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Category Archives: Cathodic Protection

Cathodic Protection

Soil Resistivity Testing for Cathodic Protection Design

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Engineers rely on soil resistivity testing as one of the most critical steps in designing an effective cathodic protection system. This soil resistivity test method provides the data needed to evaluate soil conditions and design reliable corrosion protection systems.

Accurate soil resistivity data directly impacts the anode selection, system performance, and long-term corrosion control. Incomplete or inaccurate data leads to underperforming systems, premature failure, and costly redesigns.

Soil Resistivity TestingIt also serves as a foundational input to cathodic protection design, helping engineers develop systems based on accurate field data.

This article explains how engineers perform soil resistivity testing, when they need it, and how the data supports real-world cathodic protection design decisions.

What is Soil Resistivity Testing and Why It Matters for CP Design

One of the most important design parameters when considering the application of cathodic protection for buried structures is the resistivity of the soil. Engineers use soil resistivity testing to assess the corrosivity of the environment surrounding buried structures.

Soil conditions directly influence:

  • System type
  • Anode quantity
  • System configuration

Without accurate soil resistivity data at both the structure and proposed anode locations, engineers risk designing ineffective cathodic protection systems that require costly remediation after commissioning.

How Soil Resistivity Determines Soil Corrosivity

Soil resistivity is the primary diagnostic factor for evaluating soil corrosivity. When engineers perform soil resistivity testing, they also consider factors such as:

  • Soil composition
  • Moisture content
  • pH
  • Chloride and sulfate concentrations
  • Redox (oxidation-reduction) potential

While comprehensive soil analysis may be required for failure investigations, soil resistivity testing provides the most practical and widely used field measurement for cathodic protection design.

Soil Resistivity Ranges and Corrosivity Classification

Below is a typical chart correlating soil resistivity with soil corrosivity.

Soil Resistivity (ohm-cm) Corrosivity Rating
>20,000 Essentially non-corrosive
10,000 to 20,000 Mildly corrosive
5,000 to 10,000 Moderately corrosive
3,000 to 5,000 Corrosive
1,000 to 3,000 Highly corrosive
<1,000 Extremely corrosive

SOURCE: Corrosion Basics: An Introduction, NACE Press Book, 2nd edition by Pierre Roberge

How Soil Resistivity Testing Works

Soil Resistivity Testing
Wenner four-pin soil resistivity testing method

While there are several methods for measuring soil resistivity, the most common field testing method is the Wenner four-pin method (ASTM G57).

This method uses four metal probes, driven into the ground and spaced equidistant from each other. The outer pins are connected to a current source (I) and the inner pins are connected to a volt meter (V) as shown in Figure 1.

Soil Resistivity Formula and Calculation

Engineers convert measured resistance (R) into resistivity using a standard soil resistivity testing formula:

ρ=2×π×ax 30.48 cm/ft. ×R = 191.5 x a x R

Where:

  • ρ = soil resistivity, Ω-cm
  • a = probe spacing, ft.
  • R = measured resistance, Ω

How Probe Spacing Relates to Testing Depth

Each probe spacing represents the average soil resistivity to a depth equivalent to that spacing. For example, a 5-foot spacing reflects the average resistivity at approximately 5 foot deep.

For cathodic protection system design, it is common to take multiple soil resistivity tests with various probe spacings.

For shallow anode placement, it is usually sufficient to take reading readings at 2.5 ft, 5 ft, 10 ft, 20 ft, 25 ft. For deep anode applications, soil resistivity measurements may be recommended at much deeper depths corresponding with the anticipated depth of the deep anode system.

Understanding Soil Layer Effects in Resistivity Testing

It is important to note that the soil resistivity values generated from the four pin testing represent the average soil resistivity from the earth surface down to the depth, and each subsequent probe spacing includes all of the shallow resistance readings above it.

