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