Ask us about … Natural Gas Transportation It’s about leadership.
DNV Maritime
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DNV Maritime World Natural Gas Reserves 181.46 trillion m3, end 2006 Source: BP, June 2007
Clarkson Research Services
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Increased demand, new challenges‌ The market for gas transport by sea has been stable or slowly increasing for the last 30 years, but is now expanding rapidly. The demand for LNG transport capacity is forecast to grow from 100 million tons per year (mty) in year 2000 to 270 mty in 2010. The number of LNG carriers is expected to rise from 120 to about 350 in the same period. Soon we will also see new ways of transporting natural gas at sea, for example as Gas-toLiquids (GTL) and Compressed Natural Gas (CNG). CNG has the potential to economically unlock vast reserves of already discovered gas considered to be stranded in small reservoirs for which existing technologies prove uneconomical or associated gas in existing oil fields and bring that gas to market. The potential here is huge – as about half of all known gas reserves are considered to be stranded or associated. We believe the first CNG carrier project will materialise in this decade. The LNG market is looking for more operational flexibility to enable trading in more harsh environments and operations with partially filled tanks in order to serve new market segments and trades - LNG carriers offloading
at offshore buoys (regas vessels) and/or receiving terminals, milk runners, spot trades, etc. There is a shift towards more crossAtlantic trading and trading in colder climates as well as a significant increase in the size of LNG carriers. Gas transport by sea is a technology driven market segment. DNV has had a pioneering role in this segment right from the start (late fifties) and its competence and innovative approach is recognised by all the participants in the market. We intend to remain a competence and technology leader in the LNG segment in the years to come.
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DNV Maritime DNV’s Bo Bengtsson inside the first membrane LNG tank model Built in Oslo 1962.
First Moss type with aluminium tanks, LNG/C Venator, 1972 (DNV class). Dual fuel diesel propulsion. Subsequent sister vessel arranged with gas turbine propulsion.
Material testing in DNV research laboratory
Exterior of tank model
Important mile stones include
1959 DNV establishes research team on LNG ships. 1962 First membrane tank system developed by DNV and successfully tested in Oslo. A Norwegian shipowner commissioned development of a cargo containment system for LNG to DNV. The shipowner later decided not to build LNG vessels and sold the patent to France where it was further developed and commercialised.
1962 As the first classification society DNV develops and publishes classification Rules for gas carriers. 1969–1972 Moss spherical tank design developed with strong support from DNV’s research laboratories and technology experts. 1972 Basic design criteria for type B tanks are developed and included in the DNV Rules.
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Ask us about innovation... Historical Development of LNG Technology – DNV in Pioneering Roles DNV was a key contributor to the development of both the Moss and membrane design LNG carriers and continues to be at the forefront of technical developments to support the LNG industry. DNV was actively involved in the pioneering work to develop both membrane and spherical cargo containment systems more than 40 years ago, and all current cargo containment systems have been approved by DNV. This also includes verification of the original SPB (IHI)
1970–1974 Model testing of sloshing, crack propagation, fatigue and buckling is carried out by the DNV laboratory to confirm compliance with requirements for LNG tank type B. All experience since then has confirmed that the extensive work carried out was correct. 1970–1976 Based on the wide and deep competence developed during these initial years, DNV becomes prime contributor to development of IMO’s gas carrier code.
cargo containment system more than 20 years ago and approval in principle of the recent improvements to this design. The unique accumulated experience we have gained over the years – combined with our highly qualified experts within a wide range of disciplines and state-of-the-art software for structural and hydrodynamic analysis – is more necessary than ever to support the industry’s future challenges.
1977 DNV establishes Rules and design criteria for floating LNG FPSOs. 1985 DNV carries out structural analysis and strength assessment of IHI’s SPB cargo containment system. 2002 As the first classification society DNV publishes Rules for Gas Fuelled Engine Installations. 2003 As the first classification society DNV publishes Rules for Compressed Natural Gas (CNG) carriers. 2004 DNV publishes updated standard for offshore LNG terminals.
