The challenging market environment we have seen over the last few years has led to increasing interest in new solutions as operations look to reduce capital expenditure. These new solutions include an increased attention to hybrid seawater intake risers using a combination of HDPE plastic pipes and rubber hose technology. While these hybrid solutions using plastic pipes can offer capital cost savings in the region of 20-30%, they also pose challenges that impact on operability, reliability and efficiency.

These challenges stem from the properties of HDPE itself. HDPE floats when submerged in water, and thus a HDPE riser must be weighted down to make sure that there is a consistent intake of water and that strainer is at the lowest possible depth. Ballast weighting is also required for stabilising purposes. All of this puts a huge amount of stress on the riser, increasing the risk of failure and creating a lot more risk to both the vessel and seabed assets.

Alongside the risk, the operational concerns pose a serious problem – particularly for FLNG operations. Liquefaction processes expel a lot of heat, and colder water makes it possible to produce LNG more efficiently and more safely. The natural buoyancy, relative fragility and increased pressure on a hybrid riser means that the seawater collected is from a shallower depth – when temperatures rise quickly as you get closer to the surface, significantly impacting the efficiency of the operation.