flow accelerated corrosion and erosion-corrosion … september 28 tuesday flow accelerated corrosion...
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P2-148
September 28 Tuesday
Flow Accelerated Corrosion and
Erosion-Corrosion of RAFM Steel
in Liquid Breeders
Masatoshi Kondoa, Takeo Murogaa, Akio Sagaraa, Tsisar Valentynb,
Akihiro Suzukic, Takayuki Teraic, Minoru Takahashid,
Naoki Fujiie, Yukihiro Yokoyamaf, Hiroshi Miyamotof, Eiji Nakamuraf
a. National Institute for Fusion Science, Toki, Japan.
b. Physico-Mechanical Institute of National Academy of Sciences of
Ukraine, Ukraine
c. University of Tokyo, Tokyo, Japan.
d. Tokyo Institute of Technology, Tokyo, Japan.
e. Biko chemical company, kobe, 658-0013, Japan
f. Santoku cooperation, kobe, 673-0443, Japan1
1. Background and purpose
2. Experimental condition
2.1 Experimental apparatus
2.2 Test conditions
3. Results and discussion
4. Conclusions
Contents of my presentation
2
Compatibility of liquid breeders, i.e. lithium (Li), lithium-lead
(Pb-17Li), 46.5LiF-11.5NaF-42KF (Flinak) and 66LiF-34BeF2
(Flibe), with structural materials is one of the critical issues
for the development of fusion blanket systems.
1.Background and purpose
FFHR molten salt /RAFM blanket
designed by
A. Sagara et al.,
Fusion Engineering and Design 81
(2006) 2703-2712 3
KOREAN lithium/RAFM blanket
Y. Kim et al. /
Fusion Engineering and Design 75–79
(2005) 1067–1070
Compatibility of steels in fluids
The corrosion rate must be higher at higher flow rate of these fluids,
and the phenomenon was called a flow accelerated corrosion (FAC). An
erosion of a corroded surface by the shear stress of the flow called an
erosion-corrosion is also an important phenomenon. However, these
characteristics in liquid metals and molten salts are limited so far.
Erosion occurrence in liquid metal Pb-Bi was reported in the previous
studies.
Specimen of
STBA26(9Cr-1Mo) steelSpecimen
holder
Pb-Bi flow
250µm
Cross section of eroded part
Erosion – corrosion in lead-bismuth eutectic
steel
Erosion
M. Kondo, M. Takahashi et al, J. Nucl. Mater., 343, 349-359 (2005).
steel
Erosion-
corrosion
5
Corrosion data in liquid Li, Pb-Li and molten salt was not able to be
directly compared with each other because of the different corrosion
apparatus and conditions.
(For example, comparison of weight loss data between different
corrosion systems and apparatus is not easy)
Therefore, The tests were performed at the same conditions, and the
compatibility with the fluids was compared with each other. Overall
mass transfer coefficient is proposed to evaluate the corrosion ratio
in the present study.
The purpose of the present study is to investigate the compatibility of
reduced activation ferritic/martensitic (RAFM) steel, JLF-1, in the liquid
breeders in static and flowing condition. The characteristics of the
flow accelerated corrosion and the erosion-corrosion in the fluids
were discussed.
Purpose
6
2. Experimental conditions2.1 Experimental apparatus
Heater
Thermo couple
Impeller(Mo)
Magnet
coupling
Motor for rotate
impeller
Specimens
Li
Pot (316)
Crucible
(9Crsteel)
Specimen
holder (410)
33mm48mm
16m
m3
6m
m
Li
Thermo couple
Specimens
Heater
Heat
insulation
Specimen holder
(12Cr steel )Pot
(Made of 316)
Crucible
(9Cr steel)
Specimens
Cover
gas: Ar
I.D.
48mm
Ar
Static test apparatus
Volume 92cc
Temp. 500-700
Stirring test apparatus
Li volume 65cc
Temp. 500-600
Rotating speed max 100rpm
Corresponds to 0.17m/s
2
Rend
mixing
dnv
7
2. Experimental conditions
2.2 Test condition
Test
IDStatic or
Stirred
Temp.
