THE SOCIETYOF NAVAL ARCHITECTSAND MARINEENGINEERS601RtvOIIla Avenue,Suite400,JerseyCity,NewJersey0734)6USA

Paper presenti at t% MariTwS&u@Jrallns@3ion, Maintenanm,and hhitming Sym~iumSlwatti NationalHotBl,Arlingmn,Wginia, March l&19, 1W31

Inspection and Structural Maintenance of Chevron’sTanker FleetR.A. Ternus, Chevron Shipping Company, San Francisco, California

ABSTRACTThe condition of the

structthue~alh~~;g~: pa~ratni-c~ul.a+y

~nerall y the most imp~rta~parameter governing theeconomic life of a tanker. Atanker owner has considerableleeway in planning and carryout’ his prog-ram to maintainthis structure. He must, ofcourse, meet the minimumrequirements of aclassification society in orderto keep the ship ts certificatesin force. However, theclassification society onlysets standards for thecondition of the shi~ and doesnot dictate how thebe maintained.

If an ownersafely operate a20 years or longer

skip should

plans toship for

and at thesame time minimize niaintenancecosts over the life of theship, he must establish acomprehensive maintenanceprogram. “Chevron has’developed

‘ such a program which consistsof inspection and gaugingsbeyond what is required by theclassification societies, acomp”uter system to ..assist .inhandling and interpreting theresulting data, and” amaintenance program aimed atobtaining high quality repairsat a competitive price. Thisprogram has enabled us toeconomically achieve a highlevel of maintenance in our

./ tanker fleet.

INTRODUCTION

The popular press oftenrefers to a tanker’s life asbeing somewhere between 15years and 20 years--theimplication being that a tankerolder than this is about tofall apart and is a danger tothe environment. If this werethe case and it was impossibleto properly maintain tankerhulls for more than 20 years,it would apply equally well toother steel structures seningin a marine environment and the52-year old Golden Gate Bridgeshould have been replaced yearsago. The actual safe, economiclife of a tanker is determinedprirnarilyby the maintenance ofthe ballast tanks. A properlymaintained tanker, withparticular emphasis on theballast tanks, can be operatedsafely and economically wellbeyond 20 years.

Virtually every ship isclassed by a classificationsociety which signifies thatthe ship was designed and builtand is being maintained tocertain minimum standards ofthe classification society.However, this does not implythat the ship can beeconomically operated for anyminimum number of years or thatit is being maintained in themost economical mannerpossible.

This paper focuses on the

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maintenance of the structuralelements of tankers. Itbriefly reviews the role of theclassification societies, whichset the ndnimurn standards of amaintenance program; and thendescribes in some detailchevron$srnore extensive tankerhull maintenance program. Thisprogram includes frequent andextensive inspection andgaugings; a data-base system tofacilitate the” data handlingand an’alyses, and a maintenancepiograxa designed to accomplishhigh-quality repairs o.n atimely and e-conomic basis. ,

ROLE OF THE CLASSIFICATIONSOCIETIES

The rules of theclassification societies leavean owner a wide degree oflatitude,,in”maintaining a ship(Ref 1). The reason fog thiscan be found in the basicnature of these societies. Thefirst of “these societies wasestablished in the 18th centuryby insurance underwriters.They were founded to provide anindependent agency which wouldcertify, that ,a ship was inadequate condition to be anacceptable insurance risk.Over the years, the number ofsocieties has “proliferated =..The principle ones are ABS” (Themerican ‘Bureau.d Shipping),LloydIs Registry andDet NdrslceVeritas.

