Corrosion-Resistant Steel For COT Of Crude Oil Tankers
Corrosion-Resistant Steelfor COT of Crude Oil TankersASEF 2007, Tokyo, JAPAN16th November, 2007Shin IMAIJapan Ship Technology Research Association1
Corrosion problems in COT of tankersCyclic Temp. ChangeWet & dry cycle (50 25 )Upper Deck General CorrosionInert GasUpper DeckO2H2OCO2H2SBottom Pitting CorrosionCrudeOilSludge, Drain WaterInner BottomSR-2422
How to overcome the problem?Apply Protective coating (epoxy paint)on steel ;Construct by corrosion resistant steel; orOther alternatives (future technologies)3
What is “Corrosion Resistant Steel”?Steel which has sufficient corrosion resistantperformance toProtect the structure of the top of the COTand/orPrevent leakage of oil from the bottom of theCOT.4
Facts of the corrosion problem in COTOutcome of SR242 Project (April 1999 March 2002)Intensive field investigations have been carried out fortechnical understanding on corrosion in COTUniversity & National LaboratoryOsaka UniversityTokyo Institute of TechnologyShip Research InstituteSHIP OWNERNippon Yusen KaisyaMitsui O.S.K., LinesNYK Logistics Technology InstituteThe JapaneseShipowners’ AssociationSTEEL MAKERNippon Steel Corp.Kobe SteelSumitomo Metal Corp.NKK Corp.Kawasaki Steel Corp.CLASSNippon Kaiji KyokaiABS PacificDet Norske VeritasSHIIPYARDSumitomo Heavy Ind.Mitsubishi Heavy Ind.Kawasaki Heavy Ind.Ishikawajima-Harima Heavy Ind.Mitsui Eng. & Shipbuilding Co.NKK Corp.Over 10 VLCCs with conventional steel were examined5
Key facts found by SR242 on Upper Deck CorrosionDaytimeSteelInert gas H2SProduct layerSulfurCondensatewaterRepeatSteelProduct layerSulfurInert gas H2S H2S gas exdists in high concentration Co-existence of O2 and CO2 with H2S Cyclic temperature change Wet and Dry cycle Upper deck corrosion is uniform corrosion Product layer is flaky and 60 wt.% of it is Elemental S Corrosion rate is not so high (Almost less than 0.1mm/y)SR-2426
Key facts found by SR242 (on Bottom Plate Corrosion)Oil-coating exists around pit SR-242 Result . and pitting starts at oil-coating defect7
Key facts found by SR242 (on Bottom Plate Corrosion)Pit Growth Stops at a dock(tank cleaning)Pit DepthPitting StopsNew Pitting startsat new location Dock InspectionSR-242Ship Age8
Change of pitting location -13S : Pits over 4mm at 1st inspection (repaired) : Pits less than 2mm at 1st inspection (NOT repaired)repaired : Pits over 4mm at 2nd inspection (repaired)Old pits( ) did not grow!New pits( ) appear at different points.SR-242 Result9
Change of pitting location -23C : Pits over 4mm at 1st inspection (repaired) : Pits less than 2mm at 1st inspection (NOT repaired)repaired : Pits over 4mm at 2nd inspection (repaired)Old pits( ) did not grow!New pits( ) appear at different points.SR-242 Result10
Generation of a Pitting(1) Under servicing conditionSludge & Corrosion productsBrine : NaCl 10wt.%(3) Re-Start of serviceCleaned and dried pits arere-coated by new crude oilOil coatingNew oil coating Resetting insulating condition(2) Dock cleaning for inspectionOil coating ,Sludge & Corrosion productsare cleaned and dried for inspectionCleaned Steel Surface No oil coat(4) Nuclear of new pitNew defect : by COW, Brine .Brine : NaCl 10wt.%defectNew defect in oil coating Nucleation of pittingCorrosion condition would be reset after Dock inspection Pitting growth stops at dock cleaningSR-242 Result11
Key facts found by SR242 (on Bottom Plate Corrosion)Strong Acid environmentActual VesselpH of PIT inside: 1.5 Unfavorable for MIC (SRB active pH : 6 9)SR-242 Result12
Development of Corrosion-Resistant Steel19981990 2000200220042006Shift to Double Hull Tanker1999 2002Panel SR242 Investigation(The Shipbuilding Research Association of Japan)Scientific Research & understandingof the corrosion phenomena(Over 10 VLCC s)Development ofCorrosion-Resistant Steeland Laboratory TestsBasis for Corrosion-Resistant SteelCorrosion test method2002 Field Test on actual Vessels2003 13
Evaluation of Corrosion-Resistant Steel14
