Failure analysis of the guide vanes of the Pico Wave Power Plant Wells turbine

• Failure analysis was performed to the guide vanes of the Wells turbine.
• Stalling events promote strong vibrations on the vanes, thus exciting a wide range of frequencies (up to 3000 Hz).
• Embedded region design of the vanes promotes stress concentration on a critical welded region.
• Notches were created during manufacturing due to laser cut of the vanes.
• Stalling events should have been avoided with an active control strategy.

The working principle of the Wells turbine, used in the ocean energy extraction, can sometimes lead to stall in the turbine blades and stators’ vanes, which is an unintended action considering that creates potentially damaging conditions to the mechanical components, plus reducing the efficiency of the take-off system. This work focused on the cracking damage caused to the earth-side guide vanes of the Pico Island Wave Power Plant due to the loading from turbulent air flow and consequent vibrations, as a result of turbine stall. Comprehensive analysis of the design and manufacturing phases, as well as of the constitutive metal properties (AISI 316L stainless steel), including the consequences of welding, was carried out. Strain gages were used to evaluate the loading profile in real-sea working conditions and different suggestions were made in order to postpone and prevent crack nucleation and propagation. The appearance of cracks seems to have been caused by mistakes made at both design and manufacturing phases, eliminating from the guide vanes the ability to endure the aggressive loads which they were subjected to. The lack of an active control strategy on the power plant resulted in consistent turbine stall events, thus contributing to the excessive loadings imposed to the vanes.