Category Archives: Pipeline

At What Distance Does Cathodic Protection Continue to be Effective?

This article explores the answer to a question posed by a student about the length of pipeline protected by a cathodic protection system.


What length of pipeline is protected by a cathodic protection system?

We recently received a question from our website from someone who self-identified as a Student. We love when people ask technical questions and are pleased that students visit the MATCOR website–we have always strived to have a content-rich website to help share CP knowledge. The question is as follows:

“For installed impressed current CP systems with 15 anodes, what would be the approximate radius/length of a 200-mile petroleum metal pipe that would be protected?”

So before diving into the answer, let’s frame this question with an assumption, identify some unknowns and provide a definition.

Assumption

The 15 anodes are part of a single anode bed. The anodes are electrically remote from the pipeline and connect to an appropriately-sized DC power supply (transformer/rectifier, solar power/battery unit, thermoelectric generator, etc.)

Unknown #1: Pipeline Details

Before doing any detailed engineering, there are a few details that must be specified:

  • Pipeline diameter and material of construction
  • Coating type and condition
    • The layout of the pipeline (location of pumping stations, valve stations, and metering stations)

Unknown #2: Soil Conditions

Understanding soil resistivity in terms of location, frequency, and spacing, is critical when designing cathodic protection systems for long-length pipelines.

Definition of Attenuation

a lessening in amount, force, magnitude, or value according to Merriam-Webster

When discussing at what distance cathodic protection continues to be effective along a pipeline, you must consider the attenuation of the CP current. At some point, the current diminishes along the length of the pipeline, becomes insufficient, and can no longer protect the pipeline.

The Answer: Impressed Current CP Systems are Complicated

We can effectively use attenuation calculations for signals generated on a uniform conductor and transmitted through a uniform environment.

In this case, the pipeline is not a uniform conductor; unless it is bare, it is anything but uniform. The coating has less than perfect effectiveness and an unknown number of defects distributed in an unknown manner. The environment is equally non-uniform; soil resistivities change based on location and weather changes. The more non-uniformity, the more inaccurate the results will be for any attenuation calculations.

It is virtually impossible to model mathematically for older pipelines with insufficient coatings. The only effective strategy is to collect data by installing a temporary current source to measure the effective current throw in each direction in multiple locations along the pipeline.

For new pipelines with very good coatings, it is possible to perform some attenuation calculations and empirically determine a reasonable separation distance between anode stations.

The math starts with determining something called the propagation or attenuation constant. To calculate this, take the square root of the resistance per unit length of the structure divided by the leakage conductance per unit length.

In Simple Words…

How hard is it for the current to travel along the pipeline versus how easy it is for the current to jump onto the pipeline?

The smaller this number, the further current will spread. Key factors affecting the attenuation constant include earth resistivity (higher resistivity soils mean further current spread) and coating quality (better coating means further current spread). Armed with this, there are six simultaneous equations that we can use, and that include hyperbolic sine and cosine functions.

Larger, new construction pipeline projects require you to consult with a professional engineer. A brief newsletter article will not adequately cover the mathematical gymnastics involved. We did say that the math is complex.

Well-coated, newer pipelines in moderate to high-resistivity soils can typically be protected for 20+ miles in each direction from an anode bed. Poorly-coated or bare pipelines in low-resistivity soils may require anodes every quarter mile or less.


Need more information? Please contact us at the link below.

Coke Column Guidelines for Deep Anode Systems

OH NO, My Anode Bed is Not Performing!

This article explores a deep anode system gone wrong and guidelines for properly sizing the system coke column.


Earlier this year, we received a call from a pipeline customer with whom we have a solid relationship.

Historically, they used graphite anodes for their deep anode installations. But over the past few years, they began trying the MATCOR Durammo® Deep anode System with success.

When one of their new Durammo anode installations started having strange operating data, it was time to get MATCOR on the phone pronto and figure things out.

MATCOR reviewed the RMU operating data on the wayward installation and found that the data was indeed strange.

The DC output oscillated from periods of robust DC current output to periods of no discernible DC output. We also looked at the deep anode system design and noted the rather short coke column height. The height was only 100 ft of active anode in an 8-inch column. We sent a technician to the site to investigate.

First, we checked the installation and operation of the remote monitoring unit (RMU). Was a poor RMU connection causing intermittent good/bad data? This was not the case.

Next, we checked the continuity of the two anode lead cables. The Durammo® system has a top lead cable and a bottom lead cable. These two cables should be electrically continuous. In this installation, they checked out properly.

Finally, we checked the vent pipe for obvious issues.

Having confirmed that the spurious data was not the result of a poor RMU connection and that the anode system cabling appeared to be intact, we began to suspect that the problem was in the coke column and its immediate environment.

The Culprit? A Small Coke Column.