Using the Barnes Method to Interpret Layered Soil Resistivity

To isolate resistivity at specific depths, engineers apply analytical techniques such as the Barnes method. This method:

  • Converts resistance to conductance
  • Evaluates incremental changes between readings
  • Calculates true layer resistivity

Engineers rely on this approach to identify low-resistivity zones that significantly impact cathodic protection performance.

Example of Layered Soil Analysis

For the Barnes analysis below, the data shows that a low resistance zone exists between 60m depth and 100m depth.

TEST DATA BARNES ANALYSIS

Spacing a
(m)

 Resistance
(ohms)		 Conductance 1/R
(Siemens)		 Change in Conductance
(Siemens)		 Layer Resistance
(ohms)

Layer Resistivity
(Ohm-m)
20 1.21 0.83 — 1.21 152
40 0.90 1.11 0.28 3.57 441
60 0.63 1.59 0.48 2.08 264
80 0.11 9.09 7.5 0.13 17
100 0.065 15.38 6.29 0.16 20
120 0.058 17.24 1.86 0.54 68

Choosing the Right Soil Resistivity Testing Equipment

Engineers must use the right soil resistivity testing equipment to collect accurate field data. Electrical noise from power lines, substations, railroad tracks, and many other sources can distort readings if not properly managed.

Modern soil resistivity meters include filtering capabilities to reduce interference and improve measurement accuracy.

High-Frequency Soil Resistivity Meters for Shallow Testing

High-frequency meters operate above 60 Hz and should be limited to data collection of about 100 feet in depth.

This is because they lack sufficient voltage to handle long traverses and they induce noise voltage in the potential leads which cannot be filtered out as the soil resistivity decreases and the probe spacing increases.

Engineers commonly use these meters for:

  • Shallow testing
  • Corrosion assessment
  • Shallow anode design

They offer a cost-effective solution but have limitations in deeper applications.

Low-Frequency Soil Resistivity Meters for Deep Testing

Low-frequency meters operate between 0.5 to 2.0 Hz and support deeper soil resistivity testing.

These meters:

  • Handle large probe spacing
  • Provide superior noise filtering
  • Deliver accurate readings at greater depths

Engineers typically prefer low-frequency meters for deep anode cathodic protection design.

Field Best Practices for Accurate Soil Resistivity Testing

Accurate soil resistivity testing depends on proper field procedures and site conditions.

  1. Select the Right Testing Location. The use of the Wenner four pin testing method requires sufficient open area to properly space the pins to collect data to the depths necessary. For deep anode cathodic protection systems this would require a minimum of three times the anticipated anode system depth.
  2. Avoid Interference from Buried Piping and Other Metallic Objects. The presence of any buried metallic structures (piping, conduit, reinforced concrete structures, grounding systems, etc…) provides low current paths that could cause a short-cutting effect that would distort the resistance readings and yield an erroneous soil resistivity reading.
  3. Control Probe Depth for Accurate Readings. It is important that the probes are properly inserted into the earth. For shallow resistivity readings, probes that are driven too deep can impact the shallow readings. Ideally, the pins should be no deeper than 1/20th of the spacing between the pins and no more than 10 cm (4 inches) deep.
  4. Minimize Electrical Noise During Testing. Soil testing should not be performed directly under high voltage transmission systems or near other outside sources of current in the soil such as DC light rail systems.
  5. Record Soil Conditions and Environmental Factors. It is important that the location of the testing is accurately recorded along with the soil conditions and temperature at the time of testing. Testing should not be performed in frozen soil, or during periods of extreme drought or abnormally wet conditions.

When to Use Professional Soil Resistivity Testing Services

Professional soil resistivity testing for cathodic protection becomes critical when projects require accurate field data to support system design, deep anode installations, or corrosion troubleshooting.

Engineers rely on experienced providers to perform soil resistivity tests, interpret layered soil conditions, and deliver reliable data for CP design.

Working with a qualified team helps:

  • Reduce design risk
  • Improve system performance
  • Avoid costly rework

Key Takeaways: Soil Resistivity Testing for CP Design

Soil resistivity testing provides the most reliable indicator of soil corrosivity for buried structures and plays a critical role in cathodic protection system design.

