DRILLING & COMPLETION
PIPELINES & FLOWLINES
Pipe-in-pipe technology adapts to changing
needs in deep and shallow water
Sylvain Denniel
Technip
Onshore pipe-in-pipe assembly.
(Photos courtesy Technip)
Over the past two decades, the pipe-in-pipe (PiP) product has become an essential part of the subsea field development en- gineer’s “tool box.” Due to its high insulation performance it minimizes heat losses from the transported fluid to the nvironment that more traditional subsea coatings cannot
provide. This is achieved using thermal insulation of very low thermal conductivity, such as aerogel, encased in dry atmospheric conditions between the inner pipe or “flowline,” which transports the
fluid, and the outer pipe or “carrier,” which provides the mechanical
protection from the subsea environment.
Other benefits of the PiP solution include compatibility with high
temperatures (in terms of material and enhanced compliance with
large axial loading), stability on the seabed, and protection by the
outer pipe against external loads. In some cases this may obviate
the need for burial.
In 2014, Technip installed its 50th PiP via the reel-lay method; the
first project was in Australia in 1989. Along the way, the company
has advanced the technology at various points. For example, the
company’s third PiP project in 1997 on Statoil’s Gullfaks field in the
Norwegian North Sea. This represented the first implementation of
a corrosion resistant alloy (CRA) flowline, but more importantly, the
un-bonded design was to become the essential DNA of the product
for the projects that followed.
During manufacture, flowline and carrier pipeline stalks are first
welded and inspected. Then the flowline stalk is progressively sleeved
into the carrier pipe stalk, while thermal insulation panels and nylon
rings are hand-applied at regular intervals. The function of the nylon
rings, known as centralizers, is to maintain the two pipelines concentric and to mechanically protect the thermal insulation during each
phase of the PiP assembly, installation, and operational life. Once full
PiP stalks are completed, they are spooled onto the reel-lay vessel following intermediate tie-in connections.
The next major milestone was the first implementation of a reeled
PiP on a deepwater project, BP’s Nile field in the Gulf of Mexico
(GoM) in 2001. Novel features introduced for this installation included microporous insulation, designed to meet the field’s challenging
thermal demands, and the implementation of qualified buckle arres-tors and waterstop features. The aim was to limit the potential consequences of a (very unlikely) wet buckle event. Experience gained
on this deepwater project proved important for future projects in the
GoM, West Africa, and Brazil.
In 2002, Technip installed the first reeled PiP steel catenary risers on Shell’s Nakika field in the GoM in water depths of more than
2,100 m ( 6,890 ft). Four years later, Total’s Dalia field development
offshore Angola featured the first qualification and industrialization
of superior aerogel insulation to achieve exceptionally high thermal
performance.
But there have also been technical advances in the shallower environment of the North Sea. In 2011, the first implementation of a
fully reelable bulkhead on BP’s Devenick project in the UK central
North Sea was a breakthrough for the reeled PiP product. It enabled
