Deepwater repairs at the double

October 26, 2010

Each time a hurricane sweeps through the Gulf of Mexico, operators hope for the best – that their infrastructure, from topsides to flowlines to wellheads, remains safe in the face of nature’s fury. Determined to protect its assets, Chevron sought a repair system for deepwater pipelines that wouldn’t leave the repair equipment on the seabed. Along the way, it enlisted the help of Oil States, Wachs Subsea and a number of other companies. Jennifer Pallanich reports on the creation of a next-generation repair system that will allow a rapid response to any deepwater pipeline emergency.

While pipeline repair systems exist for both shallow water and deepwater, the Deepwater Pipeline Repair System (DPRS) developed in collaboration with Chevron relies on quite a bit of established technology but differentiates itself in a number of categories.

It weighs less than existing systems, which increases the number of vessels that can be used to deploy it. Almost all the equipment used in the repair is returned to the surface for reuse, save the replacement pipe and connectors. It can use any workclass ROV of opportunity. It is modular and compact enough that it can be trucked without requiring permits, and a Boeing 747 can airfreight the system around the world. It is designed to handle a number of contingencies so repair work can continue on schedule despite hurdles that may arise.

‘We’ve taken a lot of time and effort to make sure we’ve got something that is flexible and compliant,’ Chevron team member Steve Liso said.

The story started after Hurricane Ivan, which reached Category 5 storm status, raced through the Gulf of Mexico in 2004 and damaged Chevron’s Petronius pipelines, which prompted the operator to begin reviewing the need for a repair system for a 12in pipeline in 1700ft water depth. The next year, Category 5 Hurricane Katrina caused widespread and significant damage in the Gulf.

Hurricanes, of course, aren’t the only threat. Shifting seabeds, such as the moving Sigsby Escarpment in the Gulf of Mexico, as well as mudslides, corrosion, weld problems, and thermal expansion can also damage pipelines.

Under team project manager Rote Vichaynond, Chevron sought the DPRS to ensure safety, contain pollution, and protect the company’s growing number of deepwater assets. ‘The system provided an insurance policy to cover all of these bases,’ Liso says.

The system, devised in a combined effort among Chevron’s Energy Technology Company, Pipeline Company and CNAP Gulf of Mexico Deepwater Business Unit, Oil States and Wachs Subsea, and commissioned by Chevron’s North American E&P Company, can be deployed within 72 hours, and once it’s on a vessel, over the subsea site, will take about 21 days to carry out the repair. The three-week window includes additional days to accommodate poor weather or mechanical issues.

The Chevron DPRS can repair up to 200ft of pipeline in waters to 10,000ft. Chevron can use the system on pipelines that range from 12in to 24in.

Currently, the system is configured to work on a slope to 5°, but it is designed to work on slopes to about 10°, with some modifications.

The contingency elements were vital, Liso says. ‘When you’re working two miles under the water, and something goes wrong, how do you bail yourself out of the problem? We have gone to great lengths within the design to give ourselves an alternative means of completing the operation.’

How it works
The cut-lift-remove-replace system uses surveys by an ROV of opportunity to identify damage, a Wachs tool package to cut the pipeline, a surface vessel to remove the damaged section, laser alignment to aling the replacement pipe, Oil States handling equipment to move the existing pipe and receive the new pipe in place, and the surface vessel to load and recover all ancillary equipment to the surface following the repair job.

While the system is designed to use two workclass ROVs for expedience, one of the contingencies is that it can function despite one ROV failing.

An acoustic beacon array allows the repair team to understand the pipeline angle by measuring the length of section required for the jumper spool piece, and the position of the pipe ends with respect to each other. The ROV attaches some of the beacons to the pipeline via ceramic magnetic clamps developed by Wachs.

To carry out the repair, the ROV will place the Wachs Combination Tool and deployment frame on the seabed. The tool, which Wachs designed for the DWPRS, will cut and prepare the pipe ends. The crew on the surface builds the spool piece from the metrology measurements and sends it down for installation. The Combination Tool combines five functions in one unit. It can cut pipe, conduct an outside bevel, conduct an inside bevel, remove weld beads, and remove fusion bonded epoxy (FBE) coating. It’s a primary tool, and the DPRS includes a secondary tool as a backup.

Tim Sheehan, VP at Wachs Subsea, stresses the importance of safety elements in the Wachs multipurpose tool. The Wachs tool bevels the outside so the sleeve connector will properly seal and not become damaged when the repair connector is installed. The inside bevel prevents a pig from becoming stuck. The weld seal and FBE removal ensure a better seal and grip.

‘We use standard machining practices,’ Sheehan says. The Combination Tool consists of three heads that handle the five functions. He notes the unit features minor adaptations of a subsea drill the company makes for everyday use. ‘We tried to use common parts and common tooling wherever possible.’

Each module on the Combination Tool has a camera to monitor the operation.

The system also features a go/no-go gauge that determines when a pipeline is too distorted to be cut. Straightness and ovality gauges also ensure the connectors will pass over the pipelines, and heavyduty grease pencils mark locations for seals and clamp spots on the pipelines.

