Since 2004, a joint industry project (JIP) has been working to
develop the capability to repair 10 to 24-in. ANSI 1500 pipelines in sea water
depths from 1,000 to 10,000 ft. During the first phase of the JIP, participants
identified and evaluated diverless pipeline repair methods and available repair
tools (leak clamps and connectors). The second phase involved qualification
testing of a novel low-cost method of using structural repair clamps as
connectors to repair a spool piece.
In 2005, though, hurricanes Katrina and Rita impacted the JIP
participants' thinking on repair methods and tools, which ultimately led to the
formation of DW RUPE–Pipelines, a co-ownership group consisting of four
founding co-owners (Enterprise Partners, Enbridge, BP, and Eni), for purchasing
and storing $12 million in repair system components for emergency call-out.
Now, the tools are all ready for service, and the DW RUPE tools are ready for
use when needed. (Note: The co-ownership group is open to any interested new
members.)
RUPE is an acronym for "Response to Underwater Pipeline
Emergencies" and is patterned after the shallow-water RUPE Repair Tools
co-ownership group, which has been in operation for over 30 years, and now
consists of more than 33 co-owners worldwide.
Progress to date
The co-ownership group called DW RUPE Repair Tools is in its
fourth year of operation after originating in May 2007. Four companies –
Enterprise, Enbridge, BP, and Eni – agreed to co-fund a suite of deepwater
pipeline repair tools at an overall cost of $12 million. Preceding the
formation of the co-ownership group were two JIPs starting in 2004 and running
through hurricanes Katrina and Rita in 2006. Both focused on how to make
repairs and on what tools would be required.
Pipe handing arrangement for system integration trials
In 2004, JIP
participants assessed felt that the risk of damage was remote, but the
consequences of failure in lost revenue and environmental damage were quite
high. They recognized that the essential repair tools at that time were the
traditional connectors to join pipe ends and clamps to seal a small leak in a
pipe. With further study, though, the group realized that the leak clamp would
require a pipe gripping means in addition to the traditional sealing means;
thus, a structural clamp was required.
In an issued request
for proposal to several companies, Quality Connector Systems responded with a
proposal to make a structural clamp that would fill the dual purpose of being
both a pipe joining clamp-type connector and a structural leak clamp. Hence,
the co-owners could purchase two clamp/connectors for each pipe size rather
than two connectors and one clamp – an approximate savings of 1/3 earlier cost
estimates (since the price per tool is about the same), and a low-cost
solution. A second JIP built and successfully tested the clamp/connector tool
in the 12-in. size.
Then, in 2005
hurricanes Katrina and Rita hit, and four of the JIP participants decided to
develop a pipeline deepwater repair system consisting of two connectors and one
structural clamp for each pipe size from 10 to 24-in.
Following these
storms, the co-owners evaluated the risk as higher; and as a result, they
wanted the "best" solution rather than a low capex solution (although
both solutions are workable). Consequently, DW RUPE–Pipelines was formed. (Also
being organized, but not yet formed, is DW RUPE–Flowlines.) The group's
objective is to have a complete tool inventory available for deepwater flowline
repair emergencies.
Now the collaborative
effort is complete and these key project milestones have been reached:
- DW RUPE began in 2004 and,
after three years, two JIPs, and the collective forces of hurricanes
Katrina and Rita, has become reality.
- DW RUPE has fully developed
a process and the equipment necessary to use in making emergency repairs
to deepwater pipelines while minimizing environmental impact. The project
selected, and has in storage, connectors, clamps, FBE/weld seam removal
and end preparation tools, lifting frames, and indexing bases as key
components to use in affecting ROV-assisted repairs.
- Beginning in May 2007, the
DW RUPE–Pipelines co-ownership group became the first cooperative to
provide a high-pressure, deepwater depth pipeline repair system that is
open to new co-owners both in the Gulf of Mexico and internationally. DW
RUPE has procured $12 million of ANSI 1500 tools fitting pipe sizes from
10 to 24-in. and capable of water depths from 1000 to 10,000 ft.
- An Excel-based spreadsheet
calculation tool has been created to assist in planning careful placement
of lifting means (pipe lift frames and indexing cases) to achieve a viable
repair project.
