Yards Moving Forward - GL Group

What a Wonderful Weld
WELDING TECHNOLOGY
For a new ship, many kilometres of steel plate have to be welded together. As in other
sectors of industry, the processes and manufacturing procedures are subject to
constant change
South Korea is the world leader in the construction of
container ships. As a result of the record level of orders
placed over the past few years, the yards throughout the
country are bursting at the seams. Since new dock capacities
cannot be conjured up overnight, the companies are making
renewed efforts to speed up the shipbuilding process itself.
The current focus is on reducing the assembly times in the
docks, i.e. by reducing the time required for joining the individual
sections. A key factor in achieving this goal is the welding
procedures. “Shorter welding times mean reduced dock
periods and lower costs overall,” explained Ludger
Hachmöller from the Materials / Welding Department at GL
at a conference which took place early in May in Hamburg.
To be able to “sew” together the individual sections, with
plate thicknesses sometimes exceeding 70 mm, at an even
faster pace, the yards are intensively pushing forward the
electro-gas welding process – a high-performance method
for vertical application. Here an electrode guide tube moves
up the groove between the parts to be welded. This “snout”
feeds out the filler wire to be melted under the inert shielding
gas in an electric arc, which also melts the edges of the sections.
The molten weld pool is kept in the groove by ceramic
backings and sliding copper shoes, ensuring that the parts
are properly joined after cooling. Previously, a large number
of welding passes were needed to join the thick outer plates
of the cargo ships. Moreover, the conventional procedure was
slow and labour-intensive. “Now, only one man is needed to
operate the welding machine,” says Hachmöller. The welder
controls the apparatus from a lift cage. The tractor of the
welding machine is guided along the hull by a rail, enabling it
to move at a speed of up to 2.5 metres an hour. The method
is used not only for making the butt joints between sections
but also for fabricating the blocks during preassembly. Before
this method can be applied, however, detailed procedure
tests, as is the case with other welding processes, are necessary
in order to examine the influence of the high level of
heat input during electro-gas welding on the mechanical
and technological properties, e.g. tenacity and strength. The
corresponding care must be taken in selecting the materials
and designing the seam geometry. Since the method is relatively
new for greater plate thicknesses, the yards, steel producers
and classification societies such as GL are working on
individual solutions. “We are making every effort to involve
the steelmakers more closely, so that the required steel
grades can be available ‘off the shelf’ in future,” says
Hachmöller. ■ MPH
For further Information: Ludger Hachmöller, Material and Welding Technology,
Phone: +49 40 36149-9206, ludger.hachmoeller@gl-group.com
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