Feature 1 | GREEN SHIPPING
gas at very high pressure is taken into account by RINa. “The rules are aimed at mitigating any escape or leakage which could cause an explosion and the possibility of the extremely cold liquid gas causing structural damage,” explains Cogliolo. “All materials and structure which are in gas service or could be affected by a leakage must be able to withstand the low temperatures, and the arrangement onboard of storage tanks, piping system and engine rooms must minimise the likelihood and the consequences of an accident. Tanks and gas piping must be located so as to minimise the risk of collision damage.” A key issue is to site LNG tanks in
protected locations near the centre line, but this raises questions of space on board.
“The type of tanks used for oil
cannot withstand the pressures which build up in a tank of LNG over even a short period and LNG requires a lot more space than oil. Tanks capable to sustain gas pressure are required, and even then some gas will have to be used within two weeks if pressure is not to become too high. We see that tankers can mount cylindrical tanks on the open weather deck, but other ship types such as bulkers and ro-ro’s will end up eating part of the cargo space if they want to use gas power,” says Cogliolo. Risks of gas leakage are tackled by
requiring that all gas pipelines are double walled. The space in the double
wall is alarmed so that any escape of gas from the inner pipe will be contained by the outer pipe and also let the crew know there is a problem. Routeing of gas pipes to avoid accommodation and explosion risk areas is also required. “You can see how the design
consequences of a decision to build in LNG as a fuel multiply,” says Cogliolo. “Estimates of the space penalty vary, but depending on the ship type the amount of space needed for a liquid gas fuel installation compared to a conventional oil one is in the order of three to four times as much. Either you need extensive monitored and alarmed double wall piping, or two completely separate machinery spaces. And you have to find room for the gas process machinery, at the same time, in a dual fuel installation, as having all the normal oil outfit.” RINa is working with shipyards and
owners on a possible new tanker design and retrofit of ro-ro ship with a gas fuel system, to be used to fuel the vessels in low sulphur areas and looking at the potential for gas fuel on a cruise ship. “All those are technical issues, which
can be solved by good engineering and risk assessment techniques,” says Cogliolo.
“But there is an equally
important area where we as class have less remit, and that is the crew culture and expertise. Our notation does not address crew training, but how to
keep things safe and efficient from the structural and outfit perspective. These issues are linked, because the crews of passenger ships and cargo ships are not used to handling gas, and not used to LNG ship-to-ship transfers, and both of
these will become common once
gas is in greater use. We expect LNG bunkering to be done from small LNG tankers, which will mean lots of LNG ship-to-ship transfers. Crews need training and a different attitude to safety for that.” Cogliolo insists that LNG is not a new
technology: “But so far ship-to-ship LNG transfer is done only by experienced gas carrier crews. So we will need to see a big effort to train up the crews of other ships using gas as a fuel. Te training will have to mirror that of gas carrier crews and focus strongly on ship-to-ship transfers. Tat will be an important part of the IMO Code when it is ready.” RINA has been heavily involved in the
development of onshore, offshore fixed and the world’s first offshore floating LNG terminals as Italy becomes a major gas importing and distribution hub for Europe. “We have a lot of experience with LNG, we are very keen on the environmental benefits it can offer and we see the potential of LNG as a fuel for ships,” says Cogliolo. “The role of class is to enable the benefits of LNG as a fuel to be realised in a safe and practical manner.” NA
Building a small gas carrier with cylindrical tanks.
48 The Naval Architect May 2012
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