Content of Boric Acid Corrosion Research Program · te c t ab l e V e r y t h i n f i lm for m e d...

United States Nuclear Regulatory Commission

NRC/EPRI Collaborative Presentation – March 22, 2004

Content of Boric Acid CorrosionResearch Program

Crack Growth Rates of Alloys 600 & 182 from Davis-Besse HeadDifficult to accomplish – small size of specimensMetallography, yield strength suggest relatively good quality alloys

Computational Model, Probabilistic Assessment of:Statistics of Initiation, Probability of Detection & Accuracy of SizingCrack Growth Rate Variations, Stress Intensity Factor Gradients

Measure Ecp and wastage rates for range of solution compositions, temperatures (Tasks 3 & 4)

Wastage (bulk corrosion) as function of temperature and solutionconcentration

Includes tests in molten boric acidElectrochemical Potential and Polarization Measurements of Low-Alloy Steel, Alloys 600 & 182 in Concentrated Boric Acid Solutions



Crack Initiation and Growth Non-destructive Inspection Structural Integrity Analysis

Initiation StudiesCrack Growth Studies

Corrosion StudiesCrack Growth Rate Modeling

Visual Techniques (Bare Metal Visuals)Eddy Current & Ultrasonic Techniques

Probabilities of DeectionInnovative Development

Stress Analysis – Crack Driving ForcesMaterials PropertiesWelding Processes

Probabilistic Risk Assessment ModelsCalculation of Inspection Intervals

Calculation Of Inspection Interval Is An Integrated Process



Integrated Inspection Model

Time

Flaw

Siz

e

a0

a + N•σa

af

af - N•σaf

da dt mean

dadt Nσa

Interval Between Inspections Margin to Accountfor Uncertainties



Corrosion Tests

Determine the wastage rates and electrochemical potentials for: A533 Gr B and Type 308 SS weld (diluted by A533Gr B).

- Flowing & quiescent, aerated and deaerated BA solutions - T = 100-316ºC (212-600ºF)- PWR (1000-wppm B + 2-wppm Li) - 3500-wppm B + 2-wppm Li

and

Molten H-B-O conditions



Wastage test apparatus for the aqueous solution and molten boric acid systems



Wastage test sample assembly

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

SS308 Weld A533Gr-B

Sample: 6.5 gram, OD (0.50”), ID (0.275”), length (0.5”)



CR for A533-Gr. B & SS 308 in sat’d BA sol’n(40,514 wppm-B) at 97.5ºC

1

1 0

1 0 0

A533

Gr B

-1

A53

3Gr B

-2

A533

Gr B

-3

A53

3Gr B

-4

A533

Gr B

-5

SS

308W

eld-

1

SS

308W

eld-

2

0 -2 4 -h0 -1 0 0 h2 4 -1 0 0

CR

(mm

/yr)



Corrosion rates for A533-Gr. B half-saturated BA solution (20,257 Wppm-B) at 97.5°C

0

1 0

2 0

3 0

4 0

5 0

6 0A5

33G

r B-2

0

A53

3Gr B

-21

A533

Gr B

-22

A53

3Gr B

-26

A533

Gr B

-23

A53

3Gr B

-24

A533

Gr B

-25

C R .H a lf .S a t.B A @ 9 7.5 C

0 -24h0 -24 h(use d s o l'n )2 4 -10 0h0 -76h0 -100 h

7 6 -31 1h0 -311 h

1 00 -4 11h0 -411 h

CR

(mm

/yr)



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

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 sol’n & O, interface solution/vapor)



Corrosion Rates of A533Gr-B in various BA solutions at 97.5ºC

0.1

1.0

10.0

100.0

0 100 200 300 400 500All_A533Gr_B_CR

Sat'd sol'n

Sat'd sol'n (PD)

half sat'd sol'n

half sat'd (used)

PWR water

UHP water

CR

(mm

/yr)

Exposure t (h)

Note:CR determined for times between 24 and 411 h.



Corrosion Rates vs. Wppm-B for A533Gr-Bin BA solutions at 97.5ºC

0.0

10.0

20.0

30.0

40.0

50.0

0 10000 20000 30000 40000 50000

CR411&311avg.

