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Development of Corrosion ResistantSteel for Cargo Oil Tanks
Sumitomo Metals
Sumitomo Metal Industries, Ltd.
< 1 >
6 September 2007
Sumitomo Metals< 2 >
1. Corrosion Problems of Cargo Oil Tank2. Research Results by “The Shipbuilding Research
Association of Japan”3. Corrosion Mechanism, Simulated Test Method
and Corrosion Resistance of Developed Steel・ Deck Plate・ Bottom Plate
4. Mechanical Properties of Developed Steel5. Onboard Test Results of Developed Steel
(Upper deck)6. Summary
Contents
Corrosion Problems of Cargo Oil Tank
Sumitomo Metals< 3 >
general corrosiongeneral corrosion ・maximum corrosion rate > 0.1mm/y・cost of repair coating, recoating
pitting corrosionpitting corrosion・cost of inspection and repair・pits initiate at defects of paint film
Deck plateDeck plate
Bottom plateBottom plate
vapor space
crude oil
drain water
Sumitomo Metals< 4 >
1. Corrosion Problems of Cargo Oil Tank2. Research Results by “The Shipbuilding Research
Association of Japan”3. Corrosion Mechanism, Simulated Test Method
and Corrosion Resistance of Developed Steel・ Deck Plate・ Bottom Plate
4. Mechanical Properties of Developed Steel5. Onboard Test Results of Developed Steel
(Upper deck)6. Summary
Contents
Sumitomo Metals< 5 >
The Shipbuilding Research Association of JapanPanel #242 (SR242 committee)
Ship OwnerShip Owner
Steel MakerSteel Maker
University & National LaboratoryUniversity & National Laboratory
ClassClass
ShipyardShipyard
SR242 committeeSR242 committee
Field examination of Field examination of VLCCsVLCCs were carried outwere carried out
research by SR242
Corrosion at Deck Plate
Deck Plate
Sumitomo Metals< 6 >
vapor space
crude oil
corrosion rate
corrosion products
corrosion environments
> 0.1mm/y (Maximum)
inert gas (O2, CO2, SO2)H2S (from crude oil)cyclic wet & dry condition
rust (FeOOH), elemental S
research by SR242
[ layered structure ]
Examples of Analysis Results of Gas Composition in Vapor Space of Cargo Oil Tanks
Sumitomo Metals< 7 >
High concentration of H2S exists in vapor space
COT No. 3S 4C 4S 5C
A B C D
Cargo loading ratio 93% 89% 92% 31%H2S
[vol. ppm] 2790 1330 498 817H2O [vol.%] 4.9 3.9 5.3 2.5
O2 1.7 2.5 1.8 3.9CO2 3.7 4.0 2.2 10.9SOx
[vol. ppm] 1.3 3.9 1.6 2.7N2 32.9 45.0 25.7 62.0
CxHy 54.9 42.4 62.2 15.0CO 0.0 0.0 0.0 0.0
Crude Oil type
Gas[vol.%]
research by SR242
Loss in Thickness of Upper Deck Plate with Age
Sumitomo Metals< 9 >
0
1
2
3
0 10 20Age at inspection (year)
Ave
rage
Los
s (m
m) 0.1mm/y
research by SR242
Maximum corrosion rate is over 0.1 mm/y
Pitting Corrosion at Bottom Plate
Bottom PlateSumitomo Metals< 10 >
pitting rate
corrosion products
corrosion environments
4mm/y maximum
inert gas (O2, CO2, SO2)H2S (from crude oil)drain water (Cl-)crude oil, elemental S
rust, FeS, elemental S
crude oil
drain water
research by SR242
Examples of Chemical Analysis Results of WaterSampled from the Bottom of Cargo Oil Tanks
Sumitomo Metals< 11 >
tank Na Cl SO42- S2O3
2- T-Fe pH
A 13600 42500 14 <0.1 2 7
B 40000 48000 1470 <0.1 42 7.15
C 40000 54000 1350 <0.1 2.5 7.5
[ ppm ]
Chloride is detected in high concentration
research by SR242
10mm
Sumitomo Metals
Appearance of Specimen Exposed at the Bottom of Cargo Oil Tank
< 12 >
pits
exposed for 2.5 years
research by SR242
Sumitomo Metals< 13 >
1. Corrosion Problems of Cargo Oil Tank2. Research Results by “The Shipbuilding Research
Association of Japan”3. Corrosion Mechanism, Simulated Test Method
and Corrosion Resistance of Developed Steel・ Deck Plate・ Bottom Plate
4. Mechanical Properties of Developed Steel5. Onboard Test Results of Developed Steel
(Upper deck)6. Summary
Contents
Corrosion Mechanism at Upper Deck Plate
< dawn : ∼25°C (wet) > < daytime : ∼50°C (dry) >
Wet & Drycycle
Sumitomo Metals< 14 >
inert gas H2S
Corrosion in low pH water elemental S2H2S + O2 → 2S + H2O
FeOOH
rustelemental S
deck plate
water
deck plate
pH = 2 pH = 2 ∼∼ 44H2O+SO2 → H2SO3 → H2SO4H2O+CO2 → H2CO3
inert gas H2S
O2
corrosion product contains a lot of elemental S (60% max.)
