DEVELOPMENTS IN FOUNDATION TECHNOLOGY
the oil & gas out of the ground. However, this view has cost the offshore wind industry dearly by not learning the lessons already paid for by the offshore oil & gas industry. A lot can be learned from over 40 years of offshore experience.
VIEW FROM THE OUTSIDE!
On the opposite side of the fence, the oil & gas industry views some of the problems encountered by the offshore wind industry with disbelief.
The failure of the grouted connection between the transition pieces and the monopiles is a classic case. The subsequent repairs costs have led to litigations and also a partial undermining of confidence for investors (and the public) in offshore wind.
STEEL QUALITY
Using steel from the Far East was seen as a good cost saving approach but without proper quality control and surveillance to ensure quality meant that the delivered product was not fully compliant. This caused delays, expensive remedial works and litigation. The importance of quality steel for use in oil & gas platforms was learned many years ago and strict compliance controls and surveillance are common place in the industry.
OPTIONS AND SELECTION OF MATERIALS AND EQUIPMENT The selection and deployment of concrete gravity bases in areas of shifting sand banks has cost one developer a large amount of money. To their credit, the developer abandoned further use of concrete gravity bases and switched to steel jacket structures with great success. Interestingly, for such a close to shore and relatively shallow development, monopoles were not used due to the seabed conditions and the scouring effects which would undermine them. It
will be interesting to see which foundation solution is adopted in the neighbouring wind farms now being developed.
The poor suitability of some crane vessels used for the offshore installation phases has now been shown up in quite a few offshore wind farm developments. By selecting crane vessels that are severely limited by the sea conditions has led to a number of cases of extended installation durations and even the use of very expensive Heavy Lift Vessels from the oil & gas sector as a last resort. Most of these decisions have led to expensive time and cost overruns and litigation.
If the experience of the grouted connections developed by the oil & gas industry back in the 1970 & 80’s that form the API Code (and the BS Standards of the day) had been used then the problems with the monopile to transition piece could have been avoided. The
design parameters for grouted
connections in the current API Code are based on the DECC and EU funded research
A typical jack-up type crane vessel for installing jackets, towers and nacelles
carried out by Wimpey Laboratories. (THE STRENGTH OF LARGE DIAMETER GROUTED CONNECTIONS by Colin J. Billington, Wimpey Laboratories Limited, OTC 1978)
LESSONS CAN STILL BE LEARNED Over the past 40 years, the offshore industry developed a fleet of construction
Developing foundations that are based on the experience of the oil & gas industry will lead to cost reductions and avoid the pitfalls of expensive mistakes. The majority of foundations worldwide in oil & gas are steel jackets with just a handful of concrete gravity based structures.
vessels ranging from diver support through to heavy lifting capabilities. The experience especially in crane vessels has a great deal to offer to the burgeoning wind industry. The offshore wind industry has identified a large shortfall in crane capacity required for the offshore installation and subsequent maintenance phases. The trend so far has been the construction of jack-up type ship-shaped crane vessels that are able (or claim to be able) to install foundations, towers, nacelles and blades. In effect jacks of all trades, but masters of none. The limitation of these vessels has been all too painful to see. Selecting the right type of vessel for different offshore operations will help to reduce exposure to risk and drive down costs.
www.windenergynetwork.co.uk
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