Analysis of Large Area Corrosion of High Strength Bolts in Wind Turbine Tower

In view of the current situation of large-area corrosion of wind turbine tower bolts, chemical composition, tensile performance testing and microstructure observation are used to analyze the body performance of the bolts. The results show that: the material of the bolt and screw is misused; the tensile performance of the bolt and screw meets the requirements of the standard, and the impact performance is lower than the standard value;

There are sulfide non-metallic inclusions in the core of the screw, and there is a small amount of ferrite; the regular inspection of the bolt destroys the treatment surface, and the surface treatment layer cannot effectively resist corrosion; the corrosion of the bolt is atmospheric corrosion, accompanied by Electrochemical corrosion, the generated corrosion products will continue to transform into soluble products in a humid environment, further accelerating the corrosion. Finally, relevant suggestions are put forward for the treatment measures of the bolts of the wind power plants in service.

Chemical composition analysis

Samples were taken from the screw, nut and gasket, and analyzed by the Oxford FOUNDRY-MASTER PRO full-spectrum direct-reading spectrometer. The detection position is the middle part of the sampling and three points are detected. The experimental results are shown in Table 1. It can be seen that the detected chemical composition data does not meet the requirements of the EN14399-4:2005 standard for 42CrNiMo materials. The tested Ni content is very low, so it can be determined that the bolt material used is 42CrMo instead of 42CrNiMo. This shows that the bolt is misused.

Hardness test

The center of the bolt and the outer edge of the bolt meet the requirements of EN14399-4:2005 for the hardness of 42CrNiMo material, but the hardness of other parts is low, which does not meet the requirements of EN14399-4:2005 for 42CrNiMo material; at the same time, the outer edge of the bolt can be found The hardness is significantly higher than other parts.