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