As the renewable energy, wind power development rapidly and gradually becomes the an important component of sustainable development strategies in many countries. Wind turbine equipment mainly consist of blades, wind turbine generator and wind turbine tower, among them, wind turbine tower is the support structure of wind turbine generator, also an essential part of the offshore wind turbine system. The wind turbine tower, which used widely in nowadays, is made of the steel plate which should roll and weld, such a wind turbine tower has the feature of compact structure, safe and reliable, easy to maintain, nice appearance and etc. Even so, the wind turbine also has a serious corrosion problem, especially in the marine environment.
Marine environment is a kind of physical condition in the range from marine atmosphere to seabed mud, like temperature, wind speed, sunlight, oxygen content, salinity, PH and etc, that can be divide into marine atmosphere zone, splash zone, water level variation zone, total immersion zone and under the mud, Each environment factor changes greatly, and the corrosive effect of tower is also different. The main affecting factors are the composition and content of anions and cation, effect on biological activity, temperature changes, seawater flow speed, value of PH and etc. So, only take the specific corrosion prevention measures can ensure offshore wind turbine working safely and steadily.
The corrosion mechanism and prevention measures of offshore turbine tower
The main corrosion prevention measures of offshore turbine tower are increase electrode protection, plating, spray anticorrosive paint and so on. Not as the onshore wind turbine tower, offshore wind turbine tower in a different “corrosion environment”. It should have a deep knowledge about marine corrosion, choose the corrosion prevention measures specifically through by analyze the corrosion mechanism under each environment according to electrochemistry principle and thermodynamics principle.
In the marine atmosphere zone
The main corrosion prevention measure is coating in this zone. Marine atmosphere zone is the atmospheric and coastwise zone which above the sea splash zone. In this zone has water vapor, oxygen, nitrogen, carbon dioxide and etc, so it has the feature of high humidity, high dalinity, high temperature and circulatory effect of dry and wet obviously. Because of the high humidity, the water vapor, under the effect of absorption and chemical congeal, attach on the surface of steel and come into being a layer of water film which can’t be find use the naked eyes. Carbon dioxide, sulfur dioxide and some salinity dissolve in the water film, cause it becomes the electrolyte solution with strong electrical conductivity. In addition, chloridion has the penetrating action, it can accelerate the stress corrosion, intergranular corrosion, crevice corrosion and other local corrosion. So that, in this zone, the main corrosion prevention measure is coating.
In the plash zone and tidal zone
According to the information study shows that, in the process of alternation of wetting and drying at plash zone, the cathode current of steel is higher than it in the seawater. Steel in the plash zone after drying process, the surface rust layer is used as the strong oxidant in the wetting process. But in the drying process, because of the action of oxidation, the Fe2+ in the rust layer is oxidized to Fe3+. Above process repeated cause the steel be corroded rapidly. In generally, the corrosion speed of the same kind steel in plash zone is 3 – 10 higher than it in the seawater total immersion zone. Plash zone is the most serious part of corrosion in all marine environment. Once a serious local corrosion occurs in this area, the entire steel structure will be considerably reduced the carrying capacity, shortened the working life, even cause the steel structure scrap in advance.
In the plash zone, if just coating to prevent corrosion, it will easy to peeling, and the local corrosion will very serious. Because normal cathodic protection can not come into being current circuit, in this zone also can’t give an effective effect. Composite coating anticorrosion technology has variety advantage, for example, oxygen sealing technology and the element of corrosion inhibitor; In the building construction, surface treatment is simple and it can work in water; Has the strong leakproofness and shock resistance; Environment protection, poisonless and harmless. Such a technology is widely used to prevent corrosion in the plash zone.