Corrosion-Resistant Steel for Upper deck platesCorrosion test for upper -bal.N-bal.N22-H-H22SS0.3%)0.3%)gas outletDistilledDistilledwaterwater（36 ）（36 ）gas selvessel(50 (50 20 )20 )SpecimensSpecimens25mm 50mm 4mm25mm 50mm 4mmSurfaceSurfacepolicedpoliced::#600#60015
An example of on board test of upper deckGrinded（）Grinded（ ）Epoxy painted Silicon coatedConventionalsteelCorrosionresistantsteelWeld beadTest couponTest coupons were exposed in vapor spaceof COTs of 2 aframax tankers for 1 year16
Corrosion environment of upper deck (Labo vs field)Distribution of elementsFelayered elemental SEpoxy resinCorrosion productSteelrust (FeOOH)mixture of rust and elemental SCross sectional analysis of corrosion product formedon conventional steel after test in reproducedcorrosion environment in laboratory.concentrationhighO100μmSlowCorrosion product after laboratory test – Upp. DK α-FeOOHγ-FeOOHFe3O4Elemental SOthersCOT37801243Simulated test30382138Laboratory corrosion test reproduces corrosionphenomena at upper deck of actual COTs.17
0.07Conventional Steel0.060.05Curve fitY a1Xb11/20.04Curve fitY a2Xb20.030.02Corrosion-resistant Steel0.0100Corrosion loss after 25 yearsestimated from simulated test20 40 60 80 100 120Ratio of corrosion lossAverage corrosion loss (mm)An example of corrosion test result of upper deck1.00.80.61/40.40.20.0Conventional Corrosion-resistantSteelSteelTest duration (days)18
Corrosion test for inner bottom plateConditionSolutionNaCl10 mass%pH0.85AmountNoticeAdjust by HCl20cc/.cm2 or moreChange Every 24 to 48 hoursAir openGasTemperatureSizeSpecimen Surfacerepeat30 40mm x 50mm x t#600 emery papert: less than 4mmlFollow JIS G0591Test solutionn 3 or moreDuration77hours144hoursImmersionDipping specimenSpecimenFollow JIS G0591Beaker19
An example of corrosion test result of bottom plateRatio of Corrosion Rate1.210.80.60.40.20ConventionalCorrosionSteel Aresistantsteel20
An example of on board test of bottom plateVLCCFirst dock inspection was carried outat 2 year and 3 month after launchingCorrosion resistant steel without Painting5P4P3P2P1P5C4C3C2C1C5S4S3S2S1SFWDCorrosion resistant steel with TarEpoxy painting21
An example of on board test result of bottom plateConventional steelCorrosion Resistant SteelConventionalConventionalConventionalFrequent deep PitsNo Pit observed22
An example of on board test result of bottom plateConventional steel20mmCorrosion Resistant Steel20mm PitDepth: 7.2mm PitDepth: 2.8mm23
An example of on board test result of bottom plateCorrosion Resistant SteelNoWeldPitLinearoundWeld: NO pit marksNo pit has been observed also on conventional steel24
Evaluation of Corrosion-Resistant SteelSummaryBased on the findings of SR242, steelmanufactures have developed corrosionresistant steelTest methods have been established.The performance could be evaluated bylaboratory tests for upper deck andbottom plate, respectively.25
Discussion at IMOAt MSC81 in Dec 2006, twenty one European countries,IACS and NGOs jointly proposed a mandatory requirementof “protective coating” to COT of tankers.IACS/JWG has been developing Performance Standard forProtective Coating for COT of oil tankers, which will besubmitted to DE51 in 2008.Japan has proposed “corrosion-resistant steel” and itsperformance standard (PS) as an option for corrosionprevention.DE and its Correspondence Group (CG) are discussing theissue with a target completion year of 2009.26
Draft SOLAS Amendment Developed at the CG3 All cargo oil tanks of crude oil tankers shall be:.1 coated during the construction of the ship inaccordance with the Performance standardfor protective coatings for cargo oil tanks ofcrude oil tankers, adopted by the MaritimeSafety Committee by resolution MSC.(.) ,or.2 protected by alternative means of corrosionprotection, the effectiveness of which [shall beno less than is achieved by meeting therequirements under paragraph 3.1] isapproved in accordance with the appropriatePerformance standard adopted by the27Organization.
