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Category Archives: Storage Tanks

Cathodic Protection, Horizontal Directional Drilling, Linear Anodes, Storage Tanks, Tank Bottoms

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

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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.

Contact a Corrosion Expert
Cathodic Protection, Corrosion, Storage Tanks, Tank Bottoms

Vapor Corrosion Inhibitors

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Are Vapor Corrosion Inhibitors Magic Dust or a Viable Corrosion Prevention Tool?

This article is intended to provide a basic primer on vapor corrosion inhibitors for use in corrosion prevention for above ground storage tanks and address where this technology stands.

There has been a significant effort within the oil and gas world to either promote or repudiate the use of vapor corrosion inhibitor technology (VCI) for tank bottom plate corrosion control. As a leader in the above ground storage tank corrosion control industry, MATCOR has partnered with Zerust® Oil & Gas to make VCI options available to our customers that are interested in applying this technology as part of their corrosion mitigation approach.

How Vapor Corrosion Inhibitors Work – Video Courtesy Zerust® Oil & Gas


What are vapor corrosion inhibitors and how do they prevent corrosion?

Zerust Vapor Corrosion Inhibitors can be used in conjunction with CP systems.VCIs are chemical compounds that are released into a confined space, such as the underside of a tank bottom, and diffused through the sand pad material to reach the metal surface. These compounds are adsorbed onto the metal surface forming a strong bond that promotes and maintains a passive oxide layer on the metal and blocks other contaminant molecules from reaching the surface.

Are VCIs a non-permanent solution?

Corrosion protection using VCIs requires sufficient chemical concentration to thoroughly diffuse across the entire tank bottom surface area. The VCI has a finite life, after which it ceases to remain active. When this occurs, further chemical is required to replenish the spent VCI. The frequency of VCI replacement will vary depending a range of factors:

  • The rate of leakage through the tank chime
  • The operating temperature of the tank
  • The sand properties
  • The amount of chemical initially applied
  • Other factors

As VCI technology is still in the early phase of adoption, the typical replenishment frequency remains one of the big unknowns. A conservative estimate would be a minimum of 3-5 years’ service life before replenishment although a least one source has reported upwards of 15 years of effectiveness.

How is VCI applied initially for above ground storage tanks?

There are a variety of application technologies depending on the application and whether the tank is new construction, existing tank during inspection, a tank that is in-service or a double floor tank. Other considerations include the substrate material or concrete pad. The VCI chemical can be provided in a powder or liquid form. Whatever system is utilized to deploy the VCI, consideration should be given to how it will be replenished over the life of the tank.

Can vapor corrosion inhibitor technology be used in lieu of cathodic protection?

Practically speaking, most tank operators are not looking to replace cathodic protection but are considering VCI as a supplement to cathodic protection or as a short-term solution for inadequate or depleted CP systems until a replacement CP system can be installed.

Can VCI be used as a complement to cathodic protection?

This is where VCI provides an exciting opportunity to supplement cathodic protection. While cathodic protection has a proven track record in corrosion prevention for tank bottoms, there are limits to the effectiveness of cathodic protection. Cathodic protection only works when the tank bottom is in intimate contact with the sand bottom. Localized corrosion can occur wherever there are air gaps under the tank bottom. These can occur due to flexing of the tank bottom, imperfections in the plate steel, lapping of the plate steel, poor compaction of the sand bottom, presence of aggregate or non-conductive materials such as asphalt or oil, and at crevices in the tank ring wall. These are all areas where cathodic protection may not be effective and the proper application of VCI would be an excellent means of providing corrosion protection in these localized areas. Cathodic protection and vapor corrosion inhibitors are symbiotic. CP current distribution has been shown to improve in the presence of VCI.

How do I monitor that the vapor corrosion inhibitor is working?

