Offshore contractors have added next-generation heavy-lift crane vessels in response to larger offshore structures
Offshore contractors have added next-generation heavy-lift crane vessels in response to larger offshore structures
One of the enormous challenges facing the offshore oil and gas industry is the decommissioning of old and abandoned platforms and oil and gas wells. Of the 7,800 wells drilled in the UK North Sea, hundreds are now either past or fast approaching the end of their useful lives.
UK-based energy research consultant Maritime Strategies International (MSI) estimates that spending in the global decommissioning market over the next 10 years will be US$78Bn, with the largest European markets accounting for about for 45% of the total, led by the UK with US$23.4Bn, Norway (US$8.6Bn) and the Netherlands (US$3.1Bn).
Dutch offshore marine contractor Heerema Marine Contractors (HMC) has decades of experience in the global decommissioning sector, with complex projects such as the dismantling and reuse of Brent Spar in 1999 and the decommissioning, removal and recycling of the North West Hutton platform in 2009 under its belt. Some 20,000 metric tonnes of steel was recycled from the North West Hutton platform as a result of the removal.
To enhance its heavy-lift capability to meet the demands of increasingly larger decommissioning and deepwater oil and gas and renewable projects, HMC is now adding a new tool to its toolbox: Sleipnir, the world’s largest semi-submersible crane vessel (SSCV), with an overall length of 220 m, beam of 102 m, variable operating draught between 12 and 32 m and depth of 49.5 m.
Sleipner is the fourth heavy-lift crane vessel in HMC’s fleet, following Aegir, Thialf and Balder.
Making the SSCV extremely capable are two 10,000-tonne-capacity revolving Huisman cranes that allow Sleipner to make lifts of 20,000 tonnes in tandem. The two tub-mounted cranes, which are capable of lifting 10,000 metric tonnes at a radius of 48 m, were specially designed and built by Huisman in China. Unlike traditional tub cranes, which make use of either bogies or large wheels for their slew system, the Huisman cranes use large 30 m diameter slew bearings manufactured in-house. Huisman says that one of the largest benefits of using bearings is that it allows for a substantial weight savings for the crane.
"With its single-lift capability, Sleipner will cater to larger integrated structures, minimising offshore assembly work and increasing operational efficiency"
Indeed, with its single-lift capability, Sleipner will cater to larger integrated structures, minimising offshore assembly work and increasing operational efficiency.
Fittingly, Sleipner is named for Odin’s powerful, eight-legged stallion of Norse mythology. The vessel has a deck load capacity of 20,000 metric tonnes, with a main deck working area of 12,000 m², offering a load capacity of 10 metric tonnes/m².
First dual-fuel SSCV
Sleipner is also the first dual-fuel crane vessel, with 12 four-stroke MAN 8L51/60DF engines that can burn low-sulphur marine gas oil (MGO) or LNG, providing operational flexibility. When not burning LNG as a fuel, the ship’s IMO Tier III-compliant engines are fitted with selective catalytic converter (SCR) technology to ensure operations in the strictest emissions control areas, even when LNG bunkering infrastructure is not available. The main engines each produce 8MW of power. The vessel can carry about 8,000 m3 of LNG in an IMO Type-C LNG fuel tank.
For propulsion station-keeping and manoeuvrability, the SSCV has eight Wärtsilä 5.5MW WST-65U underwater demountable fixed-pitch, variable speed azimuth thrusters, four of which are retractable. Wärtsilä Retractable Underwater Mountable Thrusters (WST-RU) can be retracted during transit, reducing the vessel’s resistance and improving overall efficiency. A special retraction system draws the steerable thruster into the hull, allowing the SSCV to navigate safely in shallow water. Two rack and pinion system drives enable the thruster to fully retract within 10 minutes, reports Wärtsilä. The ability to retract and deploy the thruster enables an increased level of operational flexibility for the vessel.
An onboard dynamic positioning (DP) system, with Lloyd’s Register’s IMO Class 3 DP (AAA) notation, facilitates station-keeping for Sleipner, but it can also use a 12-point mooring system, consisting of 12-metric tonne Stevpris Mk-6 anchors, winches and wire sheaves that can hold 1,750 m of wire rope.
At the stern of the vessel is a heli-deck large enough for either an Augusta Westland EH101 or Sikorsky S-92 to land.
The SSCV can accommodate 400 persons in single and double cabins and will be deployed globally for installing and removing jackets, topsides, deepwater foundations, moorings and other offshore structures.
First contracts secured
Sleipner will first be deploy in decommissioning and offshore wind projects. HMC has secured contracts for the Leviathan topsides installation in the Mediterranean Sea, Tyra jackets and topsides installation and removal in the Danish North Sea, Brae B jackets and topsides removal in the UK North Sea. Additionally, the SSCV will transport and install the Hollandse Kust Zuid (HKZ) Alpha HVAC platform in the North Sea, off the Dutch coast.
In the offshore wind sector, HMC sees a significant growth in the size of wind turbines and foundations, which requires specialised equipment for their installation. With its large cranes capable of a 175-m lifting height and a combined 20,000-tonne lifting capacity, Sleipnir can accommodate larger, next generation offshore wind turbines.
“Sleipnir scores several firsts in the industry”, said HMC chairman Pieter Heerema at the vessel’s christening in May at Sembcorp Marine’s Tuas Boulevard Yard. “It is the largest crane vessel yet built; it has the strongest pair of revolving cranes; and it’s also the world’s first crane vessel with dual-fuel engines running on MGO and LNG, dramatically reducing harmful emissions. Sleipnir’s innovative capabilities will cement Heerema’s position at the forefront of developments in the offshore oil, gas and wind energy industry for both installations and decommissioning.”