To carry out theirfunction, the classificationsocieties dev,eloprules (Ref 2)for the design, .const~ctionfand maintenance of ships andcertify that the ships whichtheyil’class”lsmeet these rules.Specifically, once engaged byan owner to classify a.Prospective ship, theclassification society reviews

the shipyard’s design to a’ssurethat it conforms to its rules. ,,___.Next, its suneyors inspect theship as it is being‘constructed, and, provided theconstruction also conforms toits rules, the classificationsociety issues certificates tothe ship at ‘the time it isdelivered to the owner. Thesecertificates are needed for theowrier to obtain insurancecoverage foi the ship and itscargo. “ Over the life of theship, the classificationsocietyls suneyor$ willperiodically inspect it. ‘Ifthe condition of the shipcontinues to satisfy the rules,the society renews the shiptscertificates. If the conditionof the ship has deterioratedbeyond the minimum acceptablelevel, the suneyor w’illadvisethe owner as to what repairsare requir&d’’and will inspectthe repairs once they arecompleted.

Itshotild be kept in mindthat the classification societyrequirements are minimumrequirements for building andmaintaining a,ship. The rulesare established by technicalcommittees which are composedprimarily ofrepresentatives ofthe ship owners, equipmentmanufacturers, shipyards, aswell as regulatory agencies.‘For example, the U.S. CoastGuard- is at iember of the ABSTechnical Committee. As aresult, ,the rules represent aco~promise ‘on the part of thevarious parties involved. TherU~eS do not address theexpected life of a ship ordictate an optimum maintenancephilosophy”but;r ather, specifyminimum cond~tions which mustbe met ifthe ship is to retainits certificates’. “\.._

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/..INSPECTION--THE KEY TO PROPERMAINTENANCE

Once a-ship is delivered,the inspection program beginsand continues for the life ofthe ship ,(Ref 3). The typicalclassification society’s hullinspection and maintenancecrite,ria can be summarized asfollows:

1.

2.

3*

4.

Surveys of’ thestructure arecompleted in five yearcycles called specialsurveys . Eachsuccessive specialsuney period hasprogressively morerigorous inspectioncriteria included inthe requirements (Figs1 & 2).

NDT (non destructivetesting) , i.e.,ultrasonic gauging, isrequired of variousstructural members ateach special suney tocheck the hull girderstrength. With eachsucceeding specialsurvey, the number ofcircumferential bandsgauged increases toencompass specificareas such as ballasttanks.

Close up inspectionsof selected tanks areincreasingly requiredas the ship ages.

Classificationsocieties set maximumwastage limits forvarious parts of thehull structure andrequire that theselimits be met at thetime of the inspection

for the certificatesto be renewed.

Most ship owners carry outthe inspection and gaugingrequired by the classificationsociety during the vessel’sshipyard overhaul.

CHEVRON~S HULL INSPECTIONPROGRAM

Chevronls goal is toensure that it knows thecondition of the hull structureat all times (Ref 1). Toaccomplish this, we expand uponthe classification societyrequirements as follows:

1. Visual inspection is“made and wherewarranted gaugingsare taken in areas notrequired by specialsuney. This allowsidentification ofcorrosion wherever itmay occur and therecognition ofdeveloping trends.

2. Between requiredinspections, tanks arecleaned and inspectedon ballast voyages.All structural membersare inspected forcorrosion, stresscracks, buckling andnecking. Rubber raftsare used in tankspartially filled withwater so that a closeup inspection can bemade of the under deckarea. If anabnormality is found,the inspectionactivity is increasedon sister ships todetermine if a similarsituatioh exists.

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,3.

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4.

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Gaugings for specialsuneys are taken wellbefore shipyardperiods to facilitateplanning for overhauls

In house wastage1imits have beenestablished which aremore consemative thanthose of t heclassificationsocieties to ensurethat the wastagebetween su?xey periodsdoes not significantlyexceed theclassificationsociety’s limits.

The, same gaugingcontractors are usedrepetitively to ensurethey are familiar withthe ships andChevronrs requirementsand standards.