Main issues to be discussed at DE51:How can a new measure like “CorrosionResistant Steel” be evaluated to be “no lessthan is achieved by meeting the requirementsunder paragraph 3.1(coating)”?(i.e. Coating Corrosion resistant Steel)Should “Corrosion-Resistant Steel” be specifiedin SOLAS or treated as one of the “alternatives”?28
Coating vs Corrosion-Resistant SteelItemTargetInspectorAdditionalwork duringconstructionCoating15 years,- “GOOD” conditionCorrosion-Resistant Steel25 years,- diminution within allowance- no leakageQualified coatinginspector-Edge treatment-Surface treatment (blasting,cleaning, etc.)-Multiple coating application-Measurements of salts, Dryfilm thickness etc.-Repair of Defects-Inspection of coatingAdditionalconditionwork after-Repair by recoat, weld,constructionsteel renewalNoneNone(Less Maintenance andPossibility of no repair)29
Corrosion Loss (RISK)Coating vs Corrosion-Resistant SteelConventional SteelConventional SteelWith CoatingAllowanceCorrosion-Resistant Steel0Depending on condition of coatingShip Age (Years)30
A lot of benefits are expectedin Corrosion-Resistant SteelBUTNo one can define and the effectiveness ofcoating in COT .No one can evaluate the effectiveness ofcorrosion resistant steel by comparison withcoating .No one can conduct field test for evaluation ofnew measure unless the equivalency is proved .31
Corrosion prevention system is not only coating!IMO should pursue more general Goal Based Approach ,rather than a Prescriptive Approach(Coating: epoxy, 200 micro, Blast Sa2.5, Salt, edge etc. )The “GOAL” of the corrosion prevention should be to- Maintain ship structure- Prevent oil leakageThe options of “coating” , “corrosion resistant steel” or“others” should be left to the choice of shipwoners andshipbuilders taking into account their construction andmaintenance strategies.32
Draft SOLAS Amendment (Japan’s proposal to DE51)3All cargo oil tanks of crude oil tankersshall be protected against corrosion toensure that net scantlings required meetingstructural strength and watertight integrityare maintained throughout the specifieddesign life in accordance with thePerformance standard for corrosionprevention for cargo oil tanks of crude oiltankers,Consistent with GBS33
Concluding remarkIMO should not close the door for newtechnologies!First comes, first served.Better comes, equally served.34
Sumitomo Heavy Ind. Mitsubishi Heavy Ind. Kawasaki Heavy Ind. Ishikawajima-Harima Heavy Ind. Mitsui Eng. & Shipbuilding Co. NKK. Corp. STEEL MAKER. Nippon Steel Corp. Kobe Steel Sumitomo Metal Corp. NKK. Corp. Kawasaki Steel Corp. Outcome of SR242 Project (April 1999 March 2002) SR-
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