Subsea pipelay systems, repair tools advance

Sept. 6, 1999
The pace of subsea pipelay and repair technology has accelerated in recent months, keyed by the introduction of a new deepwater vessel whose first job will be in the U.S. Gulf of Mexico.
Saipem 7000's massive J-lay tower dominates the deck of the former service vessel as it moves out to sea trials earlier this year (Fig. 1).
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The pace of subsea pipelay and repair technology has accelerated in recent months, keyed by the introduction of a new deepwater vessel whose first job will be in the U.S. Gulf of Mexico.

Italian contractor Saipem reported early last month that its new pipelay vessel, equipped with a J-lay tower, had successfully conducted sea trials and by yearend would begin laying pipe in the U.S. Gulf of Mexico.

Earlier in the summer, Coflexip Stena Offshore announced that its deepwater flexible-pipe lay vessel, the Sunrise 2000, had been commissioned after an upgrade, and that Petrobras had extended its charter until March 2003 for work offshore Brazil.

In the spring, Oceaneering International Inc., Houston, reported a successful diverless repair of a subsea pipeline in a project the company said was the deepest flow line repair on the sea floor ever attempted.

And, Sonsub International christened a new subsea pipelay, repair, and construction vessel in June.

New entry

Saipem's new entry into the J-lay deepwater pipelay market, Saipem 7000, is an evolution of what the company calls the world's largest semisubmersible crane vessel. It has been upgraded to Class III dynamic-positioning vessel and combined with the J-lay tower system (Fig. 1). It recently conducted successful sea trials in the North Sea.

The vessel's first commitment is for Exxon's Diana project in the Gulf of Mexico. The vessel is scheduled to arrive on station in a few weeks and begin installing rigid risers and flow lines.

The next major opportunity, says Saipem, will be in 2000 for the Blue Stream pipeline in the Black Sea between Russia and Turkey. That project will consist of two 24-in., 1.25-in. W.T., 390 km long lines, each at a depth of more than 2,000 m.

Saipem 7000's J-lay system has been designed to lay quadruple line pipe joints of 4-32 in. OD in more than 2,000 m of water. Weighing more than 6,000 tonnes, the J-lay tower incorporates three conventional track-type tensioners, says the company, each with a capacity of 175 tonnes, between the welding station and the non-destructive testing (NDT) station.

Two friction clamps, consisting of two 550-tonne capacity clamping units, apply the necessary tension. The system can be used as a back up for pipe laying and recovery operations or as a contingency pipe-clamping structure for pipe weld repairs at the NDT station, says Saipem.

A series of quadruple joints, each 48 m long, 10 in. OD, and 12.7 mm W.T., was successfully laid during trials in Jelsea Fjord, Norway.

Huisman-Itrec, Rotterdam, designed and, on Feb. 27-28, 1999, at Verolme Botlek Ship and Offshore yard, Rotterdam, installed the J-lay system on what was then the S7000 crane barge, incorporating pipe-handling equipment.

Design of the main construction was in cooperation with Gusto Engineering, says Huisman-Itrec. All additional systems, such as the line-up tool, were designed by Huisman-Itrec.

The quadruple joints of 4-32 in. pipe can be supplied assembled or welded on board with horizontal welding stations. Maximum weight of 48 m of 32 in. pipe is approximately 50 tons.

Once welded the quadruple joint is raised onto the longitudinal conveyer system and transported to the pipe loader, which up-ends the joint to the J-lay tower.

An elevator then picks up the joint and transports it 50 m up into the tower. The hydraulics-driven transfer system brings the pipe to the line up tool. This tool ensures a perfect positioning of the pipe for welding.

The welding station is 58 m above the main deck. Beneath the welding station, three tensioners hold the pipe with a maximum capacity of 525 tonnes (3 x 175 tonnes).

In future, the system can be upgraded to 2,000 tons. Moveable clamps will then replace the tensioners, which work like a hand-over-hand system. NDT and coating stations are under the tensioners. The NDT station controls the weld with X-ray; the coating station applies coating onto the weld.

Under the coating station lies a clamp system (hang off clamp) with a capacity of 550 tons. An abandon and recovery (A&R) winch on deck also has a capacity of 550 tons and a wire of 43/4 in.

This wire is guided by sheaves and used to pick up the pipe on top of the A&R head and lower the pipe into the sea or retrieve it after abandonment.

Total height of the J-lay tower is 135 m; total weight of the system is 4,500 tons; maximum pipe tension, 2,000 tons; and maximum angle of tower from vertical 20°.

The system is designed to be installed and removed by the vessel's own cranes. The tower is pin-connected to the system. The rear of the tower is open allowing removal of the tensioners.

