Corrosion of Reactor Pressure Boundary Materials …B2O3&Wet-HBO #3 Boric Oxide #4 W /O W ater Boric...

A U.S. Department of EnergyOffice of Science LaboratoryOperated by The University of Chicago

Argonne National Laboratory

Office of ScienceU.S. Department of Energy

Corrosion of Reactor Pressure Boundary Materials in Boric Acid SolutionsJ.-H. Park, O. K. Chopra, K. Natesan, and W. J. ShackArgonne National Laboratory

January 18, 2005

2

Pioneering Science andTechnology

Project ObjectiveProject Objective

• The overall objective of the program is to conduct research in specific areas focused to determine the conditions that can lead to aggressive and rapid rate of attack of pressure vessel steel in the presence of high concentrations of boric acid in nuclear power plants

3


Corrosion-Related TasksCorrosion-Related Tasks

• Measurement of Electrochemical Potential (Corrosion potential) of Alloy 600, SS308, and A533.Gr-B in Concentrated Boric Solutions

• Corrosion of Reactor Steels in Concentrated Boric Acid Solutions

4


Key SubtasksKey SubtasksEstablish test facilities for measuring electrochemical potential of A533B, Alloy 600, and SS308, and for potentiodynamic studies

Complete potentiodynamic anodic polarization tests and ECP measurements of A600, 308SS, and A533B, in (a) high-T high-P water with range of boric acid, (b) H-B-O solution at high-T and 1 atm, and (c) low-T saturated boric acid solution

Establish test facilities for corrosion/wastage tests in - high-T, high-P water with a range of boric acid solution

concentrations;- high-T H-B-O solutions at 1 atm; and - low-T (97.5°C) saturated boric acid solution, both in non-

aerated and aerated conditions

Perform wastage tests of A533.Gr-B vessel steel and 308SS clad inthe three environments

5


Phases present in the B-O-H system

HBO2 - 1/2 H2O = 1/2 B2O3450(mp)B2O3

B(OH)3 - H2O = HBO2236(mp)HBO2

B(OH)3 + H2O = [B(OH)4]- + H+169 (tr)H3BO3

Reaction with H2OT (°C) Phases

6


Equilibrium pH2O vs. T in the H-B-O system

B2O3(s) + H2O(g) = 2HBO2(s,l)

4.0

8.0

12.0

16.0

20.0

24.0

28.0

32.0

80

160

240

320

400

480

40 80 120 160 200 240 280 320

pH2O

(atm

) pH2 O

(psi)

T(C)

HBO2 (s,l) + H

2O (g) = H

3BO

3 (s)

B2O

3(s) + H

2O (g) = 2 HBO

2 (s)

7


Tests in

Aqueous Boric Acid Solutions

8


Experimental Electrochemical Cell for ECPMeasurements & Potentiodynamic testTests were performed inBA solution at ≈100°C• Measured ECPs and

performed PD-test -Specimen (bar shape)-Sol’n stirred (magnetic stirrer)

• PH measurement on the Sat’d BA solution at rt to 100oC

• *PH measured in (de/ae)rated BA solutions

9


E(V) vs. time in the sat’d BA sol’n @97.5°C

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120

90201%

E(V

) vs.

SH

E

T (C)

t (h)

T (C)

SS308

A600

A533Gr-B

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

30

40

50

60

70

80

90

100

0 2 4 6 8 10 12 14 16

90401% E

(V) v

s. S

HE T(C

)

t (h)

A533Gr-B

A600

T(C)

SS308

After the initial 90 h

10


EH vs. pH for Fe-O-H @ 100°C (Ref. EPRI)

11


Measurement of Wastage for A533Gr B @ 97.5°C

12


Wastage test sample assembly in solution Sample: 6.5 gram, OD (0.50”), ID (0.275”), length (0.5”)

plug shape

Bottom (BA solution) TopTeflon insulator rotate (50 rpm)

SS308 Weld A533Gr-B *Tightening mechanism

*Stack inside leak-tight filled with rubber tube between shaft

13


A B C D E F G H I J K L M N OA: Screw tightening mechanism with flat O-ring a the bottomB: A600 (30%CW), C: A600-1, E: SS308 clad weldD,F,H,J, & M: O-rings, G, I, K, & L: A533Gr-B #1,2,4, &7.N & O: Alumina (N, in the solution & O, interface solution/vapor)

Sample stack view for A533Gr-B, A600, SS308 after exposure for 311 or 411 h in sat’d BA solution at 97.5ºC

14


Corrosion Rate Conversion: Fe → Fe2+ + 2e’CR (mm/yr) = [0.306 nd/M] * JCorr

• CR (mm y-1) =Corrosion rate • Jcorr (mA cm-2) =Corrosion current • n = # of electrons freed by the corrosion reaction• M = atomic mass, d = density

