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What Is Cathodic Protection? | Process Engineering Glossary
What Is Cathodic Protection?
Cathodic protection is a corrosion control technique that makes a metal structure the cathode of an electrochemical cell, suppressing the corrosion reaction that would otherwise occur at the structure’s surface. This is achieved either through sacrificial anodes, more reactive metals that corrode preferentially in place of the protected structure, or through an impressed current system that applies an external current to achieve the same protective effect.
Cathodic protection is widely used for buried and submerged steel structures, including storage tank bottoms in contact with soil and buried pipelines, since these applications are particularly vulnerable to corrosion and difficult to inspect and maintain through conventional coating alone.
Applications of Cathodic Protection
Tank Bottom Corrosion Prevention
Storage tank bottoms in contact with soil are commonly protected with cathodic protection systems, addressing a location particularly prone to corrosion and difficult to inspect without significant tank downtime.
Buried Pipeline Protection
Buried pipelines rely heavily on cathodic protection as a primary corrosion control strategy, often combined with protective coatings for a comprehensive corrosion management approach.
Underground Storage Tank Systems
Underground storage tank systems, common in fuel distribution applications, frequently use cathodic protection to address the corrosion risk inherent in constant soil contact.
Benefits of Knowing Cathodic Protection
Provides ongoing corrosion control for hard-to-inspect areas. Cathodic protection offers continuous corrosion suppression for buried or submerged structures that are difficult and costly to inspect directly and frequently.
Extends asset service life significantly. Properly designed and maintained cathodic protection can substantially extend the service life of tank bottoms and buried piping compared to relying on coating alone.
Complements other corrosion control measures. Cathodic protection works effectively alongside protective coatings and material selection, forming one part of a comprehensive corrosion management strategy.
Limitations to Consider
Requires ongoing monitoring and maintenance. Cathodic protection systems need regular monitoring, including potential surveys, to confirm they’re providing adequate protection, and sacrificial anodes need periodic replacement as they’re consumed.
Coating condition affects system performance. Cathodic protection systems are typically sized assuming a certain coating condition, and significant coating degradation can overwhelm the system’s protective capacity.
Doesn’t address all corrosion mechanisms. Cathodic protection addresses general corrosion effectively but doesn’t necessarily prevent all forms of localized corrosion, such as crevice corrosion in certain configurations, requiring a comprehensive approach rather than reliance on cathodic protection alone.
Cathodic Protection FAQ
How does cathodic protection relate to API 653 inspection findings?
API 653 tank bottom inspections often directly inform decisions about cathodic protection system adequacy or the need for system upgrades based on observed corrosion patterns, alongside API 650 design assumptions.
How does cathodic protection relate to crevice corrosion?
While cathodic protection addresses general corrosion effectively, crevice corrosion occurring in shielded areas can sometimes persist even with an otherwise adequate cathodic protection system, requiring additional attention to bolt torque and joint design.
How does cathodic protection relate to tank settlement monitoring?
Tank bottom access needed for cathodic protection system inspection and maintenance sometimes coincides with tank settlement survey work, both important elements of a comprehensive storage tank integrity management program informed by process hazard analysis and atmospheric vessel oversight.
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