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Category Archives: Corrosion

Corrosion, Pipeline, Pipeline Integrity

Pipeline Corrosion and Prevention—A Comprehensive Guide

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Pipelines are a crucial part of the US infrastructure, but they face a serious challenge: corrosion. This guide explains pipeline corrosion, the different types, and how to prevent it to avoid costly and dangerous failures.

The Problem of Pipeline Corrosion in the United States

pipeline corrosion prevention

The United States has over 2,225,000 kilometers of pipelines transporting oil and natural gas. No other country comes close—Russia, in second place, has approximately 260,000 km. These pipelines are owned and operated by hundreds of companies and regulated by the US Department of Transportation’s Pipeline and Hazardous Materials Safety Administration (PHMSA).

Experts consider pipelines very safe—roughly 70 times safer than trucks1 and 4.5 times safer than rail2. Many pipelines are at least 50 years old. This increases the risk of corrosion, which threatens their safety and reliability..

Why Pipeline Corrosion Prevention is Critical

Corrosion is a natural process where metal electrochemically reacts with the environment and deteriorates over time. Without regular maintenance and monitoring, this can lead to leaks or even pipeline ruptures.

The good news? Corrosion is completely manageable. By using the right technologies and maintenance practices, pipeline operators can manage corrosion and prevent failures.

Two Types of Pipeline Corrosion

Two primary types of pipeline corrosion exist.

  1. External Corrosion: Happens on the outside of the pipeline and causes approximately 8% of incidents.
  2. Internal Corrosion: Occurs inside the pipeline and accounts for approximately 12% of all incidents.

How to Prevent Pipeline Corrosion

Several strategies exist to prevent corrosion, depending on whether it occurs internally or externally.

Preventing External Corrosion of Pipelines

The two most effective methods to prevent external corrosion are:

  1. Pipeline coatings: These create a protective barrier between the pipeline and its environment. However, installation can damage them, and they can wear out over time.
  2. Cathodic protection systems: This method uses electrical currents to prevent the metal from corroding and requires frequent testing.

These methods work well, but require regular monitoring and maintenance to remain effective.

Preventing Internal Corrosion of Pipelines

Internal corrosion occurs when contaminants in the oil or gas being transported react with the pipeline. Common contaminants include oxygen, hydrogen sulfide, carbon dioxide, chlorides, and water. The severity of this corrosion is influenced by several factors, including:

  • The concentration of contaminants
  • The combination of different contaminants within the pipeline
  • Operating pressure and flow velocity
  • Pipeline design and holdup points
  • Operating temperature

To effectively manage internal corrosion, operators must address these variables by using several key strategies:

  • Reducing contaminants before they enter the pipeline, minimizing the likelihood of corrosive reactions.
  • Applying internal pipeline coatings to create a protective barrier inside the pipeline.
  • Injecting corrosion inhibitors to slow down or halt the chemical reactions that lead to corrosion.
  • Frequent internal pipeline cleaning to remove the build up of contaminants before they can cause damage.

By closely monitoring these factors and implementing the right prevention methods, operators can control internal corrosion and maintain pipeline integrity.

Keep Your Pipelines Safe from Corrosion

While pipeline corrosion is a serious issue, it can be effectively managed through proper monitoring and preventative measures. Whether facing internal or external corrosion, a strong integrity management program is essential to lowering the risk of failure.

Ensure your pipelines are fully protected from corrosion and explore our expert cathodic protection solutions and other comprehensive services.

Looking for a more in-depth explanation of cathodic protection? Learn more about cathodic protection systems.

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.

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Corrosion, Pipeline, Pipeline Integrity

Cased Pipeline Crossings and VCI [Rusty Talks]

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Rusty chats with Ted Huck, Director of Manufacturing and Quality Assurance.

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

Ted: 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?

Ted: 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?

Ted: 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?

Ted: 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?

Ted: 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?

Ted: 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?

Ted: 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 on Cased Pipeline Crossings?

Ted: 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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Corrosion, VCI - Vapor Corrosion Inhibitors

Casing Repair & VCI Case Study

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Recently, at the AMPP Association for Materials Protection and Performance Big Sky Section meeting, MATCOR’s Ted Huck presented a case study featuring the casing repair of a high-pressure natural gas pipeline running under railroad tracks and feeding into a power plant.

