Rugged Hydraulics Safely Lift 900 Anchors for Australia's Largest Oil And Gas Project

Enerpac BV


Hydraulic technology engineered to deliver safe, reliable and precise power in challenging environments has been used in the laying of a 80km string of subsea pipeline anchors off Australia's north-west coast.

About 900 gravity anchors were positioned by Technip and Subsea 7 (TCS7 Joint Venture) utilizing Technip's vessel CSO Venturer as part of a US$ 55 million contract involved in the expansion of Woodside Energy Ltd's North-West Shelf project.

A high-pressure (700 bar) hydraulic system from Enerpac was custom-built for two anchor feed beds used to lift and position the 32 t anchors for lowering by shipboard crane to the ocean floor.

Reliability and accuracy was integral to the rollout of the string of anchors ­ weighing a total of 28 800 t ­ because their correct positioning ensures stability of the new 42 in. second trunkline from the Woodside operated Goodwyn and Rankin gas condensate fields. The works have now been completed.

"Reliable, punctual performance was critical to this project because of the benefits flowing from the work" said Enerpac Territory Manager Bill Henderson.

Drawing on its worldwide experience of hydraulic design for aggressive environments (ranging from Australian subsea projects to the current hydraulic pre-forming of 40 000 t concrete blocks for Cartegna Port in Spain) Enerpac produced a design that could easily and precisely handle the weights involved ­ while keeping the operator at a safe distance from anchor frames as the lift was being performed.

Four RR308 double-acting cylinders were selected to provide a total of 120 t of lift capacity for each of two anchor feed beds (each cylinder being of 30 t capacity on push function, 5 t on retraction, and having a stroke of 209 mm). These rugged cylinders, designed for high-cycle industrial uses, were powered by an Enerpac PAM-9808N air pump with manifold incorporating valving to ensure fine control of advance and retract functions, as well as safety shutdown capacity.

Control mechanisms incorporate VC-4 remote directional control valves, which facilitate fine control of individual cylinders within each group of four, while also providing shutdown capacity. Safety awareness is carried through the system's high-pressure hosing, which incorporates HC-7306 and HC-7310 hose with a 4:1 safety factor.

Safety was a keynote of all equipment specified by TCS7 for each stage of the Gravity anchor installation, which began with the anchors being winched into lifting position in travelling anchor frames that moved along the length of the vessel.

The travelling frames in each of the two feed beds involved rode on ER-60 60 t load skates running within C channels along the length of the vessel.

"The hydraulic systems involved were designed for rugged simplicity in an aggressive maritime environment where they could be operating 24 hours a day, seven days a week," said Mr. Henderson.

"As with much of the Enerpac equipment used on resources sites in and around Australia, reliability is at a premium when you're in a remote situation hundreds of kilometres from support facilities.

"Obviously also dealing with heavy weights on a ship poses its own safety issues, and optimum safety is a first priority of the global Technip organization."

The scope of the Technip and Subsea 7 project includes the tie-in of Woodside's second trunkline into the existing infield facilities near the North Rankin A platform, via hyperbarically welded and flanged spoolpieces and a 350Te valve manifold. The second trunkline work also includes the dewatering and condition of the trunkline and stabilization of the trunkline by installation of the approximately 900 gravity anchors. After startup of the second trunkline, extensive pipeline system modifications to the existing first trunkline at North Rankin A Platform will be carried out.

With a worldwide workforce of about 18 000, Technip ranks among the top five in the field of oil and petrochemical engineering, construction and services. Subsea 7 is one of the world's leading subsea engineering contractors with operations in UK, Norway, Asia-Pacific, Brazil, Gulf of Mexico, West Africa and Caspian.

Enerpac is part of the Actuant Corporation, which has worldwide sales exceeding A$ 1 billion a year. The Australasian Enerpac operation has built an enviable reputation over more than 30 years through its in-house expertise coupled with an extensive distribution and service network.

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