Residual Stress Mapping for an Excavate and Weld Repair Mockup · Residual Stress Mapping for an Excavate and Weld Repair Mockup Mitchell D. Olson, Ph.D. Hill Engineering, LLC Michael

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

© 2016 Hill Engineering, LLC

hill-engineering.com2

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



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



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



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



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



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



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



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.



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



Measurements results: P1


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





Effect of P1

• Small effect (±25 MPa)

Strong-back removal and contour method measurements are similar to P1

• Strong-back removal



• 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




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




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)


EWR

(52M)

P2

P3

P1

xz

SA

508

SS

316A82

Strong-back removal

Total

Slitting

Effect

of P1

PSR stress




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



Contour method• Tensile RS: DM and excavate weld (max: 200

MPa)


Total = effect of P1 + effect of P2 + strong-back removal + contour• Tensile RS: DM and excavate weld (max: 370

MPa)


EWR

(52M)

P2

P3

P1

xz

SA

508

SS

316A82

Strong-back removal

Contour

Effect of P1

Effect of P2

Total



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



Comparison with FE

Plane 2 (σxx)

Excellent agreement between the


profiles

• Modeled result has somewhat

larger magnitude tensile and

compressive stresses

• 50 to 75 MPa differences

P2: Measured P2: FE



Comparison with FE

Plane 3 (σxx)

Good agreement between the


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



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)



Acknowledgement

Francis Ku

Structural Integrity Associates, Inc.

Jon Tatman

EPRI Welding and Repair Technology Center



Thank you!

Hill Engineering, LLC

3083 Gold Canal Drive

Rancho Cordova, CA 95670

Mitch Olson

(916) 635-5706

[email protected]

Documents

Residual Stress Mapping for an Excavate and Weld Repair Mockup · Residual Stress Mapping for an Excavate and Weld Repair Mockup Mitchell D. Olson, Ph.D. Hill Engineering, LLC Michael