LNG carriers debut Korean tank design

A new entrant to the LNG shipment traffic from Louisiana to South Korea, SK Spica is a showcase for the KC-1 cargo system
A new entrant to the LNG shipment traffic from Louisiana to South Korea, SK Spica is a showcase for the KC-1 cargo system
KC-1 membrane LNG cargo tank
KC-1 membrane LNG cargo tank

Two new South Korean built and owned LNG carriers provide the initial applications for an indigenous membrane containment solution, a challenger to the hitherto all-pervading foreign technology. David Tinsley reports.

Heralding the start of a new chapter in LNG carrier production by South Korea, the first ships to incorporate a long in the making, home-grown cargo containment system have been phased into service. The KC-1 tank design embodied by SK Shipping’s 174,000m3-capacity sisters SK Serenity and SK Spica brings a competing technology to a field hitherto the province of overseas engineering companies, most prominently Gaztransport & Technigaz (GTT).

The efficiency benefits promised by the new membrane containment solution provide the technical foundation for its adoption, but the overarching case for KC-1 is the financial benefit it affords those domestic shipbuilders behind its development in not having to pay licence fees for using foreign, core technologies.

Such payments are said to equate to around 5% of ship price, indicating that yards will able to save around 60% of royalty costs by adopting KC-1. It therefore has the potential to sharpen the competitiveness of the South Korean shipbuilding industry and help consolidate its position as the world’s most prolific constructor of LNG carriers.

The containment design and cargo handling arrangements are the outcome of a research project launched in 2004 by natural gas importer, distributor and public utility KOGAS in collaboration with the country’s three major shipbuilders, Hyundai Heavy Industries, Samsung Heavy Industries, and Daewoo Shipbuilding & Marine Engineering. KOGAS membrane technology used for onshore LNG storage tanks has provided the basis for the shipboard system. After nearly 10 years’ R&D work, technology certification for KC-1 was obtained from the Ministry of Trade, Industry and Energy at the end of 2013. A total of some 50 patents have been secured in South Korea, the EU, China, Japan, the USA and Australia.

A fundamental characteristic of the system is the comparative simplicity of the containment structure. The development partners went on to establish a joint venture, KC LNG Tech, to commercialise KC-1, targeting not only LNGCs but also LNG-FSRU and LNG-FPSO ‘floaters’. While the initial focus is on meeting domestic industrial strategic objectives, the partners are looking in the longer-term to generate a revenue stream from licensing the technology to overseas shipbuilders.

PIVOTAL ROLE

KOGAS plays a pivotal role in Korean LNGC fleet investment and deployment, as the long-term charterer of transport capacity, and can therefore influence owners’ newbuild specifications. Nonetheless, all operators versed in the well-proven, market-dominating systems that French engineering company GTT has continued to refine and augment, with incremental gains in cargo boil-off rate (BOR), will be closely watching the performance of the new ships with the KC-1 solution.

SK Serenity was handed over at Samsung’s Geoje yard during February, followed a month later by second-of-class SK Spica. The deliveries were about six months later than originally set, attributed to production challenges associated with the introduction of the new tank technology. Membrane sheet and other elements for the stainless steel tanks were ordered from the specialised Korean manufacturer TMC, which had to create a new mould for the KC-1 system.

Both ships have been enrolled into the Korean import traffic, hauling LNG from Cheniere Energy’s Sabine Pass terminal in Louisiana under a 20-year transportation contract with KOGAS. Flourishing US exports are a result of the country’s determined exploitation of shale gas resources and price competitiveness.

SK Spica is the last of six 174,000m3 vessels ordered in 2014 by Korean operators under KOGAS contracts for liftings from Sabine Pass. The four other newbuilds all have GTT No.96 membrane systems, and were delivered during 2017 by Daewoo, two going to Korea Line Corporation and two to Hyundai LNG Shipping. The six ships are expected to transport a total of up to 2.8m tonnes of LNG per annum to terminals on the Korean peninsula.

SK Serenity and SK Spica have both been built to joint Korean Register (KRS)/American Bureau of Shipping (ABS) class requirements. Each has a primary power installation based on two dual-fuel, low-speed two-stroke engines, harnessing vaporised cargo as fuel. Manufactured under licence from MAN Diesel & Turbo at the Changwon complex of Doosan Engine Company, the two 5G70ME-C9 gas-injected engines have a specified rating of 12,222kW at 74rpm, for a combined output of 24,444kW and speed of 19.5 knots.

