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INTERTANKO UK Corrosion 2002 – Cardiff, Wales October 24, 2002. CRUDE OIL CARGO TANK CORROSION. Purpose of this paper. Provide a brief background about: Tanker structures and the cargo tank environment Tanker corrosion INTERTANKO’s Corrosion conference 1998 - Update since 1998
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INTERTANKOUK Corrosion 2002 – Cardiff, Wales October 24, 2002 CRUDE OIL CARGO TANK CORROSION UK Corrosion 2002 Cardiff 22-24 October 2002
Purpose of this paper Provide 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 – UK Corrosion 2002 Cardiff 22-24 October 2002
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. UK Corrosion 2002 Cardiff 22-24 October 2002
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. UK Corrosion 2002 Cardiff 22-24 October 2002
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 UK Corrosion 2002 Cardiff 22-24 October 2002
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 VLCC - Typical midship section UK Corrosion 2002 Cardiff 22-24 October 2002
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 UK Corrosion 2002 Cardiff 22-24 October 2002
THENAMARIS -Suez max tanker Notice the red coat on cargo tank inner bottom UK Corrosion 2002 Cardiff 22-24 October 2002
Corrosion mechanisms at work UK Corrosion 2002 Cardiff 22-24 October 2002
Volatile/stable crude oil UK Corrosion 2002 Cardiff 22-24 October 2002
Day/Night UK Corrosion 2002 Cardiff 22-24 October 2002
Pitting in the tank bottom plate(MIC) UK Corrosion 2002 Cardiff 22-24 October 2002
Pitting as discovered on new double hull tankers (MIC) UK Corrosion 2002 Cardiff 22-24 October 2002
ONE COAT ON TANK BOTTOM COATING APPLIED ON PITTING CORROSION IN PERFECT CONDITION 5 YEARS LATER NO FURTHER PROBLEM EXPECTED UK Corrosion 2002 Cardiff 22-24 October 2002
RUST FLAKE FROM ABOVE – UNDER DECK CORROSION! RUST FLAKE COMMONLY FOUND ON CARGO TANK BOTTOM SOURCE; UNDER DECK CORROSION UK Corrosion 2002 Cardiff 22-24 October 2002
Sulphur crystals FULLY FORMED SULPHUR CRYSTALS FOUND ON THE RUST FLAKES FROM THE UNDER DECK AREA OF THE CARGO TANKS UK Corrosion 2002 Cardiff 22-24 October 2002
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 UK Corrosion 2002 Cardiff 22-24 October 2002
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 UK Corrosion 2002 Cardiff 22-24 October 2002
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! So, what can be done? CARRY OUT SURVEYS AND REPAIRS AS INTENDED! NOTHING MORE – NOTHING LESS! UK Corrosion 2002 Cardiff 22-24 October 2002
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! UK Corrosion 2002 Cardiff 22-24 October 2002
Stress analysis UK Corrosion 2002 Cardiff 22-24 October 2002
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. UK Corrosion 2002 Cardiff 22-24 October 2002
No access • Arrows indicate where access is necessary for meaningful close up inspection. • Notice no access arrangement • Tank inner bottom not coated UK Corrosion 2002 Cardiff 22-24 October 2002
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 UK Corrosion 2002 Cardiff 22-24 October 2002
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 UK Corrosion 2002 Cardiff 22-24 October 2002
Probability of crack detection (source: DNV) UK Corrosion 2002 Cardiff 22-24 October 2002
Cargo tank top/bottom coating UK Corrosion 2002 Cardiff 22-24 October 2002
MEASURING METHOD Hull plate thickness can be measured with the ship afloat. A vehicle with special instrumentation will crawl along the bottom UK Corrosion 2002 Cardiff 22-24 October 2002
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. UK Corrosion 2002 Cardiff 22-24 October 2002
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 UK Corrosion 2002 Cardiff 22-24 October 2002
THENAMARIS - New Suez max tanker during construction 2000 LAST SECTION OF MAINDECK WILL CLOSE THE DECK NOTICE THE BULKHEAD PLATFORM UK Corrosion 2002 Cardiff 22-24 October 2002
THENAMARIS – ATHENSMEANS OF ACCESS WALKWAY FOR INSPECTION IN BALLAST TANK UK Corrosion 2002 Cardiff 22-24 October 2002
THENAMARIS – ATHENSWalkway in ballast tank using oversized longitudinal fitted with railing UK Corrosion 2002 Cardiff 22-24 October 2002
THENAMARIS – ATHENSCoated cargo tank inner bottom to prevent MIC corrosion UK Corrosion 2002 Cardiff 22-24 October 2002
THENAMARIS/ ATHENSCoating of tank head – ullage space Dark area – coated to prevent ullage space corrosion Note access platform with railing for inspection coated UK Corrosion 2002 Cardiff 22-24 October 2002
THENAMARIS - ATHENSCARGO TANK HEAD INSPECTION ACCESS PLATFORM COATED CARGO TANK TOP (DARK AREA) UK Corrosion 2002 Cardiff 22-24 October 2002
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 UK Corrosion 2002 Cardiff 22-24 October 2002
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. UK Corrosion 2002 Cardiff 22-24 October 2002
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. UK Corrosion 2002 Cardiff 22-24 October 2002
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. UK Corrosion 2002 Cardiff 22-24 October 2002
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. UK Corrosion 2002 Cardiff 22-24 October 2002
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 UK Corrosion 2002 Cardiff 22-24 October 2002