Most of the current marine facilities (ports, docks, breakwaters, etc.) are composed of steel pipe piles or sheet piles. Due to the seawater immersion the steel structure are subject to corrosion. It is extremely important to protect these steel structures and increase the life of this infrastructures.
Factors such as water composition, oxygen concentration, sea life, and seawater velocity also accelerate the corrosion and thinning of steel materials.
Steel corroded with different rate, the table below shows the corrosion rates for different areas.
Cathodic protection can reduce the corrosion rate of underwater and embeded zone by 95%. Special precautions are required in the splash zone and the atmospheric zone.
A combination of coating and cathodic protection can deteriorate the corrosion affect. But also coating affected during installation and from the environment conditions. Coating degradation in embedded areas can be up to 50% during installation, and 1-2%/ year in underwater zone according the coating specification.
Cathodic protection is a technique that uses electrochemical methods for corrosion protection. It uses electrical technology to achieve uniformity of potential at various points on the metal surface, thereby reducing corrosion. Cathodic protection can extend the operating life of the facility, reduce maintenance costs. We can achieve Cathodic protection with Sacrificial anodes or with Impressed current systems.
Galvanic Anode Cathodic Protection (GACP)
- In this type of CP, protection is achieved by connecting the protected structure to a sacrificial anode, which is placed close to the protected structure.
- Sacrificial anodes are made from active metals such as zinc, aluminum, or magnesium for fresh water.
- CP current is created by the potential difference between sacrificial anodes and the protected structure.
- The type of anode used depends on electrolyte resistivity and the chemical compositions of the electrolyte to which the substrate is exposed.
Impressed Current Cathodic Protection (ICCP)
- Wirth ICCP we can protect our structure by connecting to an anode bed through a transformer rectifier (TR).
- The main component of ICCP is the Transformer rectifier (TR), which forces the current to flow from the anodes to the protected structure.
- Anode can stand alone to our structure or we can create anode bed.
- The anode bed is a series of anode that are electrically connected. The anode bed should be placed remotely from the protected structure.
- Remote ground bed can also use to minimize installation cost.
- The now days two types of anodes commonly used
- the semi-soluble anodes made of high silicon cast iron (HSCI),
- non-soluble anodes made of platinum, mixed metal oxide, or polymer material
- Junction boxes used to connect anodes with our TR
- Reference electrode used to monitor the potential level of our structure and guide our TR once work on automatic mode.
Problems Created by Cathodic Protection
For coated structures, where the applied coating quality is poor, cathodic disbondment may occur due to high CP levels in case where anodes install close to structure. In such cases, insulation shields , remote ground bed or perforated cover install outside the anode to reduce current on anode nearby areas. The polarized potential of the structure pipeline must be kept at a minimum value of -850 mV.
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.