Power plant CP systems are important—especially with the growing number of gas-ﬁred facilities that have been and continue to be built.
There are several applications within a power plant where cathodic protection can be utilized:
- Underground piping
- Waterfront structures
- Cooling water process equipment
- Storage tanks
In power plants there are several underground piping systems, including fuel oil, natural gas, fire water, cooling water, condensate and drains that need to be protected. Although underground steel piping systems typically are coated, damage to the coating can result in concentrated galvanic corrosion.
Depending upon the size and layout of underground piping systems, and the soil’s characteristics, these systems can be protected using either galvanic or impressed current designs. However, the design of the cathodic protection system should take into consideration other underground piping systems and structures: conduits, copper ground grids, electrical cables and foundation steel.
In a galvanic system it is essential that the lines be electrically isolated from the plant’s grounding grid system. Otherwise, the anodes will try to protect everything attached to the grid and would be unable to generate sufficient current.
In most power plant applications, the high concentration of underground structures and piping, along with an extensive grounding circuit, preclude the use of galvanic systems. It is simply too difficult to assure proper isolation of the piping. In these cases, an impressed current system must be used.
Many power plants have waterfront structures such as docks, steel piers and pilings, cooling water intake and outlet structures and inlet screens. Whether carbon steel or steel reinforced concrete, these structures are subject to extremely corrosive environments, particularly when they are located in saltwater or brackish water areas. Even river water can be corrosive. However, cathodic protection, typically impressed current, is extremely effective for protecting these types of structures.
Cooling Water Systems
Surface condensers, shell and tube heat exchangers, valves, strainers, screens and pumps can all be cathodically protected from corrosion. Frequently the main surface condensers in a power plant have carbon steel water boxes with an internal epoxy coating or rubber lining applied. However, without cathodic protection, any defect in the coating or liner can cause corrosion to develop more quickly than on surfaces that have no coating or liners. Still, the use of coatings and liners does significantly reduce the amperage required by cathodic protection systems.
Galvanic or impressed current systems can use to protect our condensers. When an impressed current system is used frequent anode replacement is not required like galvanic anodes.
Special care must be taken when providing cathodic protection on condensers using titanium tubes and tube sheets. When these materials are subjected to excessive current they become susceptible to hydrogen embrittlement. To limit the current output below thresholds that might cause hydrogen embrittlement of the tubes and tube sheet, a reference cell must be connected to a rectifier. This allows automatic adjustment of the currant output if needed.
The bottoms of carbon steel tanks used for fuel storage are susceptible to corrosion. Today, cathodic protection for new fuel tanks is becoming increasingly common. However, older tanks can be retrofitted with cathodic protection. Tank size, geometry, and the physical characteristics of the underlying surface will determine the type of system that is most economical.
SYCHEM SA working more than 30 years in Cathodic protection doing design, supply materials, installation and commissioning’ trying to deliver some of most complex project in the world, on budget and on time for our clients.