Engineers most commonly use the Wenner four pin method to perform soil resistivity tests. When properly collected and interpreted, teams can design CP systems that perform reliably and efficiently.

Get Expert Soil Resistivity Testing Support

Learn about MATCOR soil resistivity testing services and cathodic protection design services.

Have questions about soil resistivity testing, or need professional soil resistivity testing services for your project? Contact us at the link below.

CONTACT A CORROSION EXPERT

Anodes, Cathodic Protection, Infrastructure, Linear Anodes, MATCOR

Anode Current Ratings and Soil Resistivity

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We appreciate the question: “How does soil resistivity impact current rating.”  The short answer is that resistance has nothing to do with anode rating. Here is a more detailed response:

  1. Anode current rating – all anodes have a current rating based on how long they can be expected to operate at a given current rating.  All anodes have some defined expected life based on current output and time – so many Amp-Hours of service life.  For example a magnesium anode may have an expected consumption rate of 17 lb/Amp-year (7.8 kg/amp) so if a 17 lb anode is operated at 0.1 amps it would have a life of 10 years.  For MMO anodes, they too have an expected life.  For our linear anode rated at 51 mA/m it is important to know that that rating is actually 51 mA/m for 25 years.  So a 100m anode segment with this rating would have an expected life of 127.5 Amp-years.  If this anode were operated at 5.1 amps (full rated capacity) it would be expected to operate for 25 years.  IF it were operated at 2.55 amps (50% of rated capacity) it should last 50 years.  The anode life is generally linear.  Please note that resistance has nothing to do with the anode current rating – the anode current rating merely calculates the life of the anode as a function of how many amps for how long of time.
  2. Actual current output – just because you install an anode rated for 5.1 amps for 25 years (our 100m segment of 51 mA/m SPL-FBR) does not mean that the anode will output this amount of current.  It just means that at that current rating you can expect 25 years of life.  The anode is merely one component of the overall cathodic protection circuit.  The actual output of the anode is function of Ohms Law ( Voltage = Current * Resistance).  It would make sense to note that if the system Voltage were zero (the rectifier were turned off or disconnected) then the anode would not have any current output.  Likewise if the 100m anode segment were installed in a very low resistance environment and driven by a powerful rectifier, the current could be much higher than 5.1 amps which would result in a much shorter life.
  3. Why anode rating is important to the CP designer – the CP designer is tasked with protecting a specific structure for a given period of time (protect this pipeline for 30 years.)  The CP designer then calculates, based on actual testing or established guidelines, the amount of current that should be sufficient to achieve appropriate CP levels to protect the structure.  This results in an answer of some number X of amps required.  If the requirements are to protect the structure for Y number of years, then the anode life required is X * Y (# of amps times # of years).  This defines the minimum amount of anode life that is needed.
  4. The next question the CP designer must address, once it is determined how much current is needed, is how to design a system that will generate that amount of current.  Since Ohms Law dictates that Voltage = Current * Resistance (V=IR) then if we know that the Current = Voltage/Resistance (I=V/R.)  Thus the CP designer must understand how to calculate system resistance (R) and must provide sufficient driving force (V)  Several factors affect system resistance (R) including anode geometry – the longer an anode, the lower its resistance – which in many applications is a big benefit to the linear anode.  One of the great benefits of the linear anode is that because of its length, in most applications the soil resistivity plays a lesser role since the anode resistance to earth is generally low for a wide range of soil resistivities due to its length.  For extremely high resistance environments, linear anodes may be the best option since short anodes will not have a low enough resistance.
  5. There are other factors that go into CP design including current distribution and making sure sufficient current is being applied across the entire structure.

CP Design can be very complicated.  I hope that the above explanation is helpful, but if there is a specific application to evaluate, please contact us with the details.  We are also available, for a reasonable engineering fee, to develop and/or review CP system designs.

