Category Archives: Tank Bottoms

Enhancing Aboveground Storage Tank Protection: The Role of Vapour Corrosion Inhibitors (VCIs)

In the Autumn 2024 edition of Tanks & Terminals magazine, MATCOR’s Ted Huck highlights an alternative to traditional corrosion prevention methods for aboveground storage tanks (ASTs): Vapour Corrosion Inhibitors (VCIs).

ASTs, especially those storing hazardous materials like hydrocarbons, are highly susceptible to corrosion on their steel tank bottoms. Typically built on sand or soil foundations with a concrete ring wall, these tanks are vulnerable to soil-side corrosion over time.

While cathodic protection (CP), often combined with a secondary containment liner, has been a standard solution to prevent leaks and environmental damage, it has limitations. VCIs are a newer technology that offers an additional layer of protection for external tank bottoms, addressing some of the challenges CP alone cannot solve.

To dive deeper into VCIs, its application methods, and how its performance is monitored, read the full Tanks & Terminals article.

Learn more from our valued partner Zerust about their above ground storage tank VCI solution.


To get in touch with our team of experts for more information, to ask a question, or to get a quote, please click below. We will respond by phone or email within 24 hours. For immediate assistance, please call +1-215-348-2974.

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Is My Tank CP System Working Correctly?


Ted Huck, Director of Manufacturing and QA/QC at MATCOR, recently published an article in the summer edition of Tanks and Terminals Magazine titled “Understanding Cathodic Protection Systems.” He explains how to assess the performance of cathodic protection systems for above-ground storage tank bottoms (Tank CP Systems).

When asked to summarize these performance assessments, Mr. Huck commented, “Tanks are pretty easy to test, except for those rare occasions when they are not. At that point seek professional help.”

Read the full article.


Need information or a quote for MATCOR tank CP systems? Please contact us at the link below.

MATCOR Successfully Completes Tank CP Project In Mexico

JA Electronics explosion-proof rectifiers for tank CP project in Mexico.

MATCOR recently completed a significant tank CP project in the Mexican port city of Altamira along the Gulf of Mexico. The project consisted of design, detailed engineering, supplying materials, providing installation supervision, and commissioning and testing the systems upon completion of the installation for nine above-ground storage tanks.

Tank CP Project Utilizes Linear Anodes

The cathodic protection system utilized MATCOR’s SPL Linear Anode Concentric Ring tank system that consists of individual, factory assembled, and tested anode segments. This approach facilitates a simple installation that does not require cutting, splicing, or joining anode assemblies in the field. The anode rings utilize a redundant anode cable feed system that assures reliability. This cost-effective solution protects the bottom of tanks on projects across the United States and around the globe.

Explosion Proof Rectifiers

MATCOR also supplied customized explosion-proof oil-cooled rectifiers (pictured above) for each of these tanks from our sister company, JA Electronics. These rectifiers are used in Class 1 Div 2 hazardous areas. Additionally, cast aluminum Class 1 Div 2 junction boxes were also manufactured and supplied by JA Electronics.


Click below to get a quote for your tank CP project, or learn more about MATCOR’s cathodic protection solutions.

VCI for Tank Bottom Protection

The American Petroleum Institute (API) recently issued a landmark technical report regarding vapor corrosion inhibitor (VCI) use for storage tank bottom corrosion protection (API TR 655).

VCI has been promoted as a technology for use under above-ground storage tanks for the past decade. This effort recently received a big boost with the American Petroleum Institute’s publication of its long-awaited technical report on VCI.

Vapor corrosion inhibitor technology for tank bottom corrosion protection gets boost from API technical report.

API TR 655 Vapor Corrosion Inhibitors for Storage Tanks; First Edition; April 2021 provides the first set of guidelines for VCI issued by an internationally recognized non-governmental technical standards organization.

MATCOR has been an early adopter of VCI technology as we believe that it can be an important and effective component in a corrosion prevention program for tank bottoms. We have partnered with Zerust to be an authorized distributor and installer of VCI products for tank and other applications.