When applying VCI to a tank bottom, coupons, ER probes or UT probes installed under the tank are used to measure the effectiveness of the VCI and to alert the owner when the VCI requires replenishment. One of the concerns with using ER probes to measure corrosion rates under tanks is that ER probes provide an average corrosion rate and not localized pitting rates. It is understood that pitting corrosion is the dominant factor in tank bottom corrosion related failures and pitting rates can be significantly higher than average corrosion rates. There is a distinct correlation between average corrosion rates and pitting corrosion rates and the ER probes can be used to infer changes in the pitting rates.

Where do vapor corrosion inhibitors stand with industry standards and regulations?

According to API 651, there are several situations where CP is not recommended for specific tank foundation designs. In some of these designs, PHMSA recognizes that CP is not feasible.  In these cases, VCI can be a viable option. API 2610, the Tanks and Terminals standard outlines the use of VCI for tank bottoms in section 12.5. API 651, the CP standard, is being updated currently and VCI is being included as an option in this document. The State of Florida has identified that VCI can be used in tandem with CP or a standalone solution, for more than 6 years. NACE is currently working on publishing a standard “NACE TG543”, which is a comprehensive document on the application of VCI under tank floors. PHMSA is currently reviewing Special Permit requests for the use of VCI without a functioning CP system. If a non-regulated tank’s CP system is not meeting criteria, or has depleted, but the tank is still a few years from its next inspection, VCI can be applied to protect the floor until CP system repairs can be economically accomplished.

What independent published studies exist supporting VCI?

A 2018 study published by PRCI provides the strongest validation of the effectiveness of VCI and concluded that:

  • VCIs were found to be effective in mitigating pitting of steel exposed to corrosive sand but was not as effective as CP for reducing pitting corrosion. The study confirmed the importance of using the manufacturer’s recommended concentrations, as low levels of VCI was found to be ineffective.
  • ER Probes can be used to monitor the efficacy of VCIs
  • VCIs are compatible with impressed current cathodic protection; however, VCIs change the native potential of the steel and this must be considered when selecting CP criteria in accordance with NACE SP0193

Access the full study: PR-015-153602-R01 Vapor Corrosion Inhibitors Effectiveness for Tank Bottom Plate Corrosion Control

In conclusion, the application of VCI is a viable tool in our corrosion tool box that should be considered in conjunction with cathodic protection for critical service applications and as a standalone solution in some applications.

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
Cathodic Protection, Storage Tanks, Tank Bottoms

AST Cathodic Protection System Tank Isolation Considerations

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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
Corrosion Industry News, Linear Anodes, News, Storage Tanks, Tank Bottoms

MATCOR Ships Over a Half Million Feet of Linear Anodes to Africa

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The richest man in Africa, Aliko Dangote, undertakes $12B project including 153 ASTs

Chalfont, PA (April 2019) – MATCOR, Inc., the trusted full-service provider of proprietary cathodic protection products, systems, services and corrosion engineering solutions announced that it recently completed shipment of over 500,000 linear feet (150+ km) of its SPL™-FBR linear anode product along with other ancillary materials for 153 above ground storage tanks (ASTs) in Africa.

Tank anode system materials prepped for export at MATCOR’s Chalfont PA facility. Over 520 reels of anode material have been shipped to Nigeria.

The anodes, which will prevent tank bottom corrosion, are part of an ambitious refinery project undertaken by Aliko Dangote, Africa’s richest man. The tanks are being erected on over 6,000 acres of swampland outside of Lagos, Nigeria.

MATCOR was selected for this project due to quick delivery and the company’s unique linear anode design, which does not require field splicing and saves significantly on installation time and costs.

“The ability to manufacture the large quantity of custom length linear anode segments in a very compressed time frame was key to meeting the tank contractor’s needs,” noted Ted Huck, Director of Manufacturing and Quality Assurance for MATCOR. “Our team handled a very complex order with a very tight delivery schedule while maintaining world class quality.”

Learn more about the project in our recent blog post.

