Task 3: Cracking of Nickel Alloys and Welds –CGRs of Alloys 600 and 690 in PWR Water

Work sponsored by the US Nuclear Regulatory Commission

September 25-26, 2007Nuclear Engineering DivisionArgonne National Laboratory, Argonne, IL 60439

Investigators: Bogdan Alexandreanu, Omesh Chopra, Bill Soppet, and Bill Shack

Experimental Effort: Ed Listwan and Loren Knoblich

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Outline

Experiment

CGR of Nozzle #3 Alloy 600 from Davis-Besse

CGR of Alloy 690

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Experiment

Temp: 320°C PWR Water (<10 ppb DO, 1000 ppm B, 2 ppm Li, ≈2 ppm hydrogenFlow Rate: ≈55 mL/minConductivity: ≈20 µS/cmLoading sequence chosen to facilitate the transition from transgranular fatigue cracking to intergranular SCC cracking:

- Precracking carried out in the PWR environment - Load Ratio R: 0.3–precrack;

0.5-0.7–sawtooth with up to 1000s rise time; 1.0–constant load

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The Analysis of Cyclic CGR Data for Ni-alloys

Superposition model (Kassner & Shack)

( )0.337air CF air aira a a 4.4 10 a−+ = + × ⋅

env air CF SCCa a a a= + +

SCC thref

Q 1 1a exp (K K )R T T

β⎡ ⎤⎛ ⎞= α − − −⎢ ⎥⎜ ⎟

⎢ ⎥⎝ ⎠⎣ ⎦

For Alloy 600:

10-12

10-11

10-10

10-9

10-8

10-12 10-11 10-10 10-9 10-8C

GR

env

CGRair

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Cracking of Nozzle Alloy 600 from Davis-Besse

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CGR of Nozzle #3 Alloy 600 from Davis-Besse

Specimens tested in 316°C simulated primary water:

1/4T-CTN3CL-1N3CC-2

1/2T-CTN3CC-3

L Orientation

L Orientation63.5 mm

16 mm

C Orientation

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Fracture surface of specimen N3CL-1

Completely IG fracture right from the notch

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Fracture surface of specimen N3CL-4

Completely IG fracture right from the notch

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Fracture surface of specimen N3CC-2

Completely IG fracture right from the notch

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Fracture surface of specimen N3CC-2

Completely IG fracture right from the notch

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Fracture surface of specimen N3CC-3

Did not start as IG fracture right from the notch, elements of IG are present in the TG region

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Cyclic CGRs for Nozzle #3 Alloy 600 from Davis-Besse

10-12

10-11

10-10

10-9

10-8

10-12 10-11 10-10 10-9 10-8

N3CL-01N3CC-02

N3CC-03

CG

Ren

v (m

/s)

CGRair (m/s)

Alloy 600 (Heat M3935)(Davis Besse CRDM Nozzle #3)316°C PWR Water

CGRair + 6.6 x 10–7(CGRair)0.33

1/4–T CT Specimen

1/2–T CT Specimen

Including SCC rateat Kmax = 17 MPa m1/2

Cyclic CGRs show environmental enhancement

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SCC CGRs for Nozzle #3 Alloy 600 from Davis-Besse vs. K

10-12

10-11

10-10

10-9

10 15 20 25 30 35 40 45 50

N3CC-02

N3CC-03

Exp

erim

enta

l CG

R (m

/s)

Stress Intensity K (MPa·m1/2)

Alloy 600 (Heat M3935)(Davis Besse CRDM Nozzle #3)316°C PWR Water

Median Alloy 600 at 316°C

Proposed Disposition Curve75th Percentile

Alloy 600 at 316°C

1/4–T CT Specimen

1/2–T CT Specimen

SCC CGRs are 2-4× the proposed disposition curveHeat ranks at 95% of the distribution (26 heats)

0.0

0.2

0.4

0.6

0.8

1.0

10-13 10-12 10-11 10-10

Alloy 600 HeatsD–B Nozzle #3

Cum

ulat

ive

Dis

tribu

tion

F

Constant α at 325°C

75th Percentile

50th Percentile

25th Percentile

α = 1.44 x 10-12

α = 2.98 x 10-12

α = 6.96 x 10-13

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Nozzle #3 Alloy 600 from Davis-Besse – Summary and Remaining Issues

Very high crack growth ratesIG fracture mode during precracking

Very high SCC CGRs unexpected because:Alloy with average strengthGrain boundary carbide coverage (50–60%)

