Post on 08-Sep-2018
Residual Stress Mapping for an
Excavate and Weld Repair Mockup
Mitchell D. Olson, Ph.D.Hill Engineering, LLC
Michael R. Hill, Ph.D.University of California, DavisHill Engineering, LLC
Adrian T. DeWald, Ph.D.Hill Engineering, LLC
Steven L. McCrackenElectric Power Research InstituteWelding and Repair Technology Center
2016 International Light Water Reactor Material Reliability Conference, Chicago, IL
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Overview/Outline
The talk is about:
The measured residual stress in a mockup design to investigate a new crack mitigation technique
• Excavate and weld repair (EWR) mitigation technique
Residual stress measurement technology
• Current state of the art
• Measurement principles
• Application in the EWR mockup
Outline
Background
• Excavate and weld repair (EWR) mitigation technique
Sample description
Residual stress measurement plan
Measurement techniques
Residual stress measurement results
• Comparison with modeling results
Summary
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Background
Stress corrosion cracking is one of the most serious metallurgical problems facing the nuclear power industry1
Requires: susceptible material, tensile stress, and a corrosive environment
Many plant components meet these conditions
Reactor pressure vessel penetration, nozzle DM butt welds, CRDM housing penetrations
Susceptible materials: Alloys 600/82/182
Current mitigation techniques
Weld overlays, mechanical stress improvement
Current work is focused on the development of a new mitigation technique, Excavate and weld repair (EWR)
Support ASME Code Case N-847, Partial Excavation and Deposition of Weld Metal for Mitigation of Class 1 Items
• Provides requirements for pre-EWR examination, EWR acceptance examination, design, flaw evaluation, crack growth analysis, preservice inspection, and in-service inspection
EWR concept:
Excavate a portion of the outside thickness of the original butt weld replace with SCC resistant weld metal
1 Couch, Welding and Fabrication Influence on Stress Corrosion
Cracking (SCC), ATI-CSC-11, Lake Louise, Alberta, Canada, 2011
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Sample Fabrication
To support the Code Case N-847 EPRI Welding and Repair
Technology Center fabricated two partial arc EWR mockups
Goal to assess residual stress state in post-EWR configuration
Sample fabrication
Tack weld stainless steel and carbon steel plates to strong-back
Apply dissimilar metal weld butter to carbon steel plate
Continue dissimilar metal weld to join butter to stainless steel plate
Excavate cavity
Apply excavation weld
Machine excess weld material
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Sample description
Final sample geometry
Length: 17 in long (431.8 mm)
Width: 7.12 in (180.85 mm)
Thickness: 2 in (50.8 mm)
Materials
Base metal: SS 316 and SA508
Base weld: A82/182
EWR: 52M
Material E (GPa)
Stainless steel Type 316L 193 0.3
Low alloy steel SA-508 Class 3 205 0.3
Nickel alloy 82/182 214 0.29
Nickel alloy 52M 209 0.29EWR
(52M)
52M SA
508A82
P2
P3
P1
x
y
xz
SS
316
SA
508
SS
316A82
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Strong-back removal
Removed strong-back to allow higher precision measurements
Was removed with several machining operations
Will release stress
Applied stress gages on the top of the plate
Measured strain change during each cutting step
Correlated the measured strain change with an FE computational
weld simulation
Provides the residual stress “released” during strongback removal Top & bottom
gages
Top only
gages
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Residual stress measurement plan
Measure stress maps along three planes
P1: Longitudinal stress (σzz)
P2: Longitudinal (σzz) and long-transverse stress (σxx)
P3: Long-transverse stress (σxx)
Measurement steps
Remove strong back
Contour method measurements (P1, P2, P3)
Primary slice release (PSR) mapping measurement at P2
• Remove slices adjacent to P2
• Slitting measurements in slices
Good example of a state of the art residual stress measurement
Can measure maps of multiple stress components over multiple planes
using a single sample
• Can provide a rich data set for end use applications (e.g., crack growth
predictions, model validation)
EWR
(52M)
52M SA
508A82
P2
P3
P1
x
y
xz
SS
316
SA
508
SS
316A82
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Contour method principles
Contour method is residual stress measurement technique that
gives a 2D map of residual stress over a cross-sectional plane
Will make contour method measurements at P1, P2, P3
Measurement steps
Cut part in two
• Stress release causes deformation
• Stress normal to cut surface is fully released
Measure resulting surface profile
Determine residual stress using finite element simulation
• Model cut part
• Apply reverse of deformation to surface
• Resulting stress on cut face in FEM
equals the original stress on cut face
(normal to the cut face)
Cut measure FEM residual stress
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Primary slice release (PSR) mapping principles
Primary slice release mapping is a measurement technique
that supplements a contour method measurement to measure
additional in-plane components of residual stress
Applies for parts with smoothly varying out-of-plane stress, stresses
can be decomposed into:
• Stress remaining in a thin slice (no out-of-plane stress remaining)
• Stress released with removing a thin slice from the original body, what
we’ll call “primary slice release” stress
Will make a PSR mapping measurement at P2
Measurement steps
Remove slices adjacent to P2
Perform slitting measurements in slices
Determine PSR stress using prior contour method
measurement and a supplemental finite element analysis
Find total in-plane by adding PSR stress and stress in sliceRef: M.D. Olson and M.R. Hill, "A New Mechanical Method for Biaxial Residual
Stress Mapping", Experimental Mechanics, vol. 55, pp. 1139-1150, 2015.