Following the repair, a vapor corrosion inhibitor (VCI) is installed to prevent corrosion.

Click on the presentation below to check out the development of a casing repair with VCI project scope, removing the short, sealing the casing, and installation of the VCI product through the vent pipe.

big-sky-pres

Related Articles:

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

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Cathodic Protection, Corrosion, Solar

Steel Pile Corrosion: Protecting Our Solar Infrastructure

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The US is constructing an increasing number of very large solar power generation farms, which brings about the question–what about corrosion? This new article explores solar farm steel pile corrosion. Do the buried galvanized steel piles supporting solar arrays meet service life requirements?

How do you protect the buried galvanized steel piles that support solar arrays from corrosion?
Galvanized steel pile corrosion can occur in as little as five years.

Big Footprint

We continue to construct an increasing number of solar power generation facilities. The United States plans even more as it continues to pursue policies encouraging renewable energy development.

The economies of scale make these facilities more competitive with other electrical generation technologies. These utility-scale solar farms have a capacity of anywhere from 1 MW to 1000+ MW. One feature of these solar farms is their physical footprint. The average solar farm requires 6-8 acres of land to support the tens of thousands of PV cells necessary to generate electricity at this scale.

For example, the Mammoth Solar Farm project in northern Indiana, once completed, will have a generation capacity of 1650 MW. And it will cover an area of 13,000 acres and use more than 2.85 million solar panels. This is the largest project in the US and should become fully operational in 2024.

Steel Piles That support Solar Arrays: What About Corrosion?

Given these facilities’ size, cost, and anticipated service life, a fair question to ask during the design phase is: what about corrosion? Specifically, the buried support structures that hold the solar arrays in place.

Typically, construction crews drive or screw galvanized steel piles into the soil to support the solar panels’ frames. Galvanized steel piles generally have a good service life in most environments for this application. However, as with all steel structures, they are subject to corrosion. Eventually, steel pile corrosion will adversely affect the support structure’s integrity.

Therefore, solar farm operators should consider the impact of corrosion on the service life of the galvanized piles during the project’s design phase.

Start with The Piling Details

The first step in the corrosion assessment process is to know your piles.

Any sizable solar farm project will require thousands of steel piles. The type of pile and the galvanizing thickness significantly impacting the project cost.

Unfortunately, structural engineers often do not consider corrosion when sizing the piles. They are keenly aware of loading concerns and select the pile to use based on a detailed soil load-bearing analysis and wind load analysis. They consider how big and how deep the piles need to be to support the predicted mechanical loads. This is often the only consideration. As a result, any conversation regarding corrosion is often relegated to – don’t worry, the piles are galvanized.

How Corrosive is the Environment?

But even galvanized piles are subject to corrosion, and in a highly corrosive environment, that service life might be much lower than expected. Therefore, additional corrosion mitigation measures, such as cathodic protection, might be warranted in some cases.

Given the massive footprint covering hundreds to thousands of acres these sites require, a thorough corrosion assessment for the entire area is warranted.

Typically, Geotech firms are contracted early in the project to perform detailed soil testing across these sites. This testing provides the requisite soil load capacity data to design the structural supports properly. While performing the site-wide testing, these firms will often perform some representative soil resistivity testing. While these sample soil resistivity tests may indicate the soil’s corrosiveness, they are often insufficient to evaluate correctly.

MATCOR Study: A Soil Testing Analysis

In one study performed by MATCOR, a comprehensive soil testing analysis found that much of a solar farm was in moderately corrosive soils. Still, a significant part of the facility was in very corrosive soils. In addition, the service life calculations varied significantly for the piles depending on their location within the solar farm. Estimated life ranged from 17 years to 30+ years.

Another factor in the service life calculations is the anticipated degradation of the piles during installations. The impact on the zinc coating can vary significantly depending on the soil characteristics.

MATCOR provides comprehensive soil resistivity testing services.

Steel Pile Corrosion: How Long Will the Steel Piling Last?

The first phase of the service life of driven steel piles is the outer zinc layer of the galvanized steel pile. Zinc acts as both a coating and a galvanic anode. As the zinc layer is consumed, the underlying steel substrate is exposed. Therefore, the estimated service life, in simple terms, is the anticipated service life of the zinc coating plus the expected service life of the steel substrate.