We are excited that API has led the way on recognizing VCI technology, and we would expect that other organizations–AMPP for one–will adopt similar guidelines and recommendations.

For a more detailed review of the technical report, visit our VCI partner company Zerust’s summary at the link below:

Summary of API’s Vapor Corrosion Inhibitor Use for Storage Tank Bottom Protection API TR-655


To get in touch with our team of cathodic protection experts for more information, to ask a question or get a quote, please click below. We will respond by phone or email within 24 hours. For immediate assistance, please call +1-215-348-2974.

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Horizontal Directional Drilling for a Middle East Tank Retrofit

In a recent Tanks & Terminals article, Ted Huck discusses a tank cathodic protection retrofit project in the Middle East utilizing horizontal directional drilling technology.

Existing tanks pose several challenges that must be considered when looking to install cathodic protection, since access directly below the tank is not readily available.

Originally constructed in 1995, the original design of this critical service ethylene storage tank included a cathodic protection system to protect the external tank bottom in contact with the ground. Over time, the system stopped providing enough current to meet NACE criteria for the control of corrosion. 

Discrete Anodes Along the Tank Perimeter Not Satisfactory

The first retrofit cathodic protection system consisted of installing discreet anodes around the perimeter of the tank. While relatively easy to install, this method of retrofit installation often struggles to drive current to the full tank bottom. The results were not satisfactory so another method was needed.

Linear Anodes Installed Using Horizontal Directional Drilling

MATCOR had proposed an alternate approach, successfully being performed in the US but not tried previously in the Middle East. It involves the installation of multiple strings of linear anodes directly below the tank using horizontal directional drilling (HDD) technology. By drilling under the tank, it is possible to install anodes spanning the entire length of the tank. This method also allows for a testing device to measure the effectiveness of the cathodic protection system.

Click below to read the full article regarding this tank retrofit cathodic protection system, installed successfully in December 2019.


If you have questions, or for information on MATCOR’s above ground storage tank cathodic protection solutions, please contact us at the link below.

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Better Tank Cathodic Protection

Looking for a better tank cathodic protection system?

Find our article in the April 2020 Storage Terminals Magazine. “No More Gridlock—Take the Ring Route” is a comparison of grid anode systems vs concentric ring systems for tank bottom cathodic protection.

Cathodic Protection of the external tank bottom for large diameter above ground storage tanks has been adopted as good engineering practice around the world.

Unfortunately, many existing grid anode systems have experienced premature failures, resulting in excessive tank bottom corrosion and costly replacement.

A recent MATCOR article published in Storage Terminals Magazine provides an overview of these grid CP systems and an alternative concentric ring linear anode system (link to the full article below). Here are just a few key points:

Grid Tank Anode Systems

  • Consist of field assembled MMO ribbon anodes and titanium conductor bars
  • Require flawless design and installation
  • Subject to poor welding and other concerns
  • Failures can be catastrophic

Concentric Ring Linear Anode System

  • Factory assembled—no field cutting or splicing required
  • Easy, fast and reliable installation
  • Coke backfilled sock protects the anode
  • Redundant—each ring segment has two feeds
  • Long life compared to the grid systems of the 1990s

If you have questions, or for information on MATCOR’s above ground storage tank cathodic protection solutions, please contact us at the link below.

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Does Cathodic Protection Cause a Tank Bottom to Dry Out?

Does Cathodic Protection Dry the Tank Bottom?
Will your CP System dry out the sand bedding of your tanks?

A client recently raised the concern about the cathodic protection reaction causing a drying out of the sand under a large diameter above ground storage tank.  This is a very interesting question.  We recently developed a stoichiometric analysis to assess the cathodic protection carbon footprint of a deep anode system by calculating the amount of carbon dioxide produced. The same methodology can be used to assess the risk of drying out of the tank bottom.