2004 4 x 216,000 m3 LNG carriers are ordered to DNV class by Overseas Shipholding Group, wich at present are the largest LNG carriers built. 2006 DNV publishes Class Note: “Sloshing Analysis of LNG Membrane Tanks”, Class Note 30.9 2007 Lead role in JIP to assess consequences from LNG releases 2008 “Strength analysis of LNG Carriers with Spherical Tanks”, Class note 30.2
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DNV Maritime
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Ask us about... New Operational Challenges Natural gas accounted for 23.6% of the global fossil fuel market in 2006, a level very similar to the previous year and up from 22% in 1990. Global gas consumption was 2,850.8 billion m3 in 2006, representing a growth rate which is 2.5% higher than that in 2005, and the market for seaborne gas transport is increasing at an unprecedented pace. The latter is characterised by a rapid increase in the carrier fleet, spot trading, speculative ordering, increased carrier size, a move away from the traditional one propeller steam plant towards diesel propulsion and two propellers, more cross-Atlantic trading, partial load trading (milk runs) and an emerging market for cold climate (Arctic) operations. Fatigue considerations and tank sloshing loads are becoming more important parameters. Offshore receiving/storage terminals and regasification and discharge terminals will in some parts of the world be the preferred future option due to safety considerations and environmental concerns. Floating units for receiving, storage, regasification and export (FSRUs) of natural gas as well as units for off-
shore production (FPSOs) are emerging markets. For these new applications, safe operations with partial tank fillings have to be carefully studied on a case by case basis. Sloshing loads and tank system strength are therefore key issues in the design and operation of such systems. Seaborne gas transport has historically involved high standard, low accident operations. Damage statistics from DNV in-house studies indicate an average accident rate in the range 30–80% lower than for average shipping operations. It is a challenge for everyone involved to maintain this favourable situation in order to further develop the industry. The larger sizes of carriers and the new operational profiles outlined above make relying on past experience to predict the structural performance of the vessel hulls and containment systems rather uncertain. Hence the use of state-of-the art designs for ultimate strength and fatigue will be essential for safe and trouble-free operation.
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DNV Maritime
Typical notations for Structural Fatigue for Tankers:
CSR – Common Structural Rules
CSA-2 – Computational Ship Analysis
PLUS – Extended fatigue life
CSA-FLS – Computational Ship Analysis Fatique Limit State
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Ask us about... Structural Fatigue – the invisible threat New trades will take place in harsher and more demanding environments than the eastbound trades from the Middle East. The design of the vessels for these new trades will have to focus more on fatigue in the hull and cargo tank systems. Hull fatigue damage accumulation is about twice as rapid in the North Atlantic than in the comparatively more benign environments where most LNG carriers have been successfully operating in the past. Further, there is an increasing trend towards owners specifying 40 years of fatigue life in the North Atlantic when ordering new vessels in order to ensure trouble-free operation in these more demanding environments.
ative publicity may be the consequences. Hence it is essential for owners to minimise the risk of fatigue cracks.
Steel structures may start to crack after some time in service. Such cracks may be small and non-essential, or they may be unacceptable and even dangerous. Cracks may affect the safety of the ship, cause pollution and damage the owner’s reputation. Charterers may even be interested in the vessel’s history of cracks.
DNV has for the past 30 years had an unparalleled opportunity to compare its fatigue calculations with real life and continuously calibrate its fatigue procedures. The North Sea may be considered the ultimate full-scale testing laboratory in the world, and more than 80% of the shuttle tankers operating in the North Sea are classed with DNV. Our expertise in fatigue is therefore state-of-the-art and undisputable.
Repairs can be very expensive, and even offhire may be required. A lot of money and neg-
Material technology and fatigue calculations have for many years been among DNV’s specialities. Yards, owners and oil companies have used DNV as an important resource when fatigue problems and related challenges have arisen, in many cases also for non–DNVclassed vessels. A new class notation, CSA-FLS, has been introduced for the direct calculation of the fatigue life and is equivalent to the fatigue requirements of the CSA-2 notation.
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DNV Maritime
The human factor is claimed to be the most important risk factor in coldclimate operations.
The Snøhvit LNG carriers are winterized with enclosed bridge wings.
