Why have ships transporting liquefied natural gas been safely navigating oceans and urban ports for decades without a major incident? Here are some insights into the extraordinary measures taken to ensure safe sailing
The man moves cautiously, as if in a space shuttle, focusing his attention like a technician in a cleanroom lab.
Clad in a coverall, soft overboots, gloves and a helmet, he uses his flashlight to visually inspect thousands of metres of laser-welded seams inside a 40-metre tall stainless steel tank onboard a ship.
“GTT develops all the process data and computer software for membrane tanks internally,” the shipping expert explains. His French employer, Gaztransport et Technigaz (GTT), equips roughly two-thirds of the world’s advanced membrane carriers with leading-edge tanks.
In a process requiring utmost precision, the doublewalled tanks must be installed in the ship’s hull.
“This is very time-consuming,” says Georg-Alexander Martin, tanker specialist with Germanischer Lloyd. “Everything has to be measured and fine-tuned precisely to avoid leakage.”
If the liquefied natural gas, refrigerated to a chilling 162C below zero, were to contact a large section of the ship’s steel structure, the hull would shatter like glass. It takes more than two years to install the shiny circus tent made of thin - up to approximately 1.5mm material - such as Invar, a steel alloy, or Triplex. This membrane rests flexibly in a shell of bonded wood strips within the ship’s hull, capable of accommodating 30,000 cubic metres or more of LNG.
A ship may carry four or five of these enormous, hexangular gas containers in its belly.
“The membrane is just a flexible bag unable to support itself,” says Martin.
It is held up by a complex, multi-layered insulating structure composed of glass fibres, synthetic material and a second barrier made of aluminium or other metal that will remain leak-proof even in rough seas and extreme ship movements.
The cargo maintains its temperature of minus 162C for the entire duration of its trip covering thousands of miles, continuously boiling like water in a kettle, but much, much colder. As long as a small portion of vapour is allowed to escape from the “kettle”, or tank, the internal pressure and temperature will remain unchanged.
Ball-shaped ships being replaced
Advanced membrane carriers are increasingly replacing traditional ships with their conspicuous spherical tanks on deck. Those ball-shaped tanks, the “Moss Rosenberg System” originally developed in Norway, have been in use across the seas for 30 years. Compared to the new systems, they are easier to build. A shell of aluminium four centimetres thick, surrounded by layers of insulating material, prevents the gas from warming. This technology does have its advantages: while a membrane carrier has to remain at the fitting-out pier for tank installation for a long time, spherical tanks can be manufactured simultaneously.
A spherical-tank vessel therefore takes much less time to complete. But there is a catch: spherical tanks are very heavy. Few ship-yards have cranes strong enough to hoist these behemoths into the ships. And apart from that, the sleek membrane carriers are more fuel-efficient.
Both ship types have double hulls.
“LNG is a perfect fit for the diverse regional needs of our globalized world,” says British natural gas consultant James Ball.
Safety since 1959
The first ever natural gas transport by ship occurred less than 50 years ago.
In 1959, a retrofitted tanker called Methane Pioneer carried the first cargo of 5,000 cubic metres across the Atlantic. Today, the floating pipelines regularly commute between gas-producing countries and their markets.
An increasing number of terminals are boosting the LNG trade to satisfy a rising demand. Frequently, the owners of the current fleet of 228 carriers are the gas producers themselves; in other cases, gas-producing companies charter the ships. But that is changing now.
An emerging free LNG carrier market is dominated by independent shipowners letting their vessels for a limited time or transport quantity on short notice.
“There are many new kids on the LNG block,” says Mark Ross, president of SIGTTO, the Society of International Gas Tanker and Terminal Operators, “and it is imperative that we take appropriate action to ensure they take safety as seriously as the established operators.”
Delta’s Tilbury LNG plant expects to start maritime exports soon using small 80,000 cubic metre ships.
Career opportunities – up to $16k a month
There is a shortage of experienced crews for the fast-growing LNG carrier fleet. At the world’s shipyards, more than 145 vessels are on order.
Three quarters of them are being built in South Korea by Daewoo, Samsung or Hyundai Heavy Industries. Daewoo alone employs 2,000 ship designers for cargo ships of all types.
All three shipbuilders have formed a common technology pool that is unmatched by any competitor worldwide. “While Japanese shipyards are standardizing to reduce costs, we are committed to fulfil every single request of our customers,” says Park Dong-hyuk, vice president of product management at Daewoo.
In mid-April, the Korean national energy corporation Kogas made arrangements with the three shipbuilding giants to try out their newly developed membrane tank system.
So the French manufacturer GTT may soon face competition. As early as 2015, more than 400 LNG carriers are expected to be in operation.
Counting extra crews for backup, sick leave or holidays, the LNG industry will need about 9,000 additional skilled crew members at sea.
On each ship, a minimum of 10 crew members must provide proof of special training. With the current demand exceeding the short-term training capacities, skilled crews are a hot item on the market. The monthly wage of a captain has risen from US$12,000 to $16,000 within a short time. “To hire any of my officers, shipowners now have to pay a transfer fee,” says Croatian crew manager Lahor Magazinovic. “It is just like football.”