Assumptions

For this analysis, let’s assume a typical 150 ft diameter above ground storage tank with a bare tank bottom and a 1-foot sand bed resting atop a non-permeable liner.  Based on a common design criteria of 2 mA/ft2 of bare surface area, this tank would nominally require a total of 17.7 amperes of current. 

How much water does a cathodic protection system consume?

For every 2 electrons generated, one H2O molecule is required.  One amp-year is equal to 3.1536 x 107 amp seconds or coulombs.  One Faraday or 96.487 coulombs is equal to one mole of electrons therefore, one amp-year is equal to 326.84 moles of electrons.  With the 2 to 1 ratio of electrons to H2O molecules that means that for every mole of electrons, 0.50 moles of H2O are generated.  H2O has a molar mass of 18.0 g/mol so for each amp year a total mass of 2,941.6 grams of H2O is generated – that is approximately 0.78 gallons of water per amp year. 

For our 17.7 ampere, 150 ft diameter tank anode system, that would mean 13.8 gallons of water is consumed as part of the cathodic protection reaction each year.  Assuming that there is no new water being added into the tank foundation (a perfect chime seal and a completely non-permeable liner), then over a 30-year operating life the CP system would consume a little more than 400 gallons of water. While that might seem like a lot of water consumption, what is the percentage of drying out that is occurring with the sand over that time frame?

Will the Tank Bottom Dry Out?

Well, typical sand has a bulk density of approximately 100 lb/cubic foot and the typical moisture content for commercial sand is between 2% and 6%.  For purposes of this exercise, let’s assume that the moisture content is on the low end at 2%.  This means that there are approximately 2 lbs of sand per cubic foot.  A 150 ft diameter tank has 17,671 cubic feet of sand bedding which equates to 35,342 lbs of water or about 4,241 gallons of water.  So, if no new water is added over the thirty-year operating life, the typical CP system will consume about 10% of the sand moisture for very dry sand.  

Conclusion

Given our assumptions and calculations, it does not appear that significant sand drying will occur due to water consumption.

Another Consideration: Electro-osmotic Drying

This analysis does not consider the effect known as electro-osmosis.  Electro-osmotic drying is a process that is used in the civil engineering world to dewater sludges by creating a DC electrical flow – the flow of electrons pulls polar water molecules away from the anode.  For CP applications, this is generally not considered to have a significant impact except where there are very high current densities at the anode – for example some deep anode systems operating at very high output rates in certain soil formations. For tanks, this is not considered an issue.


If you have other technical questions, or for information on MATCOR’s above ground storage tank cathodic protection solutions, please contact us at the link below.

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Replaceable Anode System Success: A First for Critical Middle East Tank Assets

Last month, MATCOR successfully completed the first ever HDD tank cathodic protection system installation in the Middle East, utilizing a replaceable anode system.

Replaceable Anode System Installation

Background—Initial Recommendation for HDD Cathodic Protection System

Equate Petrochemicals is one of the world’s largest producers of Ethylene Glycol. They initially contacted MATCOR in 2012 to discuss options for cathodic protection on a critical service Ethylene storage tank at their flagship Kuwait petrochemical facility. This tank was originally constructed in 1995, and the initial CP system installed with the tank was no longer providing sufficient current to achieve NACE Criteria. At the time, MATCOR suggested installing anodes directly under the tank using horizontal directional drilling technology. The plant’s engineering and operations team had significant reservations about this approach. The tank was critical to the plant’s operation and could not be taken out of service. Should the HDD operations result in damage to the structural integrity of the tank, the results would be catastrophic.

Perimeter Anodes—An (Unsuccessful) Alternative Approach

As a result of Equate’s concerns in 2012, they attempted an alternate approach, suggested by others, using perimeter anodes. Discreet anodes were installed offset around the perimeter of the tank—thus avoiding any possible risk to the tank during the anode installation. The use of perimeter anodes around larger diameter tanks is generally not a good idea. This is because it is very difficult to drive current to the center area of the tank, often resulting in adequate protection levels only for the outer edges of the tank bottom. For the Ethylene Storage Tank, the presence of heating pipes below the tank bottom only exacerbated the current distribution challenges. Ultimately, the results were not satisfactory.

