Geo Week News

October 16, 2007

Dimensional Control in the Arctic: Kulluk Thruster Porch Installation

Dimensional Control in the Arctic - Image 1

The Kulluk is an offshore drilling vessel maintained and operated for Shell by Frontier Drilling in the Beaufort Sea. This is the story of how advanced dimensional control services from Hi-CAD helped Frontier achieve accurate first-time fit in a project to fabricate and attach new thruster porches to the vessel.

The Kulluk – Inuit for “thunder” – was the first floating drilling unit purpose-built for Arctic waters. Its conical hull is designed to deflect ice downward, breaking it in flexure. The compartmented hull has a continuous-void double bottom to facilitate damage detection and prevent pollution in case of hull damage. Designed by Earl and Wright – Lavalin for Gulf Canada Resources Inc.’s Beaufort Sea Drilling System Division, the vessel was built by Mitsui Engineering and Shipbuilding Company and delivered in 1983. In 2005, after a period of disuse, Shell purchased the vessel and set about reactivating it.

An important part of the refurbishment program was the decision to add thrusters to this drilling barge. The impetus was “compliance with the Jones Act,” explains Tracy Harris, Engineering Manager for Construction, E & P Projects, Shell Deepwater Development, who is in charge of construction activities for the reactivation project. “Before this, the Kulluk was not self-propelled. Thus, it could be towed to its first location by a foreign vessel. But as soon as it touched that location, either by dropping anchor or by drilling, it would become a ‘port’ under the terms of the Jones Act. Moving the unit between two such points or returning back to this point would require a Jones Act-compliant tow vessel” – that is to say, a U.S.-built and U.S.-flagged vessel.

“But there are no such vessels that can operate in the conditions of the Beaufort Sea,” Harris continues. “Adding thrusters to the Kulluk was the answer. This summer, when the Kulluk goes to its second location, it will do so under its own power for the first time.” The idea to outfit the Kulluk with thrusters originated with Suman Muddusetti, formerly a ship’s captain and now a Shell in-house expert on dynamic positioning, says Harris. Muddusetti was Shell project lead for the Kulluk thruster project. As we prepared this story, he spoke to us early on from the bridge of the icebreaker/MFSV Fennica, which served as a support vessel during the installation phase of thrusters on the porches featured in this story.

Roger Burger, Shell’s representative on this project through the fabrication and erection of the thruster porches, passed away in June 2007. Besides overseeing the porch activity, he was instrumental in the design and oversight of the thrusters themselves. His colleagues report that his contributions were central to the success of the overall project.


Value of 3D work processes and dimensional control

“We believe strongly in 3D,” Shell’s Harris notes. “For all our new construction we use PDMS. We know the value of a good 3D model in minimizing clashes.” It was Shell E & P Projects’ decision to call on Hi-CAD for dimensional control. “We brought in Hi-CAD because we had just purchased the Kulluk from its previous owner, and the drawings were very old – the vessel had been sitting for some 15 years in the Arctic. To create drawings for fabricating and installing the thruster porches and other components, we needed up-to-date documentation.”

A key challenge was the complex geometry of the Kulluk’s hull, a 24-faceted shape in the form of an inverted cone. Equally challenging was the schedule pressure of operating above the Arctic Circle. “This is time-critical work,” says Harris. “The season is very short – last year they had less than a couple of months of open water. Every single month is critical, so we don’t want to be up there saying, ‘Gee, this part doesn’t fit.’ And it’s at the end of the earth” – the schedule and cost penalties of reworking or replacing incorrectly fabricated components are especially severe.

Project manager for Hi-CAD was Keith Medley, general manager, HICAD America. Hi-CAD’s Mark Macleod served as project lead surveyor. Dave Penman, Hi-CAD director and cofounder, expands on the value of dimensional control in offshore projects such as this. “In dealing with modular construction, different components – topsides, substructure, drill package, flares, others – will be built in diverse areas,” he says. “When multiple vendors are involved in a project, it’s important that they not take a global approach to the structure – each one should focus on his own interfaces. It’s critical to have a dimensional control manager who takes ownership of global dimensional responsibilities.”

