environmental effects on corrosion properties of alloy 22

Publications (YM) Yucca Mountain

1-18-2007

Environmental effects on corrosion properties of Alloy 22 Environmental effects on corrosion properties of Alloy 22

Mano Misra University of Nevada, Reno, [email protected]

L. G. McMillion University of Nevada, Reno

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Repository Citation Repository Citation Misra, M., McMillion, L. G. (2007). Environmental effects on corrosion properties of Alloy 22. Available at:Available at: https://digitalscholarship.unlv.edu/yucca_mtn_pubs/3

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Task ORD-FY04-014: Environmental Effects on Corrosion Properties of Alloy 22

NSHE Cooperative Agreement Progress Briefing18 January 2007

Environmental Effects on Corrosion Properties of Alloy 22

Task ORD-FY04-014PI: M. Misra / L.G. McMillion

2


Staff:– Dr. M. Misra: Principal Investigator– Dr. Glen McMillion: Co-Principal Investigator– Dr. Yugo Ashida: Postdoctoral Associate– Mary LaCombe: QA Specialist– Matthew Taylor: Graduate Student– Jason Strull: Undergraduate Student– Barry Greenslate: Technician

3


Task ORD-FY04-014 consists of four Subtasks:

Subtask 1: Experimental Determination of Parameters for the General Corrosion Model

Subtask 2: Corrosion Under Dust Deposits Containing Hygroscopic SaltsSubtask 3: Heated Electrode Approach for the Study of Corrosion Under

Aggressive ConditionsSubtask 4: Effect of Hydrogen Permeation on the Stability of the Passive

Film of Alloy 22

4


Goals of Subtask 1: Experimental Determination of Model Parameters

This work is being performed by Dr. Glen McMillion• Develop the ability to predict passive corrosion behavior of Alloy 22 from first-

principles modeling (Point Defect Model or ‘PDM’).• First-principles modeling can be (and has been) used to corroborate empirical

corrosion data upon which the LA design is based.• Because first-principles modeling relies on reaction rate constants and other

parameters derived from time- and space-invariant natural laws, it offers the ability to predict corrosion behavior over a wider range of conditions than the empirical approach.

• The desired outcome of this research is more accurate predictions over the Corrosion Evolutionary Path of the repository.

• To this end, the major goal of Subtask 1 is to generate the highest accuracy electrochemical data possible for determining Point Defect Model parameters.

5


• Approach• UNR has built a unique laboratory for studying properties of highly passive alloys

such as Alloy 22.• By continuously replenishing electrolyte, a single specimen can remain in the test

cell indefinitely with no changes in solution chemistry and no accumulation of corrosion products.

• This allows measurement of Electrochemical Impedance Spectroscopy (EIS) data of unprecedented accuracy.

• These highly accurate data are to be used to develop model parameters for calculating corrosion behavior from a first-principles reaction model (PDM).

6


• Results and Significant Achievements• EIS and passive current data have been collected for several combinations of

temperature and electrolyte composition covering the entire passive potential range of Alloy 22. These data are the best of their kind ever collected for a passive alloy.

• We have shown that specimen mounting techniques have profound effects on the accuracy and character of electrochemistry data. Small changes in mounting method affect both the magnitude and shape of EIS spectra, which means not only are calculated corrosion rates affected, but the interpretation of corrosion mechanisms is affected.

• To date, we have generated 9 publications/presentations.

Frequency (Hz)

0.01 0.1 1 10 100 1000 10000

Phas

e S

hift

(deg

rees

)

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

599mV, 19May05529mV, 18May05464mV, 13May05402mV, 09May05339mV, 05May05274mV, 01May05214mV, 27Apr05

Frequency (Hz)

0.01 0.1 1 10 100 1000 10000

Phas

e S

hift

(deg

rees

)

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

404 mV, 20Sept05341 mV, 16Sept05276 mV, 12Sept05216 mV, 08Sept05

Phase ShiftOrdinary mounting method

Phase ShiftMounting method developed

by Subtask 1

7


• Results and Significant Achievements• Specimen mounting techniques have large effects on the magnitude and noise of

potentiostatic current measurements. • Corrosion rates are linearly proportional to current density, so careless mounting

technique can result in calculated corrosion rates that are three times greater than what would be calculated using carefully prepared specimens.