When we investigated further, we determined that the on-again, off-again readings could be the result of excessive gas generation into a rather small coke column. Both phenomena are heavily impacted by the anode system’s coke column to earth current density.

When the anode system generates more gas than can be exhausted through the vent pipe and diffused through the surrounding earth, gas molecules begin to accumulate between the column particles and at the anode to coke and coke column to earth interfaces. Gas is not electrically conductive, and with enough trapped gas in the column, the system resistance can quickly rise to a point that the anode system cannot overcome this resistance, and the current output drops quickly.

A short-term solution is to turn off the anode system for a period, allowing the gas to disperse inside the coke column and the system should return to normal operation. At least until the gas molecules build up again to block the anode system.

Coke Column to Earth Interface Current Density: The Magic Number

The magic number often cited for anode coke column to earth interface current density is 150mA/ft2. Anything above this number might cause problems. Below this number, history shows that the impact of gas blockage and drying out are generally minimal.

In our example, a 100 ft coke column with an 8-inch diameter hole means that any current output above 31 amps would be pushing that 150mA/f2 threshold.

The 150mA/ft2 current density assumes a high-quality, properly installed coke. This forms a well-compacted column that promotes electronic conduction and limits electrolytic conduction. A well-formed coke column is critical for anode systems using mixed metal oxide anodes, since MMO anodes have an inherently smaller surface area available to be in contact with the column.

It is unclear why the cp system designer recommended a short anode active length for this anode system – other than perhaps the cost saving of using less coke backfill.

While a shorter column does have a positive cost impact, the performance can become an issue, as was the case with this installation. Ultimately, this customer is planning a new Durammo® anode installation for this location with a significantly longer active area.


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

Cased Pipeline Crossings and VCI [Rusty Talks]

Rusty chats with Dean Lioliou, MATCOR Strategic Account Manager and AMPP Central Area Chairman

Cased Pipeline Crossings - Preventing Corrosion
Rusty: Dean, thanks for taking a few minutes to discuss the application of VCI for cased pipeline crossings. First, what is a cased crossing?

Dean: Cased pipeline crossings are a common feature in the industry. They are used primarily at road and rail crossings.

The casing (also referred to as the encasement pipe) is a larger diameter pipe that is designed to take the loading from vehicle or train traffic on the road and absorb/deflect that loading from the carrier pipeline inside the casing.

In addition to the encasement pipe and the carrier pipe there are other key elements to a case crossing. Notably, there are non-metallic spacers that position the carrier pipe inside the encasement pipe, and dielectric end seals that prevent the ingress of water and soil. Finally, there are vent pipes on each end of the casing. These provide a warning and route product to a safe location in the event of a pipeline leak inside the sealed casing.

pipeline casing vents web
Pipeline Casing Vents on each side of a road crossing in Chalfont, PA

There are tens of thousands of these cased pipeline crossings throughout the United States.

Rusty: So, what are the corrosion challenges with cased crossings? What can go wrong?

Dean: Pipeline operators have found that an inordinate amount of pipeline leaks occur at cased crossings. Therefore, operators are actively looking to eliminate these whenever possible.

It is important to evaluate existing casings periodically.
Two mechanisms can adversely affect pipeline integrity at cased crossing locations.

The first is a metallic short. This results from the carrier pipe shifting inside the encasement pipe. It causes a direct metallic contact between the carrier pipe and the encasement pipe.

Shorted casings can significantly impact the cathodic protection system protecting the pipeline. This is due to the encasement pipe drawing CP current away from the carrier pipe. Shorted casings also increase the risk of AC Interference, AC induced corrosion and shock hazards at the above ground vents.

The second casing failure mechanism is related to the integrity of the end seals over time. In many cases, these end seals develop leaks allowing water and soil into the space between the carrier pipe and the encasement pipe. This creates an electrolytic couple. The introduction of these contaminants can lead to accelerated rates of corrosion of the carrier pipe.

Rusty: What are my options if my casing is shorted or the carrier pipe exhibits signs of corrosion?

Dean: You can employ several strategies to address corrosion concerns with cased pipeline crossings:

Excavate ($$$). With this first approach, you dig up the casing and either remove it entirely or repair it. Repairing involves exposing one or both ends to repair the end seals and if necessary, readjust the spacers to clear the shorted condition. This is a construction intensive operation but, in many cases, can restore the cased crossing to an as-new condition.

Fill with Wax ($$). A second approach is to fill the annular space with a high di-electric wax. There are a variety of wax treatment options available. Typically, the wax is introduced through the vents and every effort is made to fill the entire annular space with the wax material.

The wax acts much like a coating covering the carrier pipe and prevents corrosion like a coating system. The industry has found that this is not always a complete solution, since voids in the wax fill can allow pockets of corrosion.