(ºC)
Exposure time
(hours) [Ref.]
Material of
crucible
V/ Stotal (m) Re
number
for mixing
Li
A
Static 600
100 Mo 0.11 -
B 250[8], 750[8] Mo 3.3x10-2 -
C 250[9], 750 12Cr steel 1.0 x10-2 -
D Flowing 600 250[10] 12Cr steel 9.8x10-3 2859
Pb-17LiE Static 600 750, 3000 JLF-1 2.6x10-3 -
F Flowing 600 250 12Cr steel 9.8x10-3 18512
Flinak
GStatic 600
200[7],1000[7],
2200JLF-1 steel
2.6x10-3 -
H Flowing 600 250[7], 2200 SUS316L* 9.8x10-3 949
8
92cc
65cc 3cc
Specimen
Test E, GTest A, B Test C Test D, F, HSpecimen
Impeller
Non-corrosion surface area
Corrosion surface area
(Specimen, crucible surface)
Fe Cr W Non metal
Li 0.85 0.12 0.31 Nitrogen: 65
Pb-17Li 2.2 0.17 0.52 -
Flinak 52 2.6 - H2O: 42.6
Initial impurity of liquid breeders Schematic image of test assemble
Results and discussion (Li)
9BCT
a a
c
a a
a
BCC
C Fe
600ºC 250h
-Corrosion at static condition
-Depletion of carbide and carbon from steel
-Cr depletion
-Phase transformation from martensite to
ferrite due to carbon depletion
-Coalescence of subgrains
Diffusion of Li to grain boundary
decreased grain bonding
Erosion-corrosion
stirring test at 600 ?C5µm
Rough surface
5µm
Subgrain
5 micro
5 micro
Not able to be coalesced
600ºC 250h
Static Flowing
Results and discussion (Pb-17Li)
5µm
Flowing condition(250hours)Static condition (3000hours)
5µm
ICP-MS analysis for Pb-Li used for static test (unit : wppm)
Fe Cr W Ni Mo
Pb-17Li (Initial) 2.2 0.17 0.52 1.3 0.052
After 250- hour test (Static) 0.85 3.6 3.4 - -
After 3000-hour test (Static) 10 4.5 3.9 - -
Cr dissolution → Cr saturation (Cr solubility is low)
Fe dissolution → Fe has large solubility in Pb-17Li 10
Erosion- corrosion
Penetration to
boundary
Flow accelerated
corrosion
Liquid
breeders
Erosion corrosion
Peeled off of
subgrains by flow
Subgrains
PAG
Packet
boundary
Block
boundary
Lath
boundary
Li dissolves the carbide, and attacked the packet, block, lath and/or subgrain
boundaries where had the carbide precipitated. From these facts, the
mechanism of erosion-corrosion of JLF-1 steel in flowing Li was summarized
in Figure. By the flowing test in Pb-Li, the similar morphology was obtained
and this indicated the occurrence of the erosion-corrosion. In the Flinak, the
erosion-corrosion was not detected possibly because the sensitivity of the
boundaries for the Flinak was not strong due to the chemical stability. 15
Results and discussion (Flinak)
250hrs 250hrs
Pitting
corrosionAttack for
boundary* Small pit
5µm
250 hrs (Test H)
The corrosion of JLF-1 was small in
purified Flinak at flowing condition
induced by impeller in pot. The phase
transformation on the surface was
observed. The number of the pitting
corrosion on the surface was less
than that at static condition, because
the impeller induced flow removed the
local difference of impurity
concentration on the surface in Flinak.
The weight loss of the specimens was
lower than that at static condition.
10µm
11
October 12 16:30-18:30
ISFNT-9Masatoshi KONDO
E-mail: kondo.masatoshi@nifs.ac.jp
3. Results and Discussion (3.2 Corrosion in purified Flinak)
5µm
Pitting
Phase transformed zone
(C depleted zone)
Normal part
5µm
Cr depleted zone
Cr enriched zone
Phase transformed zone
Grain boundary
Fe
Cr W
Fe
Cr W
200 hrs(P-C-1) 1000hrs (P-C-2)
1000hrs200hrs
10µm 10µm
The weight loss was
much less than that in
non-purified Flinak.