BALTIC ICE NOTATIONS
ARCTIC ICE NOTATIONS
POLAR ICE NOTATIONS
ICE-1C – Ships operating in light ice conditions
ICE-05 – Vessels breaking ice of 0,5 m thickness
POLAR-10 – Vessels breaking ice of 1,0 m thickness in Polar areas
ICE-1B – Ships operating in waters with ice of 0.6 m thickness
ICE-10 – Vessels breaking ice of 1,0 m thickness
POLAR-20 – Vessels breaking ice of 2,0 m thickness in Polar areas
ICE-1A – Ships operating in waters with ice of 0.8 m thickness
ICE-15 – Vessels breaking ice of 1,5 m thickness
POLAR-30 – Vessels breaking ice of 3,0 m thickness in Polar areas
ICE-1A* – Ships operating in waters with ice of 1.0 m thickness
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Ask us about... Energy transportation in cold climates DNV has included ice-strengthening requirements in its class Rules for more than 125 years and today almost 400 of the DNV-classed tankers are ice-strengthened. Our current Rules are based on Norway’s long cold climate shipping history, extensive operational experience from modern shipping in cold climate areas and significant R&D activities over the past few decades. Since ship operations in cold climates require much more than just the ice strengthening of the ship’s structure and propeller, we have developed technical standards that are relevant for safety and reliability during cold climate operations. The degree of necessary winterization may vary from just control of icing in open waters to ice-breaking abilities in temperatures of -40°C and below. For this reason, class notations applicable for different cold climate conditions have been developed, covering the entire range of alternatives.
With the increasing trade in cold climates, other structural implications need to be considered in the design and operation of LNG carriers. The risk of collision with an iceberg has to be assessed and the hull needs to be designed to operate in icy waters or, to put it another way: “What is a safe speed for an LNG carrier in icy waters?” The low temperature will also necessitate specific steel grades. Furthermore, ice collects on the deck and equipment due to sea spray. The vessel should, however, be able to avoid associated problems so that safety equipment can be operated, stability is not endangered and loading/unloading gear and rudder and mooring equipment are operable. We are prepared to share our experience of harsh environments with owners and yards and support safe operations in cold climates.
DNV has incorporated the Finnish and Swedish Maritime Authorities’ (FMA) Rules in its Baltic Rules.
DAT (-xx) – Standard for low temperature materials DEICE – Standard for icing control OPP-F – Oil Pollution Prevention for Fuel oil thanks CLEAN – Controlling and limiting operational emissions and discharges
RPS – Fully Redundant Propulsion WINTERIZED BASIC – Standard for operation in open water with small quantity of ice WINTERIZED COLD – For operation in medium cold climate conditions with ice
WINTERIZED ARCTIC – Operating in extreme cold climate/ice conditions COMF-V – Comfort Class for noise and vibrations COMF-C – Comfort Class for indoor climate
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DNV Maritime
DNV laboratory in the 1970s – sloshing test in a spherical tank Computer simulation of liquid motions
DNV laboratory 2003/2004: sloshing tests in membrane tanks
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Ask us about... Liquid motions – Sloshing Due to more severe ship motions in North Atlantic trades and the possibility of partial tank fillings, the movement of liquids inside cargo tanks has become an important issue. However, so far LNG carriers have mostly been operated on long-term charters on fixed trades travelling with full tanks on the laden voyage (minus about 0.15% boil-off per day) and some small residue on the ballast leg in order to provide continuous cooling of the cargo tanks. Under such conditions, sloshing loads are a lesser problem, especially as the routes have been in benign, moderate waters.
Since no filling restrictions due to sloshing considerations are applicable to the IHI-SPB or MOSS spherical cargo containment systems, DNV has over the years invested heavily in R&D work related to sloshing in membrane tanks. This R&D work has been divided into four projects:
With the advent of larger LNG carriers, the sloshing behaviour has to be evaluated. These vessels will have different ship motions, different tank dimensions and different tank dimension ratios. Of particular interest as well is the number of tanks that will be accommodated in these vessels. A 4-tank design is preferred in order to minimise the costs, but sloshing loads will be larger with a 4-tank design than with a 5-tank design.
Sloshing is a highly complex phenomenon and, despite the huge R&D efforts, some aspects are still under discussion and difficult to put down in a practical guideline. Based on this, and in response to market requests, a full-scale sloshing measurement program has been designed by DNV. This measurement program is intended to provide a validation database for sloshing loads and structural responses.
