force and moment) • Stress intensity factors (circumferential and axial flaws) • Predicted crack growth behavior • Comments on validation metrics

• Assessments of outlying results • Summary and next steps

Outline of Presentation

Problem Statement Submitted Results Validation Outlying Results

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Problem Statement – Mock-up Geometry


• Geometry and materials reflect a PWR pressurizer surge nozzle – Pipe 14 inch, Ri/t = 4, L ≈ 30 inch

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• Mechanical strain relief measurement techniques: – Deep hole drilling: provides line stress – Contour method: provides stress field – Slitting: provides line stress

Problem Statement – Measurements

Deep Hole Drilling Setup Contour and Slitting Setup


PWR pressurizer surge nozzle mock-up

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• 10 submissions were received, labeled A to J • Each included:

– Results from two hardening laws: isotropic and kinematic – Output stress field: axial and hoop – Output stress through thickness along DM weld centerline: axial and

hoop • Some variations:

– One participant used prior geometry (Phase 2a) – Two participants altered structural boundary conditions – One participant included 2D and 3D results using modified material

model – One participant included results at three different interpass

temperatures

Submitted Results – Simulation Outputs


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• Center and Deep Hole Drilling: – Axial and hoop stress: 4 locations around pipe circumference, 90°

apart, in DM weld centerline region • Contour method:

– Axial stress: 5 locations around pipe circumference in DM weld centerline region

– Hoop stress: 5 locations along pipe length in DM weld centerline region

• Slitting: – Axial stress: DM weld centerline

Submitted Results – Measurement Data


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• Submission A: selected 26 pt output file, 150 °C interpass – Similar to other modelers, can assess influence later

• Submission F: excluded; used Phase 2a geometry – Analyze this data later, as an outlier

• Submission H: selected 26 pt output file (not equally spaced) • Submission J: used results with provided material data • Normalized position through thickness with respect to

participant’s model thickness – All models have t within 3% of the mean

• Except excluded submission F

• Linearly interpolate to x/t = 0, 0.04, 0.08, …, 1.0 – 26 points, evenly spaced through thickness, including ID and OD

• Compute mean of model outputs (Blue line) – Take mean at each x/t = 0, 0.04, 0.08, …, 1.0

Data Pre-process


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Pre-SS – Axial Stress

t = 37.8 mm Ri = 152.7 mm Ro = 190.5 mm


ISO KIN

AVG

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Pre-SS – Hoop Stress

t = 37.8 mm Ri = 152.7 mm Ro = 190.5 mm


ISO KIN

AVG

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Post-SS – Axial Stress

t = 37.8 mm Ri = 152.7 mm Ro = 190.5 mm


ISO KIN

AVG

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Post-SS – Hoop Stress

t = 37.8 mm Ri = 152.7 mm Ro = 190.5 mm


ISO KIN

AVG

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• Stress difference: σPost-σPre

• AVG data set

Effects of SS Weld

Axial Stress Hoop Stress

Zero uniform stress Large negative bending stress

Negative uniform stress Negative bending stress


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• Validation, as defined by ASME V&V 10-2006: – The process of determining the degree to which a model is an

accurate representation of the real world from the perspective of the intended uses of the model

• Working from this definition, validation involves: – Comparison of model output with a benchmark – Benchmark should reflect the real world, perhaps drawn from

• Measurement data • Phenomenological correlation • Expert panel opinion • Exemplar model outputs

• Our objective today: – Propose approaches for comparison of WRS model outputs – Apply approaches to data from Phase 2a round robin – Discuss results

Model Validation


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• EPRI MRP 287 (2010) – Primary Water Stress Corrosion Cracking (PWSCC) Flaw Evaluation Guidance – Suggestions on WRS validation (3 pages)

• Stress intensity factor, crack growth history • ASME V&V 10 (2006) – Guide for Verification and Validation in

Computational Solid Mechanics – Broad guidance for validation of computational solid mechanics (32 pages) – Nothing specifically dedicated to residual stress

