Galvanic Cathodic Protection of Power Plant Dock
Situated on Tampa Bay, Tampa Electric Company’s (TECO) Big Bend Power Station is located in Gibonston, Florida and was constructed in 1969. The station’s four coal-fired units produce a combined output of more than 1,700 megawatts to serve customers across the West Central Florida service area. The first unit began service in 1970; the second and third generating units were added in 1973 and 1976, respectively; and unit four was added in 1985. Coal arrives at Big Bend Power Station by ship – the plant features a reinforced concrete coal offloading dock, over 700 feet in length.
The station’s concrete started to exhibit signs of corrosion and areas of deterioration and spalling. The owner chose to upgrade the condition of the dock using an investigate-design-build approach to ensure a safe and efficient solution that would provide the desired life extension to their critical structure.
STRUCTURAL TECHNOLOGIES and STRUCTURAL were selected to develop and implement repair strategies for the owner – each of which included budgetary information and life expectancies.
STRUCTURAL TECHNOLOGIES performed a full condition and corrosion assessment of the dock and surrounding site areas to locate, qualify, and quantify the levels of corrosion and concrete deterioration. The investigation team utilized a variety of non-destructive techniques and took physical samples for laboratory testing.
The assessment findings revealed that the coal dock structure was showing signs of active corrosion of the reinforcing steel that varied across different locations. The submerged parts of the structure, including pilings, experienced minimal corrosion. Areas in the splash zone, areas that are subjected to wet and dry cycles from tidal and wave action, contained higher levels of corrosion and concrete deterioration.
STRUCTURAL TECHNOLOGIES, in conjunction with STRUCTURAL, developed several repair and protection strategies for the owner. The owner ultimately selected a solution that incorporated concrete repair to damaged areas and protection of the entire dock structure with galvanic cathodic protection. This option offered the proper amount of current to offset the corrosion activity in the dock over the expected life of the structure and would be relatively maintenance-free to the owner.
Details and measurements of the dock structure from the condition assessment allowed STRUCTURAL TECHNOLOGIES to custom design and manufacture customized LifeJacket® Systems to fit the complex dock configuration.
Project Planning & Execution
STRUCTURAL and the project team carefully preplanned the two year dock improvement in sequence by providing sound concrete repair services, then installing corrosion protection systems throughout the structure. Additionally, the scope of work included repair and/or replacement of several ancillary structural elements, including: dolphin piles, access walkways, and the deck of the structure.
Custom-designed LifeJacket® galvanic cathodic protection systems were installed to provide sacrificial galvanic protection of the supporting reinforced concrete elements of the dock. The LifeJacket® system was installed around beams located under cantilevered sections of the dock, while and customized galvanic panels were installed in the areas above the jackets and out of the splash zone.
To repair the deck surface, STRUCTURAL carefully removed 6 inches of concrete from the deck, being careful not to damage the supporting prestressed concrete beams beneath, and then replaced the locations with new concrete. One cantilevered 19-foot-wide section of the 705-foot-long dock required total replacement along with three access bridges to the dock structure. STRUCTURAL also removed and replaced nine dolphins — 5-foot diameter steel piles filled with concrete that serve as guides for ships arriving at the dock.
Turnkey Delivery Equals Success
Incorporating LifeJacket® systems allowed for a maintenance-free corrosion control solution. The LifeJacket® system offers a galvanic protection approach for the submerged and splash zone portions of the dock while the galvanic panels similarly offers the same approach for areas outside of the splash zone. Both of these systems use pre-manufactured zinc components in their systems to deliver current that provides galvanic protection to the dock.
Through the investigate-design-build delivery approach, STRUCTURAL and STRUCTURAL TECHNOLOGIES were able to analyze the extent of the problem, develop the proper repair and protection strategy, provide corrosion control systems, and finally a single source repair. Most importantly, there was a focus on safety throughout the project from investigation through construction. The combined efforts of the team brought TECO a time and cost savings package that will extend the life of the dock for the next 25 years.