Flexible market expanding as facility pushes out technical limits

Reels of 1,180-meter partially terminated flowlines from Panama City being offloaded for completion at Wellstream North Sea's 22,500 sq meter facility which is now in full operation.

A 15-in. prototype riser for Norsk Hydro's Troll Field - designed to withstand pressures of 213 bar and temperatures of 70°C - is the largest diameter riser that Wellstream has undertaken. [26,641 bytes]
With the first phase of its new £35 million production facility at Wallsend in Tyneside (UK) now complete, Wellstream's development schedule has been boosted by gaining approval for its quality management system from Lloyds Register. Wellstream transplanted the existing QMS system from its Panama City facility into the Newcastle operation. "This ensured that the learning curve in Newcastle was significantly reduced," says Mike Fenton of Wellstream.

Wellstream North Sea is fulfilling a four-year contract for Norsk Hydro's Troll Field development through an alliance with Brown & Root Energy Services. Norsk Hydro has exercised all its options in the contract which commenced in August 1996, making this the largest subsea contract ever awarded.

Wellstream's part of the contract valued at around $240 million. Wellstream designed and supplied 17 km of 10-in. flowlines and dynamic risers together with a dynamic subsea service umbilical which was installed by Rockwater last year. A further 70 km of flowlines, risers, dynamic service umbilicals and gas lift umbilicals will now be supplied to Norsk Hydro in 1998, with additional deliveries to the year 2000.

While the company's Panama City facility delivered the first 12 reels of its 1998 consignment direct to Norsk Hydro earlier this year, the second shipment involved the new UK operation in Newcastle. Fifteen reels of 1,180-meter, partially terminated flowlines together with complete and partial end-fitting kits were shipped from the US to the Tyne where the lines were completed, hydrotested and packaged for shipment to Norway. An additional 10 reels of flowlines were manufactured in Newcastle making up part of a total of 54 reels which will be supplied to Norsk Hydro this year.

Prototype designs

To qualify for supplying pipe to Norsk Hydro from Newcastle, Wellstream developed and tested a 10-in. static flowline prototype with a design pressure of 178 bar, capable of withstanding temperatures up to 68°C. Wellstream also developed a 15-in. riser prototype for the contract, which will be the largest diameter riser that it has supplied to date. The 15-in. riser has a design pressure of 213 bar and design temperature of 70°C.

Wellstream has also been contracted by Statoil to produce a 9-in. prototype dynamic riser with pressure and temperature design parameters of 500 bar and 130°C, and to conduct qualification testing to API Specification 17J and Recommended Practice 17B requirements.

Vice President of Technology, Mark Kalman, says that this is the most challenging flexible pipe structure that Wellstream has undertaken to design, build, and test. "The combination of large pressure, diameter, sour service, and high temperature resulted in all our latest technologies being combined," says Kalman. "including a new asymmetric hoop strength layer profile, high temperature end fitting barrier anchoring and sealing system, and the use of unplasticized PVDF developed by Solvay Polymers."

The pipe structures have been completed in Newcastle and are being prepared for qualification testing. Two full scale dynamic tests are planned - one to simulate the two million highest waves predicted for the field life and one to validate the pipe service life model. The non-destructive testing will be conducted at SINTEF in Norway.

In addition, static bend, burst, and failure tension tests are being conducted on the pipe structure. In parallel with these tests, thermal cycling testing between the minimum and maximum operating temperature will be conducted on two separate pipe structures in accordance with API RP 17B requirements.

"Wellstream completed successful thermal cycling tests up to 6-in. diameter for the Norsk Hydro Visund qualification in 1997," says Kalman. "The full scale and mid-scale thermal cycling tests conducted to date have resulted in our Lloyds Register Type Approval allowing service to 120°C."

Deepwater challenges

According to Kalman, Wellstream's customers are pushing for development and qualification of flexible pipe to be used in increasingly deeper water applications. "This is particularly challenging with larger diameter pipes" says Kalman, "because the collapse resistance is substantially reduced as diameters increase, and the higher weight per unit length increases the tensile capacity requirements."

Wellstream's approach to the deep water challenge has been to increase the collapse resistance of the pipe by using stronger materials for the internal carcass and designing the pipe so that the hoop strength layer provides a stronger contribution to collapse resistance.

In addition, the pipe structures are being designed to withstand the large reverse end cap load which results in deep water. To reduce the tension loads, system design optimisation is being used with a high tension capacity, lower collapse resistant structure at the top section and a lower tension capacity, higher collapse resistant structure at the bottom section. To further reduce the tension load, Wellstream has developed a flexible pipe structure employing thermoplastic/fiber composite materials for the tensile armour layer.

Deepwater technology is being developed in Panama City in cooperation with Petrobras through three Technological Co-operation Agreements which are concentrating on flowlines for deepwater floating production projects which include Petrobras' massive Roncanor field which lies in depths ranging from 1,400-1,900 meters.

Sheathed mooring cables

For the Gulf of Mexico, Wellstream has recently won a £1 million contract from Trefileurope in France to sheath wire rope mooring cables for Exxon's Diana Field. This is the first contract of its kind that Wellstream has undertaken and involves an extruding machine which covers the cables with high density polyurethane.

"There are increasing possibilities for this type of contract in the future," says Cocksedge. "We estimate that floating production systems could use up to 60 km of mooring cables a year and there is only one other company in Europe, apart from Wellstream, which has the ability to coat cables with HDPE."

The Newcastle facility has also just received a contract worth over $1 million from China National Offshore Oil Corporation to design and manufacture four dynamic jumpers for the Liaodong Bay JZ9-3 development in the Bohai Bay region. Wellstream will manufacture two 30 meter length 12-in. jumpers rated at 870 psi and two 6-in. jumpers 55 meters long rated at 2,378 psi. The flexible pipe jumpers will be used as a subsea tie back from a fixed concrete caisson structure to subsea pipelines.