DC for fabrication and fit-up

Frontier Drilling was engaged by Shell to refurbish and maintain the Kulluk, and conduct drilling operations for the next three years. Stan Wiggins, who was corporate planning and scheduling manager with Frontier in charge of the thruster porch project (Wiggins is now with InServ), describes how dimensional control saved time and money on the project.

“Physical dimensions of the Kulluk had been taken early in the project to support the engineering of the porches,” says Wiggins. “Holes were cut in the vessel’s sides and sample plates were taken from the sidewall to do metallurgical analysis. They did dimensional checks and found that every rib was spaced 600mm apart, exactly as the original construction drawings showed. Those measurements were taken by workers who entered the hull’s void spaces and did dimensional checks using tape measures. Those measurements were the basis for the design and fabrication of the thruster porches.”

The porches were fabricated by Thrustmaster of Texas, Inc. in Houston. “We contracted Hi-CAD to go to Thrustmaster and do dimensional checks of the as-fabricated thruster porches,” says Wiggins. “That went well – everything was in tolerance on site at Thrustmaster. But the porches subsequently suffered a lot of deformation in shipment.” In Houston the porches were loaded on flatbed trucks and driven to Edmonton, Alberta. There, Wiggins explains, “the porches were laid on their sides to be trucked along the Dempster Highway to Inuvik,” a port in Canada’s Northwest Territories. “Each porch contains five ribs, which were minimally stabilized at the fabrication yard. But on the trip up the Dempster Highway – basically a farm-to-market road – the porches suffered deformation in all five ribs, and breakage of reinforcing plates. We had to do trimming and cutting to fix that.”


Survey work process

At Inuvik the porches were transferred to a barge for shipment to the Kulluk. While the barge was underway, “the Hi-CAD team was already on site at the Kulluk determining the actual dimensions of the angled sides of the vessel,” Wiggins says. Hi-CAD found that the hull contour was not exactly as shown on the vessel’s original drawings – ice pressure had caused some deformation. “So Hi-CAD used total station surveying to come up with the true profile dimensions of the outside hull,” Wiggins says. “What you see here [Figure 3] is one of the Hi-CAD reps positioning a prism for total station shots. They did quite a few hundred shots on the side walls of the Kulluk.”

Hi-CAD then “transferred those dimensions to the thruster porches, so the installation contractor could adjust them to the Kulluk’s correct dimensions,” Wiggins continues. “Using that information, the installation contractor trimmed the porch ribs to fit exactly. When we attached the porches to the hull, we did not have to do any filling, thanks to Hi-CAD’s work.”

“Hi-CAD did no laser scanning – the DC process relied exclusively on total stations,” Wiggins reports. “To do laser scanning of the Kulluk exterior hull would have required having outside scaffolding and other structural attachments added to the vessel. Laws governing operations in the Beaufort Sea specify that you can’t drop anything in the water. If we paint, we have to fully encapsulate the area. When we removed paint from the Kulluk, we put up scaffolding, tarped it, duct-taped it – we made sure that nothing could drop into the water. When we finished, we vacuumed everything before taking it up.”

Hi-CAD project lead surveyor Macleod describes the work process. “We anticipated capturing the rib dimensions by surveying the ribs inside the Kulluk, then transferring our control network to the outer hull in order to mark off the rib locations there. But due to access restrictions, we were not able to do that. We weren’t allowed to go down into the so-called ‘void tank’ inside the double hull without undergoing special compliance training, which would have eaten schedule.”

“So we came up with another plan,” he explains. “There was a painting crew on board as well as support contractors that included ultrasonic technology (UT) experts – that technology lets you locate internal stiffeners from the outside of a vessel. We surveyed what we could of the ribs by looking down into the void spaces from deck level, but that only let us measure about eight feet down. We transferred those measurements to the outside of the vessel, and used them to mark off a foot-wide area on the outside of the vessel to show the location of each rib. We then had the contracted inspector use UT to identify a rib footprint from outside the hull. We used that data to mark the centerline of all the rib footprints. Then we surveyed the centerlines every six inches, and used that information to determine the cut lines to be transferred to the porches.”


Positioning the porches – right-first-time fit

In positioning each porch for attachment to the hull, two knuckles were used to suspend the porch (Figure 5). “The way that the porch was designed to fit over those knuckles, we had to meet a tolerance of only 5mm horizontally and vertically,” Wiggins said. Hi-CAD’s work to capture internal rib dimension and position information, then transfer that data to the hull exterior, was critical in meeting this tolerance.