Simulated Corrosion Test (Upper Deck Plate)
Sumitomo Metals
NaClsolution
< 15 >
gas outlet gas inlet
specimens
< Test conditions >Temperature50°C(20 h)⇔25°C (4h)[cyclic wet & dry condition]
Gas*
[A]13%CO2-5%O2-0.01%SO2-bal.N2 (simulated inert gas)
[B]simulated inert gas + 0.2%H2S
* Gas A and B are blew alternately every 2 weeks
Cross Sectional Analysis of Corrosion Product Formed on Steel after Simulated Corrosion Test
Epoxy resinCorrosion product
Sumitomo Metals< 16 >
100μm
layerd elemental S
rust (FeOOH)mixture of rust and elemental S
Steel
Layered structure was reproduced in laboratory
Fe O S
Distribution of elements low
high
conc
entra
tion
Sumitomo Metals< 17 >
Corrosion Product after Simulated Test - Upper deck -
α-FeOOH γ-FeOOH Fe3O4 Elemental S Others
COT 37 8 0 12 43
Simulatedtest 30 3 8 21 38
Corrosion product after simulated test was similar to cargo oil tank.
Laboratory corrosion test simulates corrosion at upper deck of cargo oil tank.
[ mass % ]
0
0.2
0.4
0.6
0.8
1
1.2
Corrosion Resistance - Deck Plate -
Sumitomo Metals< 18 >
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0 20 40 60 80 100 120Test duration (days)
Ave
rage
cor
rosi
on lo
ss (m
m)
Conventional Steel
Developed Steel
1/21/2
conv
entio
nal
stee
l
deve
lope
dst
eel
84 days
Nor
mal
ized
cor
rosi
on ra
te
1/21/2
Sumitomo Metals< 19 >
Corrosion resistance in low pH water by alloying elements Corrosion resistance in low pH water
0
0.2
0.4
0.6
0.8
1
1.2
Conventionalsteel
Developed steel
Ratio o
f corr
osi
on r
ate
Dew water
Rust
Low pH (2~4)
Steel + alloying elements
H2SO4 (pH=0.5), 24h
Mechanism for Improvement of Corrosion Resistance [upper deck]
Sumitomo Metals< 20 >
1. Corrosion Problems of Cargo Oil Tank2. Research Results by “The Shipbuilding Research
Association of Japan”3. Corrosion Mechanism, Simulated Test Method
and Corrosion Resistance of Developed Steel・ Deck Plate・ Bottom Plate
4. Mechanical Properties of Developed Steel5. Onboard Test Results of Developed Steel
(Upper deck)6. Summary
Contents
Pitting Corrosion Mechanism at Bottom Plate
Sumitomo Metals< 21 >
Pits initiate at the defects of oil coating film and grow rapidly by creating corrosion electric cell.
Anode : Fe → Fe2+ + 2eCathode : O2 + 2H2O + 4e → 4OH-
S + 2H2O + 2e → H2S + 2OH-
(accelerate pitting corrosion rate)
Bottom plate
Oil coating
(Cl-)
Elemental S
Pit (Anode)Pit (Anode) CathodeCathode
DefectDefect
Drain waterInert gasInert gas HH22SS(Neutral pH)
< Test conditions >Temperature
40°CGas
13%CO2-5%O2-0.01%SO2-0.2%H2S-bal.N2
Simulated Corrosion Test –Bottom Plate-
pit10mm
Sumitomo Metals< 22 >
gas outlet gas inlet
syntheticsea water
specimens
Appearance of specimenafter corrosion test
We reproduced pitting corrosion by laboratory test.
simulatedoil coating
defect
Sumitomo Metals< 23 >
Corrosion Product after Simulated Test - Bottom -
α-FeOOH β-FeOOH γ-FeOOHCOT 16 19 5
Simulated test 18 19 6
Corrosion product after simulated test was similar to cargo oil tank.
