Two cargo containment systems are being applied to conventional-size LNG carriers for the first time
It is not every day that the LNG shipping industry welcomes a ‘new’ cargo containment system. However, in 2018 two systems – KC-1 in Korea and IHI-SPB in Japan – are featuring in conventional-size LNG carriers for the first time.
The KC-1 membrane tank system is a truly new technology and has not been utilised in an LNG carrier of any size before. However, IHI’s self-supporting, prismatic-shape, IMO Type B (IHI-SPB) design is not new, as such, having been introduced as a liquefied gas carrier containment system by the Japanese shipbuilder 30 years ago. It has only been incorporated on commercial LNG carriers on one occasion: a pair of 89,900 m3 vessels built in 1993.
The first two LNG carriers fitted with KC-1 membrane tanks entered into service early in 2018. They are the 174,000 m3 sister ships SK Serenity and SK Spica, built for SK Shipping by Samsung Heavy Industries. Both vessels have been fixed on 20-year charters to Korea Gas Corp (Kogas) to carry LNG cargoes from Cheniere Energy’s export terminal at Sabine Pass in Louisiana. Each ship is expected to lift about 500,000 tonnes of LNG per annum.
The KC-1 membrane tank containment system has been developed by KC LNG Tech, an engineering firm established in February 2016 by Kogas in tandem with Korea’s three leading shipyards – SHI, Hyundai Heavy Industries and Daewoo Shipbuilding & Marine Engineering.
KC-1 has been introduced by the KC LNG Tech partners to provide Korean shipbuilders with a domestic alternative to the two established membrane technologies offered by Gaztransport & Technigaz (GTT). Like most LNG carrier builders, the Korean yards are licensees of the GTT technologies and pay a handsome royalty fee for each ship constructed with GTT tanks.
The KC-1 containment system technology received design approval from various leading classification societies over the 2007-2014 period. The latest agency to award a certification is the US Coast Guard, having granted concept approval in December 2017 for KC-1 LNG ships of up to 174,000 m3 in size.
KC-1 in detail
Both the primary and secondary barriers in the KC-1 system are of 1.5 mm thick stainless steel plate, and both barriers have corrugations to accommodate thermal expansion and contraction. The barriers are positioned close to each other and are backed by a single layer of polyurethane foam (PUF) insulation, supplied as panel pieces.
Inter-barrier spacers (IBSs) are placed between the primary and secondary membranes to maintain equidistant spacing between the two, thus ensuring that any damage to the primary barrier does not impact on the secondary barrier.
SK Serenity and SK Spica are fitted with MAN’s mechanically operated, electronically controlled, gas-injection diesel engines and a Samsung partial reliquefaction plant. KC LNG Tech reports that the KC-1 system provides a cargo boil-off gas rate of 0.12% of the cargo volume per day.
The SK Shipping pair were delivered approximately six months later than originally envisaged. KC LNG Tech states that most of the delay is down to insufficient preparations for the mass production of the membrane panels and that, considering the challenges involved in introducing a major new technology in the LNG shipping sector, the principals are not overly disappointed with the progress that has been made.
SHI is also constructing a second pair of LNG carriers to be equipped with KC-1 containment systems. Due for completion in 2019, these are 7,500 m3 coastal ships for the Jeju Aewol project and one of the pair will serve as an LNG bunkering vessel.
The two vessels will transport cargo to a new LNG terminal being built on the Korean island of Jeju. KC-1 membranes will also be utilised as the containment system for a pair of 45,000 m3 storage tanks under construction at the new Jeju terminal.
The two 89,900 m3 LNGCs built in 1993 and delivered as Arctic Sun and Polar Eagle are not the only gas vessels with IHI-SPB tanks currently in service. Two offshore LPG vessels – the 1997-built, 54,000 m3 Escravos floating storage and offloading unit and the 135,000 m3 Sanha floating production storage and offloading vessel commissioned in 2005 – also incorporate this containment system.
IHI-SPB tanks were also specified for a 25,000 m3 floating storage and regasification unit barge built for Exmar by the Wison Offshore Marine shipyard at Nantong in China. Delivered in December 2017, the LNG regas vessel has two 12,500 m3 cargo tanks which were built at the Aichi yard in Japan and barged to China.
The next IHI-SPB ships about to make the news are a series of four 165,000 m3 LNG carriers that the Japan Marine United Corp (JMU) shipyard in Japan is constructing for Tokyo Gas. The orders were placed in 2014, a year after JMU was established through the merger of the ship construction activities of IHI Marine United and Universal Shipbuilding. The hulls of the quartet are being built at JMU’s Tsu facility and are then towed to Aichi for tank installation.
Tokyo Gas will employ the ships, which are due for delivery in 2018 and 2019, in lifting cargoes from the new Cove Point LNG export project on the US East Coast. They will be the first conventional-size LNGCs to be fitted with IHI-SPB tanks.
IHI-SPB tanks are subdivided into four spaces by a centreline, liquid-tight bulkhead and a transverse swash bulkhead. This subdivision, in tandem with the stiffened plate structure of both the shell and the internal supporting elements, provides the IHI-SPB system with a high degree of strength, to the extent that the risk of cargo sloshing damage is obviated at all fill levels.
In addition, like all liquefied gas tanks designed to the IMO Type B standard, IHI-SPB units require only a partial secondary barrier. Robust Type B tanks comply with the ‘leak before failure’ principle which means that if a fatigue crack occurs, it will propagate very slowly, allowing time for remedial measures to be taken.
Another advantage is the prismatic shape; IHI-SPB tanks are the most space-efficient of the containment systems currently in use. The units can be constructed to accommodate specific hull lines so that the final shape optimises use of the space available. The main deck is flat across the width of the ship and there is no need for a trunk deck.
IHI-SPB tanks can be constructed of either aluminium, stainless steel or 9% nickel steel. Aluminium tanks are the lightest of the three options and have been chosen for all the liquefied gas vessel applications to date.
The cargo tank insulation consists of PUF panels, fixed by central studs to the tank. Cushion joints are inserted between panels to absorb relative movements between the tank and the insulation and eliminate thermal stresses in the insulation.
The first ship in the series was named Energy Liberty at an October 2017 yard ceremony and the vessel is due for a March 2018 delivery. Completion of the four Tokyo Gas ships is running several months late and IHI has attributed the delays to problems encountered in fitting the insulation system. However, the shipbuilder is confident that all four ships will be in service by April 2019, as per the latest schedule.