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CORROSION CASE STUDYSINKING OF THE ERIKA

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Scheme of Presentation

• Background of the Disaster• Introduction • Potential root causes of Catastrophe• Possible Failure mechanisms• Possible remedies• Conclusion• References

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Background

• Erika was one of a batch of eight sister ships built in Japan 1974-1976

• The tanker was a 19,666 gross tonnage conventional steel single hull oil tanker

• Despite having 10% less steel than many other tankers of similar size, Erika was very popular amongst shipping companies because of its relative inexpensiveness

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Background

• On December 8, 1999, she sailed out of with a heavy cargo of around 20,000 tons of fuel oil

• On 12 December 1999, in severe weather, the Oil tanker Erika broke in two 70 kilometers from the coast of Brittany, France

• It is considered the greatest environmental disaster to ever hit the country

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Background

• Thousands of tons of oil were spilled into the sea, killing marine life and polluting shores around Brittany, France.

• It is considered the greatest environmental disaster to ever hit the country

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Introduction

• According to the panel of experts appointed by the Dunkirk Commercial Court and the report of the subsequent judicial inquiry, the cause was serious corrosion of the internal structures of the vessel.

• This conclusion was reiterated in the decision of Criminal Court in Paris.

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• Corrosion of cargo oil tanker structure due to harsh environment at sea

• Effect of corrosion over a period of years is to reduce the material thickness and hence the strength of the structure.

• corrosion proceeded at an accelerated rate greater than that allowed for in the design of the structures and allowed to continue unchecked

Introduction

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Potential root causes

• The initial cause was reported as serious loss of thickness in hull plating and that new steel plate with thickness of 12 mm rather than 16 mm had been used during repairs in 1998

• It was also confirmed in a report by Lloyd’s in Nov 23, 2000 that wide spread general corrosion as well as numerous small patches of deep corrosion were present

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Potential root causes

• Corrosion of a bulkhead was reported in 1997 in Rotterdam in port scale inspection and the ship was detained for 24 hours

• In 1998 in Stavanger (Norway) numerous deficiencies (11) including one deficiency mentioning hull corrosion were observed

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Potential root causes

• The vetting inspection before the voyage concluded that the corrosion of the upper and lower parts of the bulkheads between the ballast tanks and the cargo tanks, with abundant rust and patches of rust breaking away

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FAILURE MECHANISMS

• GENERAL CORROSION – Due to absence of coatings

• EXCESSIVE CRUDE OIL/WATER WASHING– Crude oil cargoes can cause a waxy layer to form

inhibiting corrosion– washing mediums such as hot and cold sea water

can remove this protective layer

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• HIGH SULPHUR CONTENT OF CARGO OIL– Crude oils that contain high concentrations of

sulphurous constituents can cause high levels of general and pitting corrosion when these components react with entrained or residual sea water to form acidic compounds.

• sulphur is cathodic by nature and can promote corrosion by forming active corrosion cell

FAILURE MECHANISMS

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• INERT GAS QUALITY– Inert gas should always have an oxygen content of

less than 8% and at these concentrations the rate of corrosion of steel structure should be reduced

– corrosion rates to be significantly reduced, the oxygen content should be below 1%

– Sulphur compounds and strong concentration of acid compounds can enter in the inert gas

FAILURE MECHANISMS

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• INADEQUATE EARTHING/GROUNDING OF ELECTRICAL EQUIPMENT– Ineffective grounding of electrical equipment can

lead to stray currents circulating in the steel work• MICROBIAL ATTACK– A wide range of bacteria can exist– Most microbes produce corrosive acidic

compounds.

FAILURE MECHANISMS

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– The bacteria most frequently associated with corrosion of steel are those that generate sulphides and these are commonly called sulphate-reducing-bacteria (SRB)

– Under favorable conditions these bacteria can produce remarkable quantities of sulphide which can precipitate out as metal sulphides, dissolved sulphide or hydrogen sulphide

FAILURE MECHANISMS

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– The environmental conditions preferred by SRB include zero dissolved oxygen, water and the presence of soluble organic nutrients

– Aerobic micro-organisms use up oxygen and the oxygen deficient zone formed is anodic in relation to adjacent relatively oxygen rich zones thus causing anodic corrosion pits to develop

FAILURE MECHANISMS

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– Temperatures above ambient suit most SRB and they are known to inhabit sea water and the produced water associated with crude oil from older reservoirs where the necessary nutrients for their growth may be found

– During their life-cycle, the anaerobic SRB extract the oxygen from sulphates found in the cargo to oxidise their organic food source and form sulphides, including hydrogen sulphide

FAILURE MECHANISMS

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• These sulphides may be re-oxidised to form acidic sulphates, e.g. sulphuric acid, during the ballast voyage when the cargo tanks are normally empty

• This sulphate corrosion cycle requires the existence of aerobic conditions.

