Difference Between Cathodic Protection and Sacrificial Protection

The key difference between cathodic protection and sacrificial protection is that cathodic protection is the process of protecting a metal surface by making it the cathode in the electrochemical cell whereas sacrificial protection involves the protection of the desired metal surface by a sacrificial anode.

Cathodic protection and sacrificial protection are two related electrochemical processes. Cathodic protection involves the protection of a metal surface by making it a cathode. Sacrificial protection involves the same process, but it describes the role of the anode that makes the desired metal surface a cathode.

CONTENTS

1. Overview and Key Difference
2. What is Cathodic Protection 
3. What is Sacrificial Protection
4. Side by Side Comparison – Cathodic Protection vs Sacrificial Protection in Tabular Form
5. Summary

What is Cathodic Protection?

Cathodic protection is a type of electrochemical process that is useful in protecting a metal surface by making it the cathode in the electrochemical cell. This term is denoted as CP. Cathodic protection is important to prevent metal surfaces from corrosion. We can observe different types of cathodic protection methods such as galvanic protection or sacrificial protection, impressed current systems and hybrid systems.

In the cathodic protection method, the sacrificial metal undergoes corrosion instead of the protected metal. Moreover, if we use cathodic protection for large structures such as long pipelines, galvanic protection technique is not enough. Therefore, we need to provide sufficient current using an external DC electrical power source. Apart from that, we can use this technique to protect fuel or water pipelines made of steel, storage tanks, ships and boat hulls, galvanized steel, etc.

What is Sacrificial Protection?

Sacrificial protection is a type of electrochemical process in which the metal of desire is protected by a sacrificial anode. Sacrificial anodes are highly active metals or metal alloys that can protect the less active metal surface from corrosion. The term galvanic anode is also used to name these anodes. Sacrificial anodes can supply cathodic protection. Generally, anodes are consumed during the protection process, so the protection has to be replaced and maintained.

We can use different materials as sacrificial anodes. Generally, they are pure metals such as zinc and magnesium. However, we can also use alloys of magnesium or aluminium. Moreover, these sacrificial anodes provide protection by being more electronegative or much more anodic than the protected metal. During this protection, a current passes from the sacrificial anode to the protected metal, and the protected metal becomes a cathode. Therefore, this process creates a galvanic cell.

When placing the sacrificial anodes, we can use either lead wires (attached to the metal surface we are going to protect via welding) or use cast-m straps (either by welding or using the straps as locations for attachment). There are many applications of sacrificial anodes, including the protection of hulls of ships, water heaters, pipelines, underground tanks, refineries, etc.

What is the Difference Between Cathodic Protection and Sacrificial Protection?

Cathodic protection and sacrificial protection are important electrochemical processes. The key difference between cathodic protection and sacrificial protection is that cathodic protection is the process of protecting a metal surface by making it the cathode in the electrochemical cell whereas sacrificial protection involves the protection of the desired metal surface by a sacrificial anode.

Below infographic summarizes the difference between cathodic protection and sacrificial protection.

Summary – Cathodic Protection vs Sacrificial Protection

Cathodic protection and sacrificial protection are important electrochemical processes. The key difference between cathodic protection and sacrificial protection is that cathodic protection is the process of protecting a metal surface by making it the cathode in the electrochemical cell whereas sacrificial protection involves the protection of the desired metal surface by a sacrificial anode.

Reference:

1. “Cathodic Protection.” Wikipedia, Wikimedia Foundation, 15 July 2020, Available here.

Image Courtesy:

1. “Cathodic Protection diagram” By Cafe Nervosa – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Anodes-on-jacket” –  original uploader was Chetan at English Wikipedia. – Transferred from en.wikipedia to Commons by Armando-Martin using CommonsHelper (CC BY-SA 2.5) via Commons Wikimedia