Once the Wachs tool has cut the pipeline, beveled it and prepped it, the ROV and survey crews take metrology and send the information to the surface team to manufacture the jumper spool pipe section. The laser alignment tool is placed on the exposed pipe ends and ensures the frame and the spool are positioned correctly by the index frame and ROV.

The laser alignment tool works by firing a beam to the target. Three beams on the middle indicate the two pipelines are in alignment while two fan beams on the top and side fire beams along the longitude to ensure the pipelines are aligned on that axis as well.

Dual grip and seal connectors align and hold onto each end of the pipeline ‘like a big Chinese finger [trap],’ says Bo Povloski, technical sales specialist at Oil States.

Leave nothing behind
In previous generations of deepwater pipeline repair systems, the lift frames relied on gantry cranes to carry out repairs using vertical or horizontal jumpers, Povloski notes. With either approach, he adds, much equipment was left on the seabed post-repair and therefore could not be reused.

When seeking a concept that would not leave all the ancillary equipment behind after the repair work is complete, Povloski suggested using two mudmats with bases cut out so the frames could be lifted from the seabed. Povloski, with 22 years of technical subsea pipeline and deepwater experience, worked as a team leader for the critical deepwater repair systems following Hurricanes Ivan, Katrina and Rita.

The only consumables in Chevron’s DPRS are the new jumper pipe and the two pipe connectors.

The system features several retrieval methods to ensure no pieces of equipment will be left behind after the repair. Multiple lifts can be made to retrieve the lift and index frames. In silty and claylike areas prone to ‘sticktion’, where the frames may have embedded into the sea bottom, the ROV can remove pins from the hinged foundation mats allowing for the equipment to be recovered more easily.

A pipeline liftbag is a new contingency. According to Liso, if the team underestimates the loading of the entire system because of mud and stiction, a liftbag can fill with water to help lift an additional 25 tons. While liftbags aren’t new to the industry, they’ve tended to roll. The collaboration team created a cage around the bag to prevent rolling.

Once the pipe is repaired, the equipment is returned to the surface, where it is washed, inspected and maintained before being sent back onshore or to another pipeline repair location.

The development process
Completed in 2009, the diverless deepwater pipeline repair system is a first-of-a-kind for Chevron.

Chevron commissioned engineering firm Cronus to confirm assumptions on loads, interactions between the seabed, pipelines and frames, as well as how various sea states would affect activities.

Oil States designed and fabricated the Alignment Frame, Index Frame, Pipe Lift Frame, Dual Grip And Seal Hydraulic Connectors and Diverless Hydroclamps.

Wachs developed the Combination Tool, all the ancillary installation tooling and ROV tooling.

Oil States proved the engineering and 3D models for the pipe handling system and connectors, and Canadian company GRI Simulations used its simulation software to ‘prove the concept and check operability in a very short time’ to before freezing the design and commencing the build program, Liso says.

GRI’s simulation program carried out a virtual 3D SIT test before the real McCoy underwent SIT at Oil States’ Houston Ship Channel facility in November 2009. Because of the simulations, the team notes, SIT mostly confirmed the team’s expectations and revealed only minor interface details to be addressed.

‘We actually reduced a lot of our SIT time/costs by doing an electronic version to test the interaction between the Wachs and OSI equipment prior to the SIT,’ Liso says.

Development of the system stressed flexibility so it could use different connector styles, different manufacturers and any workclass ROV of opportunity. In addition to the built-in flexibility of the DPRS, Sheehan says, the tools rely on simple control systems.

The Wachs system is designed to be compact and modular; it carries out the actual preparation work in a single deployment after all the ancillary equipment is positioned on the seabed. ‘We’ve done that to reduce the risk of operational errors,’ Liso says.

‘We’ve taken all the pieces to the jigsaw that exist at the moment and put it together in a smart and compact package.’

Povloski notes the repair kit cost is minimal, compared to vessel dayrates. This design is smaller – about half the weight of the previous generation of deepwater pipeline repair systems, which require vessels 300-400ft long for a single deployment. The Chevron DPRS can be deployed from a vessel around 290-300ft long. The compact model is also helpful in terms of crane capacity. The heavier elements of the system are the the 28 ton index frame, 21 ton lift frame and 4 ton alignment frame. ROVs typically weigh in at 8000lbs, and Wachs’ multipurpose tool weighs about 6000lbs.

The project was the first time Chevron, Oil States and Wach Subsea had worked together to develop a system.

‘It was absolutely a collaborative effort,’ Sheehan says.

Sheehan says the team put a lot of thought into making sure the system works.

Chevron is confident about having Serial #1, especially after FEA and simulations verified the system, and the SIT showed the system was more flexible than expected. ‘We’re confident with assembly, disassembly, and putting it into storage so if we get the call we can rally to send it out.’

One of the ways the team will ensure the system remains ready to deploy on a moment’s notice is by carrying out a 7- to 10-day hurricane SIT ahead of the start of each hurricane season. In June, the team did the first pre-hurricane test to ensure all parts would function and top up fluids. The system was then disassembled, stored on pallets and trucked to a storage facility near Hobby Airport in Houston so it’s ready to send to the dock for deployment within 72 hours.

A post-hurricane season inspection will take about two days each November. OE



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