About MATCOR

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CONTACT

Ted Huck
215-348-2974		 Dana Baedke
Key Marketing Communications
844-545-3481, x700
Linear Anodes, Storage Tanks, Tank Bottoms

Tank Anode Systems for the Richest Man in Africa

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This month MATCOR will ship the final tank anode system assemblies for Africa’s most audacious industrial project. The project is being undertaken by Aliko Dangote, Africa’s richest person, and when completed this $12 billion Dangote oil refinery could, according to a 2018 New York Times article, “transform Nigeria’s corrupt and underperforming petroleum industry. Planned as the world’s largest refinery…should process 650,000 barrels of crude oil daily.” With Nigeria poised to become the world’s third most populous nation by 2050 (surpassing the USA) and having Africa’s largest economy, this project is being touted as a milestone achievement in what many are dubbing the African Century.

tank anode system installation
MATCOR Field Engineer E.Gopal (yellow vest)
at Lagos site inspecting tank anode system installation

As part of this ambitious refinery project, a total of 153 above ground storage tanks for crude oil, refined and intermediary products up to 92m in diameter (300 ft) are being erected on the 6,180 acres of swampland just outside of Lagos, Nigeria. MATCOR’s innovative tank anode system technology using linear anodes was selected by the project’s EPC contractor, Engineer’s India Limited, as the design basis for the cathodic protection for the project’s above ground storage tanks. Working closely with both the owner’s Indian based engineering team and the EPC contractor, MATCOR was successful in identifying the key tank contractors that would be bidding the tank erection and supplying the cathodic protection systems as part of their specifications.

tank anode system installation on large crude oil tank foundation
Linear Anode being installed on large crude oil storage tank foundation

Ultimately, MATCOR was successful in securing contracts to provide the linear anodes for each of the three tank packages, one from a Chinese contractor and two from a UAE based contractor.

tank anode system materials
Tank anode system materials prepped for export at MATCOR’s Chalfont PA facility.
Over 520 reels of anode material have been shipped to Nigeria.

In total, MATCOR has supplied over 500,000 linear feet (150+ km) of our SPL™-FBR linear anode product along with other ancillary materials for the under tank cathodic protection systems over an 18-month period. With all the anodes having been manufactured in MATCOR’s ISO 9001 certified Chalfont PA facility, MATCOR continues to be the global leader in the manufacturing of impressed current linear anodes for above ground storage tank cathodic protection.

Have questions about tank corrosion protection, or need a quote for services or our tank anode system? Contact us at the link below.

CONTACT A CORROSION EXPERT

Storage Tanks, Tank Bottoms

Specifying Sand Bedding to Support Above Ground Storage Tank Corrosion Protection

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The ideal sand bedding supports tank corrosion protection and long service life.
Specifying the ideal sand bedding supports tank corrosion protection and a long tank bottom service life.

For new construction tank projects and for retrofits of existing tanks, it is common practice to install clean washed sand as the pad upon which the tank bottom is fabricated. The use of oil sand, crushed stone, asphalt, or other materials directly under the tank bottom should be avoided, as these hinder effective tank corrosion protection. This article provides guidelines to the specifications for the sand bedding materials. These guidelines are based on providing a low corrosivity environment  compatible with cathodic protection to assure a long service life of the tank bottom.

Economic Considerations

For a typical 150-foot diameter tank using 12 inches of sand bedding the quantity of sand that is required is approximately 17,679 cubic feet of sand which is roughly 883 tons. The cost of the sand, including delivery, is a significant cost and far exceeds the cost of cathodic protection– especially if the sand specifications are quite stringent and require sourcing sand that requires significant transportation. Some consideration can be given to relaxing the sand recommendations, even if that warrants increasing the cathodic protection requirements, should there be a significant cost impact to complying with the sand specifications – consult your cathodic protection designer.

Recommended Sand Properties

The table below summarizes the recommended sand properties to support aboveground storage tank corrosion protection.

Property Recommended Value
Resistivity (ohm-cm) 20,000 – 100,000
pH > 6.5
Chlorides (ppm) < 10
Sulfates (ppm) < 200
Sulfides (ppm) < 0.1
Particle Size 100% pass through #4 Sieve

Soil Resistivity

The best proxy for determining corrosivity of sand materials is the electrical resistivity of the sand. Clean washed sand typically has resistivity values more than 20,000 ohm-cm and in some cases can exceed 100,000 ohm-cm. The higher the resistivity of the sand, the lower the corrosivity of the sand; however, when designing cathodic protection, the higher the sand resistivity the greater the impact on the overall system resistance and the electrical power required for the cathodic protection system. API Recommended Practice 651 Cathodic Protection of Aboveground Petroleum Storage Tanks provides the following table classifying resistivity of soil/sand.

