INTERTANKO UK Corrosion 2002 Cardiff, Wales October 24, 2002

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INTERTANKOUK Corrosion 2002 Cardiff, Wales
October 24, 2002

• CRUDE OIL CARGO TANK CORROSION

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Purpose of this paper

• Provide a brief background about
• Tanker structures and the cargo tank environment
• Tanker corrosion
• INTERTANKOs 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

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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 crack

• December 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?

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

• More inspections and more surveys.!?

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)
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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 ATHENSWalkway in ballast tank
using oversized longitudinal fitted with railing
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THENAMARIS ATHENSCoated cargo tank inner
bottom to prevent MIC corrosion
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THENAMARIS/ ATHENSCoating of tank head ullage
space
Dark area coated to prevent ullage space
corrosion
Note access platform with railing for inspection
coated
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THENAMARIS - ATHENSCARGO TANK HEAD INSPECTION
ACCESS PLATFORM
COATED CARGO TANK TOP (DARK AREA)
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VLCC cargo tank walkway
Walk way
Oversized longitudinals
Notice oversized longitudinals as access walkway
for inspection and the walk way platforms around
the web frames
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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