Looking for Arctic solutions30/11/15
Material properties in cold climate challenge oil companies going north
Oil companies have already surveyed resources in southern parts of the Barents Sea such as Johan Castberg, Wisting, Atlantis, Apollo, Gotha and Alta. If these fields are to be developed, there is need for more knowledge on how materials behave at low ambient temperatures. This is the topic of a research project lead by SINTEF, SMACC (Fundamental Studies of Materials’ Behaviour for Future Cold Climate Applications), where scientists study several materials and their response to loads at low temperature to find robust solutions for use of materials and structures.
Advantages with aluminium
The combination of low weight and excellent corrosion properties makes aluminium an attractive material for a harsh environment. However, its main benefit is that its properties do not deteriorate at arctic temperatures which is in fact the main challenge for structural steel. At low temperatures, steel may have a transition from ductile to brittle material behaviour. The low weight of aluminium reduces the production, transport and installation costs; the excellent corrosion properties reduce the maintenance cost; and the fact that there are no deterioration of material properties at low temperatures contributes to a high safety level in a sensitive environment where climate and distances make inspection and repair challenging.
|The research project “SMACC -Fundamental Studies of Materials’ Behaviour for Future Cold Climate Applications”, supported by the Research Council of Norway, is now in progress. The five-year long project (2013-2017) is carried out by SINTEF, NTNU and DNV GL in co-operation with the oil companies Statoil, ENI, Total and Lundin; polymer companies Trelleborg Offshore, Bredero Shaw and Borealis; steel suppliers JFE Steel, Posco, Kobe Steel, and SSAB; aluminium suppliers Hydro and Sapa; and the engineering companies Nexans, Marine Aluminium, FMC Konsberg Subsea, Aker Solutions and Kværner Verdal.|
Welding reduces the material strength
In general, aluminium alloys have good weldability. However, the strength of some aluminium alloys may be reduced by up to 40-50% in the worst case as a result of arc welding. If this problem was solved, a big obstacle against the use of aluminium in structures would be eliminated.
Aluminium used at -162°C
Aluminium has been used in spherical tanks on carriers for liquid natural gas transport. These are designed for -162°C, and have been made in aluminium alloy 5083 of up to 60mm thickness. The weight of such tanks was also considerable at 800 to 900 tonnes. In addition to their resistance to becoming brittle at low temperatures, they need to be lightweight, corrosion-resistant and workable to ensure safety during ocean transport. The strength of aluminium may increase when going to such low temperature.
Aluminium has gained some market in the offshore industry. Apply Leirvik has delivered many living quarters made in aluminium modules over the past decades.i Marine Aluminium produces aluminium helicopter decks and other structures (e.g. telescopic gangways, handrail systems, offshore containers).ii However, all these are secondary or tertiary structures, and aluminium alloys are not yet used in primary structures. Norway has 40 years of experience with structural steel offshore platforms, and it will be a high barrier against the use of aluminium. One of these barriers is definitely the strength loss associated with the welding of some aluminium alloys. This challenge can be reduced by applying the right design of the products to be welded. In order to increase the structural use of aluminium, the strength loss should be minimised which requires considerable R&D effort.
Barents Sea watch
Unfortunately, there is very limited experience with offshore installations in the Arctic region. Shtokman, located in the northwestern part of the Russian sector of the Barents Sea, was discovered in 1998. It was supposed to be the first such installation, but has been postponed many times. Meanwhile, the Goliat field is being developed using a floating production facility (FPSO). It will be equipped with tied-in subsea templates and will be able to process, store and offload oil. Although not yet in production, the Goliat Field is constructed in such a way that rain, snow, and ice will drain from walls and roofs, thus enabling the platform to withstand all anticipated ice loading. Heating cables will be installed in the floors in especially exposed areas such as evacuation routes and the helicopter deck. The experience from the Goliat field will be important in the years to come since conditions will gradually become harsher when moving further north.
The SMACC project is financed by the Research Council of Norway and numerous industrial companies, most of them non-Norwegian. However, there are many stakeholders in the Arctic region, and the national efforts could be better co-ordinated through the establishment of European projects, with possible participation from Canada and the USA. On the other hand, it seems that the European Union type of project does not care very much about support to oil and gas-related projects.
Odd M Akselsen
Senior Research Scientist
Sintef Materials Chemistry, Norway
+47 9340 1703
i The living quarter delivered for Saga Petroleum’s Snorre platform was the largest aluminium structure ever built for the offshore industry, it became a pioneer project for Apply Leirvik.
ii The first aluminium helideck was delivered in 1974. The first telescopic gangway delivered offshore in 1979.