• The devil is in the details!

Potentiostatic current versus time for Alloy 22 in pH 3, 0.1 M NaCl, 30°C electrolyte at 214 mV (Ag/AgCl/0.1M Cl-). The top curve w as collected using an epoxy-only mount. The bottom two curves were collected using stop-off lacquer; all other test conditions were identical. The top and bottom curves were collected using the same specimen, which had been mounted first with epoxy only (top), then remounted using lacquer (bottom).

Time (s)

3e+5 4e+5 5e+5 6e+5

Cur

rent

Den

sity

(A/c

m2 )

0.0

2.0e-9

4.0e-9

6.0e-9

8.0e-9

1.0e-8

8


• Problems and Remedies• Materials used in the improved mounting method have been unable to withstand high-

temperature testing (90ºC)• Other materials failures have also plagued the high-temperature tests.• While lower temperature data that meet the goals of Subtask 1 have been collected, the high-

temperature problems have prevented data collection using different electrolytes because the experimental apparatus was originally designed to test with only one electrolyte at a time.

• Biological activity in the electrolyte flow system has also caused difficulties.• To get Subtask 1 back on track the entire electrolyte flow system is being redesigned and rebuilt

to mitigate the effects of biologicals and to allow tests using two different electrolytes to be conducted simultaneously.

• The flow system redesign will allow 30ºC and 60ºC testing to move forward with different electrolytes while development of high-temperature mounting materials is conducted.

• Cathodic testing has been delayed. New personnel (Jason Strull) has been hired and experimental apparatus has been designed and is being fabricated.

• Funding delays have adversely affected schedule.• Long lead times (3 to 6 months) for instrument calibration services (National Security

Technologies) have also caused delays.• Commercial calibration services are being used to prevent further delays.

9


Subtask 2: Corrosion Under Dust Deposits Containing Hygroscopic Salts.

OLI Systems of Morris Plains, NJ has been retained under subcontract to perform Subtask 2. This work is being performed by Dr. George Engelhardt.

Subtask 2 is a modeling effort that is designed to work with Subtask 3, which is an experimental task using heated Alloy 22 specimens under aggressive conditions and salt deposits.


Goals for Subtask 2:A. Development of a Model for Calculating Corrosion Rates under Porous

Dust Deposit

1. To model the corrosion rates of Alloy-22 under an oxygen permeable hygroscopic dust deposit.

2. To model the concentration of oxygen, aggressive anions (for example, Cl-) under this deposit.

Metal

wd

h

Electrolyte Film

Porous Dust Deposit

Air

Geometry for the crevice corrosion under permeable deposit

11


B. Development of Model and Computer Code for Calculating Concentrations, Potential Distributions, and Corrosion Rates under Porous Deposits

Method: Solution of the system of mass transport equations along with the equation of electroneutrality for each species in porous medium and electrolyte film on the metal surface.

ϕτε

τε

∇−∇−= kkk

kkk CRT

FzDCDJ 22

r

Thus, superficial diffusion flux density in the porous medium has the form :

where ε is the porosity and τ is the tortuosity.

Final version of the code will allow the user to include all chemical and electrochemical reactions that might be necessary for quantitatively predicting the corrosion of Alloy 22 in HLNW repository environments.

12


C. Sensitivity Analysis

• The computer code that will be developed in accordance with the Task 1 will be used to perform sensitivity studies to ascertain the dependencies of the predicted corrosion rates on various input and model parameters.

• The input data will then be reassessed to determine the maximum uncertainty in each parameter that can be tolerated to yield the desired accuracy of prediction. If data are found to be of insufficient accuracy, they will be so identified to the NSHE Project Manager with recommendations for their experimental re-determination.

