In the third in a series on gas carrier history Syd Harris* looks at the master of all the chemical and petroleum gas trades – the ethylene carrier
In the third in a series on gas carrier history Syd Harris* looks at the master of all the chemical and petroleum gas trades – the ethylene carrier
The apple does not fall far from the tree is an old adage that springs to mind when considering the combined LNG/ethylene/LPG carriers currently under construction in Poland and China. This was exactly the approach taken in the early 1960s when designers were competing to find the best way to transport LNG by sea safely and economically. In those early days of prototype LNG carrier designs, the comfort of having a ship able to carry ethylene and LPG as well as LNG was an attractive cushion for owners as there was always the possibility that the LNG trades would not develop quickly enough to keep their expensive new vessel fully employed.
As with all liquefied gases, it is the physical properties of ethylene that determines its cargo containment system. Ethylene has an atmospheric boiling point of -104°C, about halfway between that of LPG at -48°C and LNG at -163°C. Liquefied ethylene gas carriers (LEGCs) have been constructed as either fully refrigerated ships with the cargo at atmospheric pressure or semi-pressurised/fully refrigerated (semi-ref) ships with pressure vessel cargo tanks. A total of 135 ships able to transport ethylene have been built or converted since the early 1960s and, of these, 28 are no longer trading. Of the 135 ships, 10 vessels ranging in size between 630m3 and 29,400m3 were designed with the ability to carry LNG, ethylene and LPG cargoes.
The initial ethylene trade routes were established around the coasts of Europe, Mexico and Japan. In addition to all those cargoes carried by a semi-ref LPG carrier, a typical LEGC could also trade with ethane, ethene and ethylene, ensuring the longest cargo list of all the gas carriers.
Ethylene ships have incorporated a grand variety of cargo tank shapes over the years, including spherical, prismatic and membrane tanks and longitudinally and transversely mounted cylindrical and bilobe tanks. Cargo tank materials compatible with the -104°C carriage temperature have included aluminium alloys and 5, 9 and 36 per cent nickel steels.
In May 1964 Pythagore, a 630m3 experimental ethylene/LNG/LPG carrier, was delivered to Gazocéan by Ateliers et Chantiers du Havre in France. Despite court battles on patents, massive cost overruns and deck damage from a liquid nitrogen spill, this small ship, built with membrane cargo tanks developed by Technigaz, was to prove that membrane techniques were a viable proposition for LNG transportation. Pythagore was used primarily in ethylene and LPG trading until 1973, at which point it switched to the transport of frozen fish for Senegalese owners.
The first ethylene carrier built in Japan was the appropriately named Ethylene Maru No 1 which was delivered from Ishikawajima Ship and Chemical Company in Tokyo in 1965. The ship had a single, horizontally mounted, cylindrical cargo tank with a minimum design temperature of -30°C and a maximum design pressure of 7 barg.
Also in the mid-1960s the Scottish shipowner George Gibson received a contract to ship ethylene for Imperial Chemicals Industries (ICI) from Teesside in the UK to Rozenburg, near Rotterdam. This deal resulted in the delivery, in July 1966, of the 833m3 Teviot and, later in the same year, the 824m3 Traquair from the Burntisland shipyard in Scotland. This pair of fully refrigerated ships each had a single prismatic aluminium-magnesium alloy cargo tank extending sloped above the main deck. The maximum cargo tank design pressure was 0.35 barg. Expanded polyurethane insulation with a secondary barrier skin was fitted on the internal surfaces of the hold and on the underside of the above main deck trunk. The void space between the cargo tank and the insulation was filled with nitrogen.
In September 1966, on the other side of the North Sea at Bremen, A G Weser delivered the 824m3 Lincoln Ellsworth to Oslo shipowner Einar Bakkevig. Like Teviot, Lincoln Ellsworth was fitted with a single, fully refrigerated cargo tank. However, the German design team adopted a different approach in the choice of tank material and insulation arrangements for their ethylene carrier.
The 5 per cent nickel steel self-supporting tank, which had external polyurethane insulation, was built to a bilobe shape to enable a maximum design pressure of 5.25 barg. The resultant ship allowed for more flexible trading patterns than the Gibson vessels and represented an ethylene carrier design first for Liquid Gas Anlagen (LGA) and the Burckhardt labyrinth-piston compressors.
The year 1966 also saw the end of the classification societies’ requirement for a secondary barrier to be fitted in way of cargo tanks designed as pressure vessels. From 1966 until the present day the majority of ethylene carriers have been designed as semi-ref ships with fixed insulation on independent cylindrical or bilobe pressure vessel cargo tanks.
Despite the industry’s preference for semi-ref ethylene carriers, there have been some notable exceptions to emerge, particularly in the early years. Delivered from Le Havre in 1967 for Gazocéan, the 1,777m3 Thales had a double hull with two pressurised, cylindrical cargo tanks surrounded by loose perlite?insulation.