For steel:• n =2, M = 55.85 g and d = 7.88 g cm-3

• CR (mm/yr) = 11.6 * JCorr

15


PD-test of A533Gr B in Sat’d BA soln at 97.5°C • 42,000-ppm B (Sat’d BA)

3.0

4.0

5.0

6.0

7.0

8.0

40

50

60

70

80

90

100

0 100 200 300 400 500

Cor

rosi

on C

urre

nt, J

Cor

r (m

A/cm

2)

CR

(mm

/yr)

Exposure t (h)

Wastage-test

PD-test

10-4

10-3

10-2

10-1

-0.50 -0.45 -0.40 -0.35 -0.30 -0.25 -0.20 -0.15

Cur

rent

den

sity

, J (a

mp/

cm2 )

E(V) vs. SHE

JCorr

= 4 mA/cm2

CR = 46 mm/yrE

Corr = -0.342 V vs. SHE

A533Gr-B at 94oC Sat'd-Areated BALSV.30.dta t = 240 h

16


Corrosion rate vs. Wppm-B for A533-Gr. B in aerated and deaerated BA solutions near 100°C

0.0

10.0

20.0

30.0

40.0

50.0

0 10000 20000 30000 40000 50000

CR

(mm

/yr)

Wppm-B in BA-solution

Deaerated

Aerated

100oC Sat'd Sol'n

rt-Sat'd Sol'n

"A533Gr-B"

17


0.0

0.1

1.0

10.0

100.0

0 100 200 300 400 500All_A533Gr_B_CR

Sat'd sol'nSat'd sol'n (PD)half sat'd sol'n

half sat'd (used)PWR waterUHP water

Cor

rosi

on ra

te (m

m/y

r)

Exposure time (h)

Wastage rates for A533Gr-B Steel in BA solutions at 97.5°C

18


Corrosion Tests in

H-B-O SolutionsAt T > 100oC

19


Corrosion Tests in H-B-O

150 ≤ T ≤ 300ºC in aerated condition1. Dry boric acid: 170 ≤ ToC ≤ 300 : Molten Salt

I) T = 300 ± 9oCii) T = 260 ± 7oCiii) T = 154 ± 4oC

2. Wet boric acid: water addition: Sat’d BA @Tiv) T = 150oC v) T = 170oC

20


Boric acid heated in ambient at 280°C Boric acid turned to snow-ball shape and then glass like transparent boric oxide collected in the bottom of the beaker by loosing water.

50.0

60.0

70.0

80.0

90.0

100.0

110.0

0.5

0.6

0.7

0.8

0.9

1.0

1.1

0.0 5.0 10.0 15.0 20.0 25.0

Wt (

g)

Wt. Fraction (w

t/wt,i)

t (h)

B(OH)3 Phase

HBO2 Phase

B2O

3 Phase

T = 280oC in air 1 atm

Note:100-g Boric acid heated in air (pH2O = 3%) at 280°C

21


Electrical lead wire

¼” OD alumina tubeSilver braze

A533Gr B working electrode (specimen)for insertion into the molten H-B-O pool

Test in H-B-O SolutionsSpecimen (Working Electrode)

22


PD-test Ambient HBO2 + B2O3 (Dry)

-10.50

-10.00

-9.50

-9.00

-8.50

-8.00

-2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50 2.00

290C.HBO2

log

J (a

mp/

cm2 )

E(V) vs. Ag/AgI (@290C)

Eocv

= -0.077 V T = 290oC

Overnight air equilibrium @ 290ºC.Measured current density indicates that A533Gr B is highly protective.

23


PD-Test & Corrosion Tests

“No Corrosion”On

A533Gr.B, A600, SS308 in the Absence of Water

Corrosion in Ambient H-B-O (150 ≤ ToC ≤ 300): Dry Condition

24


Wastage test apparatus for the Water AddingH-B-O system

25


PD-test: Water Adding HBO2 + B2O3

-10.00

-9.00

-8.00

-7.00

-6.00

-5.00

-4.00

-3.00

-2.00

-2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50 2.00

T = 240C Water injection

Log

J (a

mp/

cm2 )

E(V) vs. Ag/AgI@T

1 (water injection)

2

3

4

5

6 78

9 "open"

" ECorr

"

approaching10

ECorr

• Adding waterinto the test cell

26


T = 170 °Cwater additions for test times

between 40 h.

T = 150 °Cwater additions for test times

between 45 h.

150 and 170°C with water additions for test times between 40 and 45 h.

27


150 and 170°C with water additions for test times between 40 and 45 h.