In 2018, the plant engineering team reached back out to MATCOR to discuss our HDD solutions.

Replaceable Anode System Solution

Replaceable Anode SystemMATCOR provided the plant with a detailed proposal to design and install a complete cathodic protection system using MATCOR’s Replaceable Tank Anode system. The RTA system is based on installing MATCOR SPL linear anode assemblies in a series of parallel slotted PVC pipes that have coke backfill pneumatically blown into the PVC pipe as part of the anode system installation. In addition to the linear anode segments and coke backfill, the slotted PVC pipes have a venting system to allow gases produced during the cathodic protection reaction to vent. This prevents gas buildup and blockage inside the PVC anode pipe.

Replaceable Anode System Installation Drawing

One of the key advantages of the RTA system is that once the PVC tubes are installed, it is possible to flush out the anode assemblies and coke backfill should the anode assemblies fail and/or they are at the end of their design life making this a replaceable anode system that will assure cathodic protection for the entire service life of the tank.

Additionally, a slotted Reference Cell Tube would be installed to allow for two calibrated fixed cathodic protection reference electrodes to be inserted for full polarized and non-polarized potential measurements across the entire tank bottom. This would allow for testing of the CP system with calibrated reference electrodes for the life of the tank.

Experienced HDD Installation—Assuring a Safe Installation

Horizontal Drilling Anode InstallationWhile the plant conceptually agreed with MATCOR’s solution from a technical perspective, there remained a significant concern within the plant’s operation and safety groups about drilling under this critical service tank and the possibility of a catastrophic event should the drill head drift up to the tank bottom. MATCOR put together a thorough installation procedure including detailed information on the sophisticated drill head tracking systems being utilized to assure that the drill head location was being continuously monitored throughout the bore. Utilizing an experienced local HDD drilling sub-contractor, MATCOR deputed its senior HDD installation drilling supervisor to Kuwait for the installation. Our Senior HDD Drilling Supervisor has completed hundreds of tank HDD installations in the United States and his on-site presence, along with the advanced electronic tracking package being used, assured that each bore went as planned.

Replaceable Anode System Installation Complete!

In December of 2019, MATCOR, working with our local Kuwaiti sub-contractor and the client’s engineering, construction and safety teams, successfully completed the installation of the replaceable anode system. The initial commissioning results showed that the anodes were installed properly. Each anode was distributing current as expected, and the polarization levels were meeting appropriate NACE criteria. The system has been left to operate and fully polarize. A subsequent visit by MATCOR’s technical team is scheduled in early 2020 to make final adjustments to the anode system current output and to confirm that the system continues to meet NACE criteria.

Conclusion

MATCOR’s successful installation in Kuwait of a horizontal directional bored CP system under an existing critical service tank is a first for the Middle East Region. The innovative MATCOR design, combined with the technical knowledge and operational expertise, makes this an interesting and viable option for other tank owner/operators worldwide to consider for their existing tanks with CP systems that are not performing properly.


To get in touch with our team of cathodic protection and AC mitigation experts for more information, to ask a question or get a quote, please click below. We will respond by phone or email within 24 hours. For immediate assistance, please call +1-215-348-2974.

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Vapor Corrosion Inhibitors

This guide explores how Vapor Corrosion Inhibitors (VCIs) work, their diverse applications, and why they’re becoming a cornerstone of modern corrosion prevention strategies. Whether you’re in oil and gas, manufacturing, or aerospace, discover how VCIs can transform your approach to corrosion management.

Corrosion poses a significant threat to infrastructure and equipment across industries, from pipelines to storage tanks. VCIs offer a solution, using advanced chemical technology to protect metal surfaces and prevent costly damage.

zerust-vci-molecule

As a leader in the above-ground storage tank corrosion control industry, MATCOR has partnered with Zerust® Oil & Gas to provide innovative VCI solutions for customers seeking advanced corrosion mitigation strategies.

