Pitting Corrosion - The Storage Tank Killer

A storage tank is an important asset. But what happens when a storage tank can't do its job?

The failure of a storage tank can cause significant problems. Unfortunately, corrosion is a common issue that can lead to serious consequences, especially for underground storage tanks.

Pitting corrosion is a prevalent form of corrosion found in storage tanks and is considered a significant threat to their longevity. It can cause a variety of issues, making it a serious concern.

What is Pitting Corrosion

Pitting corrosion is a type of metal degradation that occurs locally, resulting in the formation of small holes or pits on the surface of the steel. This leads to a reduction in the thickness of the metal.

If nothing is done, eventually this will cause a breach in the tank and lead to leaking product into the surrounding environment.

The pits produced by this type of corrosion can be a variety of shapes and sizes, they can be narrow and deep, shallow and wide, and they can undercut whereby they go into the metal and then develop sideways underneath the surface.

Pitting corrosion may be visible with the pit's opening exposed, but it can also be concealed by a semi-permeable membrane. This makes it challenging to accurately identify pitting corrosion before carrying out blasting.

How Does Pitting Corrosion Occur?

Pitting corrosion is a type of corrosion that can occur due to various factors, such as localized mechanical or chemical damage to the metal's oxide film and inadequate application of a tank's protective coating.

The most common cause of pitting corrosion is the introduction of water into the storage tank. Over time, the water reacts with the metal surfaces and causes corrosion, resulting in the formation of pits on these surfaces.

Discontinuities in coating application, such as poor surface preparation or incorrect application, can create breaks in the coating, leaving a path for corrosion to reach the steel.

Damage to a tank's internal coating can also lead to the same effect, exposing paths to the steel that corrosion can exploit.

Furthermore, the presence of Microbially Influenced Corrosion (MIC), where Sulphate Reducing Bacteria accelerates corrosion within the tank, can increase the rate of pitting corrosion.

What damage will it do?

The main danger of pitting corrosion in underground storage tanks is that it can cause leaks. They can lead to environmental damage in the surrounding area. When these pits are big enough, they can contaminate the groundwater supply, which can be harmful to the local environment and community.

These pits can weaken the tank's structure. If these pits are not fixed quickly, they will continue to grow and damage the tank's metal walls. Eventually, they will reach a critical size and create holes that allow contaminants into the tank and pollute the surrounding environment.

So why should you be concerned about pitting corrosion? If left untreated, pitting corrosion will continue to grow causing further problems for your storage tank. If left untreated, it can cause leaks, tank failure, and costly repairs.

What are the Prevention Methods?

Preventing pitting corrosion in storage tanks is crucial for avoiding major damage, environmental harm, and costly repairs. The key to success is applying the appropriate industrial coating and following the manufacturer's recommended inspection program to maintain the coating's integrity over the tank's lifespan.

It is highly recommended to employ a reputable and experienced coating applicator or lining company to ensure proper steel preparation and application of a continuous coating. A competent lining contractor will conduct coating checks after application to ensure this.

Pitting corrosion is a serious issue that should not be ignored. If you suspect it is present in your tank you should contact an expert immediately, such as Abfad, for assessment and recommendations.

Detecting pitting corrosion in underground storage tanks can be challenging. Being located underground means access to the tank for regular monitoring and maintenance is limited. To prevent issues and unnecessary costs, it is essential to implement a proactive monitoring and prevention strategy.