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Slitting principles
Slitting is used to measure stress in the thin slices
Slitting principles
Incrementally cut slit into test coupon
Measure strain release at specific locations (typically back-face)
Compute residual stress from strain release
• Uses an elastic inverse developed through FE modeling to relate measured
strain to stress
Measures one stress component
Normal to slitting cut plane
Map is built up by making a series of measurements
Multiple, adjacent slitting measurements required post-measurement
correction for prior slitting measurements
Back-face
strain gage
Measured
strain
Computed
residual stress
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Measurements results: P1
P1: Longitudinal stress (σzz)
Released from strong-back removal
• Roughly linear through-thickness
• Tensile RS: top (max: 250 MPa)
• Compressive RS: bottom (min: -300
MPa)
Contour method
• Tensile RS: DM and excavate weld (max:
225 MPa)
• Compressive RS: SS and carbon steel (min:
-400 MPa)
Total = strong-back removal + contour
• Tensile RS: excavate weld (max: 400 MPa)
• Compressive RS: DM weld, carbon steel
interface (min: -400 MPa)
EWR
(52M)
P2
P3
P1
xz
SA
508
SS
316A82
Strong-back removal
Total
Contour
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Measurements results: P2
P2: Longitudinal stress (σzz)
Effect of P1
• Small effect (±25 MPa)
Strong-back removal and contour method measurements are similar to P1
• Strong-back removal
• Roughly linear through-thickness
• Tensile RS: top (max: 250 MPa)
• Compressive RS: bottom (min: -300 MPa)
Contour method
• Tensile RS: DM and excavate weld (max: 225 MPa)
• Compressive RS: SS and carbon steel (min: -400 MPa)
Total = effect of P1 + strong-back removal +contour
• Tensile RS: excavate weld (max: 400 MPa)
• Compressive RS: DM weld, carbon steel interface (min: -400 MPa)
EWR
(52M)
P2
P3
P1
xz
SA
508
SS
316A82
Strong-back removal
Total
Contour
Effect of P1
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Measurements results: P2
P2: Long-transverse stress (σxx)
Effect of P1
• Small effect (-20 to -5 MPa)
Primary slice release (PSR)
• Oscillating stress profile
• Tensile RS: bottom and around y=40 mm (max: 80 MPa)
• Compressive RS: top, mid-thickness (min: -40 MPa)
Strong-back removal
• Roughly linear through-thickness
• Tensile RS: top (max: 100 MPa)
• Compressive RS: bottom (min: -75 MPa)
Slitting method
• Oscillating stress profile
• Tensile RS: top and bottom (max: 220 MPa)
• Compressive RS: mid-thickness (min: -250 MPa)
Total = effect of P1 + strong-back removal + contour
• Tensile RS: top and bottom (max: 350 MPa)
• Compressive RS: mid-thickness (min: -275 MPa)
EWR
(52M)
P2
P3
P1
xz
SA
508
SS
316A82
Strong-back removal
Total
Slitting
Effect
of P1
PSR stress
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Measurements results: P3
P3: Longitudinal stress (σxx) Effect of P1
• Small effect (-20 to 5 MPa)
Effect of P2• Large stress release where P2 meets P3 (max:
200 MPa)
Strong-back removal• Roughly linear through-thickness
• Tensile RS: top (max: 100 MPa)
• Compressive RS: bottom (min: -50 MPa)
Contour method• Tensile RS: DM and excavate weld (max: 200
MPa)
• Compressive RS: mid-thickness (min: -300 MPa)
Total = effect of P1 + effect of P2 + strong-back removal + contour• Tensile RS: DM and excavate weld (max: 370
MPa)
• Compressive RS: mid-thickness (min: -400 MPa)
EWR
(52M)
P2
P3
P1
xz
SA
508
SS
316A82
Strong-back removal
Contour
Effect of P1
Effect of P2
Total
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Comparison with FE
Plane 1 & 2 (σzz)
Consistent stress profile between
both planes
Good agreement between the
measured and modeled stress
profiles
• Modeled result has someone larger
magnitude tensile and compressive
stresses
• 100 to 200 MPa differences
P2: Measured
P1: Measured
P2: FE
P1: FE
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Comparison with FE
Plane 2 (σxx)
Excellent agreement between the
measured and modeled stress
profiles
• Modeled result has somewhat
larger magnitude tensile and
compressive stresses
• 50 to 75 MPa differences
P2: Measured P2: FE
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Comparison with FE
Plane 3 (σxx)
Good agreement between the
measured and modeled stress
profiles
• Modeled result has somewhat
larger magnitude tensile and
compressive stresses
• ~50 to 75 MPa differences at
most locations
• Significantly different shape at the
top of the excavate weld
• FE is monotonously increasing,
measured finds stress tend
toward lower magnitude
P3: Measured P3: FE
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Summary and conclusions
A state of the art series of residual stress measurements was performed in an EWR mock-up
Two longitudinal stress maps using the contour method
Long-transverse stress map using the contour method
Long-transverse stress map using the newly developed primary slice release mapping method
Consistent results when compared with a computational welding simulation
Provides residual stress data in an EWR mockup to supports ASME Code Case N-847
Contour and PSR mapping can be applied to other components
EWR
(52M)
P2
P3
P1
xz
SA
508
SS
316A82
P3
(σxx)
P2
(σxx)
P2
(σzz)
P1
(σzz)
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Acknowledgement
Francis Ku
Structural Integrity Associates, Inc.
Jon Tatman
EPRI Welding and Repair Technology Center
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Thank you!
Hill Engineering, LLC
3083 Gold Canal Drive
Rancho Cordova, CA 95670
Mitch Olson
(916) 635-5706
molson@hill-engineering.com