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
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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
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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
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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
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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
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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)
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Tests in
Aqueous Boric Acid Solutions
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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
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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
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EH vs. pH for Fe-O-H @ 100°C (Ref. EPRI)
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Measurement of Wastage for A533Gr B @ 97.5°C
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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
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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
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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
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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
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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"
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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
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Corrosion Tests in
H-B-O SolutionsAt T > 100oC
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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
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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
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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)
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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.
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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
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Wastage test apparatus for the Water AddingH-B-O system
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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
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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.
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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
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Pioneering Science andTechnology
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
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Tests High-T & High-PAqueous RT-Saturated
Boric Acid Solution
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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
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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
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Pioneering Science andTechnology
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
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Pioneering Science andTechnology
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
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Pioneering Science andTechnology
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
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EH vs. pH for Fe-O-H @ 300°C (Ref. EPRI)
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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
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Corrosion Rates
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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.
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Pioneering Science andTechnology
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
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Pioneering Science andTechnology
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 - -
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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
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Pioneering Science andTechnology
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.%
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Pioneering Science andTechnology
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
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Pioneering Science andTechnology
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