Ted Huck

VP, Technical Sales

Anodes, Cathodic Protection, Marine

6 Sled Anodes Replace 274 Galvanic Anodes for Marine Jetty Corrosion Protection

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Marine environments can be some of the harshest environments on the planet for corrosion of steel structures. Indeed, the earliest application of cathodic protection can be traced back to Sir Humphrey Davy and the British Navy’s investigation into corrosion on copper sheathed wooden vessels. This video demonstrates MATCOR’s impressed current sled anodes that are successfully being used to protect steel piles for jetties, docks and other similar steel structures in marine environments.

At 1:03 in the video, we demonstrate how the marine anode sled operates with a trade show model.

Sled Anode
Sea-Bottom™ Anode Marine Sled Anode

At 4:05 you see a MATCOR Sea-Bottom Marine Anode Sled being lowered into the water as part of the cathodic protection system protecting a steel jetty structure in Indonesia. The jetty is constructed with four interior rows of concrete piles and an exterior row of 247 bare metallic piles. The operator initially considered galvanic anodes to protect the jetty from corrosion – until they compared the cost, time and effort to install the required 374 aluminum anodes each weighing 200 each. Instead they opted for six marine anode sleds, taking only three days to install.

For assistance with near shore marine anode systems, please CONTACT US.

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

Anodes, Cathodic Protection, Marine

Sled Anode Cable Connections

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What is the best way to prevent damage to sled anode cable connections due to rough sea current and waves?

MATCOR marine sled anodes (Sea-Bottom™ Anodes) are designed with the cable connections routed inside a high density polyethylene (HDPE) protective pipe with holes to provide a level of mechanical protection. Then we use concrete weights to help secure the HDPE pipe (with the cable inside) to the sea bottom so that they are not subject to wave or tidal action.

Sled Anode Cable ProtectionThe protective housing is pictured here and called out as item 4 on the drawing on page 3 of our Sea-Bottom Marine Anode Sled brochure. For the concrete weights, you can use a variety of methods from sacks of concrete to custom formed concrete cast weights. Below is a photo of the weights that were locally supplied to us for a recent project in Indonesia. These weights are installed by divers during the sled anode installation.

sled anode concrete weights

For assistance with impressed current anode system design, MATCOR’s Sea-Bottom Marine Anode Sleds, project management or installation, please contact us at the link below.

Contact a Corrosion Expert
Canister Anodes, Cathodic Protection, Mixed Metal Oxide

Canister Anodes: HSCI vs MMO

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Canister anodes are commonly used for impressed current anode cathodic protection applications. These can be used to protect buried metallic piping in congested plant environments, to protect distribution or transmission pipelines in either distributed shallow ground beds or as horizontal remote ground bed anodes, and to protect other structures such as above ground or buried tanks and piling systems.

mmo-canister-anode-emailMATCOR’s MMP™ Anode provides an outstanding combination of value, quality and proven reliability for use with these types of applications and are often a direct upgrade over other canister anode offerings. Below is a comparison of MATCOR’s MMO canister anode vs. conventional high silicon cast iron anodes, in addition to a real life project example comparing the costs associated with both canister anode types.

MMP Canister Anode Unique Construction Features

Understanding the value of the MATCOR MMP™ anode product, starts with its unique construction features as follows:

HSCI vs MMO/Ti Canister Anode Type

Most canister anodes consist of either a High Silicon Cast Iron (HSCI) anode or some configuration of MMO/Ti anode installed in a large metallic “canister” that is filled with coke backfill. The canister is capped with the anode cable extending out the top of the anode cap. Once installed, the exterior metallic canister housing is part of the anode system and will consume quickly as current is discharged off the anode, through the coke backfill and then off the external metallic housing.

It is important to note that the housing is only intended to survive transportation and installation. Once installed, it is expected to be consumed, leaving behind the anode and coke backfill.

One of the most important considerations in evaluating any canister anode technology is to evaluate the anode technology that is inside the canister anode.