What are Vapor Corrosion Inhibitors?

Vapor Corrosion Inhibitors (VCIs) are advanced chemical compounds that prevent corrosion by diffusing through confined spaces and bonding with metal surfaces. This process creates an invisible yet highly effective barrier that blocks water, oxygen, and other contaminants from initiating degradation.

Key features:

  • Create a passive oxide layer that inhibits chemical reactions
  • Can be applied in various forms, including powders, liquids, or impregnated materials.
  • Long-lasting protection for months or years, depending on conditions.

Why Choose VCIs?

Vapor Corrosion Inhibitors (VCIs) stand out among corrosion prevention solutions due to their ease of application, flexibility, and proven effectiveness. Compared to other methods like wax, VCIs offer several key advantages:

  1. Ease of Installation: VCIs are easy to apply, requiring no heating—just simple mixing with potable water and injection through vent pipes, ensuring efficient distribution.
  2. Broad Compatibility: VCIs work seamlessly with other corrosion prevention methods, such as coatings and cathodic protection, enhancing overall protection strategies.
  3. Cost-Effectiveness: By extending the lifespan of assets and reducing the need for frequent maintenance, VCIs provide a high return on investment over time.
  4. Allows Monitoring: VCI effectiveness can be monitored in real time using coupons, ER probes, or UT probes, with the option for remote monitoring units (RMUs). In contrast, wax requires in-line inspection (ILI) runs for evaluation.
  5. Non-Invasive: Unlike some traditional methods, VCIs do not require disassembly for application, making them a convenient choice for hard-to-reach areas.
  6. Versatile Applications: VCIs are available in various forms, including films, papers, powders, liquids, and emitters, making them adaptable to a wide range of industrial needs.
  7. Removability: VCIs can be easily washed out and removed if necessary, offering flexibility for future maintenance or operational adjustments.
  8. Environmentally-Friendly: VCIs are an environmentally friendly solution for corrosion prevention, offering biodegradable formulations, non-toxic options for sensitive industries, and contributing to sustainability by reducing waste and extending asset life.
  9. Industry-Approved Solution: VCIs are recognized and approved by leading authorities, including the Association for Materials Protection and Performance (AMPP) and the U.S. Department of Transportation’s Pipeline and Hazardous Materials Safety Administration (PHMSA).

Through our partnership with Zerust® Oil & Gas, MATCOR delivers these benefits with proven products backed by extensive research and industry expertise.

Applications of Vapor Corrosion Inhibitors Across Industries

  • Oil and Gas: Protects internal surfaces of pipelines after hydrotesting and safeguards tanks bottoms from localized corrosion. Learn more about pipeline corrosion risks and prevention methods in our Pipeline Corrosion and Prevention—A Comprehensive Guide.
  • Manufacturing and Industrial Equipment: Shields components during storage, shipping, or idle periods.
  • Marine and Offshore: Mitigates corrosion from saltwater and high-humidity environments.
  • Aerospace and Automotive: Protects critical systems like engines and fuel tanks during long-term storage.
  • Infrastructure and Utilities: Prevents corrosion in water pipelines, bridges, and utility equipment.

Monitoring and Maintenance

To ensure the long-term effectiveness of VCIs, regular monitoring is essential. Techniques include:

  • Coupons: Small metal pieces placed in the protected environment to assess corrosion rates.
  • ER Probes: Monitor changes in electrical resistance to track corrosion over time.
  • Replenishment: Determined based on environmental conditions and the observed depletion rate of VCIs. Factors influencing replenishment frequency include:
    • The rate of leakage through the tank chime.
    • Operating temperature and environmental conditions.
    • Properties of the substrate, such as sand or concrete.
    • The initial amount of VCI chemical applied.

Typically, VCIs provide effective protection for 3–5 years, though some applications may last longer under optimal conditions. Proper monitoring ensures VCIs maintain consistent protection and helps operators identify the appropriate timing for replenishment to sustain corrosion prevention.

