Sealing
success subsea for BP
Posted: 26 March 2004
A leaking sea-bed flanged connection has been successfully repaired
using Furmanite leak sealing technology, installed by ROV, at 500
metres depth for BP in the Foinaven field, west of Shetland. The
achievement has enabled oil production to continue at capacity,
by allowing water injection pressure to continue.
The success was realised by Furmanite working with Subsea 7, whose
ROV systems were used to install the bespoke Furmanite-designed
clamp and to mix and inject the specially-formulated sealing compound
— quite a challenge to achieve by remotely operated vehicle.
The 10-inch leaking flange joint was situated on the flowline termination
assembly at the base of the Foinaven water injection riser, which
feeds injected water to different parts of the reservoir. Seawater
ingress at the joint had caused corrosion, which was threatening
the output capacity of the field.
Furmanite’s clamp solution was designed to cover the flange
connection. “Space was limited and the clamp had to be operable
by ROV, with no opportunity to use heavy lifting gear, so while
designed to cover the flange connection the clamp was also kept
to minimum dimensions (some 666mm wide, 680mm high and 140mm deep,
weighing around 200kg).
It was also engineered to be compatible with Subsea 7’s bespoke
ROV deployment system,” Furmanite project engineer Mike Bowerbank
explained.
Installation involved lowering the clamp over the pipe, with the
lower half suspended by one clamp bolt; the clamp rotated until
both halves were in-plane with each other, normal to the pipe axis;
and (with both bolts now in place) the lower half drawn up on the
bolts, bringing the clamp halves together.
With the two halves some 100mm apart the clamp was moved along
the pipe and positioned over the flanges, at which point the bolts
were initially tightened to seat and compress the seals, and then
fully tensioned to the necessary pre-load to ensure that internal
pressure forces would not part the clamp halves.
Critical to the success was the sealing resin, which was injected
once the clamp was in place to seal the gap and bolt clearances.
The challenge was to get the resin mix absolutely right to match
the leak profile – in other words sufficiently fluid to allow
injection and ensure it reached the leak point, while sufficiently
viscous to ensure it bridged the 60mm hole without extruding into
the pipeline.
In keeping the clamp as small as possible (covering the flanged
connection rather than fully enclosing it), the bolt clearances
also had to be considered, as these in effect provided 32 potential
leak points that, with full pressure restored, the water would seek
to find once the original leak path was sealed. It was therefore
crucial that the resin must reach and seal these too.
A further challenge was to ensure that the resin could be mixed
and injected remotely. “Traditionally for subsea applications
the sealing resin would be mixed on the surface, and divers used
to install and inject the clamp,” Bowerbank explains.
“Clearly in this instance, with the depths involved, the
whole process had to be undertaken by ROV. If the resin were sent
down ready-mixed it would have cured before it could be injected,
so a special remotely-operated injection and mixing system had to
be developed. This involved injecting from separate storage cylinders
through a mixer unit to ensure a good homogeneous mix, and then
into the clamp.”
Bowerbank adds that extensive testing was undertaken to ensure
that this crucial element in the repair design would work as required.
Two clamps were manufactured so that one could be used for testing
purposes, and two test spools were manufactured (at Furmanite’s
facility in Carlisle), with the appropriate type of 10-inch flanges
and a representative defect in the gasket.
The testing was undertaken at both Furmanite’s and Subsea
7’s premises. A test rig was built to the Subsea 7 skid injection
unit specifications, and the two-part compound injected into the
flange via the clamp, with the injection rig hoses, clamp and test
spool flooded with water to simulate seabed conditions. The seal
was then pressure-tested, following the cure period, by pressurising
the test spool.
The clamp was successfully installed and injected, sealing the
leaking joint, in just 24 hours (including injection and cure),
ensuring that water injection pressure could be maintained.
Commenting on the project, BP senior subsea engineer Sandy Meldrum
said: “We were delighted with the solution design and implementation,
and the co-operation between Furmanite and Subsea 7. The leak was
presenting a problem to our production performance – a situation
we had to resolve, preferably without having to shut down. We’ve
long worked with Furmanite and know their capability to engineer
bespoke solutions where required.”
Bowerbank adds: “This is another example of our ability to
develop solutions to meet customers’ needs, helping them keep
their assets operating and earning at maximum capacity.”
For more information see www.furmanite.co.uk
Posted by Richard Price,
Editor Pipeline Magazine
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