We define the service life for solar structural galvanized steel piles as some allowable percentage thickness loss before compromising the pile’s integrity.

There are a lot of factors that affect the pile’s corrosion rate, including:

  • Presence of copper grounding bonded to the pile
  • Degradation of the zinc coating during the driving of the pile
  • Differential soil resistivity strata
  • Differential oxygen levels/aeration
  • Location of the water table in the area of buried piles

One of the biggest drivers of accelerated corrosion for piles is the presence of copper grounding. When steel piles are connected to a copper grounding grid, their service life can be significantly reduced as the zinc coating layer and the underlying steel substrate act as galvanic anodes. This can be very impactful in low soil resistivity environments.

Significant Steel Pile Corrosion Can Occur in as Little as Five Years

In some extreme cases, corrosion of the galvanized piles can be structurally significant in less than five years of service. In most cases, the service life in corrosive environments can be anywhere from 10-25 years of service. A service life of more than 50 years in low-corrosivity soils might be achievable.

Solar farms are a growing part of our electrical generation portfolio and will continue to see substantial investments in the next several decades. Given the footprint and cost of these facilities, design engineers should seek corrosion assessments from qualified corrosion engineering firms such as MATCOR to confirm that the piling systems used to support the solar arrays meet the facilities’ service life requirements.

If you need assistance with galvanized steel pile corrosion protection, please contact us. We will respond by phone or email within 24 hours. For immediate assistance, please call +1-215-348-2974.

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Careers, Corrosion, Corrosion Industry News, MATCOR

Training the Next Generation of Corrosion Technicians

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MATCOR hiring corrosion technicians; entry level cathodic protection jobs.

Entry Level Cathodic Protection Technician Opportunities

The Cathodic Protection industry is a great niche that offers entry-level opportunities with tremendous long-term advancement potential. Unfortunately, we do not have enough Cathodic Protection technicians for the short, medium, and long term.

It’s not a sexy industry, but it has great-paying jobs located in the US. Once you are trained and have a few good years of experience, entry level cathodic protection jobs enable you to pick where you want to live, enjoy tremendous job security, and gain new opportunities.

A growing regulatory environment, aging pipelines that require more frequent monitoring and servicing, aging of the existing CP technician workforce, and decades of failing to attract new people in sufficient numbers has led to a significant shortage of CP technicians.

The Great Resignation

You have probably heard about the Great Resignation, an ongoing economic trend in which employees are resigning from their jobs. According to a recent Times article, Ryan Roslansky, the current CEO of LinkedIn, defined this differently as the Great Reshuffle. We have seen a 54% increase in the number of people changing their job descriptions. For Gen Z, that increase is 80%.

The bottom line is that workers, especially younger generations, are quick to change jobs as they attempt to find their interests in the world. These changes are occurring in the high-paying technical and industrial jobs as well.

Looking for a Great Opportunity?

So, if you are looking for your next job and hoping to find something that can lead to a meaningful career, look no further. MATCOR is always looking for eager young men and women who have an aptitude for hands-on mechanical work and sound math and science skills to fill entry level cathodic protection jobs.

Travel and Training!

Early in your career, you can expect regular travel as you gain more experience – about 75% of the time. We will also provide the requisite training. Many of our technicians advanced within MATCOR or took an opportunity elsewhere to work for pipeline companies as area technicians where the travel requirements are significantly less.

If you are interested in a challenging, rewarding career in an industry where the opportunities are endless, please contact MATCOR. We are hiring! Learn more about MATCOR careers or click below to apply for open positions.

Apply Today

Corrosion, Storage Tanks, Water Treatment Facilities

Corrosion Control for Water Treatment Facilities

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We recently received an inquiry on our cathodic protection FAQ asking about “the best corrosion control protection for above-ground steel tanks treating wastewater.” Well, corrosion control for water treatment facilities is such an interesting and relevant topic that it warrants an expanded response, so here goes.

Wastewater treatment facilities generally have many tanks storing and processing wastewater through multiple treatment stages. These tanks and vessels are subject to corrosion, and there are a range of strategies to extend their service life.

Corrosion control for water treatment facilities' tanks and vessels

Corrosion Protection Strategies for Water Treatment Tanks and Vessels

These strategies fall into four broad categories: material selection, chemical treatment, coatings, and cathodic protection.