VCIs and Industry Standards

Vapor Corrosion Inhibitors (VCIs) are gaining recognition in industry standards as a flexible and effective corrosion prevention tool. While they are often used to complement cathodic protection (CP), they are also being acknowledged as standalone solutions in scenarios where CP may not be feasible.

  • API 651 and API 2610: Standards such as API 651 include VCIs as an alternative for situations where CP systems are unsuitable, and API 2610 outlines their use under tank bottoms.
  • Regulatory Adoption: Organizations like PHMSA and the State of Florida have endorsed VCIs for their versatility, particularly in cases where CP systems are not functional or economical.

These endorsements highlight the growing recognition of VCIs as a versatile tool for corrosion prevention, whether as a standalone solution or a complement to existing systems like CP.

Independent Studies Supporting Vapor Corrosion Inhibitors

The effectiveness of Vapor Corrosion Inhibitors (VCIs) is well-supported by independent research, including a comprehensive 2018 study published by PRCI (Pipeline Research Council International). This study offers critical insights into the capabilities and limitations of VCIs:

  • Effectiveness in Corrosive Environments: VCIs were found to effectively mitigate pitting corrosion in steel exposed to corrosive sand. However, the study noted that VCIs are not as effective as cathodic protection (CP) for reducing pitting corrosion in certain conditions.
  • Importance of Proper Application: The study emphasized the need for following manufacturer-recommended concentrations, as inadequate levels of VCIs were shown to be ineffective.
  • Monitoring Compatibility: ER probes can be used to monitor the efficacy of VCIs, providing valuable data on corrosion rates and the need for replenishment.
  • Compatibility with Cathodic Protection: VCIs are compatible with impressed current cathodic protection systems. However, they can alter the native potential of steel, which must be considered when selecting CP criteria in accordance with NACE SP0193.

For more details, access the full study: PR-015-153602-R01 Vapor Corrosion Inhibitors Effectiveness for Tank Bottom Plate Corrosion Control.

Vapor Corrosion Inhibitor Case Studies: Real-World Success with VCIs

Pipeline Preservation with VCI in West Texas

MATCOR and Zerust® collaborated on a pipeline preservation project in West Texas, injecting over 24,000 gallons of VCI solution into pipeline manifolds. This approach provided effective corrosion protection during construction and harsh environmental conditions.

For more details on how VCIs address pipeline-specific challenges, visit our Pipeline Internal Corrosion Prevention with VCI page.

Casing Repair with VCI

MATCOR conducted a casing repair for a high-pressure natural gas line that had settled, losing contact with its protective casing. The solution included sealing the casing and injecting VCIs through the vent pipe, providing effective corrosion protection without excavation.

Learn more about this project in our Casing Repair & VCI Case Study.

Q&A: Common Questions About Vapor Corrosion Inhibitors (VCIs)

Are VCIs a permanent solution?

No, VCIs have a finite lifespan. Their effectiveness typically lasts 3-5 years, depending on factors like environmental conditions, application methods, and leakage rates. Regular replenishment is needed to maintain protection, with some applications lasting up to 15 years under ideal conditions.

How are VCIs applied to above-ground storage tanks?

VCIs can be applied as powders or liquids, depending on the tank type (new,in-service, or under inspection). The method varies based on substrate material (ie. sand or concrete), but long-term replenishment planning is essential to sustain protection.

Can VCIs replace other corrosion prevention methods?

VCIs are not typically used as a standalone replacement for other methods but are effective for short-term corrosion protection or in scenarios where other solutions are not practical.

Can VCIs enhance other corrosion prevention methods??

Yes, VCIs work well alongside existing methods by addressing localized corrosion in hard-to-reach areas like gaps, crevices, and irregular surfaces. This complementary approach strengthens overall protection.

How is VCI performance monitored?

VCI effectiveness is monitored using coupons, ER probes or UT probes. These tools measure corrosion rates and help identify when replenishment is required. While ER probes track average corrosion rates, they can also infer localized risks like pitting.

