CLAXTON TAKES
THE BITE OUT OF
PIPE TENSIONING
Tension rings are designed to apply
tension to plain pipe. The traditional
design uses saw teeth that “bite” into
the surface of the pipe to hold it tight.
This produces a very effective grip,
but it also damages the pipe’s
surface. Serious fatigue issues that
can shorten component life may
occur due to the stress concentration
points in the damaged area.
The industry has long been aware of the
problems that arise from inappropriate
pipe handling. Many technical papers
describe the results of poor handling of
corrosion-resistant-alloy tubular goods.
Research has shown that conventional
spider and elevator inserts cause die
marks that promote corrosion, and that
slips and tongs produce permanent
marks on pipe bodies and tool joints that
can lead to high stress concentrations,
which promotes fatigue damage.
Early in 2013, Claxton was asked to
develop a fatigue-sensitive method for
applying pipe tension. The team took up
the challenge and broke the work into
two phases: selecting the most effective
technical solution and then running
extensive tests on the preferred option to
assess its suitability.
The grit face of the Gecko Grip tension ring
being installed on a riser.
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The Claxton team looked at various
options that would deliver the necessary
performance for pipe tensioning
applications and selected a concept
based on an established technique.
This field-proven technique has been in
service in the North Sea since the late
1990s to provide a powerful gripping
capability in a completely different oil and
gas application.
TESTING, QUALIFICATION AND
RESULTS
After rigorous and extensive testing,
Claxton finalised the design of the new
Gecko Grip tension ring, which uses slips
with a high-friction coating instead of
teeth. This approach significantly reduces
the stress in the installed area of the pipe
component and so improves its longterm fatigue performance.
Gecko Grip slips can apply tension to
slick pipe of all sizes, weights and grades,
thereby saving rig time and eliminating
space-out issues and the need for
welding. The system is available in
slimline tension rings and standard
positive grip tension rings providing a
rating up to 400 Te.
The abrasive coating in the Gecko Grip
system protects tubulars by minimising
surface marking. The indentions from
tensioning using the Gecko Grip are
typically less than half of the API-defined
allowable surface defect depth. They also
form a random pattern to help eliminate
the linear stress features that reduce
fatigue life and pipe strength. In addition,
the coating’s composition means that the
slips will not create pits containing iron or
steel contaminants that could cause
rapid, premature corrosion failure in
corrosion-resistant-alloy tubulars.
Gecko Grip is aimed at production
applications with longer installation times
and for areas where customers have
specific concerns about stress raisers
and fatigue. It is also effective when
drilling with ultra-heavy duty jackups and
when tension loadings are higher owing
to deeper depths and heavier well control
equipment. The original saw-tooth
design, meanwhile, continues to provide
good support for many exploration,
drilling and short-duration applications.
While developing Gecko Grip, the
Claxton team had to overcome some
substantial technical challenges.
Perhaps the most significant of these
was establishing confidence that the
abrasive coating would not shear off
during tensioning operations. Working
A Claxton Gecko Grip ring in use during a
North Sea Drilling campaign.
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TRADITIONAL
TENSION RING
‘TOOTH’ BASED GRIP
in conjunction with the coating
manufacturer, Claxton confirmed that the
proprietary process that applies the
abrasive material produces a bond that is
stronger than the base material. There
was no evidence of shearing during the
extensive testing.
Dannie Claxton, technical director,
Claxton says, “We developed Gecko
Grip by drawing on extensive knowledge
of the systems available within the
industry. The short development time,
less than a year from concept to
commercial application, shows the value
of applying proven technology in new
ways. We expect Gecko Grip to have
worldwide application, but our initial
GECKO GRIP
ULTRA-HIGH SURFACE
AREA GRIT BASED GRIP
focus will be on the North Sea market.”
But there was more to the development
process than taking an existing product
and repurposing it, as Matthew
Marcantonio, research and development
manager, Claxton, explains, “The
development process called for some
fundamental theoretical work. We had to
establish in-depth understanding of how
the existing products worked and take
an informed view on how any new
system we developed would perform
under field conditions. This project was
not a small step because we were
moving away from established methods
for pipe tensioning that have been in place
for 20 years or more.
TRADITIONAL TENSION RING
“In addition, we had to consider a wide
range of component variables. It was
never going to be enough to have a
tensioning system that worked on some
pipe, some of the time. So, we tested
Gecko Grip on all kinds of paint finishes
and coatings to determine its applicability.
From bare steel to greased and painted
in various combinations, we had to be
sure that Gecko Grip could handle
anything that a traditional tensioning
system would.”
The results of these tests were very
encouraging. The Gecko Grip performed
as required across the full range of pipe
types and coatings, and the reduction in
surface damage was clear for all to see.
Even better news for operators is that the
cost differential of applying Gecko Grip is
insignificant when weighed against the
potential damage to pipe and long-term
fatigue issues associated with traditional
tensioning equipment.
COMMERCIAL APPLICATION
In mid-2014, a riser project in the North
Sea provided Claxton with its first
commercial opportunity to install the
Gecko Grip tension ring.
The team delivered two 200Te systems
to tension and handle the high-pressure
drilling riser on a newly built jackup drilling
rig for an expected four-to-five-year
drilling programme.
The first (primary) unit was used
successfully for three months, before
removal to assess its performance. The
second (backup) unit was then installed.
“The customer wanted to use the Gecko
Grip for this project to stop fatigue
damage on the conductor pipe and saw
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a marked improvement by switching to
this product. The primary unit was
inspected after use and was found to be
in exactly the same condition as when it
was installed. The second unit also
worked well out in the field, so it was a
very successful result for the Gecko Grip
and the client,” says Marcantonio.
“When the units went out on the job, they
just sailed through. The project went very
smoothly and the installation team
reported the units as being very easy to
put together,” says Marcantonio. “The
extensive upfront work also meant that
there was no need to amend the design
for future projects.”
Claxton put the new tension rings
through a full development cycle of
sample testing, scale testing and then
full-size testing before sending them out
to the North Sea project.
This upfront work paid dividends in early
2015 when a third Gecko Grip tension
ring entered service for an additional
client; field proving the technology up to
400Te.
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owners have trusted Claxton to make their
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– visit our website to find out why, or learn
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