Subsea Pile Protection
Tech File: HexDefence Scour Protection for Offshore Wind
As the pace of offshore wind installation accelerates globally, all eyes turn to tools and techniques that will enable efficient installation and lifecycle protection of offshore wind towers. Balmoral, with decades of experience protection offshore oil and gas infrastructure, debuts HexDefence. Dr. Aneel Gill, Product R&D Manager, Balmoral, discusses the key benefits.
By Greg Trauthwein
Much innovation comes down to filling gaps. What gap did you see in the market that let to the invention of HexDefence?
One of the main products that we have at Balmoral is a cable protection system, protecting the cable as it's coming out from a monopile or a jacket configuration, taking it past a traditional scour protection. What we were actually looking at was how do we diminish accelerated flow, which is a phenomenon of water going past a cylindrical object [as it] increases loads.
We had a product that we knew was very good in terms of its hydrodynamic performance, hydrodynamic shape within the oil and gas sector, and that was our LDV product. Looking at those feasibilities, what we found was we found a reduction in accelerated flow. But we also noticed a reduction in prevalent kinetic energy, and we used that as an indicator to say, ‘maybe there's something else here. Maybe this can also reduce the shear stress at seabed’, which is a key factor in the phenomena of scour.
We followed up, we've done tank testing, we've done CFD work and we’ve shown that the product has some really strong performance when it comes to an alternative method to scour protection.
How specifically does HexDefence work?
It's not a magical device, all we are really doing here is redistributing flow. And if we redistribute flow, we are redistributing energy and we're dropping the load cases which are occurring on the seabed. And if you think about it like a particle of sand or a particle of rock, there's a certain amount of energy that it takes to move each particle. If we are able to drop the energies down at the seabed, we're able to stabilize it, make it less prone to erosion or the forces occurring as the current is passing through or past the object, the structure within the water column. There's bit more to it, but in a nutshell that's what we're doing: we're redistributing energy; we're moving current flow away from concentrating it on the seabed.
[HexDefence’s] inception came from oil and gas, but to be honest, they're all marine engineering. If you have something in the water column used in oil and gas, maybe the risk profiles are slightly different. However, the importance of something being used subsea for 30 years, whether it's oil and gas, whether it's renewables, really the thought process, the technology, all should be very similar. Dr. Aneel Gill, Product R&D Manager, Balmoral
Can you discuss a bit more about the materials that are used for HexDefence? How long are they designed to last, and what, if any, specific or special maintenance do they require?
Right now we are looking at a couple of different options. Both have different ways of manufacturer, also have different advantages. One is a GRP or an epoxy-based system, designed to be used in a seawater environment for 30 years plus. We're also looking at other materials, things like concrete and items like that, which again, have a different cost structure but also have a different advantage as well. Things like ballast, weight mass, which also helps with the product and making it more stable when it's around a monopile.
Does HexDefence come from the oil and gas sector?
Its inception came from oil and gas, but to be honest, they're all marine engineering in my opinion. If you have something in the water column used in oil and gas, maybe the risk profiles are slightly different. However, the importance of something being used subsea for 30 years, whether it's oil and gas, whether it's renewables, really the thought process, the technology, all should be very similar.
What is the process to install HexDefense and how does it save time or money in terms of alternative methods of protection?
We’ve had discussions with developers and installers to really hone in on a installation process that works for them. We've come up with some basic strategies, and the idea is it's sleeved over a monopile structure, and that's utilizing the same vessel, the same lift vessels that we would use for let's say the transition pieces which have to also get fitted. That's one scenario. There are obviously different scenarios within the, or different installation strategies that account happen for different fields. But one scenario would be that.
The idea here really is the total cost of ownership. It's about saying, "We'll put HexDefense on and we are able to reduce the level of rock dumping." So that eliminates the need for a number of vessels. It's also saying we are able to bury our cable much closer to the monopile, therefore it's to have reduced dynamic length and making the load cases much easier to contain on things like cables. Again, we're thinking longevity. We're thinking what can we do for the total cost of ownership of the field. And we see a lot of the time saving, a lot of OpEx cost being saved and really improving the lifespan of cables, improving the lifespan of not having to go and redo a rock dumping operation after the fact.