Resistivity Range (ohm-cm) Potential Corrosion Activity
<500 Very Corrosive
500 to 1000 Corrosive
1000 to 2000 Moderately Corrosive
2000 to 10,000 Mildly Corrosive
>10,000 Progressively less corrosive

Soil Resistivity Testing Methods »

Sand pH Range

Measuring pH indicates the hydrogen ion content of a soil. Corrosion of steel is fairly independent of pH when it is in the range of 5.0 to 8.0. The rate of corrosion increases appreciably when pH is < 5.0 and decreases when pH is> 8.0. pH may be determined in accordance with ASTM G 51 or equivalent

Chlorides

Chlorides will affect the resistivity of soil, and act as a depolarizing agent which will increase the current requirement for cathodic protection of steel. Pitting corrosion on steel can begin at chloride levels of 10 ppm. Chloride content may be deter­mined in accordance with ASTM D 512 or equivalent.

Sulfates

Sulfate levels >200 ppm frequently indicate high concentrations of organic matter. Sulfate content may be determined in accordance with ASTM D 516 or equivalent.

Sulfides

Sulfide levels > 0.10 ppm may indicate that sulfates have been reduced by bacteria. Sulfide content may be determined in accordance with EPA 0376.1 or equivalent.

Particle Size

The sand bedding material should be clean of rocks, clumps and other debris and for clean sand capable of passing through a #4 sieve, for washed river sand an alternative acceptable particle size is 100% pass through a 3/8” sieve.

Sand Depth of Cover

For new construction tanks, the typical design is to provide a minimum of 12 inches (30 cm) of sand cover; however, for tank bottom retrofits it is quite common to provide 6 inches of sand (15 cm) for double bottom installations or for applications where the existing bottom is removed, and the top layer of the underlying soil foundation is being removed.

Have questions about tank corrosion protection, or need a quote for services or cathodic protection design and materials? Contact us at the link below.

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Quick Ship Programs, Storage Tanks, Tank Bottoms

Quick Ship Cathodic Protection for Tanks

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This program applies to replacement cathodic protection systems for above ground storage tank (AST) bottoms.

cathodic protection for tanks
Tank Emergency? Contact Us About Our Quick Ship Cathodic Protection for Tanks Program

With existing ASTs, you may not always have the luxury of a planned tank bottom cathodic protection system replacement. After taking a storage tank out of service for inspection, you are often required to make an immediate decision as to the integrity of the existing floor. In some cases, this means a new floor has to be quickly planned and installed to minimize the time that the tank is out of service.

MATCOR Quick Ship Cathodic Protection for Tanks Program

MATCOR is pleased to announce our stock tank bottom anode system to meet your replacement needs with very short notice.

For your tank bottom replacement applications where a very fast delivery is required, MATCOR will now be maintaining stock of our Tank Ring Anode System.

  • Up to 200 ft diameter SPL-FBR tank ring anodes
  • Pre-assembled and ready to ship from our Chalfont PA facility
  • Two day turnaround
  • Set up in concentric rings with five foot spacing
  • Requires a minimum of just 6 inches of sand cover from the new tank bottom
  • Designed for 25 mA/ft output which is generally sufficient for 50+ year anode life based on a nominal current density of 2 ma/ft2 of surface area.

For more information please contact your MATCOR sales representative or contact us at the link below.

Have questions or need a quote for a replacement tank bottom cathodic protection system? Contact us at the link below.