HSCI anode technology is an older anode technology that remains extremely popular around the world. It is popular because it is cheap and readily available from many suppliers. Because HSCI anodes are simply castings of a specific formulation of iron, they are available from a wide range of manufacturers with casting facilities spread across the globe. Any foundry can cast the basic HSCI anode. Testing for anode composition assures that the basic elements are present in the correct ratio, however, the mechanical and more importantly the electrical (anode) characteristics are dependent on a lot more than just having the correct ratio of components. Also critical are the canister anode:

  • Casting process
  • Micro-structure
  • Density and consistency of the casting
  • Presence of trace elements
  • Consistency of the grain structure
  • and more…

Unfortunately, it is very difficult to assess the quality of a particular anode casting batch without extensive long term testing. Even the most experienced and reputable cast iron anode suppliers will admit that HSCI anode quality and anode performance can vary significantly even within different casing batches from the same manufacturer.

This leaves buyers with a real challenge in confirming that the anodes they are purchasing will provide the anode life and current output that they are specifying because of the wide range of casting quality issues that can occur with HSCI anodes and the large number of casting facilities offering this type of product.

Mixed metal oxide coated titanium (MMO/Ti) anodes are also a common anode technology utilized in canister anodes – typically these anodes consist of a titanium substrate on to which a mixture of mixed metal oxides is electro-deposited on to the substrate and thermally cured. The MMO coating typically uses a base of Iridium as the primary catalyst that allows the coating to perform as an anode.

MMO Anodes Easier to Test for Quality

As with HSCI anodes, quality is an issue with MMO/Ti anodes; however, there are some key factors that lead to making MMO/TI anodes easier to QA/QC than conventional cast iron anodes.

First, there are no real mechanical concerns other than assuring that there is good adherence between the MMO coating and the underlying substrate. Because the substrate is pure titanium the mechanical properties are quite consistent (ASTM Grade 1 or Grade 2 Titanium is considered commercial pure titanium and either can be used for MMO/TI anodes). Testing for coating adhesion is a rather simple test that can be performed on a test coupon from the same process or on the anode itself.

In addition to having a very stable, homogeneous substrate, the MMO/Ti anode performance can be tested using accelerated life testing to provide an evaluation of the performance of the specific coating mixture that is applied. As with HSCI anodes, there are a large (and growing) number of suppliers of MMO/Ti anode materials; however, testing can be used to confirm the anode material quality. MATCOR MMP™anodes use MMO/Ti anode material with a proven track record. Additionally, third party inspection and testing of MATCOR’s MMO/Ti anode material is available for a nominal inspection charge.

Canister Anode Configuration

The actual anode inside the canister can have a wide range of configurations; however, the most common configuration is the tubular anode. All HSCI anodes are cast in tubular (either solid or hollow tubular) configurations and many of the MMO/Ti canister anodes also use tubular anodes.

For HSCI tubular anodes, the brittle nature of the anode must be taken into consideration when transporting, handling and installing the anode as dropping the anode canister can lead to breaking or cracking of the HSCI anode.

MATCOR’s MMP™ Anode is unique in that we utilize a solid titanium rod as our substrate. This provides several advantages over typical MMO/Ti configurations utilizing tubular anodes. The cable to anode connection is easier and more secure when connecting to a solid rod as opposed to trying to connect a cable to the inside of an anode tube. The solid titanium rod is also stronger and unlikely to break should it be bent.

Other MMO/Ti configurations can also be used inside a canister anode including MMO/Ti strips and ribbons. There is nothing inherently wrong with these configurations as long as the anode to cable connection is properly designed. Improper anode to cable connection designs can lead to premature anode failure.

Canister Anode Connection Technology

Typical anode connections used for discreet canister anodes usually consist of some version of a pressure fit mechanical connection with an epoxy sealant covering the anode to cable connection. Anode to cable connection failures have historically been a significant cause of premature anode failure. Depending on the anode type and configuration, the location of the anode connection can also have an impact on performance – especially for HSCI anodes that consume rapidly and may be subject to necking effects– with MMO/Ti anodes that are dimensionally stable (i.e. do not physically consume) this is much less of an issue.

