INTERTANKOUK Corrosion 2002 Cardiff 22-24 October 2002 1 INTERTANKO UK Corrosion 2002 – Cardiff,...

INTERTANKO UK Corrosion 2002 Cardiff 22-24 October 2002

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INTERTANKO

UK Corrosion 2002 – Cardiff, Wales October 24, 2002

CRUDE OIL CARGO TANK CORROSION


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Purpose of this paperProvide a brief background about:

• Tanker structures and the cargo tank environment

• Tanker corrosion

• INTERTANKO’s Corrosion conference 1998 - Update since 1998

• Conclusions – way ahead – coating – access – class rule harmonization –


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INTERTANKO

INTERTANKO• The International Association of Independent

Tanker Owners.• INTERTANKO membership represents about

2000 tankers.• Chemical, Product and Crude Oil tankers.• Offices in Oslo, London, Washington D.C and

Singapore.• Regional Panels in Americas, the Far East

and Greece.


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INTERTANKO

Examples of INTERTANKO activities:• Cooperates with other organisations like

OCIMF – ICS – WWF – IACS and numerous others.

• Active in IMO. • Providing factual information.• Commenting and working group

participation.• Active with US Coast Guard.• Commenting on proposed rulemaking.


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INTERTANKO

• Keep members advised of political developments and proposed regulatory changes and other issues of general interest – like corrosion.

• Tanker events – every 6th month

• Membership criteria – quality

• Visit Intertanko home page on:

www.intertanko.com

http://www.intertanko.com/


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VLCC - Typical midship section

• Midship section • Approximate Dimensions (in meter):

• Length over all: 332 • Length B. P.: 320• Breadth moulded: 58• Depth moulded: 31• Design draft: 20.8• Scantling draft: 22.0


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VLCC – Double hull • Double hull tanker in the

building dock• Side ballast tank width

abt. 2 – 4 meter.• Bottom ballast tank height

abt. 2 - 3 meter.• Height of centre cargo

tank abt. 29 meter• Length of centre cargo

tank abt. 50 meter


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THENAMARIS -Suez max tanker

Notice the red coat on cargo tank inner bottom


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Corrosion mechanisms at work


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Volatile/stable crude oil


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Day/Night


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Pitting in the tank bottom plate(MIC)


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Pitting as discovered on new double hull tankers (MIC)


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ONE COAT ON TANK BOTTOM

COATING APPLIED ON PITTING CORROSION

IN PERFECT CONDITION 5 YEARS LATER

NO FURTHER PROBLEM EXPECTED


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RUST FLAKE FROM ABOVE – UNDER DECK CORROSION!

RUST FLAKE COMMONLY FOUND ON CARGO TANK BOTTOM

SOURCE; UNDER DECK CORROSION


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Sulphur crystals

FULLY FORMED SULPHUR CRYSTALS FOUND ON THE RUST FLAKES FROM THE UNDER DECK AREA OF THE CARGO TANKS


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ERIKA - December 1999

MAIN INGREDIENTS – OLD TANKER – CORROSION –BAD WEATHER – DISTRESS -SINKING – POLLUTION – ALL HANDS SAVED

SIGNIFICANT CONSEQUENCES OF ONE TANKER ACCIDENT ACROSS THE INDUSTRY;

•TWO TRENCHES OF MARITIME LEGISLATION KNOWN AS ;

•ERIKA I AND ERIKA II


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Castor – main deck crackDecember 2000; Part of crack

•Mediterranean – bad weather

•Fully loaded tanker – Castor developed a 22 meter long crack in the main deck

•Coastal states refuse port of refuge

•Castor survives – no cargo spilled – minor regulatory effect

•Main ingredients – corrosion – bad weather – inadequate surveys and maintenance


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So, what can be done?• More inspections and

more surveys….!?

• The answer is a clear NO! There is more than adequate survey regulations in force. If the present survey regimes are followed, that is!

CARRY OUT SURVEYS AND REPAIRS AS INTENDED!

NOTHING MORE – NOTHING LESS!


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What else can be done?

• Identify risk areas at the design stage

• Arrange access at newbuilding stage

• Apply suitable coating to areas of concern like all cargo tank tops and inner bottoms

• Produce inspection manual

• THESE COUNTERMEASURES MUST BE COMPULSORY MEASURES – EXEMPT FROM COMMERCIAL PRESSURE!


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Stress analysis


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AREAS VULNERABLE TO CORROSION

These are the areas in a tanker that are likely to suffer corrosion during its service life.

Well known!

But no permanent access.


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No access

• Arrows indicate where access is necessary for meaningful close up inspection.

• Notice no access arrangement

• Tank inner bottom not coated


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Practical logistical problems!

100% survey of a VLCC would require:

Height to climb 11 km

Area to survey 300 000 m2

Length of weld 1 200 km

Length longitudinals 58 km

Bottom area 10 700 m2

1,0 % pitting 85 000 pits


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Wing cargo tank on a small single hull VLCC (Source DNV)

• Note the surveyor in the tank bottom

• Volume of tank abt. 25.000 cubic meter

•Notice no access – no railings on stringers


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Probability of crack detection (source: DNV)

Probability of detection of cracks in ship hulls (Visual inspection)

0,01

0,1

1

10

100

0,1 1 10 100

Crack Size [cm]

Pro

bab

ilit

y o

f D

etec

tio

n,

%PROBABILITY OF DETECTION OF CRACKS


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Cargo tank top/bottom coating


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MEASURING METHOD

Hull plate thickness can be measured with the ship afloat.