Twelve-inch
clamp in test configuration
Repair tools
The co-ownership
group systematically selected repair tools for the initial inventory of DW
RUPE. Whenever any tools are removed for emergency repairs by the co-owners,
replacement tools may involve different component suppliers, depending on
competitive bidding.
For the initial
system, the co-owners carefully evaluated and selected their procurement
options, which included:
- Double grip and seal
connectors (two per pipe size)
- Structural leak clamps (one
per pipe size)
- Pipe lift frames (two for
all sizes)
- Indexing bases (two for all
sizes)
- FBE & weld seam removal as well as pipe end preparation tools (all sizes).
Repair process
The co-owners agreed
upon a methodology and process for performing repairs. Obviously, the first
step involves locating the damaged deepwater pipeline and determining the
magnitude of the damage and oil leakage condition. Depending on the findings
from an ROV video survey of the damage location, the pipeline owner (and member
of DW RUPE) will determine whether to use a structural clamp to repair a
pinhole leak or remove a damaged segment of pipe and perform a spoolpiece
repair. The top priority, though, is the need to evaluate and control any oil
or gas leakage, thus minimizing environmental issues.
Spool piece
with bolted connector
By the time a damaged
gas pipeline has been located, its condition has been determined, and a repair
crew has been mobilized, any gas loss (less detrimental than any oil loss) will
have likely already occurred. For oil, one assumes that the pipeline is shut in
by appropriate valves so that the pipeline is not purposely flowing oil.
Consequently, the only oil release would be caused by movement of the damaged
pipeline during repair (movement driven by gravity flow based on the density
difference between oil and water).
Next, twin pipe lift
frames would be lowered one at a time to specific points on either side of the
leak location of the pipeline. The first pipe lift frame would be installed far
enough from the leak area, a distance calculated to be a lift point where
"humps" are created, as seen in the associated diagram. Also shown
are the indexing bases that are deployed to stabilize the leak point above the
seafloor for clamping or to control the pipe ends after cutting out the damaged
section.
The "humps"
formed with the lift frames create "high points" that are higher than
the leak point by at least one pipe diameter in vertical distance. As long as
the leak point is below the bottom of the pipe at the "hump" point,
leakage cannot occur from gravity flow of the lifted sides. The pipe damage
point is thus located in the "valley" between "humps."
The next step in the
oil containment process is to either attach a structural leak clamp, if there
is a pinhole leak, or cut out a section of damaged pipe if the damage is more
severe or extensive. If cuts are necessary, the lift frames must be positioned
far enough away from the cut location so that any occurring spring-back, which
ultimately creates a gap, will not cause the pipe ends to slant upward (thus,
potentially losing oil by gravity flow). DW RUPE has carefully constructed a
finite difference computer model, verified with finite element methodology, to
achieve the downward sloping pipe ends past the pipe cuts.
Further, considering
pipe spring-back, one understands that deepwater routes have very large radius
curves; hence, the presence of residual bending moment in the vertical plane
will likely be mild. For design purposes, the maximum allowable strain
(reference API RP 1111) is 0.15% so any residual spring-back is negligible.
Thus, for the 100 ft of pipe adjacent to the cut, one would expect the
spring-back to be fewer than a few inches per side.
Another potential
problem in the pipe sagbend area (a location of compressive bending stresses on
the top) is the pipe's "binding" the cutting device during the
cutting process. Experience suggests that either diamond wire saws or milling
heads deployed subsea would be more resistant to binding than a conventional
bladed saw. The circular cross section of the wire or the milling head tends to
bore a hole which can relieve lateral compression effects in the process.
Even if there were a
binding problem, though, there would also be a delay in the cutting process
until the diamond wire was replaced. In that case, the second cut would also
take advantage of relief provided by the first cut, and the pipe would
eventually be cut completely.
Once the pipe ends
are downward sloping, the ROV can insert low pressure flexible sealing plugs
(pigs) capable of maintaining a seal during subsequent pipeline spoolpiece
placement activities that follow.
Source : http://www.offshore-mag.com/articles/print/volume-71/issue-7/flowlines-__pipelines/improving-deepwater-pipeline-repair-capability.html
Source : http://www.offshore-mag.com/articles/print/volume-71/issue-7/flowlines-__pipelines/improving-deepwater-pipeline-repair-capability.html
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