OIL RIG RISER
PIPE LINING
Rehabilitation of a
corroded oil production
platform rise liner pipe
from a single access point,
in order to reduce the
seawater contamination
of diesel fuel.
APACHE
North Sea Ltd.
CONTRACTOR
Wood Group Engineering Ltd.
LOCATION
North Sea
YEAR
2006
CHALLENGE
Rehabilitate a corroded riser
liner pipe to prevent seawater
contamination of diesel fuel.
SOLUTION
Insertion of a 140m PE liner
from a single access point using
sliplining technique.
BENEFITS
Reduction of costs by >90%.
Achieved bunkering targets.
As North Sea oil production platforms age, remedial
maintenance is required to sustain rig operations.
In the Forties field, the Alpha platform had begun to
experience a significant increase in the expenditure
associated with the consumption of filters that are
used to reduce the levels of seawater contamination
in the diesel fuel to an acceptable level. Wood Group
Engineering (North Sea) Ltd (WGE) were asked to
identify the issue and engaged Radius Subterra
to assist in the implementation of an economical
solution to improve the quality of the fuel.
CHALLENGE.
By 2000, an increasing consumption rate of filters used
to reduce the inevitable seawater contamination in
the diesel fuel was costing approximately £300,000pa
across Apache North Sea Ltd’s Forties field.
On the Forties Alpha oil production platform, diesel
fuel for the powering plant is stored in the hollow steel
platform legs. The fuel floats on a column of seawater
in the base of the leg. To decant fuel for use, seawater
is pumped into the base of the leg through a 6” NB
steel tube. The fuel is discharged from a second port
elsewhere on the leg. Bunkering of fuel is the carried
out by reversing this procedure.
A CCTV survey revealed substantial corrosion and
perforation of the riser bore, particularly at the upper
levels, which was significantly adding to the level of fuel
contamination. A sludge/oil mixture adhering to the
riser bore was also reducing its flow efficiency.
SOLUTION.
Enhanced diesel filtering was rejected in view of the
already unacceptable fuel decontamination costs, whilst
conventional pipe relining technologies would fatally
compromise the platform’s stability, due to the need for
Radius house, Berristow lane, South Normanton, Alfreton, Derbyshire, DE55 2JJ
T: +44 (0)1773 582317 | [email protected]
www.subterra-pipelines.com
A part of Radius Systems
liner pipe, and then be inflated from the
liner insertion point to form a closed-end
annular space around the PE liner in the
bore of the bend.
Finally, Subterra used its in-house resin
technology expertise to devise a bespoke
grout that would have sufficient pot life
to ensure that the closed annular space
in the bend could be fully grouted, but
which would cure within 2 hours, so as to
expedite the completion of the works.
Lowering of
pushing machine
access to both ends of the liner pipe and the removal of its
contents. Single-end launched cured-in-place pipe lining
North Sea
Ltd.infeasible, as contact with the leg
technologies
were also
contents would have either contaminated the resin, or
impaired the curing process. Strapping a new steel riser
to the outside of the platform leg was a possibility but was
expensive at approximately £3.5M.
It was essential that the chosen solution did not reduce
bunkering rates to unacceptably low levels, to minimise
any additional time spent by the supply vessels conducting
the hazardous refueling task. Thus, Subterra suggested
that sliplining the riser with an undersized PE pipe from a
single access point might be feasible.
The riser was decommissioned and
drained before the PE liner was inserted
and the fast-setting annulus grout
applied, with the full process taking
approximately five hours. The lined
riser was then reconnected and
successfully recommissioned.
RESULT.
Radius Subterra developed a number
of innovative adaptations of its
existing technologies to devise a
method, which succeeded in sliplining
the riser from a single access point.
As a result, the revised target
bunkering rate of 80m3/hour was
achieved and the cost to complete
works was less than one tenth of
other proposed solutions at £250,000.
IMPLEMENTATION.
Full-scale yard trials confirmed it was possible to push
a 110mm OD SDR 11 MDPE/PE-80 pipe around the 90o
bend and on down the riser past the two 45o bends to the
bottom along approximately 140m without collapsing.
The material’s suitability for use in contact with diesel fuel
was confirmed and calculations supported that the PE pipe
would not collapse under the predicted subatmospheric
pressure excursions, despite the slight transverse
indentations induced in the liner within the 90o bend.
To assure the stability of the inserted liner, Subterra also
devised a shroud that could negotiate the bend with the
Flanged spool piece
Radius house, Berristow lane, South Normanton, Alfreton, Derbyshire, DE55 2JJ
T: +44 (0)1773 582317 | [email protected]
www.subterra-pipelines.com
A part of Radius Systems