VomBaur.qxp 1/7/09 4:14 pm Page 62
LNG
Aluminium Double-barrier Tanks
a report by
Michael vom Baur
Managing Director, Wadan Yards CNG Technology GmbH
The aluminium double-barrier tank (ADBT) system is an independent to qualify and proof material properties and tolerances.
type A tank design. It is self-supported in the ship’s cargo hold by Manufacturing technology for these tanks has also been one of core
bottom supports and a keying system for antirolling and research and development areas, with full-size mock-ups of various
antiflotation. The tank is prismatic in shape with or without tank parts and construction details carried out.
chamfering to suit the ship’s hold form and provides for a flat main
deck for floating production, storage and offloading (FPSO) Primary Concept
modules. Thermal insulation is external. It can be built in various The primary structural elements of the ADBT are various flat panels,
sizes from small 1,000cbm fuel tanks up to very large 150,000cbm which are produced by friction-stir-welding (FSW) large extruded
tanks for storage use. aluminium sections together (see Figure 1). Double-wall-panel
sections are joined by both flanges simultaneously, which produces
ADBT is primarily constructed of aluminium H-extrusions forming the both tank barriers in one operation. Single-wall panels are used for
primary and secondary barriers. Racking and shear forces are met by the large webframes. FSW is nowadays a well established material-
an internal frame system including tension beams connecting the joining method pioneered by TWI. Today it is used in many
opposite walls. The tank internals act as effective sloshing applications in the automotive, aircraft and train industries; large
suppressors and hence the tank system allows operation at any aluminium FSW panels are also used in the shipbuilding industry for
filling level. the construction of lightweight decks for cruise ships.
The ADBT liquefied natural gas (LNG) containment system originates
The primary structural elements
from joint development between Aker Yards LNG Unit and Aker
Kvaerner Engineering & Technology, in close co-operation with DNV of the aluminium double-barrier
Research & Innovation. Since first approval, DNV has withdrawn as a
tank are various flat panels, which
project financier, and responsibility for the development now rests
with what has become Wadan Yards LNG Technology GmbH as part
are produced by friction-stir-
of Wadan Yards Group and Aker Engineering & Technology AS as
welding large extruded aluminium
part of Aker Solutions.
sections together.
Development work was started in early 2005 and first approval in
principle (AiP) was granted by DNV in September 2006. Further Double Walls
concept development brought second AiP in March 2007 by DNV. ADBT utilises the good strength properties offered by sandwich-type
Similar approvals were granted by ABS, LR and BV in 2008. panels for the tank boundaries: the bottom, side and end walls, as well
Currently, documentation for general approval for ship application as the tank top (see Figure 2). The beauty of the sandwich-wall structure
has been completed with DNV Maritime as the approval level is that it provides the primary and secondary barriers at the same time,
towards full qualification of technology, as well as for design as it utilises the high bending stiffness offered by the fact that both
approval with Bureau Veritas. barriers provide strength. This is possible on the condition that IGC
4.7.4.3 is fulfilled: the mechanism of failure for the primary barrier does
A complete materials development and testing programme has been not also cause the failure of the secondary barrier and vice versa.
undertaken, including extrusion tests and cryogenic testing, in order
Because the H-extrusion section utilised incorporates a section web
connecting both flanges (barriers), there must not be any failure
Michael vom Baur is Managing Director of Wadan Yards
CNG Technology GmbH, where he previously served as
mechanism through that web from one barrier to another. This
Senior Vice President of Technology. In 2006 he was means that there must not be any welds in the said web, but only
Head of LNG Activities at Aker Yards ASA, and occupied
base metal. ADBT J/V has succeeded in designing a way to join the
several management positions covering marketing and
sales, business development and general management
sandwich panels to each other such that the webs are not connected
in the shipyards sector. He is a Member of the Council
to the next panel, but these are discontinuous, thus fulfilling the
of German Society of Naval Architects (STG). Mr vom
requirement of no welds in the webs.
Baur graduated as a naval architect at Technische
Universität Berlin with post-graduate qualifications in
marketing and finance.
Webframes
E:
Michael.vomBaur@wadanyards.com Rigidity against racking and shear forces is provided for by large
ring webframes (see Figure 3). These webframes also support
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© TOUCH BRIEFINGS 2009
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