Tank bottom pitting isanother type of corrosion foundin tankers. It is particularlya problem on older non-segregated ballast tankers. Onthe. Chevron tankers of, thisvintage the bottoms of theswing tanks, which are usedalternately for cargo andballast,, were coated at thetimeof construction. In thesetanks a pinhole size coatingfailure exposes the underlyingmetal. The metal acts as ananode and slowly wastes. Theresult is an ‘inverted conical,pit. .While these pits do nottypically threaten the shiplsstructural strength, they dopose a threat of causing oilpollution. Therefore, weexpend considerable effort to,find these pits and repair thembefore they hole through theplatting. ,

As part of th,epreparationfor a shipyard overhaul, alltanks must be cleaned and theresidue removed. In additionwe hand mop the coated tankbqttonks and inspect for pits.Each pit found-is measured andmarked w-ith spray paint. Adiamond is painted around thedeeper pits . During theoverhaul the shallower pits arerepaired by filling with anepoxy pit filler. The deeppits are repaired by weldingand recoated.

“DATA HANDLING AND ANALYSIS

The procedures forcollecting,” handling and

interpreting; gauging and

inspection data have remainedlittle changed over the years.An ultrasonic qauging t~am oftwo to four men would board thevessel, take gaugings in thetanks, record them in anotebook, and then at the endof the”dayl transpose them to adraft report. It generallytakes” two to three weeks tocomplete such a survey.After leaving the ship, the

team would ‘return to theiroffice and again transpose thedata, c“otiine it with drawingsand photographs that had beentaken and prepare a final

report which would be sent toClievron. One of our navalarchitects would sort throughthe data and compare the

gauging re~d$ngs with the

original “~hicknesses and

wastage allowances. He or she

would then decide what steelshould be replaced and whatshould be cpa~ed, and manuallyprepare the periodic overhaulspecifications ,and drawings.

Over the years; a.libraryconsisting “of - inspectionreports and.kepair’ records for .....

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each vessel in. the fleet hasbeen accumulated. This libraryprovides voluminous amounts ofinformation which could,be usedto evaluate trends.in corrosiondevelopment= However; the timerequired .to sort through thedata and analyze it is adeterrent to using it for thispurpose.

Several years. ago, Chevrondecided to develop a.computersystem which would s“implifytherecording and handl”ing of thegauging” and inspection data.Together with Ocean Systems, asoftware .developrnent companylocated in Houston, Texas, wedeveloped a PC-based computersystem called CATSIR (ComputerAided Tanker StructureInspection and Repair) whichcombines a data base programand -AUTOCAD, a computerizeddrafting program. Inspectioninformation and gauging dataare entered into the CATSIRdatabase, by the gauging teampersonnel while they are on theship. The hull structuredrawings, together. with thesteel grade.. and originalthickness for each element ofthe structure., are stored inthe AUTOCAD program.

The naval architect who isinterpreting the gauging dataand deciding on the maintenancerequired can display thestructural drawing for any partof the s,hiptstank structure onthe computer screen (Fig 3).Annotated comments with thedisplay contain the generalinspection information. Thegauging data itself isannotated at the appropriatelocation on the drawing(Fig 4).

If the naval architect decidescoating needs to be replaced in

a certain area,the area with aprogram will

he can outlinecursor and thecalculate the

number of square meters ofcoating required.Alternatively if he decidesthat part of the structureshould be renewed, the computerwill calculate the number ofpounds of steel required (Fig5). The data base is thenupdated to include the requiredrepairs.

CATSIR has the followingadvantages:

1. It improves theproductivity of thegauging team byeliminating the draftreport and simplifyingthe final report. Thefinal report consistsof a floppy diskcontaining the gauginginformation and thecomments regarding thevessel inspection.

2. It improves repairplanning productivityby eliminating manualwriting of the steelrepair specificationand by automaticallycalculating steelquantities and coatingareas. It alsoeliminates manualdrafting of repairdrawings and providesthe capability toquickly update repairspecifications anddrawings in the field.