CONTACT A CORROSION EXPERT

Cathodic Protection, Storage Tanks, Tank Bottoms

Tank Farm Design Recommendations for Corrosion Prevention

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Tank Farm Design RecommendationsWhether designing a few above ground storage tanks or performing tank farm design for an entire facility, proper consideration should be given to the adverse impact of corrosion that can occur on the tank bottoms. When addressing the issue of tank bottom corrosion, consider the environment, the tank size and design, and the type of tank foundation to be employed. There are definite advantages in certain materials based on the size and requirements of an above ground storage tank (AST) foundation. By carefully assessing the tank farm surroundings and long-term requirements, costly and potentially dangerous corrosion related tank failures can be avoided. Whether you are relying on a reputable company in the industry or taking on your own front-end engineering and design, there are across-the-board tank farm design recommendations to consider when it comes to corrosion prevention:

In terms of corrosion prevention for under ground storage tank (AST) foundations, is cathodic protection (CP) effective?

For tanks erected on compacted soil or sand foundations, with or without a concrete ring wall, cathodic protection is considered a “good engineering practice” and has been proven as an effective means of addressing tank bottom corrosion concerns. When you compare various methods of corrosion prevention for above ground storage tank bottoms, CP is shown to prevail over asphalt or concrete unless your project involves smaller diameter tanks. The corrosion failure rate is greater for tanks built on asphalt or concrete compared to tanks where a concentric ring cathodic protection system is installed.

In terms of corrosion, when is asphalt or oil/sand acceptable for above ground storage tank (AST) foundations?

Asphalt foundations are not common in the United States, as the mechanical integrity of asphalt can be an issue depending on the AST environment. As well, the use of oil/sand layer designs has been phased out by most tank owners in the United States due to the adverse impact that these oil/sand layers have on tank bottom cathodic protection systems. While historically prevalent in the Middle East and Asia, most larger national oil companies have abandoned this approach because it causes shielding of cathodic protection (CP) current, allowing corrosion to occur. Kuwait Oil, Aramco, and others now prefer clean sand combined with CP as the base material of choice. This is standard in the United States and has been for several decades.

What is a Concentric Ring Cathodic Protection System for above ground storage tanks (AST)?  

A. Designed for long-term storage, an AST cathodic protection ring system offers a factory-assembled design whereby the anode rings are ready to install with cable leads that extend past ring wall penetration. Concentric rings sizes are made to order, requiring no onsite welding, cutting, or splicing. The anode locations are marked, rings are laid out, and cabling is placed using a proven labeling system for future monitoring. A mixed metal oxide (MMO) anode is centered among a low-oxygen-generating coke backfill to eliminate depolarization.

Learn about MATCOR’s complete AST cathodic protection design services.

Are there some cases where concrete foundations are advantageous for tank farm corrosion prevention?

During installation of above-ground storage tanks, there are some advantages to concrete foundations for tanks when it comes to corrosion—the high pH of the concrete acts to passivate the steel, unless you have an above ground storage tank (AST) liner pad or something that is between the concrete and the tank bottom. If you can effectively seal the chime from the ingress of water and oxygen, the corrosion rates are generally quite small. Unfortunately concrete foundations for larger diameter tanks are not typically practical and can be quite expensive to properly install. Concrete foundations with appropriate AST liners are best for smaller diameter tanks.

In tank farm design for corrosion prevention, what are the best recommendations for above ground storage tank (AST) liners?

Plastic secondary containment liners are largely phased out in the United States and have been replaced by geotextile membranes that serve the same secondary containment purpose as plastic—they are conductive to allow cathodic protection (CP). The general standard in the United States is to have a CP system directly under the tank in order to minimize stray current or current losses due to earthing systems around the tank. Since the tank bottom is a large bare structure and the anodes are closely coupled to the tank bottom, there is usually very little current drain to other structures; the system if properly designed can accommodate modest current drain. While a plastic liner provides isolation from other nearby structures, when a problem arises with the CP system or if the CP system reaches the end of its projected service life, there is no way to install a new CP system without replacing the tank bottom.

Tank farm corrosion prevention is more manageable now than ever before. The MATCOR Concentric Ring Cathodic Protection System™ is just one of many excellent options for protecting your above ground storage tank (AST) from damaging corrosion.