Fill with VCI ($). The third approach is to pump the annular space full of an aqueous gel or powder, or a slurry formulation of corrosion inhibitor material. The corrosion inhibitor is typically a combination of volatile corrosion inhibitor (VCI) and soluble corrosion inhibitor (SCI) that combine to stop corrosion. This method has received industry and regulatory approvals over the past decade and is gaining market share as operators become familiar with the technology and its advantages.

Rusty – How challenging is it to fill a pipeline casing with wax or with VCI?

Dean – Both operations are similar in many respects.

For both wax and VCI filling installations, repairing the existing casing is often the first step. You inspect the end seals and spacers, and where appropriate, remove and replace them.

The interior space between the carrier piping and the casing is flushed clean of dirt and other debris. Once the repairs are complete and the ends are sealed, you calculate the volume of product needed to completely fill the space between the carrier pipe and the casing.

Then the product is prepared according to the manufacturer’s recommendations. Pumping or filling the space is different for each of the type of fill, but both technologies require appropriate equipment and experienced installers.

Wax fills typically use a heated wax product for larger casings. Cold flowing wax can be used on some smaller casings.

For wax fill applications, the space between the carrier pipe and the casings must be completely flushed and cleared out during the repairing of the end seals.

Even with a well-prepared casing, achieving a complete wax fill is very difficult. Voids and gaps are typical.

One published study of 143 wax filled casings found that the average fill was 81%.

For VCI installation plans, the appropriate vapor corrosion inhibitor types and delivery methods are an important considerations. The VCI slurry needs to be mixed properly before being pumped into the casing using the appropriate pumping equipment.

Because VCI applications typically use an aqueous slurry with an experienced installer, VCI is easier to install than a similar wax application. The VCI component is designed to release from the aqueous solution after being pumped into the casing to fill all vapor spaces. Therefore, concerns over gaps and voids are non-existent.

Rusty – What about concerns with bacteria in the space between the carrier pipe and the casing?

Dean – This is an area where the two fill types differ significantly.

For wax filled casings the goal is to completely fill the space with wax displacing or encapsulating any bacteria. However as noted above, areas of incomplete fill or voids in the wax encapsulation can leave space for bacteria to continue to grow.

With VCI, the VCI chemistry increases the pH (9 to 9.5 is typical) inside the casing. This range makes it very difficult for bacteria to grow, while also neutralizing any acid secretions from the bacteria.

Rusty – Can Cathodic Protection help with protecting carrier pipes inside filled casings?

Dean – With wax filled casings, the wax has a high dielectric value and does not allow cathodic protection current to pass.

This prevents the carrier pipe and casing from draining cathodic protection current from the pipeline CP system, but it also provides no protection to the carrier pipe. The VCI gel that sets up is conductive and allows cathodic protection current flow. Some evidence supports the benefit of cathodic protection and VCI working in tandem to prevent corrosion.

Rusty – How can pipeline operators monitor the effectiveness of any cased crossing corrosion solution?

Dean – Most pipelines can be assessed using In Line Inspection (ILI). These pipelines can use smart tools with MFL, and other tools, to assess and monitor corrosion in the carrier pipe with a casing.

For wax filled casings, if ILI is not an option, there are no other good monitoring options. For pipelines that cannot be inspected using smart pig technology, conventional above ground pipeline testing technology is limited.

For VCI filled casings, we employ various technologies in conjunction with VCI including coupons, ER Probes and /or UT probes installed between the carrier pipe and the pipeline casing, to monitor the effectiveness of the VCI in the casing. These are installed and connected to RMUs for remote monitoring, or wired to a local junction box for direct reads during surveys.

Rusty – Any final comments Dean on Cased Pipeline Crossings?

Dean – Cased crossings are a challenge for pipeline owners.

Should you have any additional questions, please reach out to a MATCOR account representative for more information. As a full-service corrosion company, we have extensive experience and a wide range of capabilities including both wax and VCI installations for casings.


Learn about vapor corrosion inhibitors for aboveground storage tank corrosion prevention.


Have questions or need a quote for corrosion prevention materials or services? Contact us at the link below. For immediate assistance, please call +1-215-348-2974.

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Linear Anodes for Hard-to-Reach Places [Rusty Talks]

Rusty and Josh Johnston chat about a recent project and case study involving the use of linear anodes for hard to reach places.


This month, MATCOR exhibited at the AMPP Central Area Conference held in Kansas City. MATCOR’s Mr. Josh Johnston, along with Mr. Chad Farris of Energy Transfer, jointly presented a paper—a case story using linear anodes as a shallow horizontal anode bed installed along two pipelines in central Kansas.

Rusty: Josh, tell us how it felt to finally be in a real-life conference interacting with people in person after the last year and half of cancelled conferences and virtual conferences.

