corrosion investigations of steels in pb-bi at fzk j. konys, g. müller, j. knebel

Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft

Corrosion Investigations of Steels in Pb-Bi at FZK

J. Konys, G. Müller, J. Knebel

• Materials- Materials and test parameters for corrosion investigation

• Test equipment- Stagnant liquid metal test stand COSTA- Liquid metal loop tests

• Results- Corrosion in stagnant liquid lead- Discussion of corrosion in stagnant Pb- Differences between corrosion effects in Pb and Pb-Bi- Corrosion in flowing lead- Comparison results obtained under stagnant and flowing conditions

•Conclusions

Content


Materials and test parameters for corrosion investigation in lead

Stagnant Lead Tests:Materials: 1.4970, OPTIFER IVc, MCrAlY coatings,

surface alloyed 1.4970 and OPTIFER IVc,Dimension: small specimens 2 x 10 x 20 mm,Temperature: 550 °C,Oxygen concentr.: 8•10-6 at%

Loop Tests at IPPE:Materials: 1.4970, 1.4948, OPTIFER IVc, EM10Dimension: rods 8mm x 110 mmTemperature: 400 °C and 550 °C Oxygen concentr.: 5•10-4 at%Flow velocity: 2 m/s


Structure of 1.4970 after surface alloying with Al (GESA treatment )

30 40 50 60 70 800

50

100

150-Fe

-Fe

-Fe

max. 400 cps

2

original

cps

0

50

100

150

-Fe-Fe -Fe

-Fe -Fe

GESA

0

50

100

150-Fe+FeAl

-Fe+FeAl-Fe-Fe

FeAlFeAl

GESA+Al

10µmbulk

alloyed layer

Cross section of alloyed layer

Structure analysis


Stagnant liquid metal test stand COSTA

furnace

tube

thermostatoxygendetector

steel-specimenPb

flowcontrol

Ar5%H2

moisturesensor

moisturesensor

Ar

water


Conceptual Scheme of CM-2 Lead Loop (IPPE, Obninsk)


Results of tests in stagnant Pb!


Protective layer formation on steel in leadwith controlled oxygen concentration

Cross section of the typical structure of a test specimen after 3000 h in liquid Pb at 550 °C.Lead in the upper part contains SiC grains from grinding.

100 µm

100µm

bulk material

corrosion layer

Pb


Original and GESA Al-alloyed 1.4970 after 3000 hin stagnant lead at 550°C and an oxygen content of 810-6 at%

-15 -10 -5 0 5 10 150

20

40

60

80

100

Con

cent

ratio

n [a

t %]

Depth [µm]

Original +spinel in grain boundary

Fe(Fe1-x

,Crx)

2O

4+ Ni

Fe3O

4Pb

Fe Cr Ni Pb O

0 2 4 6 8 10 12 14 16

0

10

20

30

40

50

60

70

Con

cent

ratio

n[at

%],

O-N

et In

t.

Depth [µm]

Fe Cr Ni Pb O Al

Original Al-alloyed by GESA

Concentration profiles


Original and GESA Al-alloyed OPTIFER IVc after 3000 hin stagnant lead at 550°C and an oxygen content of 810-6 at%

Original Al-alloyed by GESA

Concentration profiles

-20 -15 -10 -5 0 5 10 15 20 25 300

20

40

60

80

100

PbOriginalcompostion

Diffusionzone withprecipitationof

Fe(Fe1-x

,Crx)

2O

4

Fe(Fe1-x

,Crx)2O

4

Fe3O

4

Fe Cr Pb O

Con

cent

ratio

n [a

t %]

Depth [µm]-2 0 2 4 6 8 10 12 14

0

20

40

60

80

100

Pb

Fe Cr Pb Al O

Con

cent

ratio

n[at

%],

O-N

et In

t.

Depth [µm]


Corrosion Investigation of GESA treated MCrAlY Coating in stagnant Pbafter 3000 h at 550°C and an oxygen content of 810-6 at%

100 µm

MCrAlY

Pb

No measurable corrosion attack after 3000 h!


