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Proposal of Countermeasurefor Cargo Oil Tank Corrosion

by Anti-Corrosion Steel

JAPAN30th November 2006

MSC/82/23/8：Saｆety of Double-Hull Tankers

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Contents

1. Values of anti-corrosion steels

2 Development of Anti-Corrosion Steels for COT/Bottom Plates (Actual Vessel Results)

3 Development of Anti-Corrosion Steels for COT/Upper Deck Plates

4 Conclusion~ Future Works ~

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1-1 Corrosion Problem in COT of Crude Oil Tanker (Bottom and Upper Deck Plates)

Inner Bottom

Upper Deck

Inert Gas

H2S

Crude Oil

Sludge, Drain Water

Upper Deck⇒ General Corrosion

Bottom ⇒Pitting Corrosion

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1-2 A New Countermeasure for COT Corrosion

Is ‘Coating’ the only answer to The Problem?

Constant quality and reliabilityLess Inspection and Less Maintenance during service Minimize the Environmental loadProtect Worker’s healthRecycling after scraped down …

・The Corrosion Test Method has been already established.・Anti-Corrosion Steels for COT has been also developed.・Large scale field test on actual vessels has been finished.

Anti-Corrosion Steels can provide sophisticated solution.Up to now …

The problem is not only corrosion, but also …

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1-3 The Studies on COT Corrosion2000 2002 2004 20061998

Shift to Double Hull Tanker1990~

1999~2002 Panel SR242 committee(The Shipbuilding Research Association of Japan)

2002~

2003~Field Test on actual Vessels

Anti-corrosion steelsLaboratory Test

Scientific Research & understandingof the corrosion phenomena

(Over 10 VLCC s)Basis for Anti-corrosion SteelCorrosion test method

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2. Development of Anti-corrosion Steelsfor COT/Bottom Plates

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Contentsa) Mechanism of pitting corrosion on bottom platesb) Important Basis for Anti-corrosion steelc) On Board Evaluation results (Steel-A)d) Benefit of Applying Steel-Ae) Property of Steel-Af) Other developed Anti-corrosion Steels

(Steel-B,C)g) Summary

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a).1 The facts of Pitting Environment Onborad (New Finding by SR242)

pH of PIT inside: low

(Lower than 1.5)pH about 1.5pH about 1.5

COT No Na T-Fe Fe3+ Cl- SO42- S2O3

2- pH H2SDH-1 13600 2 2 42500 14 ND 7.0 NDDH-3 1S 40000 42 11 48000 1470 ND 7.2DH-3 2P 40000 2.5 1 54000 1350 ND 7.5

Chemical analysis of water sampled from COT bottom (ppm) (crude oil loading Condition)

High concentration of NaCl solution was detected: NOT seawater

High Conc.of Cl-in water

(10mass% NaCl)

solid state S exists

Chemical analysis of sludge sampled in COT

I.D.Total Swt%

Total Fewt%

pH10g/100cc

Cl-

mg/kg

SO42-

mg/kgS2-

mg/kgSludge-A 2.3 19.7 4.5 83 151 4Sludge-B 7.5 22.8 6.8 766 2570 319

Solid Water solubles

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a).2 Environment inside Pit

Target Environment

crude oil

BrineNot Sea Water

pH~0.85NaCl10%pH~0.85NaClNaCl 10%10%

Sulfur

Inert gas + H2S+O2

Brine (Cl- )Not Sea Water

Crude Oil

Oil coating(Crude oil + Sludge)

Defect

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a).3 Simulated corrosion test based on the FACTS& the Newly Developed Steel

Beaker

Specimen

Test solutionNaCl 10%pH~0.85

0

0.2

0.4

0.6

0.8

1

1.2

Conventional Steel A

Ratio

of C

orro

sion

Rate

Steel-A

Conventional

Developed Steel-A provides excellent anti-corrosion Property

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b).1 Pit Growth Stops at a dock

Pitting Stops

Pit D

epth→

Dock Ship Age→

New Pitting starts at new location

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b).2 Mechanism of termination of Pit Growth at a Dock

Findings- Pit growth terminates at dock inspection- New pit appears at new location.