Josh: It is always great to get to interact with our friends and industry colleagues, clients, suppliers and competitors to share information and discuss the challenges that our industry faces—especially given the events of the past couple of years. Presenting this paper was a great opportunity to highlight the use of linear anodes to protect hard to reach areas on older pipelines.

Rusty: Can you describe the problem that you covered in your presentation?

Josh: Energy Transfer had two older pipelines that were not meeting criteria in a rural location. As is typical in a lot of pipeline cathodic protection applications, the pipelines were being protected by impressed current anodes located at road crossings where power was readily available. The roads ran parallel to each other and were located one mile apart. The pipeline traversed these two roads and the area in between was mostly farmland. As a result of the age and coating condition, the shallow horizontal anode beds, located at the road crossings, were not able to project much more than a ¼ mile from each end, leaving approximately ½ mile in the center under protected. This was clearly identifiable in the close interval survey (CIS) data.linear anodes hard to reach places

Rusty: Couldn’t they simply increase the current output of the existing shallow ground beds at each end of the pipeline to drive more current to the center section in between?

Josh: They tried that approach, and it did not work, raising concerns that driving excessive current onto these older pipelines could actually make the situation worse by further disbanding any coating close to the existing ground beds.

Rusty: So where did MATCOR come into this project

Josh: MATCOR proposed linear anodes be installed parallel to each of the pipelines in the area between the two roads. MATCOR developed the very first MMO (mixed metal oxide) linear anodes over 30 years ago and we have the most experience designing linear anode CP systems.

Rusty: So it sounds easy, you take a couple of ½ mile segments of linear anode, trench them in parallel to pipeline and run a couple of long extension cord cables back to the road where there is power.

Josh: Well it does sound easy; however, in practice it is critical that any linear anode design carefully addresses voltage drop, and that the power feed cabling is configured so that each anode segment output is balanced. If this is not engineered properly, you could have a large disparity in the voltage being applied on one end of the anode segment relative to the other end. This would result in a very uneven distribution of current. Discussing the design considerations for the power feed cabling was the primary focus of this presentation.

Rusty: So how did it work out?

Josh: MATCOR was able to use some creative cabling analysis and routing to assure that the voltage difference from one end of an anode segment to the other was no more than a 10% variance. The post installation and commissioning CIS data delivered an outstanding current distribution.

Rusty: Thanks for providing a very quick overview of your presentation—any final thoughts or comments?

Josh: When designed properly, linear anodes can be a real problem-solving solution for older pipelines with current distribution and attenuation issues.

Oh yeah, Kansas City BBQ still rocks!

Have questions or need a quote for linear anodes or installations services? Contact us at the link below. For immediate assistance, please call +1-215-348-2974.

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Pipeline Internal Corrosion Prevention with VCI

MATCOR recently completed a significant pipeline preservation project at a newly constructed pipeline station in West Texas. The project involved injecting Zerust Vapor Corrosion Inhibitor into multiple above ground pipeline manifolds to prevent internal corrosion. The rest of the pipeline remains under construction.

Using vapor corrosion inhibitors (VCI) to protect internal pipeline surfaces is an established technology proven very effective for pipelines post hydrotest.

Preparing for VCI Installation for pipeline internal corrosion prevention

Typically, all pressure-containing piping requires hydrotesting once the piping fabrication is complete. This ensures that there are no faulty welds and that the piping system can handle the design pressure without any leakages.

This fitness for service testing, unfortunately, introduces water and possibly bacteria into the piping. After the hydrotest is completed, and the water is drained, there remains residual moisture (and potentially bacteria) that can prove very corrosive even with efforts to dry the internal surfaces.

For pipeline preservation applications, the VCI chemical is typically mixed with water into a slurry. Then, it is pumped into the piping manifolds using a series of injection pumps and injection ports through hoses from multiple mixing tanks.

How Does VCI Prevent Pipeline Internal Corrosion?

The VCI molecules diffuse and adsorb to the surface, forming a very thin (molecular level thin) protective layer that blocks water and oxygen from reacting with the internal metallic surface of the piping. The molecular level VCI barrier, when properly applied, can last for months and even years as the balance of the pipeline construction is completed.

For this project in West Texas, MATCOR prepared and installed over 24,000 gallons of VCI Solution inside the piping manifolds after their fabrication and testing. Because of the above ground nature of the project, we added methanol (anti-freeze) to the VCI slurry mixture to provide freeze protection for the winter months.

In addition to pipeline preservation projects, VCI is a great product for tanks and pipeline casings.


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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Solar Powered Cathodic Protection Systems—Design Considerations

This article reviews the design of solar powered cathodic protection systems to minimize power requirements.

For most impressed current cathodic protection systems, the use of AC powered transformer/rectifiers are the preferred means of supplying power to the system.

However, where AC power is not readily available, there are other alternative power supply systems available. One of the most common of these are solar powered systems.

