Lead Session Chair:
Stephan Barth, Managing Director, ForWind - Center for Wind Energy Research, Germany
Isaac Tavares (1) P Brian Wyatt (2) F Robin Jacob (2) Petra Ernst (4) Gareth John (5)
(1) Centrica Energy, Windsor, United Kingdom (2) Corrosion Control Associates, Stafford, United Kingdom (3) Intertek, Manchester, United Kingdom
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Presenter's biographyBiographies are supplied directly by presenters at OFFSHORE 2015 and are published here unedited
Isaac Tavares has over a decade of combined experience of capital project planning, delivery and operational phases.
After completing a BEng in Civil & Environmental Engineering at UCL, Isaac went on to do a Masters specializing in the use of nano-manipulated steel.
He went on to work as an engineering consultant for several years, being involved in the design of many of the existing Offshore Wind farms, and subsequently their construction and commissioning. Isaac is currently engaged with the operations and asset integrity of several windfarms in Centrica’s portfolio.
Corrosion threats to offshore wind foundations
Although not often appreciated corrosion is a major risk for offshore wind foundations. Its effects could mean costly offshore retrofit work, result in the loss of generation and expose operatives to additional health and safety risks. Corrosion protection therefore is of vital importance to assure the integrity of offshore foundations minimizing exposure to these risks.
Current offshore standards were developed for conditions mostly associated with jacket structures in deeper waters, lower tidal currents and uniform anode distribution. The external protection of most offshore windfarms differs considerably; additionally no competent guidance exists for internal corrosion protection.
To address the current gap in knowledge, work was carried out to develop a body of information that enables standards agencies to include appropriate guidance and designers to effectively assess and design internal protection systems using parameters that are appropriate to the conditions experienced by these structures.
This paper sets out the results of two independent studies, a small study which produced unprecedented results leading to developing a larger test looking at different anode materials, cyclic water ingress and egress, different aeration levels and the evolution of gases followed by multiple offshore trial applications which equally provided astonishing results.
Main body of abstract
The authors reviewed the currently available body of knowledge for the assessment and design of corrosion protection of offshore structures and established that if used at face value will only partially address the external conditions of offshore windfarms due to the way in which anodes are distributed, increasing water depths and importantly the current velocities.
With regards to internal corrosion protection there is no specific guidance available. The authors have discussed with naval engineers to establish if parallels could be drawn from marine ballast tank design but found this to again be a different set of circumstances to the internal compartments of monopiles.
Based on the results of this study the use of existing guidance for the design of galvanic anodes for internal corrosion protection would result in a number of issues developing over time and in some cases result in a more aggressive environment ultimately leaving the structures under protected.
This study builds on a progressively larger scale number of laboratory tests to observe the behaviour of galvanic anodes utilised in internal conditions to evaluate the use of different anode materials, the effects of an internal tidal range versus no tidal range, variations to the aeration of the water column and the rates of gas evolution by using potential control mechanisms.
Additionally a number of offshore full scale internal cathodic protection systems were installed to assess the behaviour under real life conditions and provide validation to the laboratory work enabling further understanding of the characteristics that can be expected.
Corrosion protection, or the lack of, is a major threat to offshore wind foundations with cost and safety implications.
Existing guidance does not cater for the design of galvanic anodes for the protection of the internal compartment of monopile foundations.
This study shows that the use of existing guidance for such purposes would likely result in an environment where, overtime, the structure would become under protected.
Finally the authors set-out an evidence based body of knowledge forming the basis for effective guidance and design parameters that allow standards agencies to upgrade existing standards and provide designers with adequate design tools.
This study enables the reader to understand how galvanic anode behaviour in the internal compartment of monopiles deviates from accepted wisdom and explores a number of conditions relevant to offshore wind monopile foundations.
Crucially it provides the tools for the effective design of such systems using different materials and highlighting key considerations which are critical to ensuring long term system performance and the effective corrosion protection of the internal compartment of offshore wind monopile foundations.