New Finding New Finding bySRbySR--242 Result242 Result

(1) Under servicing condition

(2) Dock inspection

(3) Re-Start of service

(4) Nuclear of new pit

Sludge & Corrosion products

Oil coating

Cleaned Steel Surface = No oil coat

Oil coating ,Sludge & Corrosion productsare cleaned and dried for inspection

Cleaned and dried pits are re-coated by new crude oil

New oil coat = Resetting insulating condition

defect

New defect in oil coat =Nucleation of pitting

New defect : by COW, Water …..

(1) Under servicing condition

(2) Dock inspection

(3) Re-Start of service

(4) Nuclear of new pit

Sludge & Corrosion products

Oil coating

Cleaned Steel Surface = No oil coat

Oil coating ,Sludge & Corrosion productsare cleaned and dried for inspection

Cleaned and dried pits are re-coated by new crude oil

New oil coat = Resetting insulating condition

defect

New defect in oil coat =Nucleation of pitting

New defect : by COW, Water …..

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On board Results

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c).1 Max. Pit Depth of Conventional Steels Onboard Repair is Essential! (by Welding a/o Painting)

SRSR--242 Result242 Result

Conventional

Maxim

um P

it Dep

that

Dock

(mm)

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c).2 Applied area of Steel A in a VLCC#3 and #4 P,C,S COTs have been built without coating 2 years and 3 month after building2 years and 3 month after building

COW applied every voyage=Damages the protective oil coating↓

Severe condition for the corrosion

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c).3 Number of Pitting over 4mm Depth (Onboard result)

020406080

100120140160

Conventional Steel A

Aver

age P

it Cou

nts (O

ver 4

mm D

epth)

ZERO

No pits over 4mm depth

Developed Steel A: No need to repair

2.25yearsOnboard Test

Conventional Steel-AZERO

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7 7 7 20 4 270

200

400

600

800

1000

1200

1400

3P 3C 3S 4P 4C 4SCOT Position

Pits

Coun

t ove

r 2mm

Dep

th

c).4 Pitting Frequency of Steel-A OnboardOnly very few shallow pits (Over 2mm less than 4mm)

are observed!

No Pits over 4mm Depth

Pits

Coun

ts ov

er 2m

mDe

pth

COT Position

Conventional

Max. Pits Counts Over 4mm Depth

18

0

2

4

6

8

10

12

3P 3C 3S 4P 4C 4S

COT Position

Observed Max pit depth

mm/at 1st Dock

COT built by NS-GP1 without tar epxy painting

No need to repair

c).5 Max. Pit Depth of The Steel-A Only pits less than 4mm depth!

Maxim

um P

it Dep

th at

Dock

(m

m)

COT Position

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c).6 Appearance of typical pitConventional Steel and developed Steel-A

Pit on Steel-A(Small and Shallow)(Small and Shallow)

Pit on Conventional Steel(Large and Deep)

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b) Important Basis for Anti-corrosion steel for COT/bottom platesPit Growth Stops at a dock

Pit D

epth→

Dock

Conventional Steel

Anti-corrosion steel

Make Low

Ship Age→

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d) Benefit of Applying Steel-A

0

2

4

6

8

10

12

0 2.5 5 7.5 10 12.5 15Ship Age / years

Maxim

um P

it Dep

th / m

m

Pit less than 4mm

Pit Stops at Dock

Steel-A

No repair

Pits Over 4mmConventional Steel

Repair being Essentialat EVERY dock

Pit Stops at a dock New Finding by SR242

Pits Less than 4mm ＋

IACS Rule requires repair over 4mm depth pits

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e) Property of Steel-A

A typical chemical analysis （mass%)

With Least Micro-alloy ElementsSteel-A established high corrosion resistance

↓Same Physical Properties to Conventional Steel

C Si Mn P S Al Ti CeqNewly Developed 0.124 0.331

AH32 0.140 0.20 1.09 0.018 0.006 0.031 0.014 0.322IACS Standard ≦0.18 ≦0.5 0.9～1.6 ≦0.035 ≦0.035 ≧0.02 ≦0.02 ≦0.36

meets IACS Standard (including all ally elements)

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Specimen303K

Water bath

NaCl solution Including Sulfur

*Assuming that specimen iscorrespond to pit inside.

f) .1 Other Anti-corrosion Steel for Bottom Plates

Steel-B provides excellent corrosion resistance property for very high concentration of sulfur.