• AWS A9.5 (2013) – Guide for Verification and Validation in Computational Weld Mechanics – Guidance on weld modeling practice – No detailed guidance on model validation (2 pages on conducting validation

measurements, 3 sentences on stress measurement) • R6 - Revision 4 (2013) – Assessment of the Integrity of Structures

Containing Defects – Substantial guidance on weld modeling

• Procedures for model parameter calibration using experimental data – Substantial guidance on WRS validation, including on experimental practice

• Differences between calibration and validation

Published Approaches to WRS Model Validation


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• Identified benchmark – Used the mean of model outputs – As an example (caveat emptor)

• Statistical analysis – RMS difference from benchmark

• Section force analysis – Average (uniform stress) – Linear (bending stress)

• Fracture mechanics analysis – Stress intensity factor

• Complete internal circumferential flaw • Internal axial semi-elliptical flaw

– Crack growth analysis • 60% or 80% through wall • 720 months

How we analyzed Phase 2a/b outputs (Post-SS weld)

Post-SS, ISO, Axial Stress


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RMS Difference – Post-SS, AVG Set

RMS difference: • Can identify

deviation from benchmark

• Does not indicate direction of deviation


Benchmark = Model Output Mean Normalized by A182 yield strength (380 MPa)

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• Stress due to uniform section forces (average through wall)

• Stress due to bending section forces (linear through wall)

Stress due to Section Forces

Axial Hoop


Axial Hoop

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Stress due to Uniform Section Forces – Pre-SS, AVG Set


Axial stress near zero

High positive hoop stress

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Stress due to Uniform Section Forces – Post-SS, AVG Set


Axial stress near zero

Hoop stress is smaller than in Pre-SS

Effect of SS weld: 1. Reduces uniform hoop stress

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Stress due to Bending Section Forces – Pre-SS, AVG Set


Positive internal bending stress

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Stress due to Bending Section Forces – Post-SS, AVG Set


Negative internal bending stress

Effects of SS weld: 1.Reverses direction of axial bending stress 2. Reverses direction of hoop bending stress

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• SIF from weight function (Wu and Carlsson): Geometry: ri/ro = 0.8

• Total SIF, including applied loads:

where:

(ref MRP-115 for membrane, bending stress, and internal pressure)

SIF: Complete Circ Flaw – Axial Stress


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Total SIF: Complete Circ Flaw – Post-SS, Axial Stress


WRS reduces Total SIF

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• SIF from weight function, deepest point A (Glinka): Geometry: ri/ro = 0.8 Aspect ratio: c/a = 2

• Total SIF:

where: (ref MRP-115 for internal pressure)

SIF: Axial Semi-Elliptical Flaw – Hoop Stress


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Total SIF: Axial Semi-Ellip. Flaw – Post-SS, Hoop Stress


WRS increases Total SIF

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Crack Growth History Crack growth rate (MRP-115): Assumptions for current analyses: • Initial flaw: a/t = 0.1 • Crack size increment: Δa/t = 0.001 • Final flaw: α = 0.6t (complete circ. flaw) or 0.8t (axial flaw) • Operating temperature: 343 °C (650 °F)


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CG: Complete Circ Flaw – Post-SS, Axial Stress


WRS slows flaw growth

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CG: Axial Semi-Ellip. Flaw – Post-SS, Hoop Stress


WRS speeds flaw growth

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Assessment of Outlying Results – Post-SS, Axial, ISO


Higher at ID

Lower at ID

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Assessment of Outlying Results – Post-SS, Hoop, ISO


Higher through wall

Lower through wall

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High, deviation from problem statement:

Assessment of Outlying Results

Back weld: 3 extra beads

Mechanical BC: Axially fixed at bolt hole


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Low, deviation from problem statement: • Mechanical BC: axially fixed the entire left side of stiffening plate • Back weld:


Back weld off center


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Assessment of Outlying Results– Post-SS, Axial, ISO


High: revised submission (no difference)

Low: orig. submission

Low: revised submission

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High: revised submission (no difference)

Low: orig. submission

Low: revised submission

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Phase 2b and Phase 2a Comparison – Axial Stress