MATCOR’s MMP™ anode utilizes a multi-step welded connection technology to assure the anode to cable connection is mechanically and electrically secure and properly sealed from the ingress of moisture that can lead to premature anode failure. The multi-step anode connection includes a mechanical crimp followed by a welding process. The mechanically secure welded connection then has a layer of non-conductive hot melt sealant followed by a heat shrink sleeve with a second sealant layer on the interior of the heat shrink. This heavily engineered connection technology has proven to be exceptionally effective with hundreds of thousands of connections in service over the past 20 years.

spiral-thin-wall-canister-anode
Typical spiral wound 0.7mm thin walled canister

Heavy Duty Canister Anode Construction

Most canister anodes are constructed using a thin walled galvanized steel spiral wound pipe material. This material is commonly used in the HVAC world as a ducting material and is readily available commercially. This material is typically 0.7mm thickness (24 gauge) with a spiral wound construction. This type of canister provides only a modest amount of mechanical strength and must be very carefully handled during transportation and installation.

matcor-mmo-canister-anode-pipe
MATCOR’s 1.85mm EMT seamless steel pipe offers 250% thicker wall

MATCOR’s MMP™ Canister anode utilizes a thicker walled EMT seamless steel pipe with a typical material thickness of 1.8 mm or 250% times the thickness of typical canister anodes. This additional wall thickness makes the MMP™ anode a much stronger product – you can drive a fork truck or backhoe over our anode and not significantly damage the canister.

Economic Considerations

The actual installed cost of the anodes is an important consideration in selecting the optimal anode solution. As noted previously, the anode system quality and design integrity should also be factored into the evaluation as these factors can serve to reduce the anode system’s life in the field.

Some factors that should be considered include:

Anode Operating Life (Amp-Years)

Every anode has an operating life. For HSCI anodes the calculation of an anode life is complicated by the inherent variability in HSCI anode casting. The nominal consumption rate of HSCI anodes is typically assumed to be between 0.5 to 1.0 lbs/amp-year (0.23 kg/amp-year to 0.45 kg/amp-year) in a coke backfill. This wide range is consistent with the variation in anode consistency and quality inherent in the anode type. The consumption rate can also vary depending on the environment and the operating current density.

Additionally, a utilization factor is typically applied to the calculations as the anode can never be fully utilized – at some point the anode consumption is such that the anode to cable connection is lost prior to fully consuming all of the anode’s mass. For stick anodes with an end connection this is typically 65% (meaning that 35% of the anode mass is unusable) while for tubular anodes with center connections this utilization factor is closer to 85%.

MMO/Ti anodes are considered dimensionally stable anodes and do not physically consume. They are instead electro-catalytic in nature – they cause a reaction to occur that generates DC current flow without actually being a reactant and thus are not consumed. The catalytic component in the MMO coating does; however, have a finite life that is relatively consistent and can be determined based on the accelerated testing performed by the manufacturer.

The challenge with MMO/Ti anodes is that the coating loading is on the order of mg/m2. With such a light coating load, it is often difficult for the anode manufacturer to control the coating loading to exactly the thickness that would be optimal. Most MMO/Ti anodes are supplied with more coating than required to assure that the coating thickness QA/QC spot checks exceed the minimum specified coating loading. MATCOR’s experience has been that the anode coatings tend to exceed that required coating loading by a significant margin assuring even longer life than the stated design life.

Anode Weight

One of the key advantages of the MATCOR MMP™ anode is the low weight over HSCI anodes for a similar current capacity. HSCI anodes consume at a relatively high rate and require significant anode mass to provide the current output and life required. Weight has two key impacts; one is economic as the lower the anode weight the cheaper it is to transport and install, and the second is a safety issue as the heavier the anode the greater the risk of injury associated with the proper transportation and handling of the anode during installation. While the transportation costs are easily quantified, the safety benefit of a much lighter anode to be installed is much more difficult to quantify but should be considered in the anode selection.

