ABSTRACT
Protection barriers are implemented to provide corrosion protection for offshore windfarm monopile foundations. Such protection methods have been applied since the beginning of the offshore windfarm industry with regard to the external surfaces and more recently, since 2010’s for the internal surfaces. Design life extension combined with an increase of foundations dimensions lead currently to the requirement for high efficiency / high capability protection barriers.
Main findings and engineering lessons learned on how to optimize the above protection barriers design are reviewed in this paper, specially:
i. Appropriate interpretation of the new revision (2017-2018) of ISO(1) 129441-5 to define the right environment corrosivity category and subsequent painting systems durability.
ii. Relevance of design current densities and drained current into sediments for cathodic protection system from codes & standards.
iii. Use of cathodic protection modelling to optimize cathodic protection system design; Findings on mitigation of galvanic anodes interferences are presented to illustrate the purpose.
iv. Design of a passive water/air renewal system to prevent side effects resulting from cathodic protection system installed in a nearly closed environment like monopile foundation internal areas.
v. Environmental impact of galvanic anodes: ‘‘Myth or reality’’?
INTRODUCTION
Corrosion protection of offshore wind farm foundations is designed based on technical requirements provided by International standards (e.g. DNVGL(2) RP 041615 or national standards (German VGB/BAW(3) standard, e.g. VGB-S-021-01-2018-0416). These standards refer to other proven standards widely applied in Oil & Gas industries for details of painting specifications (e.g. ISO 129441-5 and Cathodic protection design (e.g. DNVGL-RP-B40114, etc.
The current paper focuses on our recurrent findings when looking for the optimized corrosion protection systems for typical monopile foundation that has to satisfy both technical and cost saving requirements.
CORROSION PROTECTION FOR MONOPILE FOUNDATION - GENERAL PRINCIPLES
Six basic types of foundation have been used in offshore wind farm: monopile, jacket, tripod and gravity foundation and floating foundation. The last one is currently at the demonstration stage. For example an offshore floating windfarm Hywind with five turbines were installed in North Scotland in 201817. All foundations are prefabricated onshore in one piece, carried offshore by barge and set on bottom by crane or derrick barge.
