Sacrificial anodes, as the name implies, sacrifice their lives for the protection of some major parts of vessel, boat, engine, pipeline etc. They are usually attached to the major areas that are prone to corrosion or decay. There are two types of cathodic protection techniques used world-wide to protect the parts from rusting. They are:
Sacrificial anodes, passive system
Impressed-current, active system
As sacrificial passive system is simpler and effective, it is widely been used to control and prevent corrosion. This type of cathodic protection system requires only anodic material to protect the steel parts. The materials used must be anodic to steel and also must corrode reliably.
Commonly, Zinc, Aluminum and Magnesium and their alloys are used to act as anodes for boats and vessels and other partially and fully submerged structures. The characteristics of these materials differ considerably and these are chosen depending on various applications.
Commonly used anodes are:
Magnesium Anodes – Magnesium anodes come in different verities, shapes and sizes. Magnesium anodes have the highest driving voltage compared to other anodes and are widely used in onshore like buried soil applications. In USA, magnesium anodes are supplied with Bentonite clay backfills to ensure the conductivity and reliability. As these anodes corrode quite fast in salt water compared to other anode materials, people avoid using these types of anodes in long-term cathodic protection requirements.
Zinc Anodes – Among the other cathodic sacrificial anodes, Zinc ranks first in the cathodic protection of structures both in fresh as well as marine water. As Zinc has relatively low driving voltage compared to Magnesium, it is suitable for offshore applications than onshore activities. Zinc becomes an anode when it is connected to the steel using an electrolyte. Current flows to the steel parts from the Zinc through electrolyte. This makes the steel resistant to corrosion and thus gives a long life. These marine anodes sacrifice itself in the brackish and marine water to protect the steel parts from corroding.
Aluminum Anodes – Aluminum anodes are mostly used in offshore cathodic protection applications. Aluminum anodes are not readily available like other anode materials and they do not passivate in salt water in the presence of alloying add-ons like Tin, Antimony and Mercury.
Some of the main features of these anodes are:
Last long because of large current capacity
Lighter than Zinc
Eco-friendly compared to other marine anodes
Cathodic protection using sacrificial anode became popular these days because the method is simple to install and also preferable for localized protection. In addition, the operation of these anodes doesn’t require any source of external electric power.
Sacrificial Anodes and Its Types