0

5 0

1 0 0

1 5 0

A53

3GrB

(#9)

A53

3GrB

(#10

)

A60

0CW

-2

A53

3GrB

(#11

)

A53

3GrB

(#12

)

SS30

8

CR

(mm

/yr)

1 7 0 o C

1 5 0 o C

C R ~ 0 C R ~ 0

28


5 0 0 .0

1 0 0 0 . 0

1 5 0 0 . 0

2 0 0 0 . 0

2 5 0 0 . 0

3 0 0 0 . 0

3 5 0 0 . 0

4 0 0 0 . 0

1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0H 3 B O 3 a n d H - B - O

Inte

nsity

(arb

)

2 T h e ta

3 0 0 o C ( a i r )H e a t / c o o l

" B o r ic A c id a s R e c 'd "

0 .0

5 0 0 .0

1 0 0 0 . 0

1 5 0 0 . 0

2 0 0 0 . 0

2 5 0 0 . 0

3 0 0 0 . 0

1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0

B 2 O 3 & W e t - H B O

# 3 B o r ic O x id e# 4 W /O W a t e r B o r ic O x id e

Inte

nsity

(arb

)

2 T h e ta

0.0

2000.0

4000.0

6000.0

8000.0

10000.0

10 20 30 40 50 60 70 80

BA&Wet H-B-O

#1 As rec'd Boric Acid#5 Wet powdery

Inte

nsity

(arb

)

2 Theta

B2O3

Water & T HBO2

H3BO3 = B(OH)3

XRD: Boric Acid Cycles with H2O and T

29


Tests High-T & High-PAqueous RT-Saturated

Boric Acid Solution

30


Corrosion facility for tests in High–T & P of BA solutions at T up to 316°C

COVER GASSUPPLY

PRESSURERELIEFVALVE

HIGH- & LOW-PRESSURE

REGULATORS

FLOWMETER

GASPURIFIER

VENT

FEEDWATER TANK

SPARGE TUBE

PRESSUREGAUGE

HIGH-PRESSUREPUMP

RUPTUREDISK HEAT

EXCHANGER

PREHEATER

BACK PRESSURE RELIEF VALVE

PRESSURERELIEFVALVE

PT COUNTERELECTRODE

WORKINGELECTRODES

REFERENCEELECTRODE

THERMOCOUPLE

HEATEDTEST

CHAMBER

PRESSUREGAUGE

DRAIN

WORKINGELECTRODE

31


ECP & Corrosion Tests at High T & P

Sol’n pathK-type T.C.

W.E. (4ea)

C.E.Pt

Ref. EAg/AgCl-0.1 Mol KCl

32


ECP for A533Gr-B, A600, SS308, and Pt in the hydrogen covered UHP-water at 288 &316ºC

-0.700

-0.650

-0.600

-0.550

-0.500

288

292

296

300

304

308

312

316

320

0 5 10 15 20 25 30

E(V

) vs.

SH

E

T(C)

t (h)

P =1800psig. T = 316oCHydrogen cover UHP-water

T(C)

A600PtSS308A533Gr-B

-0.600

-0.550

-0.500

-0.450

-0.400

250

255

260

265

270

275

280

285

290

10 15 20 25

E(V

) vs.

SH

E

T(C)

t(h) 91701

Pt

T(C)

A600

SS308

A533Gr-B

91701 9 31 17 AM 9/16/2003

33


ECP for A533Gr-B, A600, SS308, & Pt in the hydrogen covered PWR-water at 288 & 316ºC

-0.800

-0.750

-0.700

-0.650

-0.600

288

292

296

300

304

308

312

316

320

5 10 15 20 2592601.PWR

E(V

) vs.

SH

E

T(C)

t (h)

T(C)

A600

A533Gr-B SS308

Pt

-0.800

-0.750

-0.700

-0.650

-0.600

250

260

270

280

290

300

0 5 10 15 20

92501.pwr288c

E(V

) vs.

SH

E

T(C)

t (h)

T(C)

Pt

A600 SS308A533Gr-B

34


ECP for A533Gr-B, A600, SS308, and Pt :hydrogen covered 3500-wppm-B, 2-wppm-Li at 288/316 ºC

-0.700

-0.650

-0.600

-0.550

-0.500

288.0

292.0

296.0

300.0

304.0

308.0

312.0

316.0

320.0

0 5 10 15 20 25 30 35

101701.3500-wppm-B

E(V

) vs.

SH

E

T(C)

t (h)

T(C)

A600PtA533Gr-BSS308

I II

-0.700

-0.650

-0.600

-0.550

-0.500

285

290

295

300

305

310

315

320

0.01 0.10 1.00 10.00 100.00

101701.3500wppmB

E(V

) vs.

