Anchor chain manufacturer Ramnäs has developed a shackle for joining chain to steel wire that simplifies mooring line installation. First use of the new RAM-plate shackle will be on Statoil’s Volve development in the Norwegian North Sea.
The RAM-plate, for which a patent is pending, has been developed at the request of Ramnäs’ customer APL, which is supplying a submerged turret loading (STL) system for the Volve floating storage unit. A total of 29 RAM-plate shackles, each weighing just over one ton, will be supplied for Volve, as part of a consignment of 1,640m of 125 mm dia. Grade 4 anchor chain.
Currently, the connection between chain and wire is effected using a triplate with a joining shackle attached to either end. Attachment of the chain to the joining shackle has to be performed using a special end-link, which is larger than the standard links. The end-link is therefore made from a different bar size, and requires different tools in the production process.
The RAM-plate does away with the need for a special end-link and for the triplate, says Nils Nilsson, Ramnäs’ area sales manager. Instead, a standard link is attached to the RAM-plate with an oval pin, while the wire is attached to the other end of the shackle by means of a pin inserted through a socket.
The new shackle has the further advantage that, because there is no end-link, it is possible to cut a few links off the chain for a final length adjustment at the time of installation.
Higher-strength chain
Meanwhile, in response to market demand, Ramnäs has decided to extend the range of its anchor chain grades with the addition of an extra high strength chain to be known as Grade 5. Draft specifications for the new grade are expected to be issued by classification society DNV for comment by Ramnäs in the spring, Nilsson says. The new specs should therefore be in place later in the year.
Grade 5 will have a proof-load and a break-load both 16% higher than Grade 4. Its yield strength will be 700 MPa and its ultimate tensile strength 1,000 MPa. This compares with 580 MPa yield strength and 860 MPa ultimate tensile strength for Grade 4. Ramnäs has made one-off deliveries of high-strength and extra high-strength Grade 4 chain with mechanical properties close to those of Grade 5.
Weight savings
The customer can take advantage of the new grade in two ways, Nilsson says. By using Grade 5 instead of a lower grade, the same break-load can be achieved with smaller dimensions, thus saving weight and installation costs; alternatively a higher break-load can be achieved with Grade 5 than is provided by lower grade chain of the same dimension.
Achieving a higher break-load is clearly the aim of some rig operators in the GoM following the destructive effect of last year’s hurricanes on the moorings of floating rigs and platforms. Ramnäs’ first order for what is in effect Grade 5 chain was placed by Diamond Offshore late last year, and amounts to 2,500 tons of 3.3/4-in chain for mobile units in the GoM.•
For more information contact Nils Nilsson, Ramnäs Bruk. Tel +46 220 220 27, fax +46 220 358 37, [email protected], www.ramnas.com.
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GoM demand remains strong
Demand for anchor chain, which was already strong due to the boom in newbuild drilling rigs and floating production facilities, has surged further as rig contractors in the GoM move to upgrade mobile unit moorings following last year’s hurricanes. Nilsson expects demand to stay high this year and next.
Several of Ramnäs’ current orders are from APL, in addition to the Volve delivery. These include an order for two FPSO projects operated by CNOOC in the Chinese offshore sector - Xijiang and Wenchang. Both call for Grade 4 chain of 147 mm diameter - 2,097 m for Xijiang and 1,647 m for Wenchang. Delivery is due in October.
Among other orders the company also has a contract to supply Grade 4 chain of 127 mm diameter to ConocoPhillips’ CoroCoro project in Venezuela.
Orders for replacement chain have been received from Transocean for theTransocean Driller,Henry Goodrich, and Jim Cunningham drilling rigs.
