ICON designs world first subsea buoys

• Local content ‘double whammy’ win on Ichthys LNG project
• World first use of robust, long life composite subsea buoys
• Designed to withstand 1 in 10,000 year cyclone event

A new generation of mid water depth buoy modules (MDBs) has recently been installed on the Ichthys LNG project in the Browse Basin.  The MDBs are a local content ‘double whammy’, having been designed by West Perth’s ICON Engineering Pty Ltd, in support of McDermott Australia Pty Ltd, and the buoyancy modules being manufactured in Matrix Composites and Engineering Ltd at its Henderson facility.

Bulk syntactic foam has previously been used in applications for drilling risers but this is its first global deployment in a mid depth buoy system. In this instance, it forms part of two mid depth buoys that each supports five flexible risers or umbilicals.

These parts of the Ichthys LNG project each incorporate a 680 tonne gravity base structure that holds the MDB in position 150 metres below sea level.  Each MDB provides 285 tonnes of net buoyancy when anchored to the gravity base structure by chains, which are backed up by secondary tethers.  The operator had specified a stringent 40 year operating life and 1:10,000 year cyclone event criteria.

This new syntactic foam design has alleviated a number of safety and structural issues.  Buoyancy designs to date are usually variations of steel pressure vessels which must resist crushing by water pressure, and which are susceptible to physical impact damage and chemical corrosion by environmental agents such as destructive SRB’s (sulphate reducing bacteria) which can weaken and penetrate the pressure vessel.  Testing verified that bulk syntactic foam exhibits minimal degradation from dropped object or impact damage.

Ichthys operator Inpex required very high system integrity.  ICON responded by designing a fully redundant, secondary tether system, built from high performance polyester rope to provide a back up against potential failure of the tetherering chains.  The 150m water depth also meant that the MDBs had to be designed for full diverless technology for all intervention points.

In this role, syntactic foam buoyancy avoids the need for the certification and maintenance of steel pressure vessels. The material comprises a high performance epoxy matrix, which binds millions of microscopic hollow glass spheres and macroscopic carbon fibre spheres, enabling it to absorb substantial impact energy.

ICON also designed the assembly and transportation cradles that house the two buoys, along with the gravity base structures, which were fabricated in Batam.

The ICON team is reinforcing its reputation as an X+1 supplier, with its input bringing the installation time down from 20 hours on the first module to 12 hours for the final module.
ICON cofounder and Principal Engineer Garrick Aberle said it was another practical ICON solution:  “It is very pleasing to see that in an open tender environment, a WA consortium was able to offer a competitive, innovative and long life engineering solution.”

“Syntactic foam buoyancy has solved a number of significant engineering and management issues in this single application,” he said. “This is how operators are working smarter in a tough environment.”