Analysis Points To Pipe Alloy For Safe And More Economical LNG Transport

Access to natural gas will be a vital part of the world’s energy strategy in the years to come. Because the regions of greatest new supplies are distant from sources, demand for liquefied natural gas (LNG) is forecast to more than double by 2020 compared to an increase of only 2-3% in overall gas demand for the same period (Wood Mackenzie LNG Tool 2008). LNG technology provides the means to transport large volumes of gas around the world in liquid form thus bridging the transportation gap.

Conveying LNG from plant to transportation vessel and back again requires a pipeline along which the liquid gas flows. LNG pipelines must be kept below circa minus 160oC, thus introducing the need for insulation and steels that can perform at ultra-low temperatures.

Corus Tubes is developing a cost-effective solution for LNG conveyance and jetty lines using 9% nickel steel, which has an established track record of use for cryogenic applications, but has not been fully utilized in pipelines. The company commissioned J P Kenny Ltd, one of the world's largest pipeline and subsea engineering and management contractors, to study its relative performance for an LNG jetty-supported unloading line compared to conventional and alternative technologies and to quantify the resultant potential material, design and construction cost savings.

Innovation In LNG Transportation

LNG is created when natural gas is cooled from ambient temperatures to less than minus 160oC. The cooling is performed in large industrial (liquefaction) plants that take gas gathered from contiguous fields and process it for despatch via vessel. The vessels themselves contain from approximately 80,000-145,000 cubic meters of LNG (M.W. Kellogg; LNG Terminals 2002), which is then transported to receiving terminals (re-gasification plants) worldwide.

As demand for energy increases LNG technology is being increasingly used to exploit reserves of “stranded gas.” LNG technology is expensive but for distances greater than 1,000 km, it represents the most economical method to transport natural gas. For lesser distances, gas can be transferred in high-pressure pipelines.

Thus far, LNG installations have been politically sensitive for a number of reasons, not least the question of safety. Large volumes of gas stored in liquid form present a potential catastrophe should the incorrect approach to design and specification be taken. As such, there is pressure on LNG-processing plants to be remote from habitation. Furthermore, the potential risks involved in the transfer of LNG from plant to vessel are managed by locating and performing the loading operation remote from the plant and in deeper water berthing. This requires a pipeline to move the LNG safely from the plant to the vessel.

Material Choice And Design

There is now only one option to transfer LNG from the shore to the vessel – through a stainless steel rigid pipeline supported above sea level on a jetty. There are approved systems for running the pipeline subsea but, to date, such a system has not been applied in practice. The transportation of LNG presents the following challenges: