Feature 5 | FPSO TECHNOLOGY
clamp to activate and lock the connector’s balls in position and satisfy the DBSC’s torque requirements, preventing the bend stiffener from rotating in the I/J tube. Te DBSC employs the same connection principle used with ball and taper-based, subsea mooring connectors. Developed and deployed in over 300 deepwater mooring systems worldwide, the mooring connector is subjected to typical minimum breaking loads (MBL) of 17,998kN. Manufactured from precision-
machined forged materials and super duplex balls, the ball and taper type connection is optimised to maximise the connector’s strength and resilience. In order to protect the connector from corrosion in the splash zone, the DBSC has a thermally sprayed aluminium (TSA) coating. Anodic protection may also be employed to complement any corrosion protection system that may be in place within the connecting I/J tube. The key engineering challenge in
developing the DBSC has been the pull-in load experienced during riser connection. In-house testing is conducted
to determine the pull-in loads at different angles and various loads, replicating the loads likely to be experienced by the DBSC in the field. Whilst pulling-in the DBSC into the I/J
tube, side/angled loads are induced due to the tension in the risers and the angle of the riser. Pull-in loads for the DBSC vary for different inclined angles and side/ angle loads. It has been shown that for an angle of 10° or less the required pull-in load is less than the side/angled load. However, for angles between 10-15°, the pull-in load exceeds the side/angled load by a small factor. Even so, the loads experienced will
be well within the expected DBSC installation loads offshore. In general, the larger the riser diameter, the smaller the available pull-in angle. Moreover, the pull-in angle is also dependent upon the type of DBSC used.
Newbuild riser connections For newbuild projects, a two-part (male / female) connection or Type II DBSC has been developed, enabling a full ball
The Type II DBSC, with automated release clamp, pictured during testing to
determine the pull- in loads at various angles.
and taper connection with a smaller connector footprint where space is
limited. As both elements of the
connection are manufactured to designed tolerances, this allows for a simpler and more compact connector. This type of DBSC is intended for
installations where the pre-machined, female receptacle is fixed to the ‘I’ or ‘J’ tube during an FPSO’s or buoy’s structural fabrication stage. Te Type II DBSC is designed to release
the end fitting once the male DBSC has engaged within the female receptacle. And, unlike the Type I version, the Type II connection is only used during installation; once installed, it does not require a hydraulic locking mechanism and/or clamp to hold it in position. Tis type of connection was used on the
installation of four diverless bend stiffeners for gas offloading risers and umbilicals carrying electrics and hydraulics on two submerged turret loading (STL) buoys for the Neptune Deep Water Project North and South, off the coast of Gloucester, Massachusetts, US. Both the Type I and Type II
release DBSCs require some level of ROV intervention. The latest DBSC development is a ROV-less Type II for ‘crowded’ turrets or buoys on FPSOs where space is either limited or shallow water, splash zone environments make a ROV impractical. The new Type II DBSC uses an Automatic Release Clamp (ARC) self-latching
disconnection
system attached to the riser end fitting which, once engaged with the female receptacle, uses a system of rubber springs to maintain the pre-load on the male connector’s ball configuration, and dogs to release the end fitting from the DBSC. Te ARC design addresses the problem
of the ‘weak link’ oſten experienced with some bend stiffener connectors, where the shear-pin breaks ahead of complete installation, or is too strong, resulting in the connector being ‘over-pulled’ and leading to installation problems. Instead, the ARC DBSC connector uses an integrated pull-in head locking mechanism, automatically de-latching when it is fully connected and eliminating the need for a ROV and diver during termination head connection. OMT
30 Offshore Marine Technology 4th Quarter 2011
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