Cathodic Protection Monitoring, Challenges, and Mitigation Measures

Introduction

Corrosion is a natural process that results in a gradual deterioration and loss of metal due to an electrochemical interaction with the surrounding environment where ions on the surface of a metal are transferred to another substance. These electrochemical reactions cause most of the corrosion in oil and gas facilities. Four elements are required for the corrosion to occur, as shown in Figure 1:

1. An anode where corrosion occurs
2. A cathode, which is a structure being protected
3. The existence of an electrolyte in which oxidation and reduction reactions occur, and
4. A metal path through which electrons move from the anode to the cathode.

Cathodic protection (CP) is a corrosion control method used to protect metal surfaces from corrosion by making it the cathode of an electrochemical cell. The first application of cathodic protection is credited to Sir Humphrey Davy in the 1820s. He applied CP principles to protect the Royal Navy’s ships’ copper sheathing from corroding by using iron anodes [1].

Cathodic Protection Principle

Cathodic protection is an effective method used to protect assets from corrosion in the oil & gas and chemical industries. The main concept of CP is to make the base metal (a metallic structure such as a pipeline, tank, etc.) the cathode of an electrochemical cell. This can be accomplished by connecting the base metal to a sacrificial (anode) metal that corrodes in lieu of the base metal. CP preserves the metal by providing a highly active metal that can act as an anode and provide free electrons, and, as the active metal sacrifices its ions, it keeps the less active steel (the cathode) from corroding. The anodic area where the iron dissolves to produce electrons and ferrous ions is iron-rich (ferrite).