What standards and regulations support VCI use?

VCIs are recognized by standards such as API 651 and API 2610 for specific applications, and they are included in the upcoming NACE TG543 guidelines. Regulatory bodies like PHMSA also acknowledges VCIs as a valid corrosion prevention tool, especially when other methods are infeasible.

Conclusion: The Future of Corrosion Prevention with VCIs

Vapor Corrosion Inhibitors (VCIs) are transforming the landscape of corrosion prevention across industries. From pipelines and storage ranks to marine and aerospace applications, VCIs provide a versatile, cost-effective, and environmentally friendly solution for protecting metal assets. Their ability to adapt to various environments and integrate with other corrosion prevention methods makes them a critical tool for modern infrastructure and equipment management.

Through our partnership with Zerust® Oil & Gas, MATCOR delivers proven VCI solutions backed by extensive research and industry recognition. Whether you’re seeking to enhance existing systems or explore standalone VCI applications, our team is ready to help you develop a customized strategy to protect your assets and reduce long-term maintenance costs.

To get in touch with our team of corrosion experts for more information, to ask a question or get a quote, please click below. We will respond by phone or email within 24 hours. For immediate assistance, please call +1-215-348-2974.

Contact a Corrosion Expert

AST Cathodic Protection System Tank Isolation Considerations

cathodic protection tank isolation considerationsEvan Savant, EnLink Midstream reached out to the MATCOR Technical Team asking about AST cathodic protection system tank isolation:

“Can you advise on the importance of isolation for a new AST connected to a Pipeline, and can you advise on the need to isolate the tank cathodic protection from the tank grounding?

MATCOR’s Director of Engineering, Kevin Groll PE, NACE CP4 responded:

I am unaware of any papers or technical documents on the subject, but I will summarize as follows:

  1. Why can a lack of isolation hurt your cathodic protection?
    When trying to protect any type of structure from corrosion, cathodic current loss to nearby structures is always a concern. Losses can occur when the structure in question is directly bonded to other structures which may “steal” current. Offending metal structures that are close to the cathodic protection anode and structures with better resistance to earth (e.g., bare copper grounding, bare driven piles, etc.) will more likely take a significant amount of current.
  2. How do you obtain isolation without losing overvoltage protection?
    To prevent current loss, your target structure must be electrically isolated from the offending structures.  However, once you isolate a structure, you will lose grounding (if it was purposefully grounded) and you will lose protection against overvoltage events, AC faults, and lightning strikes.  Therefore, to obtain DC isolation but maintain AC continuity and overvoltage continuity, we use solid state decouplers (SSDs) and polarization cell replacements (PCRs). The primary difference between these devices is how much surge current they will carry.
  3. Tank cathodic protection design considerations.
    When we design an under-tank CP system with concentric rings, we assume that we will not have isolation from grounding and facility piping, and we also assume that most of the current will get to the tank bottom because of the proximity of the anodes.  This is not always the case, as we saw in a recent project, but for the most part concentric ring systems can be powered high enough to overcome the lack of isolation.

Horizontal directional drilling installed linear systems show approximately 1.5 to 2 times as much current is required as a concentric ring system due to current losses.  Again, we usually factor in enough current capacity to overcome these losses.

Deep anode systems and semi-deep anode systems suffer the worst losses. These systems will sometimes require isolation of the tanks to prevent critical current loss.  If a system is already in place, testing can be performed to determine how much loss there is to existing structures by measuring the current returned on ground rods and pipes. This is accomplished by using clamp-on current meters around wires/rods and Swain meters around pipes.

It is important to note that tank terminal isolation and grounding are factors in these complex tank terminal applications that must be considered in the proper design of Cathodic Protection.  MATCOR’s experienced team of engineers can evaluate your specific application and make the appropriate recommendations.


To get in touch with our team of cathodic protection experts for more information, to ask a question or get a quote, please click below. We will respond by phone or email within 24 hours. For immediate assistance, please call +1-215-348-2974.

Contact a Corrosion Expert

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