Sleipner also pushed the boundaries for Sembcorp Marine, becoming the Singaporean shipbuilder’s largest offshore vessel built to date. At its peak, the construction of the vessel involved 3,700 workers in a single shift.
Sleipner’s concept and basic design was undertaken by Swedish naval architectural firm GVA (now part of KBR) in 2014. A shipbuilding contract valued at US$1Bn between HMC and Sembcorp Marine was signed in July 2015.
Pioneering Spirit has single-lift, motion-compensation technology to facilitate topsides removal or installation
Privately held Swiss-based offshore marine contractor Allseas Group SA shares family history with HMC. Allseas was founded in 1985 by owner and president Edward Heerema, the son of the late Pieter Schelte Heerema, the founder of HMC.
Allseas Group’s fleet includes Pioneering Spirit, the world’s largest heavy-lift and pipelay vessel. In June, Pioneering Spirit completed the single lift removal of the 25,000-tonne Brent Bravo topsides from the North Sea. Pioneering Spirit was able to complete the operation in approximately four hours, from positioning the vessel around the platform to the moment of the lift. Using its single-lift, motion-compensated technology, Pioneering Spirit was able to “fast lift” the topsides in nine seconds, successfully concluding two years of intense planning and offshore engineering works.
“Pioneering Spirit was able to “fast lift” the topsides in nine seconds, successfully concluding two years of intense planning and offshore engineering works”
It is the unique design of the vessel that makes such a single lift possible. The twin-hulled vessel is 382 m long and 124 m wide. At the bow is a slot, 122 m long and 59 m wide, that enables Pioneering Spirit to move around a platform and lift and transport entire topsides using eight sets of horizontal lifting beams. For jacket removal and installation, two 170 m-long lifting beams, which can rotate on hinges, are located at the vessel’s stern.
Complementing the lifting systems is a 5,000-tonne special-purpose crane for additional lifts, such as lighter topsides and jackets, modules and bridges.
Propulsion for Pioneering Spirit is supplied by eight diesel generators that produce 95MW power. Pioneering Spirit has 12 azimuth thrusters that enable class 3 DP operations and propulsion.
Brent Bravo is the second of four platforms, after Brent Delta in 2017, to be decommissioned and removed from the Brent oil and gas field under a contract from Shell UK Limited.
Located 186 km off the northeast coast of the Shetland Islands, the Brent Bravo platform comprised a topsides structure supported by three 12 m-diameter steel-reinforced concrete legs, which stand in 140 m of water.
Cuts between the topsides and supporting legs were made during the final months of platform preparations. Until the lift, the structure was held in place by purpose-built shear restraints that prevented lateral movement. The concrete legs remain in situ, capped with concrete covers fitted by one of the vessel’s cranes. For navigational safety, a solar-powered navigational aid has also been installed on top of one of the capped legs.
The 125 m tall, 70-m wide topsides have since been sea-fastened on board Pioneering Spirit for transport to the Able UK decommissioning yard in Teesside, North East England. At a nearshore location off the coast of Hartlepool, the topsides will be transferred to Allseas’ cargo barge Iron Lady for the final leg of its journey, towage up the Seaton Channel and load-in to the quay at Able UK’s yard for dismantling.
Built by South Korea’s Daewoo Shipbuilding and Marine Engineering, Pioneering Spirit has lifted more than 130,000 tonnes of topsides weight and installed over 1,500 km of subsea pipeline since starting operations in 2016.
The single-lift removal of the 24,200 tonne Brent Delta topsides in April 2017 set a new record for a lift undertaken at sea, until Pioneering Spirit’s installation of the 26,000-tonne production platform for Equinor’s Johan Sverdrup development offshore Norway, earlier this year.
Pioneering Spirit was used to make the final two platform topsides lifts. The processing platform lift set a new lifting record offshore and was carried out in only four hours with a clearance of just 25 m from the rest of the field centre. The lift of the utility and living quarters topside, 18,000 tonnes, was completed in three and a half hours.
Derrick barge incorporates advanced pipe-lay technology
A derrick pipe-laying barge built by container crane manufacturer Shanghai Zhenhua Heavy Industry Co, Ltd uses advanced pipe-laying technology from Danfoss Drives for its 3,000-tonne, fully rotating slew crane.
Driven by Vacon AC drives from Danfoss Drives, the vessel’s slew crane is highly efficient, with the capability of laying two pipelines simultaneously; it can hoist a fixed weight of 3,000 tonnes while stationery and 2,000 tonnes while slewing full circle.
Motors produce 7.1MW of power to operate the crane, which has two main hooks, two auxiliary hooks, two beams, six slewing gears, two rigging hooks, two cargo control winches and one hook control winch. The entire AC drive system consists of two 12-pulse common DC bus systems. The two systems are supplied through a quasi 24-pulse Vacon AC drive system.
The system has four Vacon NX rectifiers and 17 Vacon NXP inverters to control all the actuators. An additional two Vacon NX braking units are set to dissipate extra braking energy.
Modular and compact, Vacon NX products use a closed-loop vector control mode and have speed and torque control with a speed differential of less than 0.01% and torque precision of less than 2%. The system can be controlled at full torque under any speed, including zero speed. A special application was developed, based on the Vacon Marine application, for the full-circle-swinging crane.