3. It enhances theefficiency and qualityof the inspection andrepair. Theinspection team andthe repair team canboth communicate with

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4.

the home office navala rch i t e ct ,.transmitting copies oft“h e informationconta”in”ed thefl”oppy dis~ vias at e 1 1 i t e’communications. Navalarchitects in the .horneoffi”ce can thenpartiei.pate. indecisions to modifythe inspection programor to change therepair specification.

CATSIR provides al’one-stopll data bankfor all of the tankerstructural maintenancedata. The analyses oftrends is facilitatedby sorting data in thedata. base to collectand display’ gaugingdata, “which has beenobtained over a numberof years, from thesame “location.

CARRylNG ouT THE REPAIRs

The final element in themaintenance program is the

repaik activity itself.

Chevron’Is primary objective isto protect the crew, the ship,the cargo, and the environmentat all times. Our goal is tohave zero, injuries and zero=p”ills. of “0$1 into the ocean.Within”this constraint, we makeour, maintenance decisions onth~”basis ofmjnimizing the netpresent ‘cost of the total

maintenance expenditures overthe expected remaining life ofthe ship. ““Th”is often meansthat our maintenanceexpenditures are out of stepwith those of the rest of theindustry. For example, in the,early to mid-1980s when theshipping industry was going

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through a severe recession,most ship, owners restricted {,,7.,

t~eir maintenance expendituresto the absolute minimum.Throughout that time pe’riod,’w”econtinued to base ourmaintenance decisions” onminimizing t~e total netpresent cost of anticipatedfuture expenditures. Thismeant that we were spendingseveral hundred thou=hnddollars per ship for coatingand steel workwh.en others werespending merely tens ofthousands of dollars or evenless per ship for theserepairs. Now that the shippingindustry” is profitable again,Inost owners would like tocontinue to run their existingships until, they ‘are 20-30years old (Ref 4). However,because they deferredmaintenance in the early to mid80s, many are now having tospend “five to ten milliondollars per ship on st~el and ‘--coating work “to extend thelives of their ships. On theother hand, Chevron~sexpenditures on steel andcoating repairs for lifeextension of similar ships area million dolla~s or less pership.

The ‘ best inspectionprogram and preparation for an‘overhaulwillbe negated if thethey ‘are not followed byquality repa$rs.” HistoricallyChevron along with most of theindust~ has operated on acompe~itive’ ~.id “approach inwhich the overhaul is awarded,tothe shipyard submitting thelowest bid adjusted forpositioning costs. The bidswere generdlly based upon apartial description of the workrequired. The overhaul wasthen carried out on a quas”i- ..‘adversarial basis in which we

attempted to minimize the coststo complete the work and theshipyard attempted to maximizeits profit.

To improve the quality ofthe repair work upon itsvessels, Chevron has enteredinto partnering relationshipswith three shipyards: JurongShipyard in Singapore; LisnaveShipyard in Lisbon, Portugal;and West State Incorporated inPortland, Oregon. Eachshipyard and Chevron arecommitted to producing thehighest quality work atcompetitive costs througheffective use of planning andnew technology.

Since better than 50% ofthe overhauls are conducted byJurong, Chevron has stationedseveral of its personnel in theJurong Shipyard. Theshipyards, in return, havededicated’ specific individualsto the overhaul of the Chevronships.

Each of the shipyards hasthe CATSIR program so thatinformation regarding the steeland coating work i.s submittedvia computer disk. Theshipyards can use the CATSIRprogramto produce drawings forthe repair shops indicatingwhere steel is to be renewedand coating replaced. Thisallows the yard to plan thework before the ship arrives soas to minimize interferencebetween crafts.

To further improve thequality of the overhaul and theproductivity of all involved,Chevron and the three shipyardsare jointly developing a PCbased specification generationprogram called SPEC GEN. Eachjob normally conducted by the

shipyard during an overhaul isdescribed in the programsdatabase. The data base issubdivided by class of ship sothat nameplate data and drawingreferences can be included.Agreed-to pricing informationis included so that theshipyards commercial sectioncan use the program to developthe final invoice. Thecommercial section of ashipyard has access to only itspricing data and the productionshops only have access to thetechnical data thus preseningconfidentiality of thecommercial data.