“The purpose of these attachment knuckles is to capture the next item – the hang-off beam [Figure 6],” Wiggins continues. “That beam is bolted to the top of the thruster porch during installation, and it has to be bolted in exactly the right position. If it’s too far forward, the gap when we position the thruster against the wall will be too large. If it’s too far back, the hang-off beam will get stuck and won’t drop all the way down into position. If that happened, we would have had to lift the porch, move it back to the barge and reposition the beam.”

The starboard porch was positioned by a crane operating from the Russian icebreaking vessel Vladimir Ignatyuk adjacent to the Kulluk, and the port porch was carried to location by the Russian icebreaker and installed using the Kulluk onboard crane (Figures 7, 8, 9). “Any removal and modification would have been a time-intensive operation,” Wiggins notes. “In this case, as a result of the overall team approach, everything fit correctly.”


DC business value

What was the business value of the DC services on this project? “Once you set a 25-ton porch,” Wiggins explains, “having to lift it back out of the way to make cuts costs hundreds of hours of professional time to get it in position, make the cuts, make the bevels, then clean everything up and get it ready to weld. Here, because we did all that beforehand, once the porch was set against the hull, all we had to do was move it over a little bit to line up with the center of the rib. Then we could start welding. There was no trimming required.”

“You can see, in the side porch setting sequence, two large turnbuckles [Figures 7 and 8],” he continues. “They have two purposes. Once we got the porch in position, we would lower the turnbuckles. That provided safety – if something happened to the lifting arm, there would still be the safety of the two turnbuckles. Second, they would help if we needed to lift the porch. Not only did we have to meet a 5mm vertical tolerance, but the top of the thruster porch had to align with the lower deck inside the vessel, to transmit the load.”

“One thing Hi-CAD was able to do that saved significant work – the original design called for those hang-off beams to be lower, to give us some flexibility, then we were going to have chain hoists lift the porch an inch to get it into position,” Wiggins adds. “But once we had the thruster porch on the vessel and Hi-CAD had shot the dimensions, we knew exactly the distance from the steel rod in the hang-off beam to the top of the thruster porch. So instead of positioning the porch approximately, then lifting it with chain falls, we were able to position it exactly without a separate lifting step. That step would have taken more time, and it would have put us in a position where nothing but two chain falls were holding up the porch.”

“Because of Hi-CAD’s work, we were able to align the porch with the lower-deck steel on the first try,” Wiggins sums up. “That saved untold hours and added to safety – it allowed us to maintain full contact with the hang-off beams at all times.”

Next steps

The thruster porch project was completed in September 2006. For Frontier, the value of the project was significant, according to Wiggins, and included the costs of an accommodation barge and the Russian icebreaker.

As of July 2007, says Harris, “We’re installing the thrusters themselves and their control units.” The control equipment has to fit into the already-crowded pilot house, “then we have to tie it in with the generators and other equipment. All that involves a lot of pipe and cable routing – dimensional control is critical.” Harris says the value of Hi-CAD services in the thruster porch project convinced Shell to extend Hi-CAD’s contract through completion of the overall thruster project.

About Frontier Drilling, Inc.

Frontier Drilling, Inc., domiciled in Norway with administrative offices in Houston, TX, is an independent supplier of drilling and production services for the oil industry that focuses on the operation and management of conventional drillships, semi-submersibles and floating production, storage, offloading (FPSO) vessels. Frontier Drilling seeks to compete in market segments such as the Arctic that are not dominated by larger competitors and where its assets offer customers cost savings and a competitive advantage.

About Hi-CAD Ltd.

Hi-CAD Ltd., Dingwall, Scotland; Rio, Macae, Brazil; Villahermosa, Mexico; and Houston, TX, was established in 1988 and is a world leader in providing as-built documentation using 3D laser scanning technology. Hi-CAD’s expertise is in data capture and measurement for purposes of 3D laser scanning for new offshore platforms and vendor packages, 3D data capture using 360-degree scanning, dimensional control management for new offshore platforms and vendor packages, as-built data collection for brownfield retrofit projects, and asset records management for all project types. The firm is currently managing dimensional control for a number of major offshore projects.

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