Sloshing loads Sloshing Structural response and strength Sloshing guideline Full scale sloshing measurements onboard an LNG carrier
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DNV Maritime
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Ask us about... New Containment Systems; CNG System Designs Compressed Natural Gas (CNG) technology offers interesting possibilities for the handling of associated gas and exploitation of marginal gas fields (stranded gas). The system does not require a gas liquefaction plant or LNG storage tanks, and nor will LNG storage and regasification at the discharge location be necessary. A fleet of CNG ships may serve as both storage and transport vehicles and can discharge directly into the land-based gas grid via an on/offshore discharge terminal, an offshore platform or offshore buoys. Methods for shipping gas on keel without a costly liquefaction process have been studied for decades without any apparent success. Designing containment systems using pressure vessel codes such as the International Gas Carrier Code (IGC) leads to heavy containment systems with virtually no lifting capacity left for cargo, unless unreasonably large and costly ships were to be used. The majority of CNG concepts being proposed or under development are based on using pipelines as the pressure vessels. The steel-based systems can be designed using the DNV Submarine Pipeline Standard, which has become the “World Industry Standard� within
the pipeline industry. Some selected examples are shown in table below and on the previous page. The CNG concepts apply high pressure in order to keep the gas in a gaseous state with basically no liquid hydrate fall-out. Concepts using such high pressure (250 bars) are far beyond the scope for pressure vessel type C tanks as defined in the IGC. This gap has been filled by the DNV Class Rules for Compressed Natural Gas Carriers (2003) following an equivalent Formal Safety Assessment (FSA) approach according to IMO MSC 72/16 and MSC 74/19. System
Coselle (Sea NG) Knutsen PNG EnerSea VoTrans Trans Ocean Gas CETech
CNG Tanks
Horizontal Steel Coils Vertical Steel Pipes Vertical Steel Pipes Vertical Composite Pipes Horizontal Steel Coils
Design condition [bar]
[oC]
240
Ambient
250
Ambient
130
-30
250
Ambient
250
Ambient
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DNV Maritime
Class notations
RP – Redundant Propulsion
RPS – Fully Redundant Propulsion
GAS FUELLED – Gas Powered Ships in domestic trade
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Ask us about... Alternative Propulsion Arrangements The majority of LNG carriers contracted prior to 2005/6 have been equipped with boilers and steam turbine propulsion. They use boiloff from the cargo as fuel in combination with bunker oil. Vessels on order today are mainly contracted with either low speed diesel engines with reliquefaction or diesel electric propulsion systems. LNG carriers, even the big ones, are all designed with a loaded draft of about 12 m. With the increasing capacity, these vessels are growing wider. Due to the widening of the hull and desire to maintain the full aft cargo tank width, certain hydrodynamic issues have to be considered, particularly the effect of the water flow around the aft body to the propeller. In order to maintain a good laminar flow to the propeller and hence propulsive efficiency, a twin shaft design has become inevitable. So not only are we seeing a move away from steam turbine propulsion but large LNG carriers (200,000–260,000 m3) will also
need two propeller propulsion systems if designed for the same service speed as existing LNG carriers. In order to meet the market demand, the class notations RP/RPS (Redundant Propulsion/Redundant Propulsion Separate) and GAS FUELLED are tailor-made for the next generation of propulsion systems. DNV has been a pioneer in developing the first Classification Rules for Gas Fuelled Engine Installations. These were published in January 2001 and are becoming an industry standard. Subsequently DNV has classified the first LNG-fuelled passenger ferry (delivered January 2001) the first two LNG-fuelled offshore supply vessels (delivered April and August 2003) the first modern LNG carrier with gasfuelled diesel engines (delivered January 2004)
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DNV Maritime
Active Customer Service Management (CSM)
Risk studies
Technology qualification
Concept evaluation
Design support
Design review
Strength and fatigue analysis support
Approval in principle
Specification review
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Ask us about... DNV – Follow-up during construction and operation DNV has an international team of extremely well qualified surveyors spread around the globe in its extensive network of survey stations.
has established approval centres with expertise covering most disciplines in all regions where major shipyards are located.
All are qualified through our internal Qualification Scheme, which is part of our internal and recognised QA system.
After delivery, we are able to tailor-make survey arrangements to suit the owner’s specific needs; a number of alternative survey arrangements are available, including voyage surveys and condition monitoring of rotation machinery, etc. These are all intended to harmonise the class involvement with the owner’s needs and avoid conflicts with cargo operations and terminal requirements.
Our approval engineers and site teams work in a project organisation to ensure that all relevant and critical aspects of the approval and construction phases are well taken care of. By using one common global database, all our personnel are linked together via our international computer network which ensures effective communication and enhances the consistency and quality of our work. This benefits both the yard and owner. In addition, DNV
Yard
Owner
Condition Monitoring of machinery
Trouble shooting/damage investigations
DNV has put a lot of effort into establishing services with attractive cost-saving potential and better support to avoid problems and maintain effective and trouble-free operations.