In conclusion, it can besaid that while theclassification society rulesand requirements may beadequate to ensure that a shipis a reasonable insurance risk,they cannot be used as a guidefor a maintenance program whichwill ensure a ship can beoperated for an extended numberof years at a reasonable cost.This objective can only be metby: 1) carrying out a programof frequent, thoroughinspection and handlinginspection and gauging data ina manner that facilitates gooddecisions; and 2) conducting amaintenance and repair programwhich is not side tracked byfluctuations in the chartermarket, butt rather, is aimedtoward minimizing the netpresent value of maintenancecosts over the life of theship. Finally, a cooperativeprogram with the repair yardwhich is aimed at producinghigh quality repairs ‘essential to obtaining t::desired results.

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References:

1. R. A. Ternus, Royal Aeronautical Societyls Safety at Sea andin the Air - Taking Stock Together Symposium,‘lInspectionand Maintenance of the Chevron TankerFleet,” November 1990.

2. llRulesfor Building and Classing Steel Vessels,” AmericanBureau of Shipping, 1990.

3. ‘!GuidanceManual for the Inspection and Condition Assessmentof Tanker Stkuctures,ll International Chamberof Shipping and Oil Companies InternationalMarine Forum, 1986.

4. Iloil Tanker Design and Pollution Prevention,tt International,.Chamber of Shipping - Oil CompaniesInternational Marine” Forum -.Interna$io,nalAssociation of Independent Tanker Owners,.May1990.

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DISCUSSION

R.A. Ternus

I’d like to make some additional comments concerningdouble hull tankers. We pay considerable attentionto thedesign of theseshipsto makesuretheyareinspctable andmaintdnable, We have hem operating our five doublehull U.S. fIagged tankers for 15 years, currently havecontracts for two 130,000 ton double hull crude carriersand are about to sign contracts for two more. We’respendinga considerable amountof timeworking with theshipyarddesigning theballast tanksof thesenew tankersso thatthey’reaccessible andcattbepttrged. Forexample,instead of a two meter double bollom, we’ve s@l%xl a3.1 meter double bottom; we are applying a two coatepoxy coating system. The top coat in the &uble bottomarea is a bleached coal-tar epoxy, so thatcoating break-downs will h r@y eviden~ This is going to be verycritical,

.-No coating manufacturerhas a system, thatwe’ve kenable to find, thatwill last 20-25 years. The blasting andrecoating of these tanksis extremely expensive, If theseshipsaren’tdesigned so thatsomeone can easily get in anddo the work, it’s going to be prohibitively expensive,

Thisbringsme to theconceptofshort-livedships.You’veheardtodayaboutshort-livedshipskauseoftheirhigh=tensile stcsl and minimum scantlings. I see this as aproblem created yesterdaythatisbeingaddressedtoday.Theproblem for tomormw thatis not king addressd bymost shipyardstoday is the design of double hull spacesso thatthey can be maintained.

LCDR Paul Brinkhurst

I think the systemyou’ve described looks very interesting.I’d be interested to how though whether Chevron islooking atwaysofimprovingultrasonicthicknessgaug-ingtechniques, as the system is only as gml as the datayou’ve got in i~ Do you haveNDE systemsinplaceforarea mapping the thicknessof thesidesof yourtankers,forexample, or do you still usepointsampling techniques?

R.A. Ternus

We use point wmpling techniques and follow the proce-dures outlined in the gui&lines published by the TankerSh-uctureCooperative Forum. Thatk, we gaugeanumberof points in an ar~ and then record the readings andlocation so thatwhen we go back next time we can takegaugings at the same Iwation.

