Development of Corrosion Resistant Steel for Cargo Oil Tanks

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


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







Contents


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


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


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

Appearance of Upper Deck Plate


flaky corrosion products

research by SR242

Loss in Thickness of Upper Deck Plate with Age


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


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







Contents

Corrosion Mechanism at Upper Deck Plate

< dawn : ∼25°C (wet) > < daytime : ∼50°C (dry) >

Wet & Drycycle


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


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


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 -


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


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]







Contents

Pitting Corrosion Mechanism at Bottom Plate


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


gas outlet gas inlet

syntheticsea water

specimens

Appearance of specimenafter corrosion test

We reproduced pitting corrosion by laboratory test.

simulatedoil coating

defect


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


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


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







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


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]







Contents


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 >







Contents

Summary


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.


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

0

0.2

0.4

0.6

0.8

1

0 0.1 0.2 0.3

H2S concentration (%)

Cor

rosi

on lo

ss, p

it de

pth

(mm

)

Sumitomo Metals

Effect of H2S on corrosion at bottom (simulated test)

with oil coating

without oil coating

H2S accelerate corrosion in this environment.

Documents

Development of Corrosion Resistant Steel for Cargo Oil Tanks