Solar powered systems, when properly designed, can provide reliable power for an impressed current cathodic protection system where AC is not readily available. There are, however, some technical considerations that should be taken to assure that the system is cost effective and reliable.

solar powered cathodic protection systems
Solar Powered Cathodic Protection System – Front view showing 8 x 390W solar panels. This 225W solar system powers a deep anode system to protect a remote pipeline.

Design of Cathodic Protection Systems to Minimize Power Requirements

This may seem obvious; however, the typical CP system design is not designed based on optimizing power requirements. For AC powered impressed current cathodic protection systems, the cost of the electrical power required is very low and the overall power draw is not significant. Therefore, CP designers focus on optimizing the overall cathodic protection installation costs and not reducing the power requirements. AC power is relatively low and AC power costs are very low.

But when we are talking about designing a CP system where AC power is not an option, the economic drivers are different.

The cost of the power supply for a solar powered cathodic protection system increases exponentially as the wattage increases. Therefore, investing additional monies on the CP system design to reduce power requirements can have a significant impact on the overall installed cost of the solar power system.

Power is simply defined by the equation W=I2R where W is Power, I is the total design current, and R is the total system resistance.

There are two ways to reduce power requirements for a solar powered cathodic protection system

The first has to do with the required current output for the system. Typically, CP designers are overly conservative in terms of design current. If we believe 20 amps of current is needed, then why not install 40 amps of capacity. If we need more current, we will have that capability by simply turning up the voltage on the rectifier. AC power is not a concern.

However, when considering solar powered CP systems, reducing the maximum current density has a huge impact on the solar system sizing.

A 25% reduction in the system’s current requirements reduces the power requirement by 44%.

For solar powered cathodic protection systems, the design current needs to be scrutinized to make sure that we are not being overly conservative and installing excessive current capacity that is not warranted by the application.

solar powered cathodic protection system installed in Wyoming
Rear view of a 225W solar system with 7 days autonomy designed for installation in Wyoming. The system includes dual 8-battery enclosures, load management controller and cathodic protection controller.

Another important factor in reducing the power requirements is designing the cathodic protection system to reduce anode bed resistance. This can easily be achieved by understanding that anode bed resistance is largely a function of the overall total anode system length. Designing the anode system to increase anode length can drastically reduce anode bed resistance. For deep anode groundbed systems this means spending a little more in drilling costs to extend the active anode length.

This will increase the cost of the CP system, but these additional costs can often generate a much larger savings in solar power system costs. Also consider the use of long length linear anodes for shallow anode bed systems as these systems also have a much lower anode bed resistance.

Multiple Small Systems May Be Less Expensive Than One Large System

Another consideration is the quantity and spacing of CP systems.

Given the exponential costs associated with solar cathodic protection systems as the wattage increases, it often makes more sense to install multiple smaller anode systems, than to try and design one large CP system.

A single 30-amp system with 1 ohms resistance would require a solar power system rated for a minimum of 900-Watt plus a design safety factor. Installing two 15-amp CP systems in different locations can improve the CP current distribution by eliminating some attenuation concerns, but more importantly it also reduces the total wattage of solar power required by 50%. The cost savings of installing 2 x 225-Watt versus a single 900-Watt system can far exceed the incremental costs of having two installations.

Solar Cathodic Protection System Application in Wyoming

The photos above provide some perspective on the size and space requirements of a typical Solar Power system. These photos are from a recent MATCOR installation in Wyoming and are based on providing continuous power for a 15 amp, 1 ohm anode bed. The battery capacity is sufficient to provide 7 full days of autonomy.

Autonomy is the term used for describing how many days without sunlight the system is sized to support using stored solar energy in the battery reserves. As can be readily seen from the photos above, the solar power systems do take up a reasonably large footprint for a relatively small system, further emphasizing the value of minimizing the CP system power requirements

Should you have a need for a Solar Powered CP System, contact your MATCOR representative. MATCOR’s engineering team is available to help you with optimizing the overall system design.


Have questions or need a quote for a solar powered cathodic protection system? Contact us at the link below. For immediate assistance, please call +1-215-348-2974.

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Understanding AC Corrosion Criteria

AC Corrosion Implications for New and Existing Pipelines

Pipeline AC Corrosion
AC corrosion is a threat for both new and existing pipelines.

AC inference can result in significant and rapid corrosion and is a threat that must be considered for both new and existing pipelines. NACE provides a detailed standard practice to specifically address the threat of AC corrosion; however, it is very important for corrosion professionals to understand the guidelines and their implication for pipeline design, monitoring and risk assessment.

