Case Study — originally published 31 May 2016. This article has been revisited and updated for republication.
Syntactic foam buoyancy achieved a world first on the Ichthys LNG project in 2016, when a new generation of mid water depth buoy modules (MDBs) was installed in the Browse Basin, offshore Western Australia. The modules were designed by West Perth’s ICON Engineering in support of McDermott Australia, with the buoyancy elements manufactured by Matrix Composites & Engineering at its Henderson facility. The project combined a local content double win on Ichthys LNG, the world-first use of robust, long-life composite subsea buoys, and a design rated to withstand a 1-in-10,000-year cyclone event.
Local content double win on Ichthys
The MDBs were a local content “double whammy”: Western Australian design and Western Australian manufacture, delivered on one of the largest resource projects in the country. ICON co-founder and Principal Engineer Garrick Aberle called it 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,” he said at the time.
A world first for syntactic foam buoyancy at mid depth
Bulk syntactic foam had previously been used in applications such as drilling risers, but this was the first global deployment of syntactic foam buoyancy in a mid depth buoy system. In this application it forms part of two mid depth buoys, each supporting five flexible risers or umbilicals.
Each buoy is held in position 150 metres below sea level by a 680 tonne gravity base structure, anchored by chains that are backed up by secondary tethers. Each MDB provides 285 tonnes of net buoyancy when anchored to its gravity base structure. Ichthys operator INPEX had specified a stringent 40 year operating life and a 1-in-10,000-year cyclone event as design criteria.
Why syntactic foam instead of steel pressure vessels
The syntactic foam design alleviated a number of safety and structural issues. Subsea buoyancy designs to that point were usually variations of steel pressure vessels, which must resist crushing by water pressure and are susceptible to physical impact damage and chemical corrosion by environmental agents such as sulphate reducing bacteria (SRBs), which can weaken and penetrate a pressure vessel.
Syntactic foam buoyancy avoids the need for the certification and maintenance of steel pressure vessels. The material comprises a high performance epoxy matrix binding millions of microscopic hollow glass spheres and macroscopic carbon fibre spheres, enabling it to absorb substantial impact energy. Testing verified that the bulk syntactic foam exhibited minimal degradation from dropped object or impact damage — a meaningful consideration for an asset specified to remain in service for 40 years with minimal intervention.
Full redundancy and diverless intervention
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 tethering chains. The 150 metre water depth also meant the MDBs had to be designed for fully diverless technology at all intervention points.
Faster with every module
Beyond the buoys themselves, ICON designed the assembly and transportation cradles that house the two buoys, along with the gravity base structures, which were fabricated in Batam, Indonesia. ICON’s input also sharpened the offshore campaign, bringing installation time down from 20 hours on the first module to 12 hours on the final module.
“Syntactic foam buoyancy has solved a number of significant engineering and management issues in this single application,” Mr Aberle said. “This is how operators are working smarter in a tough environment.”
The engineering has since been put to the test in service: Ichthys LNG went on to commence production in July 2018 and is designed to operate for decades in the Browse Basin. The syntactic foam buoyancy work sits within ICON’s broader subsea capability, spanning subsea structures and systems, subsea umbilicals, risers and flowlines (SURF), and subsea installation engineering.
