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The Effect of Sulfur on the Corrosion Fatigue Behavior of Austenitic Stainless Steels in High Temperature Water
Lindsay O'Brien1, Lun Yu2, Denise Paraventi1, Ron Ballinger2 1. Bechtel Marine Propulsion Corporation, Bettis Laboratory
2. H. H. Uhlig Corrosion Lab, MIT
17th International Conference on Environmental Degradation of Materials in Nuclear Power Systems – Water Reactors
Ottawa, Ontario August 9-13 2015
Agenda
I. Background II. Work Scope III. Experimental
IV. Results & Discussion V. Future Work
I. Background
• Contradictory observations on sulfur effects in fatigue crack growth • Low Alloy Steels (LAS) – accelerated fatigue
crack growth rates (FCGR) • Austenitic Stainless Steel – retardation of FCGRs
• Reduction in fatigue crack growth rate for high sulfur heats – especially at: • long rise times • higher R • lower values of ∆K
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Material Chemistry
Environment
Loading
SCC CF
II. Work Scope
• Goals: • Examine the effect of sulfur on the corrosion fatigue behavior of austenitic stainless steels in
Deaerated Pressurized Water (DPW). • Provide additional insight into the likely mechanisms controlling retardation of fatigue crack
growth in higher sulfur material.
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Complete Test Machine Set-up
and Configuration
Targeted CFCGR Testing
Characterization of Crack Tips from CFCGR Testing
Electrochemical Characterization of test
Materials
Modeling & Simulation
Development of Mechanisms for Enhancement and Retardation of
CFCGR in High Temperature Water
III. Experimental
• Materials • 304/304L SS 1.0T – CT specimen
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Heat C Mn S Cr Ni N Fe Orientation A16830
(High Sulfur) 0.021 1.73 0.032 18.5 8.2 0.089 Bal LR
E5174
(Low Sulfur) 0.020 1.60 <0.0025 19.8 10.1 0.085 Bal LR
D2739
(Low Sulfur) 0.019 1.60 <0.0025 18.3 9.4 0.051 Bal LR
Material Chemistries (wt%) and Specimen Orientation
III. Experimental • Experimental system • Direct current potential drop (DCPD) system with autoclave, fatigue machine and water
loop
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Water board Autoclave & Fatigue machine Autoclave & Specimen DCPD & data acquisition
III. Experimental – Test Plan • Multiple-Step test
• Specimen A16-LR-10 (High S) • Sawtooth waveform (85% rise/15% fall), Kmax = 28.6 or 31.9 MPa√m and ∆K = 17.1 or 8.6 MPa√m • Deaerated Pressurized Water (DPW) with overpressure hydrogen • 288 °C, autoclave pressure of 9.54MPa
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Step # pH R Rise time (second) Step 1 10.7 0.4 5.1 Step 2 10.7 0.4 51 Step 3 10.7 0.4 510 Step 4 10.7 0.4 5.1 Step 5 10.7 0.4 5100 Step 6 10 0.7 5.1 Step 7 10 0.7 51 Step 8 10 0.7 5100
III. Experimental – Test Plan • Two-Step test
• Specimen A16-32 (High S), Specimen 2739-LR-2 (Low S), Specimen 2739-28 (Low S) • Sawtooth waveform (85% rise/15% fall), Kmax = 28.6 MPa√m and ∆K = 8.6 MPa√m • DPW with overpressure hydrogen • 288 °C, autoclave pressure of 9.54 MPa
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Step # pH R Rise time (second) Step 1 10 0.7 5.1 Step 2 10 0.7 51
IV. Results – Crack Growth Rates
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Tr =5.1 Tr =51 Tr =510 Tr =5100
R=0.4
R=0.4
IV. Results – Crack Growth Rates
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Crack retardation was observed under long rise time JSME curves failed to
describe the behavior of high sulfur material (Specimen A16-LR-10)
JSME PWR curve JSME PWR curve
Multiple-Step Test
ASME 2010. Rules for Inservice Inspection of Nuclear Power Plant Components. Boiler and Pressure Vessel Codes, Section XI. JSME, 2010, Rules on Fitness-for-Service for Nuclear Power Plants, the Japan Society of Mechanical Engineers, JSME S NA1-2010, Tokyo
ASME ASME
IV. Results – Crack Growth Rates
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Crack retardation was observed under long rise time in high sulfur materials (Specimen A16-32 and A16-LR-10) Crack enhancement was observed in
low sulfur materials (Specimen 2739-LR-2 and 2739-28) N-809 code curves capture the
behavior of low sulfur materials better than JSME curves
R = 0.7
SR ST STr
R. Cipolla. “Case N-809 – Reference Fatigue Crack Growth Rate Curves for Austenitic Stainless Steels in Pressurized Water Environments”, draft Revision 5, 14 May 2014.”
IV. Results – Crack Growth Rates
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Enhanced line for low sulfur materials
airenv aa log8048.00395.1log +−=
IV. Results – Fractography
• Low sulfur materials
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Precrack CF Crack Post-test
Crack propagation direction
Secondary cracks
Slip lines
Crack propagation direction
Crack propagation direction
IV. Results – Fractography • High sulfur materials • Distinct surface morphologies (Specimen A16-32)
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Precrack
Post-test
Crack propagation direction
Step 1
Step 2
Crystallography Featureless
IV. Results – Fractography • High sulfur materials • Distinct oxide morphologies (Specimen A16-32).
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STEP 1 STEP 2
IV. Results – Fractography • High sulfur materials • Transition in long rise time step (Specimen A16-32).
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Step 1 Step 2
Sub A
Homogeneous
Sub B
Alternating
Transition 5.1s 51s
IV. Results – Fractography • High sulfur materials • Alternating oxides/oxide morphology in long rise time step (Specimen A16-32).
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Step 1 Step 2
Sub A
Homogeneous
Sub B
Alternating
a b
a. SEM image of alternating features in Sub B of Step 2; b. corresponding BSE image of a for high sulfur material (specimen A16-32).
IV. Results – Fractography • High sulfur materials • Dissolution holes (Specimen A16-32).
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Mag = 200X, HV = 15 kV, Spot size = 5.0
V. Future Work
• Characterization of crack tips
• D2O test with nano-SIMS analysis • To understand the role of hydrogen in crack growth
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D2739-LR-2 (Low S) Technique: Atom probe tomography TEM
Of interest: Dislocation structure Oxide intrusion Sulfur distribution
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THANK YOU Q & A
Backup Slides
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III. Experimental • Test plan • Multiple-Step test
• Specimen 5174-LR-11 (Low S) • Sawtooth waveform, Kmax = 31.9 MPa√m and ∆K = 17.1 MPa√m • DPW with overpressure hydrogen • 288 °C, autoclave pressure of 9.54MPa
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Step # pH R Rise time (second) Step 1 10.7 0.4 5.1 Step 2 10.7 0.4 51 Step 3 10.7 0.4 510 Step 4 10.7 0.4 5100
IV. Results – Fractography
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High sulfur material Low sulfur material (E5174) Long rise time Long rise time
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