DNV Project Manager
Survey Team
DNV Approval Co-ordinator
Approval Team
Wide range of training courses for designers, yards’ and owners’ personnel
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Š Hans Strand
DNV Maritime
Present services with goal of reducing depletion of natural resource
Certification of Management for Safe and Environmentally sound Recycling Facilities
Green Passport Declaration
Green Passport Inventory
Energy and environmental management
Accredited body for NOx measurements
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Ask us... because we care about the environment DNV’s purpose is “To Safeguard Life, Property and the Environment”. As a leading international ship classification society, we provide several services to the shipping industry. Transport accounts for 14% of the world’s carbon dioxide emissions, and 2% comes from the shipping industry. It is clear that emissions will have to be reduced, that regulators will require a further reduction of CO2 emission levels and that new technical solutions will be introduced.
bly to a larger extent be regarded as a global pollutant rather than a local problem due to slow depletion rates, and hence be connected with long-distance transportation. NOx emissions due to heavy fuel oil being used in diesel engines are mainly a result of the high combustion temperatures in such engines and the relatively long reaction period during the combustion process.
Although shipping is seen as a fuel efficient and hence ‘environmentally friendly’ mode of transportation, shipping operations will in the near future be increasingly focused on by society at large and stricter national regulations will be imposed with the aim of further improving environmental performance. Due to current operations using high-sulphur heavy fuel, emissions of sulphur oxides (SOx) are significant and solutions should be found to reduce them. Whether this will be achieved through a switch to low-sulphur fuels or by abatement technologies on board remains to be seen. Emissions of nitrogen oxides (NOx) are also likely to attract more attention and will proba-
Shipboard Oil Pollution Emergency Plan
Fuel quality testing
Fuel energy content testing
Biofuels and emissions
R&D on alternative energies, LNG, fuel cells
Environmental excellence, decision support tool
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DNV Maritime
Environmental class notations and services
IAPP – International Air Pollution Prevention Certificate, Marpol Annex VI CLEAN – Design requirements above mandatory requirements CLEAN DESIGN – Prevention of accidental spill FUEL – Arrangement for dual fuel arrangements in low sulphur areas, SECA
EIAPP – Engine International Air Pollution Prevention certificate, Marpol Annex VI EPS – Environmental Performance System measurements IAFS – International Anti-Fouling System Certificate, EU countries APPC – Arctic Pollution Prevention Certificate
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Ask us about... The environmental challenges While the sulphur and SOx issue can possibly be resolved through improved production technology for marine fuels at the refinery, NOx emissions will have to be resolved on board the vessel unless new fuel types, e.g. LNG, are introduced. When it comes to CO2 emissions, these are directly proportional to the amount of fossil fuel being consumed. Since liquid petroleum fuel, low-sulphur or not, is likely to be dominant for marine propulsion in the foreseeable future, effective energy management and optimisation will be the only practical way to reduce CO2 emissions. This can be addressed by introducing improved technologies, such as new hull shapes and designs to ensure less resistance, bigger ships, better hull and propeller surface treatment and coating, enhanced propulsion and engine designs and, for example, heat recovery systems to optimise energy utilisation.
AFSC – Anti-Fouling System Certificate, Statement of Compliance, Non EU countries TBT – TBT-free Anti-fouling Systems, Type Approval BWM – Ballast Water Management, Type Approval of Systems IOPP – International Oil Pollution Prevention certificate, A or B, Marpol Annex I
For ship owners, the energy consumed to move a vessel with crew and cargo from A to B directly impacts on the bottom line. The less energy used, the greater the potential earnings and profits. Energy is about consumption and saving. It is about using energy sources to generate enough power to enable propulsion, heating, cooling, auxiliaries, etc. The maritime industry will be subject to stricter requirements concerning emissions to air in the future. The commercial conditions and operational framework will change. Alternatives to fossil fuel will no doubt be required. DNV is actively engaged in protecting the marine environment in all areas, ensuring that your vessel will meet tomorrow’s expectations and requirements. A newbuilding today is expected to trade for the next 30-40+ years. Is your ship prepared to face the future environmental challenges and requirements?
ICCP – International Certificate of Fitness for Carriage of Dangerous Chemicals in Bulk, Marpol Annex II, Chemical code NLS – International Pollution prevention Certificate for the Carriage of Noxious liquid substances in Bulk, Marpol
ERS – Emergency Response Service OPP-F – Protection of fuel tanks ISPP – International Sewage Pollution Prevention Certificate, Marpol Annex IV USPOL – US Pollution, Prevention and Sanitation Regulations, Declaration of compliance
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