Jose Mishael Chakkalakkal Joseph PhD

Methodology for Optimal Inspection and Maintenance Planning of Offshore Wind Support Structures subjected to Corrosion – Fatigue

The need for sustainable renewable-energy power plants has been consistently on the rise to replace the shortage of fossil fuels and to meet the regulations for the climate changes. Wind energy industry stands out as one of the most environmental friendly, economically feasible and profitable alternatives to conventional sources of energy. The wind industry commenced by exploring energy with onshore wind turbines and gradually moved to offshore in order to take advantages of strength and consistency of the winds in the sea. The offshore wind turbines (OWTs) installed in Europe are mainly supported by fixed bottom foundations. Monopile foundations are popular among different fixed foundations for offshore wind turbines in terms of its simple fabrication and installation. The steel monopile foundations of OWTs are subjected to corrosion and fatigue as they are exposed to harsh environments, which may lead to the significant reduction of their service life. There is a need for accurate lifetime assessment methods to optimise the new and existing wind farm operations, therefore reducing the Levelized Cost of Energy (LCoE). This can benefit various stakeholders, such as owners, operators and suppliers as the methods can be used to extend the lifetime of the OWTs and exploitation of the wind farms in future. The objective of the research is to develop an innovative methodology for the inspection/monitoring and maintenance optimisation of OWT support structures subjected to corrosion-fatigue. The research is carried out in the framework of a project named MAXWind (MAintenance, Inspection and EXploitation Optimization of Offshore Wind Farms subjected to Corrosion-Fatigue) funded by Energy Transition Fund (ETF), Belgium.

The inner side of OWT monopile foundations is severely affected by uniform corrosion and localized forms of corrosion such as pitting, water-level corrosion, microbiological corrosion (MIC), etc. The localised corrosion increases the stress concentration in areas with risk, e.g. at welds, making them susceptible to corrosion fatigue. Since corrosion is one of the major issues in OWT support structures and therefore, monitoring corrosion is highly desirable for ensuring the proper functioning of OWTs. Corrosion monitoring provides information on the current corrosion state, prevailing mechanisms and cause of changed conditions. Monitoring campaigns increase the reliability of service life assessment and give the option of corrective actions if corrosion rates are higher than expected. The monitoring can be effective only if the data obtained shall be assessed relative to an acceptance criteria set for the system, which has to be established beforehand. An optimal monitoring strategy will be capable to reduce the maintenance efforts. It is envisaged to develop a methodology for optimal monitoring of the OWT support structure also.

Publications

AN INTEGRATED FRAMEWORK FOR SHIP STRUCTURAL OPTIMISATION IN CONTRACT DESIGN PHASE, Article, 2019