Petrobras has extended to 2003 the charter for its use of Coflexip Stena Offshore's Sunrise 2000 in waters offshore Brazil.
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In the growing market for flexible pipelay capacity, Coflexip Stena Offshore, Paris, earlier this summer announced commissioning of its deepwater flexible-pipe lay vessel, Sunrise 2000, after an upgrade that had been completed ahead of schedule. At the same time, Petrobras announced it had extended the vessel's charter until March 2003 (Fig. 2).

Upgrading to a capability of laying flexible pipes in 2,000-m water depths allows Petrobras to fulfill its deepwater production objectives, says Coflexip Stena. The company performed the engineering, design, and project management in house; the upgrade was completed at the Rio de Janeiro navy dockyard within a 45-day schedule.

The Sunrise 2000 resumed operations May 14 with a new tensioning capacity allowing her to install three flexible lines simultaneously in 2,000 m waters.

Subsea repair

In spring 1999, Oceaneering and Mariner Energy Inc., Houston, completed what the companies claim to have been the world's deepest pipeline repair using diverless, on-bottom methods on the Dulcimer project in Garden Banks (GB) in the U.S. Gulf of Mexico.

The project ties-back a single gas well in GB 367 in 1,167 ft of water to a host platform in GB 236, more than 14 miles away. Gas moves through dual 4-in. OD flow lines at up to 60 MMscfd. The flow lines were installed in August 1998.

When the flow lines failed to hold their rated pressures of 6,200 psi, a multiservice vessel with a remotely operated vehicle (ROV) was dispatched to locate the leaks and clear sediment from around the lines. Revealed was an abraded oval-shaped hole 4 in. long and 2 in. wide in each flow line.

The damage had apparently been caused during a bottom-tow installation of another operator's flow line bundle. Because Dulcimer's lines were out of service, no product release occurred, say the companies.

Mariner Energy and Oceaneering chose from among five options the on-bottom installation of a spoolpiece section using a sleeve-type mechanical connector that slides over the ends of the line to be joined.

For the Dulcimer project flow line repair, Oceaneering's Ocean Intervention deployed its WASP atmospheric diving system to complete the spoolpiece installation in 1,000 ft of water, Gulf of Mexico (Fig. 3).
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In a proprietary Oceaneering design, the connector is bolted to a standard ASME-ANSI flange. The tightening of the bolts compresses a piston into the connector body, energizing a slip and cone mechanism that sets and locks the connector to the pipe (Fig. 3).

At the same time, this action compresses an elastomeric element to provide the necessary seal. The connector is thus set, locked, and sealed in a single bolt-tightening operation.

The connectors were custom-manufactured for the Dulcimer repair. In addition, Oceaneering also fabricated eight adjustable pipe stands and a flow line alignment and spoolpiece installation A-frame.

The repair was carried out by Oceaneering's newly built MSV Ocean Intervention. It is equipped with a Simrad SDP-21 (DP-2) dynamic-positioning system: two 1,000-hp bow tunnel thrusters and two 2,000-hp azimuthing stern thrusters designed to hold station in any Gulf of Mexico weather short of a named storm.

The MSV also has two moonpools, one for launch and recovery of its resident ROV, thereby avoiding the weather limits of standard over-the-side launch, says Oceaneering.

After the 7-day repair of the damaged sections that began Mar. 25, 1999, the flow lines were hydrotested to 7,800 psi for 8 hr.

June 1999 saw the christening of yet another multipurpose, deepwater construction vessel, Polar Prince, in Bergen, Norway, by Sonsub International (Fig. 4).
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In June 1999, Sonsub International christened its new inspection, maintenance, repair, and subsea construction vessel, Polar Prince, in Bergen, Norway (Fig. 4).

The vessel, designed and owned by Rieber Shipping A/S, has been chartered by Sonsub International long-term.

The company says that in addition to light subsea construction and intervention, the vessel is designed to support various Sonsub trenching machines, including the specialized, client-specific systems developed by newly acquired Sonsub subsidiary Tecnomare Industriale SpA.

With Class II dynamic positioning and measuring 94 m long by 22 m, the vessel, according to the company, displays low motion and low noise.

The Polar Prince includes an actively heave-compensated offshore crane with the pedestal mounted on the aft starboard side. The crane's capacity is 75 tonnes at 11-m radius (40 tonnes at 20-m radius) for lifts down to 2,000 m on the seafloor, and in excess of 120 tonnes at 11-m radius (60 tonnes at 20-m radius) with double fall reeving (150 tonnes in harbor conditions).

In addition to the crane, the vessel has a 100-tonne, 13-m high A-frame as well as a 60-tonne stern roller.

The main deck is more than 1,000 sq m with a 10-tonne load capacity with two moon-pools, one (7 x 6.5 m) for module lowering and a second (4.9 x 5.2 m) for ROV operations.

A built-in ROV launching cursor system is designed for operations up to sea state 8, says Sonsub, while a port side opening supports the ROV hangar for launch and recovery of a second work-class ROV.

Additionally, a 5-tonne crane is included for the launch and recovery of a third ROV from the upper deck.