PROPRIETARY PACKAGE

The main machinery allows ingestion of cargo boil-off as fuel, and operation in gas mode ensures compliance with US Emission Control Area (ECA) criteria. Samsung has applied its proprietary LNG core package technology, including the gas treatment system (CHS), fuel gas supply system (FGSS), and partial reliquefaction system (S-Reli), commensurate with the indigenous KC-1 containment.

In the unique KC-1 containment system, the primary and secondary barriers are positioned close to each other and are both formed from 1.5mm-thick SUS 504L corrugated stainless steel membrane. They are fixed to membrane anchors and supported by the insulation system. A single layer of high-density (115kg/m3) polyurethane foam (PUF) is used as the insulation material, rather than the reinforced PUF employed in GTT’s Mark III membrane tanks.

The arrangements are intended to minimise the effect on the insulation system of hull and primary barrier deformation, simplify heat dissipation and make the insulation panels easier to manufacture.

Inter-barrier spacers are placed between the primary and secondary membranes to maintain equidistant spacing, ensuring that any damage to the primary barrier does not impact on the inner, secondary membrane. The membranes are made from World Premium-branded stainless steel supplied by POSCO, and the corrugations afford strength and accommodate thermal expansion and contraction in the task of carrying cargo at minus 163degC and at a maximum pressure of 0.35 bar. It is understood that the anticipated boil-off rate in service is in the order of 0.1% of cargo volume per day.

With regard to construction, productivity is increased by straight-line welding of the membranes. Large membrane panel installation is automated using the Moving Scaffolding System (MSS).

ABS worked with KOGAS towards design approval of the KC-1 concept for about a decade, resulting in the assignment of the society’s Extended Approval in Principal and General Design Approval for the system in 2014.

SLOSHING ANALYSES

Beginning in 2005 and expanded in 2008 and 2013 to cover additional components, the work scope of ABS was extended to include a sloshing evaluation using sloshing model tests as part of the structural strength assessment. The associated pump tower design and sloshing analyses were reviewed in accordance with the society’s relevant Guidance Notes and other applicable industry standards.

In the final assessment, ABS analysed tank and ship motions, including sloshing impact and fatigue loading, on the basis of an LNGC operating in North Atlantic wave conditions.

The German company LIOS Technology (now NKT Photonics) was retained to carry out a series of tests in 2009 to validate the system with regard to containment integrity and fabrication, assembly and construction procedures. The work called for the building of open and closed tank mock-ups.

ABS issued an Extended Approval in Principal and General Design Approval for the KC-1 system in 2014.

The two new gas tankers denote a further milestone as the first recipients in the LNGC category of Samsung’s new-generation S.VESSEL ‘smart ship’ system.

Samsung’s goal with its proprietary Smart Ship Solution is to improve vessel efficiencies using real-time data from hull and equipment sensors in conjunction with oversight from land-based technical and fleet managers. The S.VESSEL integrated system addresses navigation planning and speed optimisation, automatic monitoring of fuel consumption and motion safety, automated reporting functions, remote fleet management and analysis of ship operating performance. The ongoing development of the technology promises to give further added-value to vessels designed and constructed at the Geoje shipyard.

ABS has recently granted a certificate of cyber safety compliance for the shipbuilder’s Smart Ship Solution, confirming adherence to the society’s Guide for Cybersecurity Implementation for the marine and offshore industries and the ISO’s IT Security Control Code of Practice.

FURTHER ORDERS

The orderbook at the Geoje shipyard includes a further commitment to the KC-1 solution through a newbuild project implemented last year by Korea Line Corporation. Constituting Korea’s first ‘small-scale’ LNG carrier scheme, two vessels of 7,500m3 have been ordered on the strength of 20-year KOGAS cargo guarantees covering short-sea movements, and are due for completion in May and December 2019.

The primary role of the KC-1-equipped newbuilds will be to shuttle LNG to a new terminal on Jeju island from the KOGAS import, storage and regasification complex at Tongyeong, on the mainland’s south coast. One of the ships will also be equipped to serve as an LNG bunker tanker.

PRINCIPAL PARTICULARS - SK Serenity

Length overall

296.2m

Length b.p.

288.4m

Breadth, moulded

45.6m

Depth, moulded

26.2m

Draught

12.42m

Deadweight

93,167te

Cargo capacity, 100% filling

174,117m3

Cargo capacity, 98.5% filling

171,390m3

Main engines

2 x 12,222kW

Generators

2 x 3,438kVA + 2 x 4,563kVA

Class

KRS/ABS

Flag

Panama

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