More recent investigations Good grain boundary carbide coverage Low special boundary fractions- could explain the high SCC CGRs- can not explain IG fracture mode during precracking

0

100

200

300

400

500

600

700

0 10 20 30 40 50 60 70

N3TL-1N3TL-2N3TL-3

Stre

ss (M

Pa)

Strain (%)

Alloy 600 CRDM Nozzle #3316°C

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Stress Corrosion Cracking of Alloy 690

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Alloy 690 specimens

<0.010.010.4730.8259.670.040.020.0030.0018.530.330.04ANL

29.559.50.010.07<0.0019.90.200.03VendorA 690WC (NX3297HK12)

CoNbTiCrNiCuSiPSFeMnCAnalysisAlloy ID (Heat)

Alloy 690 in plate form (MIL-DTL-24802∗)

Cold-rolled in three passes to achieve approx. 26% reduction in thicknessSpecimens cut in both SL and ST orientations

Approx 1.5”

3.5”

17”

rolling direction

1 2 3 4

∗MIL-DTL-24802- vacuum induction - melted - electro slag - removed - hot - rolled - de-scaled- annealed at 1900F for 2h- air-cooled

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Results - Alloy 690 specimen A690WC-SL-1

13.00

13.20

13.40

13.60

13.80

14.00

10

20

30

40

50

60

70

80

400 800 1200 1600 2000 2400 2800

Cra

ck L

engt

h (m

m)

K max

(MP

a m

0.5 )

Time (h)

Alloy 690Specimen # A690WC-SL-1320°C, Simulated PWR Water

71.46 x 10–11 m/s26.7 MPa m0.5

Constant Load

63.63 x 10–10 m/s26.2 MPa m0.5

0.50, Rise time = 1000 s

Kmax

8

10

Crack Length

92.83 x 10–11 m/s28.0 MPa m0.5

Constant Load

Crack lengthKmax

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Results - Alloy 690 specimen A690WC-ST-1

13.00

13.20

13.40

13.60

13.80

14.00

14.20

14.40

20

25

30

35

40

45

50

55

60

2600 2800 3000 3200 3400 3600 3800 4000

Cra

ck L

engt

h (m

m)

Km

ax (M

Pa

m0.

5 )

Time (h)

Kmax

Crack Length

Alloy 690Specimen # A690WC-ST-1320°C, Simulated PWR Water

12

Period 133.3 x 10–11 m/s31 MPa m0.5

Constant Load

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Fracture surface of A690WC-SL-1

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Fracture surface of A690WC-ST-1

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Fracture surface of A690WC-SL-1

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Fracture surface of A690WC-SL-1

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Cyclic CGR data for Alloy 690 and Davis-Besse Alloy 600

10-11

10-10

10-9

10-8

10-7

10-11 10-10 10-9 10-8 10-7

1/2-T CT DB N3CC-31/4-T CT DB N3CL-11/4-T CT DB N3CC-2A690WC-SL-1A690WC-ST-1

CG

Ren

v (m

/s)

CGRair (m/s)

Alloy 690 and Davis-Besse N#3 Alloy 600Simulated PWR Water

Best-Fit Curve for Davis-Besse N#3 A600CGRair + 6.6 x 10–7(CGRair)

0.33

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SCC CGRs for Alloy 690 and Davis-Besse Alloy 600 vs. K

10-12

10-11

10-10

10-9

10 15 20 25 30 35 40 45 50

DB N3CC-2DB N3CC-3A690WC-SL-1A690WC-ST-1

Exp

erim

enta

l CG

R (m

/s)

Stress Intensity K (MPa·m1/2)

Alloy 600325°C

CGR Curve Alloy 60075th Percentile α

Alloy 60050th Percentile α

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Summary

Nozzle #3 Alloy 600 from Davis-BesseFracture is predominantly IG, even during mechanical fatigue loading Cyclic CGRs show environmental enhancement in PWR water at 316°C SCC CGRs are a factor of 2-4 higher than the proposed disposition curve for Alloy 600; growth rates correspond to 95th percentile of the data

Alloy 690Fracture surfaces were uniform for both Alloy 690 specimens Cyclic CGRs of Alloy 690 show environmental enhancement The SCC CGRs in simulated PWR water at 320°C were as high as:

2.8-3.3 x 10-11 m/s for Kmax = 28-31 MPa m1/2 for Alloy 6905.4 x 10-11 m/s for Kmax = 30.2 MPa m1/2 for Alloy 152