The pitting corrosion
was partially observed
on the surface.
The corrosion in
purified Flinak at
static condition
was the local
corrosion for the
grain boundary,
though the
intensity was
lower than that
in non-purified
Flinak.
Steel
Pitting corrosion in Flinak
Grain
boundary
Anode
Flinak
Cathode
Electrical circuitFe2+
Weight loss
Li Pb-17Li
FlinakAfter the tests in Li, specimens were rinsed in
water at room temperature. The specimen tested in
Pb-17Li was rinsed in Li at 350 ºC for 3 hours to
remove Pb-17Li from the specimen due to the
dissolution of Pb-17Li into Li. The adhered Li on
specimen was then removed by water. The
specimen tested in Flinak was rinsed in LiCl-KCl at
500 ºC, and the adhered LiCl-KCl was rinsed in
water. All the specimens were finally rinsed in
acetone to remove water. The weight change of the
specimens by the exposure to the liquid breeders
was measured using an electro reading balance
with accuracy of 0.1mg.
Solid line and dotted one by modeling calculation shown in next page
Erosion-corrosion
12
Li (65wppm nitrogen) Pb-17Li PbFlinak
(42.5wppm H2O)
Cs wppm<molppm>
Fe - * 47 (600ºC) ~<145> 34 (600ºC) <126> 50 (600ºC)
Cr52.4 (800 ºC) <7>~
94.3 (600ºC) <12.6>**10 (500ºC) <40> 1 (600ºC) <3.7 > 50 (600ºC)
D (m2/s)Fe 4 x10-8 (600ºC) 4 ±2 x10-14 (500ºC) 1.2x 10-9(600ºC) 5.4x10-8
Cr 2.1x10-8 (570 ºC) 8 ±2.5 x10-11 (500ºC) - 2x10-9***
Solubility and diffusion coefficient
Nomenclature
C: concentration of metal element in fluids [wppm]
Cs: Solubility of element in fluids [wppm]
D: diffusion coefficient [m2/s]
d: Width of impeller [m]
e: Thickness of boundary layer for concentration [m]
J: Overall mass transfer ratio [g/m2s]
h: Overall mass transfer coefficient [m/s]
hm, e : Overall mass transfer coefficient at flowing
condition in experiment
hm, t : Overall mass transfer coefficient at flowing
condition in theory [m/s]
n: Rotatig speed [s-1]
Ss: Surface area of specimens [m2]
Sc: Surface area of crucible [m2]
t: Test time [s]
ρ: Density of liquid breeders [g/m3]
μ: Viscosity of liquid breeders [mPa•s]
ν: Kinetic viscosity of liquid breeders [m2/s]
V: Volume of liquid breeders [m3]
v: Averaged velocity of liquid breeder [m/s]
Δm: Wight loss of specimen in total [g/m2]
Ω: Constant for mass transfer in mixing flow D
νSc 0.7f0.644D0.344ν0.45.67de
C)-(CshJdt
dC
ScSs
Vρ
)C(Cse
D)Cs-C)(hJ
mt
1/3(Sc)2/3)mixing
(ReD
dhSh mt
))V
Sc)th(Ssexp(Cs(1C
))V
hStexp(ρVCs(1Δm
13
Mass
transfer of
element in
flow
FAC modeling based on mass transfer
Li (65wppm nitrogen) Pb-17Li Flinak
(42.5wppm H2O)
h static experimental (m/s) 2.8x10-8 1.2x10-9 -
h flow experimental (m/s) (erosion-corrosion) 4.2x10-9 1.2x10-8
h flow theory (m/s) 9.9x10-5 - 1.3x10-4 2.1x10-8 - 1.4x10-7 2.2x10-5 - 3.5x10-4
Modeling (Overall mass transfer coefficient)
Discussion on release rate in corrosion process
14
Overall mass transfer coefficient
obtained from experiment ( hm,e)
Overall mass transfer coefficient
obtained from hydrodynamic non
dimension number
Flow Flow
No binding
of element
on specimen
surface
Binding of
element on
specimen
surface
Release rate
( hm,t)
Erosion- corrosion
Penetration to
boundary
Flow accelerated
corrosion
Liquid
breeders
Erosion corrosion
Peeled off of
subgrains by flow
Subgrains
PAG
Packet
boundary
Block
boundary
Lath
boundary
