World-class welding technologies - Subsea 7

demonstrates how careful assessment of project requirements
and production factors can deliver cost-effective welding
solutions. The new technology is about to be deployed in
Brazil, and will thereafter be rolled out to Subsea 7’s other
fabrication sites worldwide.
In the case of larger-diameter carbon steel pipelines, the use
of the mechanised Pulsed Gas Metal Arc Welding (PGMAW)
process is now established as the welding method of choice
for both riser and flowline applications. The process utilises
low-heat input which results in excellent mechanical properties
in the girth welds.
The process can be deployed using either single torch, or in
the case of larger diameter pipe, dual torch welding in order
to improve productivity. This system is highly mechanised so
that the role of the welding operator is simply to supervise the
process with minimal intervention required.
Since the current welding system was introduced to Vigra in
early 2011, about 400km of carbon steel pipeline have been
fabricated, with productivity and quality exceeding targets.
The overall weld repair rate, which is a key quality indicator, is
less than 0.5%.
Subsea 7 has further developed the PGMAW process for use
in the fabrication of metallurgically clad pipe.
Welding of clad pipe requires the use of dissimilar welding filler
material, i.e. Alloy 625. Subsea 7 has carried out extensive
welding trials to optimise pulsed welding parameters and
shielding gas composition.
The qualified PGMAW solution makes use of the Controlled
Metal Transfer (CMT) process for root welding, an advanced
PGMAW technique which allows the weld root to be deposited
very precisely, giving good control of the root bead quality and
profile. These features are essential to maintain the corrosion
03
performance of the clad pipeline. During production, an
internal camera and laser profiling device is utilised to perform
an assessment of the quality of the root bead.
The developed welding solution will be implemented in
production this year for a number of pipeline projects, which
will involve over 70km of metallurgically clad and mechanically
lined pipe risers.
For smaller diameter pipes (4-inches and below) a mechanised
welding system has been developed by Subsea 7 and
implemented at Vigra. A key benefit of this system is to
provide a more precise control of the heat input in order to
maintain the optimum mechanical and corrosion performance.
This solution, initially deployed on a 2-inch duplex stainless
steel service line, was based on the use of the orbital Gas
Tungsten Arc Welding (GTAW) process using the Polysoude
welding system. Production welding has been in progress
since November 2011 with weld quality and productivity
meeting expectations, and has confirmed that this technology
can be successfully deployed on a global basis.
The 2-inch duplex line was also a Vigra “first” for the use of an
automatic arc monitoring system on the firing line to capture
and record the essential welding parameters.
Operations will begin in 2013 at Subsea 7’s new Global
Welding Development Centre in Glasgow, which will
incorporate 18 welding bays including facilities for J-lay and
S-lay pipeline welding, and will act as a central technical
authority for the development and qualification of all welding
procedures for all Subsea 7 pipeline fabrication bases around
the world.
This major initiative by Subsea 7 will give clients the assurance
of quality and delivery of pipeline welding performance at a
competitive cost.
For further information contact eric.law@subsea7.com
seabed-to-surface