Walter Maclean

As a professor at the Merchant Marine Academy I rwd alot of sea projects from midshipmen that go to sea in awide variety of ships, including a sizable numkr oftankers.I mustsay, in deference to whatyou’ve Adhere,I understandwhy I’m pleased with thosemidshipmenthat

goonlmrd ,@e Chevron tankerstwause, quite frankly,they Wrn to be much Wtei run thanothers thatthey goaboard. I’m quiteappalled at the stateof maintenanceon ““’some of thesetankersthatthey send back inform~on onas part of their sea Projtits. I’m very concerned about

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them gettingbad idas out of thiso@rational e~encewhich we try to dissuade them from and wluch pre-sumably they will carry out of the school and into the-indus~.

The work thatyou’ve talkedabouthere seems tome to bemost forward looking and quite cost effective I’m sureaswell as technically plausible. Are you or do you plan to-tihmyoftiohw*ao-m ho*bqto bring thislevel of tec~logy to them? It-s to methat we badIy need to bring up the state-of-them in anatihtofti*ti~ timouttimmd Itiwktyou are doing is carunendable, I’d like your cdermHowin theworld can wemovethestate-of-theartforwardwith the others as well?

R.A. Ternus

We work primarily through the Tanker StructureCqerative Forum. We have sharedwhatwe do and ourexperience withtheotherForum membersandwe’ve beendkdy i.llVOhCdinpIqMriIIgthethidanCehhU~ andthecurrentupdate. We’ve also been active in advising theCoast Guardon theproblems thatwe m with the doublehull tartkersin the hops that these problems will be ~addressedin theirupcoming ndemaking.

It’s unfommate}but thestatelaws thathoId both thecargoowner andtheshipowner liable withoutlimit for oil spillsmay lx what is going to cleanup the indusby, It’s goingto k prohibitively ex~nsive to have accidents. I don’tthinkmany cargo owners yet realize what theirexposureis, This is particularlytruefor thosethatarein thetradingbusiness who aren’t producing the oil, aren’t refining it,but just buying a cargo and selling it to somebody else.When a couple of these tradersget burned with seriousaccidents, the sub-standardtankerowners will be forcedto improve or go out of business.

Dag Kavlie

Iwouldliketoaskyouaboutyourexperiencewithrespecttostrucmmldetailsof high tensilestd. Have you foundit necessary to inqmse a stricter standardthan what theshipyardswould do according to the classillcation socie-ties? That’s one quesdow the sxon~ haveyou found thataccurding to the different routes that your tankers aresailing thatyou have a different experience in failures instructuraldetails because fatigue loading obviously isdifferent? Do you have any special practice for sometraderoutes thatyou have to watch especially carefully?

—

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DISCUSSION

R.A. Ternus.— Inregard to the fust partofthequestion,wehittheuse-\ ofhigh-tensilesteekwe don’tallowtheyardstouse

anythinghigher thanH-32 and even therewe limit whereit’s used - we specify mild steel in certainareas. We alsodo extensive finite element analysis mode-fig of thedetailsonournewships.We decidedtodesignthedetailsforafatiguelifeof40years,figuringthatifwedesignfor40years,weshouldget20yearsallowingfortheactualconstructionpracticesintheyard.

As to the second part of the question, we have not kenable to find any comelation between structuraldetailfatigue fdltuc and trade patternson our ships, On theotherhand,we have found acceleratedballasttankcoatingbreakdown and corrosion on tankers that are primarilyu=d in shorthaul tradescarrying heatedcargoes.

Mo Husain

A couple of shortquestions. The five double hull tankersyou have, are they @uct carriersor cru& oil carriers?Secondly, you ordered two more ships, are they actuallyordered or are you exercising an option to build doublehull and are they to be crude oil carriersor oil carriers?

R.A. Ternus

We are cmently operating two crude oil carriers, twoproduct carriersand one is a swing ship thatalternatesintrades. We have ordered two 130,000 ton crude carriersandwe expect to order two more sometime before theendof April.

/ -..,

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