The DW RUPE–Pipelines group now offers a quick-response repair system for GoM and international offshore operators
Ray R. Ayers, PhD, P.E.
Stress Engineering Services Inc.
Armando Rebello, P.E.
Stress Subsea Inc.
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 handling 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.|
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).
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.
This is just a sample of some of the findings of the DW RUPE–Pipelines co-ownership group. There are also important considerations with regard to the spoolpiece repair process, the connector-indexing base interface, and the calculation process for making an inline spoolpiece repair. Progress has been made on these fronts as well. For more information on the co-ownership project and its progress to date, please visithttp://www.dwrupe.org.
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