• Mean output follows measurement • Similar trend and spread in both • Lower axial stress near ID in

Phase 2b • Wall thickness:

- Phase 2b, t = 37.8 mm, Ri/t = 4 - Phase 2a, t = 47.3 mm, Ri/t = 3


Phase 2b, ISO Phase 2a, ISO

Phase 2a, ALL

Avg RMS diff = 22.74% Avg RMS diff = 20.26%

Avg RMS diff = 19.60%

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Phase 2b and Phase 2a Comparison – Hoop Stress

• Mean output follows measurement • Similar trend and spread in both • Wall thickness:

- Phase 2b, t = 37.8 mm, Ri/t = 4 - Phase 2a, t = 47.3 mm, Ri/t = 3


Phase 2b, ISO Phase 2a, ISO

Phase 2a, ALL

Avg RMS diff = 29.40% Avg RMS diff = 29.18%

Avg RMS diff = 27.97%

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• Described Phase 2b measurement data and model outputs • Described output from four validation metrics:

– RMS difference – Section forces (force and moment) – Stress intensity factors (circumferential and axial flaws) – Predicted crack growth behavior

• Mean of model outputs was used as benchmark – Some results similar if benchmark is mean of WRS measurements

• Two outlying model outputs examined – More apparent after application of SS weld

• Phase 2b and Phase 2a comparison – Phase 2b and Phase 2a show similar dispersion of model outputs

Summary


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• Developing consensus – Confirm that model outputs are

• Interpreted correctly • Analyzed appropriately

– Are four figures of merit presented appropriate as validation metrics? • RMS difference • Section forces (force and moment) • Stress intensity factors (circumferential and axial flaws) • Predicted crack growth behavior

– Are there opportunities to validate model outputs relative to crack growth behavior?

• Crack growth is the intended use of the model (see ASME V&V 10) • Measurement and model precision can be established • Measurement and model accuracy relative to crack growth still unknown

– How should model acceptance be determined? • Identify benchmark similar to intended application (an “accepted” reality)

– Within some limited space of materials and geometry • Demonstrate capability relative to a benchmark

Analysis Discussion


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• Immediate need is to have verified one-dimensional stress vs thickness values to use in K calculation for crack growth analysis – Stresses are used to support relief requests for

inspection of Ni-based alloy welds and base metals • Address inspection coverage issues, inspection interval based on material

considerations • Calculate response of hypothetical flaw

– In service flaw evaluation is rare • Consensus based standards can help serve this immediate need • Three tiered approach currently in process with ASME Code

– Simple conservative stress vs thickness when time and/or conditions can support their use

– Prescribed stress vs thickness for common configurations • Must meet geometric and dimensional parameters • Uses FEA results, measurement data, consider uncertainty to develop profiles • Technical basis for prescribed stress vs thickness profiles in PVP2015 paper

– Discussion for FEA of configurations not considered for prescribed stresses • Possibly acceptance standards, point to other best practices published documents

– In process as Code Case

Model Acceptance Discussion


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• Complete Analysis of Results and Model Validation – March • Publish Final Report for DMW Butt-weld WRS FEA Model

Validation Program – June • ASME Code Non-mandatory Appendix Inputs (as needed) • Potential Meetings (preliminary/tentative – for discussion)

– “WRS FEA Model Acceptance Requirements Workshops” • Technical approach for FEA model evaluation

- TBD, based on needs, approach, readiness and availability • Coordinated with ASME Code Weeks and PVP; Jan 25-30, Houston,

TX; Apr 26-May 1, Colorado Springs, CO; July 19-23, Boston, MA

• Summary of Anticipated MRP Final Report – Coordinated with Annual Materials R&D Tech Update – June 2-4,

Rockville, MD

Anticipated 2015 MRP Program Schedule


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THANK YOU!

QUESTIONS?

Documents

12/15/14, U.S. NRC Perspective on Phase 2b Round Robin Study. · 1 U.S. NRC Perspective on Phase 2b Round Robin Study Category 2 NRC Public Meeting and Webinar on the NRC/EPRI Weld