SH

E

T(C)

t (h)

T(C)

A600PtA533Gr-BSS308

35


EH vs. pH for Fe-O-H @ 300°C (Ref. EPRI)

36


Measured Corrosion Rates for Carbon and Low-Alloy Steels at 12.4 MPa Pressure

10-2

10-1

100

101

102

100 150 200 250 300

9,090 wppm B4,000 wppm B

Cor

rosi

on R

ate

(mm

/y)

Temperature (¡C)

Carbon & Low-Alloy SteelsBoric Acid Solutions12.4 MPa Pressure

37


Corrosion Rates

38


Measured Corrosion Rates for A533-Gr.-B Steel in Various Boric Acid Solutions

10-2

10-1

100

101

102

100 150 200 250 300

Cor

rosi

on R

ate

(mm

/y)

Temperature (¡C)

A533 Gr.-B Low-Alloy SteelBoric Acid Solutions

Open Symbols: 12.4 MPa pressure, saturated at room temp.Closed Symbols: ambient pressure, saturated at temp.

39


Measured Corrosion Rates for Low-Alloy Steels at 80-104°C

100

101

102

103 104 105

ANLBNLWestinghouseCombustion EngineeringArioka

Cor

rosi

on R

ate

(mm

/y)

Solution Concentration (wppm B)

Boric Acid Solutions 80Ğ105¡CAmbient PressureBoric Acid Solutions 80-104oCAmbient Pressure

40


Cr effect: Chemical compositions of the alloys exposed in room-temperature-saturated boric acid solution

Alloy C Cr Mo Ni Si Mn Nb VH-1 0.096 1.0 0.47 0.08 0.09 0.001 0.002 -H-2 0.096 2.1 0.48 0.06 0.09 0.001 0.002 -H-3 0.094 4.5 0.46 0.06 0.13 0.005 0.005 0.002H-6 0.098 9.5 0.50 0.07 0.01 0.002 0.005 0.001H-9 0.094 11.9 0.49 0.05 0.01 0.001 0.010 -

308SS 0.029 21.1 0.39 9.37 0.56 1.27 - -

41


Effect of Cr on average corrosion rate in rt-saturated boric acid solution (9090 wtppm B) at 150, 288, and 316°C and 12.4 MPa under H2 cover gas

0.01

0.10

1.00

10.00

0 5 10 15 20 25 30

150¡C288¡C316¡C

Ave

rage

cor

rsio

n ra

te (m

m/y

r)

Cr concentration in the alloy (wt.%)

Note: Data indicated by open symbols correspond to A533 steel

150oC288oC316oC

42


Effect of Cr Concentration• The effect of increasing the Cr content of the alloy is to

lower the corrosion rate at all temperatures of the study• At 150°C, there is a dramatic drop in corrosion rate when

the Cr content of the alloy increases to 9 wt.%• The effect of increase in temperature is to decrease the

corrosion rate for the same boric acid concentration in the solution and for the same Cr content in the alloy

• For a typical 308SS weldment with a nominal Cr content of 21 wt.%, the corrosion rate in room-temperature-saturated boric acid solution is in the range of 0.01-0.03 mm/y. The rate increases to 0.05-0.11 mm/y as the Cr content drops to 9 wt.%

43


Summary

• We have developed experimental data on ECP and corrosion/wastagerates for materials used in the RPV head and nozzles of a typical PWR in boric acid solutions of varying concentrations at temperatures of 95-316°C (203-600°F)

• For A533 Gr.-B steel, an average corrosion rate of ≈40 mm/y was measured in aerated saturated solution of boric acid at 97.5°C and ambient pressure; The corrosion rate in aerated half-saturated solution was a factor of ≈2 lower than in saturated solution

• The rates in deaerated solution were ≈40% lower than in aerated solution

• Very high corrosion rates were observed for A533 Gr.-B steel at 140-170°C in super-saturated H-B-O solutions of boric acid with addition of water; short term rates up to 150 mm/y were measured at 150°C

44


Summary (continued)• Corrosion tests in high-temperature high-pressure water containing

9090 ppm B, ≈2 ppm Li, <10 ppb DO, and ≈2 ppm dissolved hydrogenshowed rates of ≈5 mm/y at 100-150°C and decreased to <0.1 mm/y at 316°C

• The effect of increasing the Cr content of the alloy is to lower the corrosion rate at all temperatures of the study; At 150°C, there is a dramatic drop in corrosion rate when the Cr content of the alloyincreases to 9 wt.%

• For a typical 308SS weldment (21 wt.%Cr), the corrosion rate in RT-saturated boric acid solution is in the range of 0.01-0.03 mm/y. The rate increases to 0.05-0.11 mm/y as the Cr content drops to 9 wt.%

• We have compared the results from this study with data available in literature; current results obtained at 97.5°C are in agreement with data generated in the past at 80-104°C

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Corrosion of Reactor Pressure Boundary Materials …B2O3&Wet-HBO #3 Boric Oxide #4 W /O W ater Boric...

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