OPTIFER IVc after 470 h at 550 °C in the gas atmospherewith H2/H2O = 0.4 (= 10-25 bar)

element concentration


Structure analysis of OPTIFER IVc after 500 hat 550 °C in the gas atmosphere (H2/H2O = 0.4)

OPTIFER IVc OPTIFER IVc Al alloyed by GESA

30 35 40 45 50 55 60 65 70 75 80 850

50

-Fe(Al) + FeAl

FeAl

-Fe(Al) + FeAl

0 h

110 h

210 h

500 h

cps

2

0

50

0

50

0

50

FeAl

30 35 40 45 50 55 60 65 70 75 80 850

50100150 -Fe

-Fe -Fe0 hmax. 500 cps

2

cps

050

100150

20 h

110 h

050

100150

210 h

050

100150

HH

M

M HH

H

M

500 h

050

100150


Structure analysis of 1.4970 after 500 hat 550 °C in the gas atmosphere (H2/H2O = 0.4)

30 40 50 60 70 800

50100150200

-Fe-Fe-Fe

-Fe max. 400 cps0 h

2

cps

050

100150200

110 h

050

100150200

210 h

050

100150200

M-Fe-Fe -FeHMM -Fe 500 h

30 40 50 60 70 800

50

100

150

FeAlFeAlFeAl -Fe-Fe 0 h

2cp

s

0

50

100

150

110 h

0

50

100

150

210 h

0

50

100

150

-Fe-Fe

-Fe FeAlFeAl FeAl

FeAl

500 h

1.4970 1.4970 Al alloyed by GESA


Discussion of corrosion in stagnant lead

O 2- Fe O3 4

pore belt

bulk material

oxygenin solution

spinelprecipitations

original surface

Fe (Fe Cr ) O2 + 3+ 3+2 4

(Fe Cr ) O ?1-x x 2 3

FeFe

2+

3+ 1-x x

Oxide layer formation scheme Growth of spinel and diffusion zoneas a function of time at 550 °C

spinel


Comparison of Pb and Pb-Bi corrosion at 550 °C, 8•10-6 at% Oxygen

OPTIFER IVc after 800 h in stagnant Pb-Bi OPTIFER IVc after 800 h in stagnant Pb-Bi OPTIFER IVc after 800 h in stagnant Pb

Solubilities in Pb and Bi

Bi (at 600°C)[at%]

Pb (at 600°C)[at%]

Ni 21 2Cr 0,056 0,02Fe 0,017 0,001

The higher solubility in Bi may causehigher dissolution attack of Pb-Bi.

Increase of oxygen activity!

Pb-Bi Pb

bulkbulk

corrosion layer oxide layer


Results of tests in flowing Pb!


Exposure to flowing Pb

EM 10 3000 h at 550 °C

OPTIFER IVc2000 h at 550 °C

50 µm 50 µm


EM 10 for 3000 h in flowing Pb at 550 °C



Optifer IVc 3000 h at 400 °C

Optifer IVc2000 h at 400 °C

50 µm 50 µm



1.4948 3000 h at 550 °C

1.49482000 h at 550 °C

50 µm50 µm



1.4970 3000 h at 550 °C

1.49702000 h at 550 °C

50 µm 50 µm


Exposure of specimens in flowing Pb (IPPE loop) at 550 °C


Comparison of oxide scale growth in stagnant Pb (8•10-6 at% Oxygen)and flowing Pb (5•10-4 at% Oxygen) at 550 °C


Conclusions

• Oxide layers can effectively prevent the steel from leaching of the alloy components.

• To maintain the oxide layers over long exposure time it is necessary to controlthe oxygen concentration in lead.

• By this procedure corrosion is changed from that of solution attack to that of oxidation.

• Thus, it is needed to find materials that form stable protective oxide scalesunder oxygen control in liquid lead.

• No corrosion attack at all is observed if Al is alloyed into the surface.

• Oxide scale formation in liquid lead obeys the same principle mechanismsas in controlled gas atmosphere.

• There are no principal differences between results of tests in stagnant and flowing lead.

corrosion investigations of steels in pb-bi at fzk j. konys, g. müller, j. knebel

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