The Corrosion and Biofouling Characteristics of Sealed vs. Perforated Offshore Monopile Interiors: Experiment Design Comparing Corrosion and Environment Inside Steel Pipe
Maher, Monica M.
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This research addresses the need to improve on the existing methods for the corrosion control of the monopile interiors used to support wind powered turbines by incorporating a design that also enhances marine habitats and fisheries. Retrofitting monopile interiors with cathodic protection has been attempted on existing windfarms to mitigate corrosion, however, this can cause new problems including water acidification and hydrogen sulfide formation. Such chemistry changes can lead to unique localized corrosion concerns. This study investigated internal corrosion, chemistry and biofouling inside partially submerged hollow steel pipes. Watertight pipes with stagnant water inside were compared to pipes with holes that allow circulation with the surrounding seawater. By adding holes to the structure walls, surrounding seawater consistently flushed the internal space. The goals of opening up monopile walls were to improve corrosion control of internal surfaces and to create an environment that enhances local ecosystems. With ambient seawater flushing, cathodic protection design used for external surfaces can be applied to protect the interior steel. The field experiment presented here has demonstrated that a cathodically protected perforated monopile structure created an environment with more favorable corrosion mitigation and water chemistry compared to a sealed structure. Furthermore, the perforated cathodically protected pipe created a habitat for marine life and recruited a diverse population of settled and mobile organisms. The development of healthy ecosystems within a monopile structure would add to the benefits of constructing offshore windfarms.