The Role of Anodes in Deepwater Cathodic Protection

Simply put, corrosion is defined as the process or action of corrosive chemical behaviour, which is a progressive modifi-cation or deterioration due marine growth prevention system, antifouling system, copper anodes
to chemical oxidation.

When it comes to certain job responsibilities and daily tasks many people associate the process of corrosion to the wasting away or rusting of a pipe that’s buried beneath the ground. And so, corrosion can be thought of as the way natural forces continuously try to restore the developed works of humans to revert back to their original state of natural symmetry. Therefore, when it comes to a buried pipe, the process of corrosion is the earth and surrounding natural elements simply trying to restore the existing iron within the steel pipe to its original constant form of native iron ore or iron oxide.

The kind of corrosion that most people are familiar with and the kind that causes the most amount of damage to a buried pipe is known as electrochemical corrosion. This type is also commonly referred to as galvanic corrosion and sometimes known as electrolysis.

Using Anodes in Cathodic Protection

Sacrificial anodes’ are often used in cathodic protection systems. The anode consists of metal alloy containing a more active voltage than the structure’s metal it’s protecting, or the cathode. When it comes to potential, the difference between either metal indicates that the material of the sacrificial anode will corrode rather than the structure itself. This process successfully stops how the oxidation process reacts to the structure’s metal that’s being protected.

Also, there needs to be two other existing conditions in addition to the cathode and anode in order for the sacrificial anode process to work. Essentially, there needs to be a return existing path for the electrons to properly flow from the said anode to the targeted material it’s intended to protect (physical contact is the most common way) and an electrolyte (i.e. humidity or water) to transmit the electrons.

Sacrificial Anodes

Sacrificial anodes usually come in three different metals: zinc, aluminium, and magnesium. Of the three, magnesium contains the most negative electro-potential and is more appropriate for on-shore pipelines since electrolyte (water or soil) resistivity is considerably higher. However, if the difference in electro-potential is too much, the cathode (protected surface) can possibly become brittle or sometimes cause the coating to “disbond”.

Aluminium and zinc are typically used in salt water since the resistivity is usually lower. General uses include the hulls of boats and ships, in salt-water-cooled-down marine engines, inside the walls of storage tanks, on small boat rudders and propellers, and on offshore production platforms and pipelines.
The main benefits of using sacrificial anodes include the following:

• Easy to install
• No external power source required
• Overprotection is highly unlikely
• The low voltage and current that runs between the protected surface and the anode rarely produces stray current
• Monitoring and inspection is easy for trained staff

On the other hand, there are some disadvantages as well such as a restricted current capacity relative to the anode’s mass, ineffectiveness regarding high-resistivity environments, increased water and air flow on moving structures (i.e. ships), and more weight on the structure being protected as well. Find out more at www.cathodicme.com.