Anode Installation Replacement Cost

Another consideration that should be given is the cost of having to replace an anode installation more frequently. This metric is often not considered; however, there is a very real value to having an installation that lasts 25 years versus only 18 years and the additional incremental cost for the additional life has a real value that should be considered in the economic evaluation.

Savings from using fewer, higher output anodes

Another consideration that is often overlooked is the savings that might be achieved by using fewer anodes that are capable of higher output to reduce the overall installation costs. The incremental cost of fewer, larger anodes could result in a significant cost savings over using more anodes that are rated for lower output. When considering the use of fewer, higher output anodes the impact on system resistance could be an issue as the power supply may have to be larger and the operating power higher to overcome the additional system resistance from fewer anodes. Typically power costs are rather nominal and not a major consideration in this type of economic evaluation.

Canister Anodes System Example

Please note that this is a real project example and is intended to show the methodology used to evaluate two different options – one using HSCI anodes and the other using MMP™ canister anodes. The costs associated with this project are not suitable for other applications – each project has its own costs that must be evaluated for that specific project.

Cathodic Protection Requirements

Shallow horizontal ground bed rated for 60 Amps using multiple anodes in parallel at a depth of 12 feet and spaced 15 feet from each other. Each hole would be 8” diameter and the hole would be filled with coke around the anode including one foot below the anode and one foot above the anode. System to be suitable for 30 years anode life. Soil resistivity is assumed to be 3000 ohm-cm.

Canister Anode Options

Two anode options were considered as follows:

HSCI Solid Stick AnodeMATCOR MMP™3605
Anode TypeBare HSCI AnodeCanister MMO/Ti rod
Anode Dimensions3" x 60"3" x 60"
Anode Weight, ea110 lbs44 lbs
Anode Life, ea95.3 amp-years*125 amp-years
Anode Cost$325$210
Freight Cost/Anode$22$9
* Based on 0.75 lbs/amp year consumption rate and 65% utilization factor for solid stick anode

Additional Costs

  • Installation cost to drill each hole, install anode and make header cable connection estimated at $700 USD/hole
  • 180 lbs of coke backfill per hole, including freight, estimated at $135/hole
  • Cable costs for header cable, estimated at $1 per foot
  • Cable to anode splice kit estimated at $35 per connection

Calculations

Minimum number of anodes required to meet 30 year life operating at 60 amps:

Roundup {(60 amps x 30 years) / Anode life} = minimum # of anodes

  • HSCI Stick Anode – 19 anodes resulting in 30.19 years design life
  • MATCOR MMP™ – 15 anodes resulting in 31.25 years design life

Anode System Resistance

Based on Dwight’s equation using an 8” diameter hole and 7 ft coke column in 3000 ohm-cm soil the resistance of a single anode (Ra) is 7.68 ohms. The resistance for multiple anodes in parallel is Ra/Number of parallel anodes

  • 19 HSCI anodes – anode bed resistance is 0.40 ohms
  • 15 MMP™3605 anodes – anode bed resistance is 0.51 ohms

Installed Cost

Based on the cost assumptions the total installed costs are:

  • HSCI 19 anode system:    $23,408.00
  • MATCOR MMP™ 3605:    $16,560.00

Contact MATCOR about your canister anode cathodic protection requirements or learn more about our MMP Anode (MMO) canister anodes.

Cathodic Protection, Linear Anodes, Storage Tanks

External Tank Bottom Cathodic Protection

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External corrosion of above ground storage tank (AST) bottoms is a significant problem for tank owners. Corrosion professionals tasked with protecting these structures should consider multiple factors. One thing is clear: proper installation of an impressed current tank bottom cathodic protection system plays an important role in reducing corrosion and extending the service life of the tank bottom.

Concentric ring anode configuration ideal for tank bottom cathodic protection

Tank Bottom Cathodic Protection Article from NACE Materials Performance

Learn more about this newer method of AST cathodic protection and its benefits over the more traditional grid system.