For assistance with tank farm design, our Concentric Ring AST Cathodic Protection System™, project management or installation, please CONTACT US.

Learn more about Tank Cathodic Protection

Cathodic Protection, Mixed Metal Oxide, Storage Tanks

Tank Cathodic Protection Trends | Above Ground Storage Tanks

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This presentation explores current tank cathodic protection trends, specifically for above ground storage tanks.



Statistics show owners of above ground tanks often experience external corrosion issues because of limited or poor installation methods. Typical above ground storage tank (AST) methods of the past involve a ring wall foundation that is generally formed with a sand or soil base, or even concrete for smaller tanks. It has previously been acceptable to use a galvanic ribbon anode system (generally magnesium), but this system often fails prematurely due to unstable sand-based foundations and poor connections. For this reason, the industry is moving away from the galvanic anode system and to newer concentric ring tank cathodic protection systems for above ground storage tanks.

Good Engineering Practices

While there are newer designs for AST cathodic protection systems, your first consideration should always be good engineering practices. The proper installation of a high-end tank cathodic protection system begins with known design specifications based on the tank size and diameter. This presentation compares traditional grid anode systems with newer linear anode concentric ring systems for the cathodic protection of above ground storage tank bottoms. In addition, congested terminal environments often lead to interference and less current at the tank bottom.

Grid Anode vs. Concentric Ring Tank Cathodic Protection Systems

tank cathodic protection
Tank Cathodic Protection using MATCOR Tank Ring Anode System for Above-Ground Storage Tanks (ASTs)

While the field-fabricated and field installed grid anode system has been in use for over 20 years, some faults have been discovered. Field installation presents welding challenges for the contractor because the system must first be secured, and it cannot be installed directly over sheet liner. The ribbon anode and titanium conductor bars have to be field cut to the appropriate lengths. At the conductor bar to anode ribbon intersections, a weld is applied. The field assembled grid system is subject to weld failures, the spot welds can be damaged easily during subsequent sand installation, and care must be taken to hold the system in place so that it does not short to the tank bottom. All of these installation challenges can adversely impact the system performance. Additionally, bare MMO in sand is an oxygen generator when used for cathodic protection. Oxygen is a depolarizer and in some instances this can lead to issues with maintaining polarization criteria.

Advantages of the Concentric Ring System

tank cathodic protection designerIn comparison, newer concentric ring systems for above ground storage tanks include factory assembled anode rings that come equipped with the appropriate cable leads to extend past the ring wall penetration. No onsite field assembly is required. The system is pre-assembled in concentric ring sizes designed for your tank and requires no cutting, splicing, or welding, and the MMO wire is backfilled within a braided fabric sleeve with coke breeze. Anode locations are simply marked, each ring is laid out at the proper diameter, and cabling is extended toward the ring wall. The anode cables are labeled for ease of identification and to allow for monitoring of current to each anode ring. Unlike the grid system, the MMO anode is centered in a coke backfill – this coke environment inhibits the generation of oxygen eliminating the issues with depolarization.

The concentric ring tank cathodic protection system is designed for longevity. A typical under-tank ring system using MMO anodes exceeds a 30-year life, however can be designed to extend life beyond 100 years.

Additional Considerations for Tank CP

  • Some tank operators opt for a “replaceable” anode system, however time and manpower are required to extract and replace the anodes and backfill and the design life is only 30 years.
  • Volatile corrosion inhibitors (VCI) are often used in conjunction with cathodic protection systems where CP cannot be installed or may be ineffective, such as ring wall crevices, poor bottom-to-sand contact, and more. It can be pumped under tanks via shielding high-density polyethylene (HDPE) containment liners.

Today, tank owners have more effective choices than traditional grid anode systems for tank cathodic protection. The MATCOR Tank Ring Anode™ System is trending as a high-end solution for above ground storage (AST) tanks.

For assistance with tank cathodic protection design, MATCOR’s Tank Ring Anode System, project management or installation, please CONTACT US.

Learn more about AST Cathodic Protection

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