Technical Presentations at the July 2009 Meeting
Tidal turbines offer an exciting opportunity to exploit ocean current flows to generate sustainable energy. However, a key to their success is the ability to operate with minimal intervention in the ocean over extended periods (15-20 years). This talk explored the likely design and operational issues that will influence satisfactory performance associated with material corrosion and biofouling. The main difficulty is that turbine economic viability is capital driven so whole system, including operation and maintenance needs to be as cost-effective as possible. Although can use approaches developed from those applied for ship design and in the offshore industry there is a need to appreciate that cost-drivers are different. For instance a ‘Gold plated’ technology approach from oil and gas industry may not deliver cost-effective solutions. [Dr Stephen Turnock, Froude Building (28), School of Engineering Sciences, University of Southampton, SO17 1BJ, [email protected]]
Tidal turbines that survive?, S.R. Turnock, R. Nicholls-Lee, R.J.K. Wood and J.A. Wharton
Fluid-structure interactions, School of Engineering Sciences and national Centre for Advanced Tribology at Southampton (nCATS), School of Engineering Sciences, University of Southampton, SO17 1BJ, UK.
Applications using Phased Array Ultrasonic Testing and / or TOFD are well documented for the inspection of weldments however there appears to be very little relating to the inspection of corrosion which is perhaps one of the most common in service forms of material degradation. The presentation addressed applications ranging from automated pulse echo ultrasonic applications, Time of Flight Diffraction (TOFD) and Phased Array (PA) applications. Examples were given where bespoke software has been used to optimise reporting of corrosion. A kaleidoscope of images obtained from inspections were shown exemplifying various forms of material degradation including corrosion, pitting, cavitation, erosion, hydrogen induced cracking (HIC), microbiological induced corrosion (MIC) along with various images demonstrating basic principles of each advanced inspection method.
Severe corrosion of anodized titanium bolts has been discovered when immersed in seawater at temperatures up to 34C. A mixture of red and blue anodized bolts and un anodized titanium were immersed at a range of depths. The corrosion was confined to red anodized bolts (with the thickest oxide) located in shallow waters. Corrosion was caused by crevice corrosion under barnacles, a mechanism not expected at temperatures below approximately 70C. Acidic conditions are produced by hydrolysis of seawater. Anodizing produces a TiO2 layer (anatase) which was found to be photocatalytic to UV light. This generated voltages which moved the titanium from the passivated region to the corrosion region of the Pourbaix diagram. Shielding of the bolts from UV light has prevented further corrosion.
This presentation related to the Thames Barrier Rising Sector Gates Cathodic Protection systems.
Note: Several of these presentations are available in pdf format to staff of MCF member companies. Please contact the Secretariat for details.