Criteria for Control of AC Corrosion

Approved in December of 2017, NACE SP21424-2018-SG “Alternating Current Corrosion on Cathodically Protected Pipelines: Risk Assessment, Mitigation, and Monitoring” provides supplemental guidance for the control of corrosion for cathodically protected pipelines that are subject to influence from close proximity high voltage AC transmission systems. This standard practice expands significantly on the earlier standard SP0177 “Mitigation of Alternating Current and Lightning Effect on Metallic Structure and Corrosion Control Systems” and introduces new criteria for addressing AC Interference for cathodically protected pipelines.

The criteria detailed in Section 6 of SP21424 allow for two means of assuring that effective AC corrosion control has been achieved:

  1. Document that the corrosion rate is less than the common benchmark for effective corrosion control of 0.025mm/y (1 mil per year). This can be achieved using weight loss coupons, corrosion rate probes or through in-line metal loss inspection tools—provided the inspection tool resolution is sufficient to detect small-diameter attacks such as AC corrosion. This approach is great for areas where AC corrosion risk is considered minimal. Essentially this says we don’t expect AC corrosion and we will demonstrate that AC corrosion is not occurring with a modest testing program. In those areas where AC corrosion can be reasonably anticipated; however, a second criteria is provided.
  2. For areas where AC corrosion mitigation can be anticipated, the criteria for effective control is based on reducing the time weighted average AC current density below a specific threshold that varies depending on the DC cathodic protection current density as follows:
    • Where the DC current density is controlled to less than 1A/m2, the AC current density should be controlled to less than 100 A/m2
    • Where the DC current density is not controlled to less than 1A/m2, the AC current density should be controlled to less than 30 A/m2

This first criteria, much like the first criteria for cathodic protection in SP0169-2013, allows for a prove-it type criteria based on documenting that corrosion is not occurring.  

The second criteria, unlike the criteria for cathodic protection, is not based on a measured potential, but is instead based on measuring current density on a time weighted basis. Not just one type of current density must be considered, but instead the criteria requires evaluation of the time weighted average of both AC and DC current densities.

Current Density vs. Polarization

While conventional criteria associated with control of corrosion through the application of cathodic protection is based on shifting potentials on the pipeline, the control of AC induced corrosion is based on limiting current density criteria on a time weighted basis. These requirements are quite different—and when AC corrosion control is a concern this will require a change in how pipelines are monitored, a shift in CP design philosophy in those areas where AC corrosion is a concern and some understanding of the impact of AC mitigation.

Pipeline Monitoring

Pipelines are typically designed to monitor polarization levels with the installation of test stations at frequent intervals to support measuring polarization levels at the test station and to facilitate continuous close interval polarization surveys.  When AC corrosion is a threat, the monitoring provisions need to shift from providing connections to the pipeline for polarization measurements to the installation of coupon test stations to facilitate current density measurements.

CP System Design Philosophy

The primary concern with cathodic protection design is typically making sure that more than enough current is available to ensure minimum polarization levels (either 100mV shift or -850mV off potential) are met along the length of the pipeline. This often means the CP system is over-designed and overdriven—there is little cost associated with over-polarizing some segments of the pipeline to ensure that the entire pipeline meets the minimum requirements. If the pipeline does not meet criteria in some locations, the first step was to push more current over the entire system until those low potential sections also met the polarization criteria. Little consideration is given to concerns with areas receiving too much current.

However, when we overlay the concerns with AC induced corrosion and the desire to control the DC current density below 1A/m2 or face the requirement to mitigate to a much lower threshold for AC current density, it becomes a more challenging CP system design. Now the CP system designer must:

  • Understand the interaction between cathodic protection system design and its impact on AC mitigation requirements
  • Provide provisions to monitor (on a time-weighted basis) both AC and DC current densities
  • Give consideration to being able to intentionally control DC current densities in those AC corrosion risk corridors—this might require additional CP stations to reduce over-polarization, the strategic use of isolation devices to create DC current density control zones, and the use of auto-controlled rectifiers to vary current output to control DC current densities. Improving the control of DC current density can significantly reduce the amount of AC mitigation that might be required.

AC Mitigation

For existing pipelines, the AC mitigation requirements should be based on some actual data on the CP current density in specific areas of concern. Current densities are typically highest closer to a CP station and in areas of low soil resistance. Another factor that can impact current density is the quality of the coating. Poorly coated pipelines have more uniform and lower CP current densities while well coated pipelines may have higher localized current densities because of the small size and infrequent nature of the coating defects. For new pipelines, the AC mitigation designer should be careful to presume that the higher AC mitigation threshold based on controlling DC current density can be applied without consultation with the CP system designer to assure that the design provides for sufficient control of CP current density.

