Understanding cathodic disbondment, its causes, and its importance is an excellent first step in ensuring long service life and optimal performance on buried or immersed steel structures that utilize cathodic protection systems. Steel pipelines, transfer and storage tanks, equipment, etc. are critical for the storing, transport, and delivery of commodities like oil, gas, and water.
Our infrastructure depends on the continued functionality of these systems to ensure safe and prompt transfer of critical materials.
Related Article: The Dangers of Tape Failures on Pipelines
Steel Structures, Corrosion Protection, and Cathodic Disbondment
Steel structures exposed to water and environmental elements are subject to corrosion. Untreated corrosion over time leads to the complete degradation of the steel, which will result in a variety of problems for owners of these structures. The best way to approach corrosion is to understand it can, and often will, happen.
Protecting the steel to prevent corrosion from the start, monitoring routinely for the start of corrosion and defects, and maintaining the protective systems installed on the structure are the best ways to prevent damage. In the pipeline and tank industries, exposed steel structures are commonly equipped with cathodic protection systems and protective coatings to prevent corrosion from occurring.
Owners of buried or immersed steel structures with these protective systems in place have yet another thing to be aware of, cathodic disbondment.
Caption: Exposed steel structures including pipes, pipelines, tanks, equipment, and other steel structures are at risk of corrosion.
What is Cathodic Disbondment?
Hydrogen generation is an electrochemical reaction that occurs on the surface of all cathodically protected pipelines. When a protective coating is damaged on a steel structure that utilizes a cathodic protection system, electrolytes present in groundwater react with the protected steel to form hydrogen gas at the site of the damaged coating.
Pressure builds from the hydrogen gas and begins to push the coating off the steel. This phenomenon is referred to as cathodic disbondment. Over time as more steel becomes exposed, the defect grows exponentially.
As more steel is exposed, more hydrogen gas forms, and more pressure pushes the defect out along the entire structure until eventually, the protective coating that is protecting the system and steel, has completely delaminated from the structure.
Caption: Cathodic Disbondment on a pipe.
Why is Cathodic Disbondment Important?
As cathodic disbondment spreads across the structure, the area of steel at risk of corrosion increases. The exposed steel will now need to rely on the cathodic protection system for protection from corrosion.
In the case of an active cathodic protection system, an increased draw on the electricity will be required to run the system. This results in higher power costs, i.e. a big electric bill. In the case of a passive cathodic protection system, the sacrificial anodes will need to be replaced more frequently to avoid corrosion to the steel.
Once the anodes are exhausted, pipeline corrosion will begin and spread along the structure. Corrosion threatens more than just the integrity of the pipe. Other risks include:
- Leaks resulting in environmental cleanup
- Loss of product and profit
- Failed delivery to customers
- Reduced performance
- Shortened service life
- Costly repairs
Due to the risks associated with structure failures, regulatory action and/or fines may be imposed by local and federal governments.
Caption: Corrosion
Tape Coating for Continued Pipeline Service and Safety
The snowball effect of damage due to cathodic disbondment is far-reaching and fast. Just being aware of this chemical phenomenon from the onset is a big step in planning your next steel pipeline or tank project that will be equipped with a cathodic protection system. Luckily, there are many ways you can prevent, detect, and repair cathodic disbondment and we will be addressing just that and more in our next blog in this series.
Related Article: APWA Pipeline Color Guide by Material
Tapecoat and Royston, tape coating systems provide corrosion protection to critical pipeline infrastructure. Our technical representatives can provide product information to meet your coating needs. Please contact us.
.png)
.png)