For additional information about tank bottom cathodic protection, please read our article in the special supplement “Corrosion Control for Aboveground and Belowground Storage Tanks” in the May issue of NACE International’s Materials Performance.

READ THE FULL ARTICLE

Contact MATCOR about your AST cathodic protection requirements or learn more about our Tank Ring Anode™ System.

Learn more about Tank Cathodic Protection

Cathodic Protection, Piping, Storage Tanks

Cathodic Protection for Missile Defense Shield in Romania

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As you watch the evening news or pick up your daily paper you will very likely read about the new Missile Defense Shield in Romania that came on line this week. The Russian response has been loud and indignant. This story will be all over the evening news, cable channels and newspapers.

But did you know that the Deveselu facility in Romania has a MATCOR Cathodic Protection system protecting the buried piping and process tanks? MATCOR VP of engineering Glenn Shreffler made three trips to the site during its construction. So when you watch the evening news and they discuss the “controversial” missile defense base in Romania, we are proud that MATCOR anode systems are hard at work protecting the assets that protect our NATO allies.

Contact MATCOR about your tank and piping cathodic corrosion prevention requirements or learn more about our wide range of cathodic protection products.

Anodes, Cathodic Protection, Corrosion, MATCOR, Mixed Metal Oxide

MMO Anode Technology: The latest in Cathodic Protection

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MMO anode technology has taken over the cathodic protection industry and MATCOR has been on the forefront for the last 20 years. Ted Huck, our VP of International Sales was interviewed at the recent NACE Corrosion Conference. In this video he discusses MMO anode technology for cathodic protection systems and the importance of reliable anode to cable connections.

MMO Anode Technology

MMO anodes, or mixed metal oxide anodes are the latest technology in the corrosion industry. Mixed metal oxide anodes are lightweight and durable with a very low consumption rate. 

MMO anodes are a mix of metal oxide electrocatalysts. In the presence of a DC voltage source they cause an electrical reaction that generates cathodic protection current. Unlike conventional impressed current anodes that physically consume as part of the cathodic protection reaction (at rates measured in kg/amp-year), MMO anodes are dimensionally stable and do not consume. Instead, they have a long and predictable catalytic life. MMO anodes consist of a thin coating of the MMO catalyst over an inert lightweight titanium substrate and are available in a wide range of shapes and configurations.

Why Cathodic Protection Systems Fail

Waterproof Anode to Cable Connection to protects MMO anode cathodic protection systems
Kynex® Patented, Waterproof Anode to Cable Connection

The most critical component to any cathodic protection anode system is the connection of the anode to the cable that runs back to the power supply. Because the cable is part of the anode system, if it has any nicks or defects or is not water tight, that cable can become part of the anode and will very quickly consume. When that happens, the anode fails. So, with cathodic protection systems it is imperative to have the highest quality connections.

Typically, when a cathodic protection anode system fails, it is not the anode that fails, it is the anode connection that fails. MATCOR has developed a proprietary technology for connecting wire anodes to cable, called Kynex®. Wire anodes are the heart of a lot of our products and this proprietary anode technology is a huge leap forward in the reliability of these connections.

Cost-effective, Reliable Cathodic Protection Solutions

At the end of the day, for our clients, it’s all about delivering value. It’s providing a cost effective solution that’s going to serve them for a very long time. As a designer and manufacturer of cathodic protection anode systems, we are able to specifically address client needs with customized corrosion prevention solutions that provide:

  • Long life
  • Great economic value
  • Superior reliability

MATCOR Products and Services

MATCOR is one of the world’s leading cathodic protection companies. We design, manufacture, install and service cathodic protection systems for clients worldwide. MATCOR provides services to the pipeline, midstream and oil & gas industries, protecting assets such as pipelines, storage tanks, and compressor stations. We also do a lot of work in the power industries, petrochemical, and chemical industries. Anywhere where you have buried steel structures, we are there to stop corrosion.
We encourage you to contact MATCOR through our website where our corrosion specialists and engineers can provide a solution tailored to your needs.

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