CR

(mm

/yr)

at 9

7.5o C

Concentration ( Wppm-B )

Note:Corrosion rates based on 311 & 411 h exposure



CRs of A533Gr-B in oxygenated PWR & UHP @97.5ºC

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

28 29 37 38

PW R (rinsed)

UHP (w/o rinsed)UHP (rinse)

CR

(mm

/yr)

Sample # (A533Gr-B)

PW R sim ulated water (1000-W ppm -B,2-W ppm-Li)

UHP waterNegative CR, Form ation of scale

PW R (w/o rinsed)

Error bar (+/- 0.03 mm/yr)



A533-Gr. B, A 600, and SS 308 at 150°C &170ºC with H2O additions in molten H-B-O

0

5 0

1 0 0

1 5 0

2 0 0

A53

3GrB

(#9)

A533

GrB

(#10

)

A60

0CW

-2

A53

3GrB

(#11

)

A533

GrB

(#12

)

SS3

08

CR

(mm

/yr)

T = 1 5 0 o C T = 1 7 0 o C

A60

0 no

t det

ecta

ble

Very

thin

film

form

ed

SS30

8 no

t det

ecta

ble

Very

thin

film

form

ed



Molten H-B-O wastage tests: A600 and A533-Gr. B with and without H2O additions

3.0

4.0

5.0

6.0

7.0

8.0

A533Gr-B#9 A533Gr-B#10 A600 (HT)-2

As Rec'd24 h 300C

26 h 260C

24 h 150C45 h 150 C (add-H

2O)

Sam

ple

Wt (

g)



Summary - (TASK #3)Wastage tests for the A533Gr B in the BA solution at 97.5ºC were completed. -CR value of 2-in/yr in the saturated solution was highest -CRs shown to have a linear relationship with the concentration of BA

Note: CRs for A600 & SS308 were negligible when compared with those of A533Gr-B.

Wastage tests in the molten H-B-O at 150-290ºC were performed.-Without water addition, none of the metallic samples showed corrosion, except thin oxide scale formed on A600 & SS308. -With water addition, A533Gr B at 150ºC showed the highest CR value, and higher the T the lower the CR.

Wastage tests in the Hi-T & P conditions - ongoing



pH for BA & Sat’d BA (rt < T < 100°C)

1.0

1.5

2.0

2.5

3.0

3.5

4.0

20 30 40 50 60 70 80 90 100

Sat'd BA sol'n @ rt(9,086-wppm B)

O2 purge

Ar purge

pH

T(C)

1.0

1.5

2.0

2.5

3.0

3.5 3.9

4.0

4.1

4.2

4.3

4.4

4.5

4.62.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4

Ar purgeO

2 purge

Solubility of Boric AcidpH

Log Wppm

-B

1000/T(K)

1.0

1.5

2.0

2.5

3.0

3.5

4.0

20 30 40 50 60 70 80 90 100

H3BO

3 Sat'd Solution @ T

Ar purgeAr purgeO

2 purge

pH

T(C)



E(V) vs. t 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 2 4 6 8 10 12 14 16

90401%

E (V

) vs.

SH

E T(C)

t (h)

A533Gr-B

A600

T(C)

SS308

-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



PD-test of A533Gr B in Sat’d BA solution at 97.5°C

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

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

42,000-ppm B (Sat’d BA)



Electrochemical Corrosion Products for the A533Gr B in Sat’d BA at 95°C

Darker brown color precipitates bottom of the test chamber: X-ray analysis shows iron borate (FeBO3)

Brown color slurry deposited around the A533B: X-ray diffraction shows boric acid (H3BO3)



5 0 .0

6 0 .0

7 0 .0

8 0 .0

9 0 .0

1 0 0 .0

1 1 0 .0

0 .5

0 .6

0 .7

0 .8

0 .9

1 .0

1 .1

0 .0 5 .0 1 0 .0 1 5 .0 2 0 .0 2 5 .0

Wt (

g)

Wt. Fraction (w

t/wt,i)

t (h )

B (O H )3 P h a s e

H B O2 P h a s e

B2O

3 P h a s e

T = 2 8 0 o C in a ir 1 a tm

Boric acid turned to snow-ball shape and then glass like transparent boric oxide

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



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

-0.600

-0.550

-0.500

-0.450

-0.400

250

255

260

265

270

275

280

285

290

10 15 20 25

91701 9 31 17 AM 9/16/2003

E(V

) vs.

SH

E

T(C)

t(h) 91701

Pt

T(C)

A600

SS308

A533Gr-B -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

Content of Boric Acid Corrosion Research Program · te c t ab l e V e r y t h i n f i lm for m e d...

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