During the 1967-70 period Japanese shipyards flexed their muscles with eight LEGC deliveries. Ishikawajima of Tokyo delivered the 830m3 Tonen Ethylene Maru in 1968, the first of three refrigerated types with prismatic aluminium alloy cargo tanks, and the 918m3 Taikasan Maru in 1970, the first of three with cylindrical steel cargo tanks designed for 20 barg and -30°C. The Sumitomo yards at Asahi and Kyokyo built the 785m3 Ethylene Daystar in 1968 and the 1,188m3 Ethylene Dayspring in 1969 for Daiichi. Each ship had two aluminium membrane cargo tanks developed by Bridgestone, utilising 3mm thick plate, and the cargo tank area was protected by a double?hull.
European shipbuilders introduced more LEGC variations at the start of the 1970s. The Hebburn shipyard of Swan Hunter in the UK delivered the 3,344m3, fully refrigerated Emiliano Zapata to Petroleos Mexicanos in 1970. Fitted with two prismatic, 9 per cent nickel steel cargo tanks, Emiliano Zapata was the first gas carrier to incorporate an ethylene gas plant supplied by Liquid Gas Equipment (LGE).
Another Technigaz prototype for Gazocéan, the 4,073m3 LNG/ethylene/LPG carrier Euclides, built at Le Havre in 1971, was the first LNG carrier with spherical cargo tanks and the first without a secondary barrier. This ship, with its cargo tanks cunningly hung from the main deck, completed 14 voyages carrying LNG from Algeria to the US before entering the ethylene trades. The German shipbuilder Heinrich Brand in Oldenburg delivered the 2,741m3 Melrose with aluminium bilobe cargo tanks in 1971. The ship was the first in a series of five LNG/ethylene/LPG carriers for George Gibson and Bernhard Schulte from Brand but none of the quintet ever carried LNG.
Moss Værft in Norway introduced what was to be the first in a long line of successful LEGC designs in 1971, through the delivery of the 4,100m3 Roald Amundsen for Einar Bakkevig. Then, Vestri, Hera and Heros – three LEGCs in a larger series of 12,600m3 gas tankers – were delivered between 1971 and 1978.
In 1971 the Moss yard also delivered the 7,400m3 Bow Elm, a combined ethylene/chemical carrier. The vessel was the first of nine ships of this type from the yard, the cargo-carrying capacities of each new batch exceeding that of its predecessor. The last of such ships from Moss was the 10,850m3 Igloo Espoo, delivered in 1985 to a Finnish/Norwegian partnership of Neste, Kværner and Havtor. Transverse-mounted, stainless steel, cylindrical cargo tanks were a feature of the combined carriers. Several of these combined ethylene/chemical carriers still sail in the Eitzen Norgas Gas Carriers pool.
To round off 1971, a remarkably varied 12 months for LEGC newbuildings, the Yokohama yard of Mitsubishi delivered the 1,120m3 Shinryo Ethylene Maru, a ship with two Technigaz membrane tanks, to Shinwa Chemicals.
In 1972 Italy completed its first ethylene carrier, the 1,100m3 Capo Verde, a vessel with a simple, two cylindrical tank arrangement and a cargo plant designed by LGA. In 1974 Hitachi’s Innoshima yard delivered the 1,106m3 Sankyo Ethylene Maru, a unique experimental LNG carrier embodying two different cargo tank systems. The forward aluminium spherical tank was based on a Chicago Bridge & Iron design and the aft 9 per cent nickel steel prismatic tank had a part Exxon pedigree. The cargo handling systems were tested with ethylene and liquid nitrogen before the ship was handed over to owners Akashi Kisen for service as an ethylene carrier.
The largest ships ever built with an ethylene-carrying capability – the 29,388m3 Venator and Lucian – were delivered from Moss Værft in 1973 and 1975, respectively. Each was provided with four aluminium spherical cargo tanks and the two ships have been primarily engaged in the carriage of LNG and LPG throughout their working lives.
In an attempt to rival the Moss multicargo concept embodied in Venator and Lucian the Spanish built the 4,936m3 Sant Jordi, a prototype LNG/ethylene/LPG carrier to a design by Sener at the Tomas Ruiz de Velasco yard in Bilbao in 1976. The ship had four spherical 9 per cent nickel steel cargo tanks and, finding no employment as an LNG carrier, was used in the transport of ethylene and LPG. When trading as Red Star and carrying a full cargo of butane, the vessel sank off southern Portugal in January 1994 after the engine room flooded in heavy weather but not before all 17 crew were rescued. A legal battle with Moss over an alleged containment system patent infringement during the ship’s construction and a battle with the elements in the end gave Sant Jordi a stormy history.
By the mid 1970s the experimenting in LEGC construction had stopped and an ever increasing number of shipyards, particularly in Germany and Italy, successfully built semi-ref ethylene carriers with independent cargo tanks of similar design. The capacity of these ships has risen steadily, culminating in the 22,000m3 Navigator Mars and its four sisters built at the Jiangnan yard in China in the late 1990s and the early part of this decade. The Bonn-based Tractebel Gas Engineering designed the cargo-handling plant and systems for this series.
However, because even the largest LEGCs have relatively limited overall ship dimensions, many small and medium-size shipyards are able to compete for orders for such ships. The accompanying table of LEGC deliveries by country of build, featuring the first such ship from each yard and the first vessel in any notable series, indicates the progress in ship size over the evolution of these sophisticated gas carriers with cargo lists that are second to none. LPG
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