Coupons

Remote monitoring units can record and transmit AC and DC current density information from AC coupon test stations to support the prevention of AC corrosion.
Mobiltex Cathodic Protection Test Station Remote Monitoring Unit

The use of AC test stations with specific AC and DC current density coupons is necessary to ensure that localized conditions do not exist where AC corrosion risk is not properly being controlled. These coupon test stations should be equipped with remote monitoring to allow for data polling at regular intervals to allow for time-weighted averaging of the current density data. Mobiltex recently introduced a new series of Test Station RMUs specifically designed to be installed in a conventional cathodic protection test station. These remote monitoring units can record and transmit AC and DC current density information from AC coupon test stations.

The frequency and location of these coupon test stations is a design issue. It is critical to note that within areas subject to AC corrosion risk, coupon test stations should be installed at all significant “inflection” points where predictive modeling and/or AC mitigation design experience would dictate elevated risk including:

  • Entrance/exit points for HVAC / pipeline collocations
  • Low soil resistivity areas or areas with notable differential soil resistivity changes within the collocation
  • HVAC phase transpositions
  • Pipeline crossovers

Conclusions

The criteria for AC corrosion control are different than those typically associated with conventional cathodic protection to control corrosion.  The requirements for monitoring both AC and DC current densities are interrelated and can have a significant impact on the AC mitigation requirements and on the cathodic protection system design and operation.  Understanding this relationship between AC and DC current density and properly controlling each is critical to properly controlling AC corrosion risk.


For information on MATCOR’s AC mitigation solutions or for assistance setting up testing to prevent AC corrosion, please contact us at the link below.

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Pipeline Corrosion — All You Need to Know

This article provides an overview of pipeline corrosion in the United States, the two categories of corrosion in pipelines and the primary methods of prevention.

Corrosion of Pipelines in the United States

pipeline corrosion prevention

The United States has over 2,225,000 kilometers of pipelines, the vast majority of which are transporting oil and natural gas. No other country comes close—Russia is a distant second with approximately 260,000 km of pipelines.  The US Pipeline network consists of hundreds of public and private companies that own and operate these pipelines within a national regulatory framework managed by the US Department of Transportation’s Pipeline and Hazardous Materials Safety Administration (PHMSA).  While pipelines have proven to be exceptionally efficient and very safe—pipelines are roughly 70 times safer than trucks1 and 4.5 times safer than rail2—the aging network of pipelines continues to be of concern because much of the nation’s pipelines are at least 50 years old and getting older.

Pipeline Corrosion Prevention Mitigates Devastating Failures

Corrosion is one of the biggest problems contributing to leaks and ruptures of pipelines. Corrosion is the natural process where materials made from metal electrochemically react with the environment and deteriorate.  Without proper engineering and preventative maintenance, this deterioration from the natural process of corrosion will result in an increasing frequency of pipeline incidents.  The good news is that with proper pipeline monitoring and maintenance, corrosion is completely manageable. Operators can utilize existing technologies to ensure the integrity of these critical assets and prevent damaging failures.

Two Categories of Corrosion in Pipelines

Pipeline corrosion can be broken down into two primary categories.  Internal Corrosion, which causes approximately 12% of all incidents, occurs on the inside of the pipeline, while External Corrosion, which results in approximately 8% of all pipeline incidents, occurs on the outside of the pipe. 

Pipeline Corrosion Protection Strategies for External and Internal Corrosion

Two primary mitigation strategies are employed to prevent external corrosion of pipelines:
  1. Pipeline coatings
  2. Cathodic protection

When these mitigation strategies are properly employed, monitored and maintained, steel pipelines can last indefinitely. While this sounds simple, pipeline coatings are never perfect and are themselves subject to damage during construction and degradation over time, while cathodic protection is a complex process that requires continuous monitoring and extensive testing, combined with regular maintenance to be effective.

Internal corrosion, in most cases, is a result of contaminants naturally occurring in the product being transported by the pipeline. Common contaminants include oxygen, hydrogen sulfide, carbon dioxide, chlorides, and water.

Many variables can affect the nature and extent of a particular internal corrosion reaction on a pipeline:
  • Contaminant concentrations
  • The combination of contaminants within the pipeline
  • Operating pressure and velocity
  • Pipeline geometry and holdup points
  • Operating temperature
  • Other factors
The primary pipeline internal corrosion prevention strategies include:
  • Controlling or minimizing contaminants prior to transporting them in the pipeline
  • Internal pipeline coatings
  • Injection of corrosion inhibitors
  • Increased frequency of internal pipeline cleaning to remove the accumulation of contaminants

For controlling both external and internal corrosion, regular monitoring and testing programs combined with the appropriate mitigation strategies, are a critical part of any pipeline integrity management program.  When performed properly, corrosion can be effectively controlled, assuring that pipelines remain safe from corrosion indefinitely.

1 propublica.org – Pipelines Explained: How Safe are Americas 2.5 Million Miles of Pipelines?