Li dissolves the carbide, and attacked the packet, block, lath and/or subgrain
boundaries where had the carbide precipitated. From these facts, the
mechanism of erosion-corrosion of JLF-1 steel in flowing Li was summarized
in Figure. By the flowing test in Pb-Li, the similar morphology was obtained
and this indicated the occurrence of the erosion-corrosion. In the Flinak, the
erosion-corrosion was not detected possibly because the sensitivity of the
boundaries for the Flinak was not strong due to the chemical stability. 15
Conclusion
Corrosion experiments for RAFM, JLF-1 steel (Fe-9Cr-2w-0.1C) in 3types
of flowing liquid breeders (i.e. Li, Pb-17Li and Flinak) were performed at
the same conditions. The compatibility of the fluids for the steel was
compared with each other. Major conclusions are as follows;
(1) The weight loss of specimens in liquid breeders was evaluated by a
corrosion model based on mass transfer. It was found that the model can
be applied for the different test system with different quantity of liquid
breeders and different surface area of the systems.
(2) The overall mass transfer ratio in Li at static condition was larger than
that of Pb-Li, though the solubility of the metal element of the steel in Pb-
17Li was higher than that of Li. The flow enhanced the dissolution of
element of the steel in liquid metals. In the Flinak, the effect of the flow was
negligible.
(3) An erosion- corrosion of JLF-1 in Li and Pb-Li was caused by the
peeling off of the subgrain on the corroded surface by the flow.16
October 12 16:30-18:30
ISFNT-9Masatoshi KONDO
E-mail: kondo.masatoshi@nifs.ac.jp
Back up Results and Discussion (3.1 Corrosion in non-purified Flinak with H2O)
5µm5µm
Normal partCr rich inner
oxide layerFe rich
outer oxide
layer
Outer layer was damaged
10µm
230 hrs (N-C-1)230 hrs (N-C-2) 1000hrs (N-C-3) [4]
Fe
Cr W
Surface state is similar
Outer layer
Inner layer Inner layer
Dissolution of oxide into Flinak
and peeled of oxide layer
Oxide layer
formation
Steel Steel Steel Steel
O H O
Oxidation corrosion in Flinak
Cr rich inner layer
formationFe rich layer
Cr rich surface
5µm
10µm
230 hrs1000 hrs
Cr depleted zone
10µm
The local corrosion
at grain boundary
and lath boundary
was detected. Fe was
selectively dissolved
from the JLF-1
surface into Flinak.
The formed oxide
layer in non-purified
Flinak had double
layer structure as
outer Fe-rich oxide
layer and inner Cr –rich oxide layer. The
oxide layer was
damaged, and non-
protection for the
corrosion was
indicated.
M.P.
(K)
Thermal conductivity
(W / (m x K))
Density
(kg/m3)
Viscosity
(mPas)
Li Alkali metal 453.7 53.7 (800K) 481 (800K) 0.344 (800K) Fusion blanket
Na Alkali metal 371 66.1 (800K) 826 (800K) 0.232 (800K) Coolant for FBR
Pb Heavy metal 600.7 15.4 (800K) 10360 (800K) 1.74 (800K) Coolant for FBR
Pb-17Li Heavy metal 508 9568 (800K) - Fusion blanket
Pb-Bi Heavy metal 397 14.9 (800K) 10087(800K) 1.33 (800K) Coolant for FBR
Flinak(LiF-NaF-KF)
Molten salt 727 1.2 2146 (800K) 4.1 (900K) Fusion blanket
Flibe(LiF-BeF2)
Molten salt 772 1.2 1993 (800K) 7.5 (800K) Fusion blanket
FlinakLiquid
LithiumLi+
Free
electron
High thermal conductivity in liquid metal High chemical stability of molten salt
Li+ F-+
Already stable
state by ion
bonding4
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