• Experience would indicate that sufficient oxygen for the aerobic phase will be available even in an efficiently inert cargo tank

FAILURE MECHANISMS

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• SLUDGE/SCALE ACCUMULATION– It is not unusual for significant quantities of sludge

and/or scale to be found accumulating in the bottom of cargo tanks

– This debris from previous cargoes or dislodged corrosion scale can create an ideal breeding ground for bacteria and which can hide subsequent pitting damage

FAILURE MECHANISMS

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• WATER IN CARGO TANKS– cargo can cause electrolytic or microbial influenced

corrosion of structural components, particularly on after end tank bottom plating around the suction bell mouths where water tends to accumulate due to the trim of the ship

• STRUCTURAL FLEXING– flexing contributes to the shedding of scale on vertical

and inverted surfaces. The newly exposed steel presents a renewed opportunity for general corrosion to occur at an accelerated rate.

FAILURE MECHANISMS

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POSSIBLE REMEDIES

• COATING APPLICATION– The aim is to be proactive and prevent that

corrosion in these important structural areas– There is grit blasting, humidity, salt content on the

steel surface, adhesion, welds and welding fumes and smoke stains, dust, coating ageing and elasticity etc. just to mention a few factors to consider that affect coating life

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• ENHANCED INSPECTION– Should accelerated corrosion be suspected then an

enhanced program of tank inspection and corrosion data recording should be undertaken to determine trends and the criticality of the situation

• PIT FILLING– A common repair method for pitting is to thoroughly

clean or blast the surrounding area and fill the pits either by welding or with epoxy filler or by welding and over-coating with an epoxy paint or filler

POSSIBLE REMEDIES

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• COATING CARGO TANK VAPOR SPACE AND BOTTOM PLATING– Experience has shown that grit blasting and epoxy

coating of the upper and lower areas of cargo tanks is effective in controlling corrosion

• PITGUARD ANODES– Accelerated corrosion requires the presence of water

and for this reason the installation of pitguard anodes, i.e. anodes which are only a few millimetres from the tank bottom, may mitigate the general and pitting corrosion process

POSSIBLE REMEDIES

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• REDUCING THE TEMPERATURE OF CARGO TANK STRUCTURE– Elevated temperatures of the cargo tank structure

of oil tankers may be conducive to accelerating general corrosion and the proliferation of microbes influencing corrosion

– The temperature of the steel could be reduced by changing out the relatively warm ballast loaded alongside with cooler deep sea ballast on the way to the load port

POSSIBLE REMEDIES

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– replace the relatively warm inert gas in the cargo tank• BIOCIDE ADDITION TO THE CARGO TANK BOTTOM– A broad spectrum biocide may be added to the bottom

water in the cargo tank on an on-going basis to ensure that bacteria do not have an environment which will allow proliferation

• BACTERIAL CONVERSION (NITRATE ADDITION)– A nitrate rich chemical may be introduced to the

bottom water in a cargo tank to divert SRB from reducing sulphate to the less harmful reducing nitrate type

POSSIBLE REMEDIES

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• CHEMICAL CONTROL– Chemical additives (alkaline) may be introduced to

the bottom water to modify the pH beyond the range which facilitates the proliferation of SRB and to offer some protection against acidic corrosion.

POSSIBLE REMEDIES

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• The weakening of the structure of section No.2 of the ERIKA was thus due to insufficient maintenance and the corresponding rapid development of corrosion, leading to a succession of ruptures which caused the whole structure to collapse

CONCLUSION

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REFERENCES1. “Corrosion Prevention and Protection: Practical Solution”, V. S. Sastri, E. Ghali, Materials Technology Laboratory, CANMET, Ottawa, Canada.2. “Techniques for corrosion monitoring”, L. Yang, The Institute of Materials, Minerals & Mining, CRC Press 3. “Nace Corrosion Engineer’s Hand Book” , Robert Baboian, Third Edition, NACE INTERNTIONAL4. “Factors influencing Accelerated corrosion of Cargo oil tanks”, Oil Companies International Marine Forum5. “Corrosion Mechanisms in Theory and Practice”, Second Edition, P. Marcus, Ecole Nationale Supérieure de Chimie de Paris Paris, France6. “Designing Cathodic Protection Systems for Marine Structures and Vehicles”, H. P. Hack, ASTM7. “Report of the enquiry Into the sinking of The Erika Off the coasts of Brittany On 12 December 1999”, Permanent Commission of enquiry into accidents at sea (CPEM)8. www.wikipedia.com