A vehicle with special instrumentation will crawl along the bottom


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THICKNESS MEASUREMENT SHIPS BOTTOM PLATING

THE COLOR DIAGRAM SHOWS THE IN-WATER BOTTOM PLATING THICKNESS MEASUREMENT RESULT.

THE RED AREA NEEDS ATTENTION.

THE YELLOW NEEDS WATCHING.


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Building blocksBLOCK SIZE IS IMPORTANT TO REDUCE THE AMOUNT OF PAINT REPAIRS – WHEN THE BALLAST CARGO TANKS ARE COATED AT THE BLOCK STAGE.

BLOCK WELDS - EXTERNAL


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THENAMARIS - New Suez max tanker during construction 2000

LAST SECTION OF MAINDECK WILL CLOSE THE DECK

NOTICE THE BULKHEAD PLATFORM


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THENAMARIS – ATHENSMEANS OF ACCESS

WALKWAY FOR INSPECTION IN BALLAST TANK


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THENAMARIS – ATHENS

Walkway in ballast tank using oversized longitudinal fitted with railing


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THENAMARIS – ATHENS

Coated cargo tank inner bottom to prevent MIC corrosion


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THENAMARIS/ ATHENS

Coating of tank head – ullage space

Note access platform with railing for inspection

coated

Dark area – coated to prevent ullage space corrosion


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THENAMARIS - ATHENS

CARGO TANK HEAD INSPECTION ACCESS PLATFORM

COATEDCARGO TANK TOP (DARK AREA)


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VLCC cargo tank walkway

Notice oversized longitudinals as access walkway for inspection and the walk way platforms around the web frames

Oversized longitudinals

Walk way


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CONCLUSIONS (1/5)• CORROSION CAN BE DUBBED MANY NAMES – BUT

NAME CHANGE IS NO SUBSTITUTE FOR INSPECTION, DISCOVERY AND REPAIRS.

• CORROSION RISK CAN BE PREDICTED, LOCATION IDENTIFIED AT DESIGN STAGE, PERMANENT ACCESS ARRANGED FOR MONITORING IN SERVICE.

• CORROSION, CRACKS AND BUCKLING CAN BE DISCOVERED – ACCESS FOR CLOSE-UP INSPECTION IS NEEDED.


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CONCLUSION (2/5)• MODIFY LONGITUDINALS ON NEW SHIPS TO BE

USED AS ACCESS PLATFORMS.

• OWNERS MUST DEMAND THAT – CLASS MAKE PERMANENT ACCESS REQUIREMENT COMPULSORY AND HARMONIZED FOR ALL CLASS SOCIETIES.

• COATING MUST BE APPLIED TO CARGO TANK TOP & INNER BOTTOM AS COMPULSORY IACS COUNTERMEASURE AGAINST CORROSION.


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CONCLUSION (3/5)

• NEGATIVE TOLERANCE ON STEEL PLATE THICKNESS MUST STOP – POSITIVE TOLERANCE ONLY ACCEPTABLE.

• SHIPBUILDERS MUST EXTEND HULL STRUCTURE AND COATING GUARANTEE FROM ONE TO FIVE CALENDAR YEARS TO MATCH THE FIRST SPECIAL SURVEY.

• GUARANTEE LENGTH IS A SAFETY MATTER – NOT A COMMERCIAL ISSUE.


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CONCLUSIONS (4/5)

• SHIP REPAIRERS MUST REPAIR SHIPS IN A RESPONSIBLE AND PROFESSIONAL MANNER – SHIP REPAIRERS SHOULD BE HELD LIABLE FOR INADEQUATE REPAIRS.

• OWNERS, CLASS AND THE INDUSTRY HAVE COMMON INTEREST IN NEVER AGAIN SEEING A TANKER OR ANY SHIP GOING DOWN AND SPILL HER CARGO BECAUSE OF CORROSION AND LESS THAN SATISFACTORY REPAIRS.


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CONCLUSIONS (5/5)

• ALL CLASS SOCIETIES’ GOVERNING BODIES HAVE SIGNIFICANT NUMBERS OF SENIOR EXECUTIVES FROM SHIP OWNING, SHIP OPERATING INTERESTS.

• THESE SENIOR EXECUTIVES HAVE A PARTICULAR DUTY TO TAKE THE LEAD, BE PROACTIVE AND ENSURE CLASS/IACS SPEED UP THE PROCESS OF;

– UNIFORM SCANTLING REQUIREMENTS– UNIFORM FATIGUE CALCULATIONS– GENERAL HARMONISATION OF CLASS RULES– INSPECTION ACCESS AND COATING FOR CARGO TANKS

INTERTANKOUK Corrosion 2002 Cardiff 22-24 October 2002 1 INTERTANKO UK Corrosion 2002 – Cardiff,...

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