13


Quality Assurance

OLI Systems shall develop a technical work plan and document control procedures that are compliant with all of the quality assurance (QA) requirements from the Nevada System of Higher Education (NSHE) Quality Assurance Program administered by the Harry Reid Center (HRC). During the course of this subcontract, the work controlling documents will remain compliant with revisions of the QAP.

14


Results and Significant Achievements

• We have conducted a literature survey of work on localized corrosion mechanisms and modeling.

• OLI Systems subcontract has been released and became effective January 2, 2007. Dr. George Engelhardt will visit Reno January 22-24 for Quality Assurance training and technical discussions.

Problems and Remedies

• Recruiting students and/or post doctoral associates qualified to perform the modeling has been difficult.

• To expedite schedule a decision was made to release funds on a subcontract to OLI Systems, which already has the tools and expertise to perform this work.

15


Goals of Subtask 3: Heated Electrode Approach for the Study of Corrosion Under Aggressive Conditions

This work is being performed by Dr. Yugo Ashida• Subtask 3 is intended to more directly address repository service conditions than

conventional corrosion testing under steady-state, fully immersed conditions.• Develop experimental methods to investigate corrosion of Alloy 22 on heated

metal surfaces under dust deposits, salt scale, and in crevices.• Evaluate corrosion resistance under aggressive corrosion conditions in

simulated YM ground waters (SAW, BSW, SCW) using Heated Electrode Approach.

• Investigate passive film breakdown or time-dependent aging under cyclic wet-dry conditions of salt deposits that may result from dripping ground waters on the hot surface.

16


• Approach• Traditional experiments control the temperature of the electrolyte. The condition

of a Yucca Mountain waste package, however, is that of a heated metal surface.• The electrode is heated from below with a reservoir of electrolyte above it.• SCW, SAW, and BSW are used as electrolytes.• Evaporation to dry conditions is allowed to take place, and the residual salt

deposit is re-wetted to simulate drip cycles.• Temperature oscillation is used to assess temperature dependence and

reversibility of the corrosion potential and potentiostatic current density.

17


• Results and Significant Achievements• A method for studying heated surface conditions has been developed.• Different simulated Yucca Mountain waters produce differing corrosion potentials and

passive potential ranges.• In SAW, as the solution evaporates we see that pH becomes more acidic and

corrosion potential increases.

10-9 10-8 10-7 10-6 1x10-5 1x10-4 10-3 10-2 10-1

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

P

oten

tial,

V A

g/A

gCl

Current Density, A/cm2

Heated Electrode ApproachAlloy 22, 90 ± 0.5 °C5 fold diluted SAW, pH 2.810 fold diluted BSW, pH 12.25 fold diluted SCW, pH 10.3

18


• Results and Significant Achievements• At 90ºC, as SAW concentrates over a heated electrode, corrosion potential rises.• The wet-dry cycle results in sharp increases in corrosion potential as the salt deposit

nears dryness. • The increasing corrosion potential trend continues during cyclic wet-dry conditions.

19


0 120 240 360 480 600 7200

20

40

60

80

100

120

Time, mins

Tem

pera

ture

, o C

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

Cur

rent

Den

sity

, A/c

m 2

70 75 80 85 90 95 100 105-0.30

-0.29

-0.28

-0.27

-0.26

-0.25

0 10 20 30 40 50 60

-0.30

-0.29

-0.28

-0.27

-0.26

-0.25

ΔT30oC

102οC

72.0οC

Cor

rosi

on P

oten

tial,

V

Ag/

AgC

l

Time, mins

Cor

rosi

on P

oten

tial,

V v

s. A

g/A

gCl

Temperature, oC

• Results and Significant Achievements• During Temperature Oscillating Heated Electrode Tests (TOHET), the corrosion

potential and potentiostatic current density are observed to be reversible with temperature.

• Corrosion potential versus temperature is observed to be linear.