2 fraserinstitute.org – Pipelines are the Safest Way to Transport Oil and Gas


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

Case Study: AC Mitigation Design Criterion – It Matters

This case study highlights some of the challenges associated with choosing AC mitigation design criterion for a new pipeline construction project.  The specific project consisted of approximately 200 miles of pipeline with another 35 miles of lateral lines and included compressor stations, metering valves and a valve station.  The final approved right of way consisted of 41 identified transmission lines spanning 5 different utility owners.  MATCOR’s scope of work included designing both the CP system and modeling and designing an AC Mitigation system to address the extensive HVAC colocations.

For the AC Mitigation effort, MATCOR performed extensive field data collection along the right of way and MATCOR sent requests for utility operating data for AC Mitigation Design purposes.  After 6 months of requests from the various utilities, the results were inconsistent with some utilities providing only emergency and peak data, others provided seasonal average data and one utility would not provide any data.  Ultimately, modeling was performed based on actual data wherever possible, supplemented by assumptions based on experience from other AC Mitigation designs projects.

While this engineering project was being started, NACE was adopting its latest version of SP 21424-2018-SG “Alternating Current Corrosion on Cathodically Protected Pipelines: Risk Assessment, Mitigation, and Monitoring”.  This latest version presented an updated criteria standard based on DC Current Density.  Basically, if you can assure that the CP Current Density along the length of pipeline is controlled to below 1 A/m2 then you can tolerate a much higher AC Current density threshold of 100 A/m2 requiring less AC mitigation.  If you are unable to control CP Current to the 1 A/m2 level, then the acceptable AC current density drops to a much lower 30 A/m2 threshold often requiring more extensive mitigation.

For the initial AC modeling effort, MATCOR based the AC Current Density limit to the lower, more stringent, 30 A/m2 criteria that assumes that the CP Current Density could not be controlled to below 1 A/m2.  The modeling, given all the assumptions that we had to make, came back with:

  • Numerous locations where Step and Touch Potential concerns required mitigation
  • No concerns over fault current given the separation distances and fault currents presumed
  • A very significant mitigation requirement to bring the induced current densities below the 30 A/m2 criteria including approximately 81 miles of parallel mitigation and 8 x 600ft deep grounding wells.

These results warranted additional review given the extensive AC Mitigation requirements from the initial modeling.

After some sensitivity assessments, a second modeling effort would be taken based on some revisions to the HVAC operating data based on updated information and some revisions to the input assumptions.  This new modeling effort would also be run using 50 A/m2 as the AC Current Density limit.  Additionally, based on input from operations, it was determined that all deep grounding wells would be limited to 200 ft depth.  The new modeling effort resulted in a significant reduction in AC Mitigation required eliminating almost 50 miles of parallel mitigation.

The dual modeling efforts showed that there were numerous locations that were only slightly above the 30 A/m2 threshold but below that of 50 A/m2.  In those areas, the owner opted to install additional monitoring systems but forego the initial installation of AC Mitigation and instead focus on those higher risk AC Interference areas by installing AC Mitigation.

This case story highlights the role of AC mitigation design criterion selection and the complexity around the current criteria that correlates CP Current Density levels, which are not typically controlled, to the AC current design threshold to mitigate the induced corrosion AC Interference risk.  With judicious design decisions and a healthy amount of monitoring systems, there is significant value in your modeling criteria.


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

PHMSA Mega Rule Update

PHMSA Mega Rule
The PHMSA Mega Rule significantly impacts the US pipeline industry.

It has finally landed – the PHMSA MEGA rule has hit and will have a tremendous impact on the US pipeline industry, adding significant scope to the current pipeline integrity management requirements.  Some of the industry impacts that the PHMSA MEGA rule will have include:

  • An approximately 20% increase in the number of regulated pipelines in the United States
    The exact impact depends on some additional details not yet released; however, it is very clear that the addition of 20% more regulated pipelines will have a significant impact on an industry where highly qualified integrity professionals and related services are limited in supply and the industry is already struggling to meet demand.  These additional pipelines will require significant integrity resources.
  • Expedited reporting requirements
    The time restrictions for implementing the new rule have been accelerated, with initial reporting requirements in July, 2020, less than a year away. Time to comply with these regulations has been reduced 20% from the initial draft order timeline.
  • Increased cathodic protection requirements
    Many pipelines that previously were not regulated and have not had proper CP will now require a properly designed, maintained and tested cathodic protection system.

The PHMSA MEGA rule will be a challenge and an opportunity for MATCOR as midstream pipeline operators will be looking for partners to help them address these new regulations.  MATCOR provides a full range of cathodic protection and pipeline integrity services including:

  • Field Integrity Surveys
  • ECDA
  • CP Assessments
  • CP Design
  • CP Installations
  • Annual Testing Services
  • Test Station Installations
  • Remote Monitoring
  • CP Maintenance
  • AC Interference

It is going to continue to be exciting times in the midstream market.

Learn more about PHMSA regulations.


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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