0

0.2

0.4

0.6

0.8

1

1.2

Ratio

of C

orro

sion

Rate

Steel-B

Conventional

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f).2 Other Anti-corrosion Steel for Bottom Plates

Temp. 40°CGas13%CO2-5%O2-0.01%SO2-0.2%H2S-bal.N2

Pitting corrosion and corrosion productsPitting corrosion and corrosion productswere reproduced by simulated test.were reproduced by simulated test.

gas outlet gas inlet

artificial sea water

specimenssludge

gas outlet gas inlet

artificial sea water

specimenssludge

pits

10mmAppearance of specimen after corrosion test

Corrosion rate after 2.5 years estimated fromsimulated test

00.20.40.60.8

11.2

Conventionalsteel

Ratio

of co

rrosio

n rate Bottom

1/51/5

SteelSteel--CC

Steel-C provides excellent corrosion resistance in simulated environment of cargo oil tank.

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g) Summary on Anti-Corrosion Steelsfor Bottom Plates

• Anti-corrosion steels (Steel-A.B and C) showed good corrosion resistance in laboratory simulated tests.

• Newly developed anti-corrosion Steel-A has been adopted to a VLCC/COTs without coating for 2years and 3 months.

• There was NO PIT over 4mm depth on steel-A onboard.She docked out with NO repair.

• The Validity of Steel A was conformed onboard. Potential Ability for Repair-Free was recognized based on “pit stops at a dock” and “Pit Depth less than 4mm”..

• With Least Micro-alloy Elements, Steel-A established high corrosion resistance.

↓Same physical properties to conventional steels.With Good Workability, the VLCC has been constructed.

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3.Anti-Corrosion Steel for Upper Deck Corrosion

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3.1 Corrosion of Upper Deck Plates

Inner Bottom

Upper Deck

COT Gas

H2S

Crude Oil

Sludge, Drain Water

Inner Bottom⇒ Pitting Corrosion

Cyclic Temp. ChangeUpper Deck⇒ General Corrosion

Bottom Plate⇒ Pitting Corrosion

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3.2 Corrosion test Results of Steel-CWet & dry cycle (50℃ 25℃)Simulated COT gas (13%CO2-5%O2-0.01%SO2-bal.N2-H2S 0.2%)

NaCl solution

gas outlet gas inlet

specimens

00.20.40.60.8

11.2

Conventionalsteel

Ratio

of co

rrosio

n rate

Upper deck

Corrosion rate after 2.5 years estimated from simulated test

Results of simulated corrosion test

1/41/4

SteelSteel--CC

Steel-C provides excellent corrosion resistance in simulated environment of cargo oil tank.

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・Based on the facts found by the SR242 investigation,Simulated test methods is developed.

・Developed Anti-Corrosion Steel for Upper Deck plateimproves corrosion resistance largely.

3.3 Summary on Anti-Corrosion Steel-Cfor Upper Deck

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4. Conclusion• Anti-corrosion steels are countermeasure against Oil

Tanker Corrosion.• Corrosion Tests for COT bottom and Upper deck plates

has been developed.• Validity of Anti-corrosion steels was confirmed based on

laboratory tests and actual vessel result.• Potential ability for repair free for whole ship life is

recognized.• Anti-corrosion steel provides sophisticated solution for the

Oil Tanker safety problem.

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~ Future Works ~2007/02 DE50

Proposal of Anti-Corrosion Steel Performance StandardOutline of the StandardSimulated test procedure

(Inner bottom, Upper deck)

2008/02 DE51

Decision of detailsAcceptance criteriaVerification

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Thank you