Corrosion Potential Reversibility Potentiostatic Current Density

20


• Problems and Remedies

• J-13 Well Water cannot be prepared according to published information– A recipe has been written which will allow all of the salts to be in solution, while

being as close as possible to the published ratios of ions.• Equipment for timed drop test is behind schedule.

– Equipment to perform timed drip tests on stressed specimens has been ordered. This includes a temperature chamber with humidity control capable of 170ºC and 20% - 95% relative humidity, and a computer-controlled metering pump capable of delivering 0.05 mL drops.

21


Goals of Subtask 4: Effect of Hydrogen Permeation on the Stability of the Passive Film of Alloy 22

This work is being performed by Matthew Taylor• Hydrogen may be introduced into the passive film of Alloy 22 through

electropolishing, welding, cathodic corrosion processes (acid, water, or oxygen reduction), and microbial activity.

• Subtask 4 is designed to observe the effect of hydrogen on the stability of the passive film on Alloy 22 using electrochemical methods.

• We wish to quantify the effect of hydrogen on possible degradation of the corrosion resistance of the passive film of Alloy 22.

• We wish to understand the synergistic effect of hydrogen, chloride, and nitrate on possible breakdown of the passive film.


• Approach• The Devanathan Cell uses electrolysis to generate hydrogen, which diffuses thorugh

the metal foil.• Hydrogen egress is measured on the opposite side of the foil as a current density

above the background for the material.• Electrochemical properties of the passive film are investigated at various points of

the permeation curve with Electrochemical Impedance Spectroscopy (EIS) and Mott-Schottky Analysis (MS).

• Hydrogen generation/permeation is interrupted to gather EIS data at various points along the experimental timeline.

Devanathan Cell for Hydrogen Permeation

Permeation Timeline

Luggin Probes

ChargingSide

Sample

OxidationSide

EIS, MS Data

23


• Results and Significant Achievements• With increasing hydrogen flux, Nyquist plots show collapsing low frequency

impedance which indicates breakdown of the passive film.• Discharging the hydrogen allows some recovery, but the effect is not completely

reversed within the observed time.

original material

Charging

Discharging

Early

Steady State

original material

24


• Problems and Remedies• Chloride Contamination

– Old Luggin probes leaked Chloride into the test solution.– New Luggin probes filled to stopcock with test solution instead of KCl. KCl kept

in top chamber to preserve the reference electrode stability.• Sample Scarcity

– New samples will not be fabricated due to cost and difficulty– redesigned cell to handle 12 mm samples (instead of 25-mm)

• Temperature Control– New Cell incorporates water-jackets to maintain a stable temperature– Samples can now be tested reliably at elevated temperatures, reducing time

required for each test run from one month to one week.– Facilitates recovering schedule slippage

• Calibration delays– Using MicroPrecision for future calibration to avoid costly delays by NST

• Hydrogen gas bubbles cut off Luggin probe connectivity– Luggin probe tip positioned at bottom of tube, so that bubbles that form do not

break connectivity with the electrolyte– Looking into palladium coating of the back-surface.

25


60%Effect of Hydrogen Permeation on the Stability of the Passive Film of Alloy 22.

4

20%Heated Electrode Approach for the Study of Corrosion…(Timed drop tests).

3b

45%Heated Electrode Approach for the Study of Corrosion…(Fully immersed tests).

3a

20%Corrosion under Dust Deposits Containing Hygroscopic Salts.

2

30%Experimental Determination of Parameters for the General Corrosion Model. (Cathodic).

1b

30%Experimental Determination of Parameters for the General Corrosion Model. (Anodic).

1a% CompleteDescriptionSubtask

• Summary• This Task has done a lot of good work despite having experienced

delays.• Measures are being implemented to recover schedules, complete our

scope of work, and answer important questions about the long term corrosion resistance of Alloy 22.

Estimated percent completion of Subtasks.

environmental effects on corrosion properties of alloy 22

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