Fe3O4 Elemental S Others8 1 FeCO3, FeS
24 11 FeCO3, FeS
Laboratory corrosion test simulates corrosion at bottom of cargo oil tank.
[ mass % ]
0
0.2
0.4
0.6
0.8
1
1.2
Sumitomo Metals< 24 >
Corrosion Resistance - Bottom Plate -
00.20.40.60.8
11.21.41.6
0 20 40 60 80 Test duration (days)
Max
imum
pit
dept
h (m
m) Conventional Steel
Developed Steel
conv
entio
nal
stee
l
deve
lope
dst
eel
1/31/3
56 days
Nor
mal
ized
pitt
ing
rate
1/21/2
Sumitomo Metals< 25 >
Fe
S
O
Cu
RustFeS
200μmlow
high
SteelSulfide film
SE
Cross section
conc
entra
tionSulfide filmSulfide film
Drain
H2S
Steel + alloying elements
Oil coating
Rust
Mechanism for Improvement of Corrosion Resistance [bottom]
Sulfide film suppresses growth of pitting corrosion
Distribution of elements
Sumitomo Metals< 26 >
1. Corrosion Problems of Cargo Oil Tank2. Research Results by “The Shipbuilding Research
Association of Japan”3. Corrosion Mechanism, Simulated Test Method
and Corrosion Resistance of Developed Steel・ Deck Plate・ Bottom Plate
4. Mechanical Properties of Developed Steel5. Onboard Test Results of Developed Steel
(Upper deck)6. Summary
Contents
Sumitomo Metals
Mechanical Properties of Developed Steel
Plate thickness : 16.5 mm
≧≧3131--2020≧≧2222440/570440/570≧≧315315D32D32
258 258 --20202424504504432432
Absorbed EnergyAbsorbed Energy( J )( J )
Test Temp.Test Temp.((°°CC))
EL EL (%)(%)
TSTS(N/mm(N/mm22))
YPYP(N/mm(N/mm22))
CharpyCharpy Impact TestImpact TestTensile TestsTensile Tests
<Spec.>
< 27 >
Grade
Mechanical properties satisfied the specification.
Sumitomo Metals
Toughness of Welded Joint
< 28 >
Toughness of welded joint is good.
174174W.M.W.M.
132132F.L.F.L.
172172F.L. + 1mmF.L. + 1mm
224224F.L. + 3mmF.L. + 3mm
250250F.L. + 5mmF.L. + 5mm
Absorbed Absorbed Energy at 0Energy at 0℃℃ (J)(J)
NotchedNotchedPositionPosition・Plate thickness : 16.5 mm
Method 3 electrodes, FCB(Single side 1 pass)
Heat input 108 kJ/cm
edge preparation
16.5
3
55°
Corrosion Resistance of Weld Metal
Sumitomo Metals< 29 >
Corrosion resistance of weld metal is Corrosion resistance of weld metal is equivalent to that of base metal. equivalent to that of base metal.
[ Deck ] [ Bottom ]
0
0.2
0.4
0.6
0.8
1
1.2
Base metal Weld metal
Ratio o
f corr
osi
on r
ate
[initia
lized
by r
ate
of
base
meta
l]
0
0.2
0.4
0.6
0.8
1
1.2
Base metal Weld metal
Ratio o
f pitting
rate
[initia
lized b
y r
ate
of
base
meta
l]
Sumitomo Metals< 30 >
1. Corrosion Problems of Cargo Oil Tank2. Research Results by “The Shipbuilding Research
Association of Japan”3. Corrosion Mechanism, Simulated Test Method
and Corrosion Resistance of Developed Steel・ Deck Plate・ Bottom Plate
4. Mechanical Properties of Developed Steel5. Onboard Test Results of Developed Steel
(Upper deck)6. Summary
Contents
Sumitomo Metals< 31 >
test couponstest couponstest couponstest couponstest couponstest couponstest couponstest coupons
platesplatestest couponstest coupons
DeckDeck BottomBottom
--AFRAAFRA--MAXMAXAAtest couponstest couponsAFRAAFRA--MAXMAXBB
platesplatesVLCCVLCCCCplatesplatesVLCCVLCCDD
platesplatestest couponstest couponsAFRAAFRA--MAXMAXAA
Exposure testExposure testTypeTypeShipyardShipyard
Certification of ClassificationLRLR, NKNK, ABSABS, DNVDNV
Developed steel has been applied to cargo oil tanks for trialDeveloped steel has been applied to cargo oil tanks for trial
Trial Applications to Cargo Oil Tanks
0
0.2
0.4
0.6
0.8
1
tank A tank B tank C
Ratio
of c
orro
sion
rate
of
dev
elop
ed st
eel t
o co
nven
tiona
l ste
el Upper deckUpper deck
Onboard Test Results of Developed Steel(Upper Deck Plate)
Developed steel has good corrosion resistantDeveloped steel has good corrosion resistantin actual environments at upper deckin actual environments at upper deck
Sumitomo Metals
Test coupons were exposed in vapor space of 3 tanks for 1 year
< 32 >
Sumitomo Metals< 33 >
1. Corrosion Problems of Cargo Oil Tank2. Research Results by “The Shipbuilding Research
Association of Japan”3. Corrosion Mechanism, Simulated Test Method
and Corrosion Resistance of Developed Steel・ Deck Plate・ Bottom Plate
4. Mechanical Properties of Developed Steel5. Onboard Test Results of Developed Steel
(Upper deck)6. Summary
Contents
Summary
Sumitomo Metals< 34 >
1.1. We established simulated corrosion test methodWe established simulated corrosion test method.2. We developed corrosion resistant steel plateWe developed corrosion resistant steel plate
for cargo oil tank which can be used at both at both upper deck and bottomupper deck and bottom.
3. Performance of developed steel :corrosion ratecorrosion rate < 1/2< 1/2 [ at deck plate ]pitting rate pitting rate < 1/3< 1/3 [ at bottom plate ]
4. Mechanical properties of developed steel satisfy the specification.
5. Corrosion resistance of weld metal is good.6. Developed steel has good corrosion resistancegood corrosion resistance
in upper deck of actual cargo oil tanksin upper deck of actual cargo oil tanks.
Sumitomo Metals< 35 >
September 2007Sumitomo Metal Industries, Ltd.
THANK YOU FOR KIND ATTENTION
END OF PRESENTATION
Sumitomo Metals
Steel
FeOOHFeS
Sulfide
Steel
FeOOH
elemental S
Conventional steel Developed steel
Structure of Corrosion Product on Pit
Sulfide film that is hard to dissolve improves corrosion resistance
2FeS + 3/2O2 + H2O → 2FeOOH + 2S
Sumitomo Metals
Corrosion resistance of welded joints
developed developed developedconventional
Corrosion resistance of welded joints was good No galvanic corrosion on these welded joints
Simulated corrosion test for bottom on FCB welded joints
0
0.2
0.4
0.6
0.8
1
1.2
HAZ(developed)
weld metal HAZ(developed)
Rat
io o
f pit
dept
h[in
itial
ized
by
conv
entio
nal s
teel
]
corrosion depth ofdeveloped steel
0
0.2
0.4
0.6
0.8
1
1.2
HAZ(conventional)
HAZ(developed)
Rat
io o
f pit
dept
h[in
itial
ized
by
conv
entio
nal s
teel
]
weld metal
Sumitomo Metals
Corrosion resistance of developed steel in sea water
Corrosion resistance of developed steel is equivalentto conventional steel in sea water.
0
0.05
0.1
0.15
0.2
Conventionalsteel
Developedsteel
Cor
rosi
on ra
te (m
m/y
) 6 months
Sumitomo Metals
Test coupons on deck and bottom
Weld bead
Conventional steel
Corrosion resistant steel
Grinded( ) Grinded( )
+ Epoxy painted
+ Silicon coated
Grinded ( )
+Epoxy painted
+Silicon coated
A A’
A A’
Grinded ( )
Weld bead
8
300
300
3030 240
240
8
8
φ12
3030
Grinded ( )+
Epoxy painted+
Silicon coated
A A’
A A’
Grinded ( )
Weld bead
8
300
300
3030 240
240
8
8
φ12
3030
Deck
Bottom
Sumitomo Metals
Effect of oil coating on corrosion at bottom (simulated test)
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8Test duration (weeks)
Cor
rosi
on lo
ss, p
it de
pth
(mm
)
with oil coating
without oil coating
Corrosion of specimen with oil coating is acceleratedGeneration of corrosion electric cell in this environment