Wastewater Tank and Vessel Material Selection

From a material selection perspective, most wastewater treatment vessels are carbon steel. However, some chemical wastewater treatment facilities may require more “exotic” materials early in the treatment process due to the wastewater feed material.

Once the wastewater feed material has been treated and/or neutralized, the remaining process tanks and vessels are likely to be carbon steel construction.

Corrosion Protection via Chemical Treatment

The next broad category of corrosion control strategies is chemical treatment. While chemical treatment is an integral part of the wastewater process, specifically in terms of pH neutralization and chlorination processes, the chemical treatment performed during the treatment of wastewater is not typically intended to control corrosion.

One area where chemical treatment might be a viable corrosion control strategy is with the use of vapor corrosion inhibitors (VCIs) to protect the underside of steel storage tanks.

Coatings for Corrosion Control of Water Treatment Tanks and Vessels

The appropriate selection and application of coatings is a key corrosion control strategy for wastewater treatment facilities.

Coatings are particularly effective in protecting carbon steel structures including above ground piping, atmospheric external tank shells, wetted internal tank walls, submerged steel structures, and many other structures.

Coatings, however, are not perfect and they have a finite life. For structures that are easy to access, inspecting and re-coating are often the sole means applied to protect against corrosion.

Cathodic Protection

The final corrosion mitigation strategy that can be effectively employed to protect wastewater tanks and process vessels is the use of cathodic protection.

Cathodic protection can be used to protect bare steel structures, or in conjunction with coatings.

There are two basic types of cathodic protection, galvanic (often termed sacrificial) and impressed current. Some typical cathodic protection applications in wastewater treatment facilities include protecting the soil side bottoms of large above ground storage tanks and vessels, and protecting the internal wetted surfaces of tanks and process vessels including rotating equipment such as rakes and wiper arms.

MATCOR has extensive experience designing, supplying and installing cathodic protection systems for wastewater tanks and process equipment, including several proprietary impressed current anode systems that are especially well suited for these applications.

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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Anodes, Corrosion

Preventing Corrosion of Near Shore Structures

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Rusty Talks about the MATCOR PW® anode, which protects near shore structures in water from the effects of corrosion…

“It’s summertime and our thoughts go to water—backyard swimming pools, kayaking along rivers, boating on lakes, and lounging around the ocean.

Well, here at MATCOR, when we think water, we think about the very versatile MATCOR PW® ANODE system.

Check out some details below and contact our team for assistance.” — RUSTY

Corrosion Prevention of Structures in Water

The MATCOR PW Anode is ideal for corrosion protection of docks, piers, pilings and more.

The PW anode is a lightweight, long life anode system that can be installed to protect a wide range of near shore marine structures from corrosion, including:

  • Docks
  • Piers
  • Jetties
  • Sheet pile walls
  • Wind turbine jackets and monopiles
  • Stationary floating vessels such as riverboat casinos and historic naval vessels

The PW anode system consists of a custom fabricated PVC anode housing and a MATCOR Mixed Metal Oxide anode assembly.

The PW Anode can be supplied with a lowering rope, eye bolt assembly, and optional weight assembly for hanging.

This versatile anode is available in a wide range of sizes and current outputs or can be custom designed for a specific application’s requirements.

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

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Corrosion, Corrosion Industry News, Storage Tanks, Tank Bottoms

VCI for Tank Bottom Protection

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

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

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

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

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

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

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

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

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

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Corrosion, MATCOR

And the winner is – RUSTY!

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The Jolly Green Giant, the Pillsbury Doughboy, the Geico Gecko, Ronald McDonald, the Energizer Bunny… please all step aside and make room for the world’s newest, and soon to be famous, icon, RUSTY the MATCOR Chili Pepper spokesperson.

“My mission is to protect the world’s infrastructure from the evil scourge of corrosion.”

—RUSTY

RUSTY is not trying to sell vegetables, biscuits in a can, hamburgers or batteries. No, RUSTY’s mission is to protect the world’s infrastructure from the evil scourge of corrosion. We look forward to RUSTY’s corrosion adventures.

A big shout out to Ted Morris of Nustar Energy, a 38-year veteran of the pipeline industry who has spent the last 29 years in Corrosion Control. Ted Morris was the grand prize winner of our “Name MATCOR’s Icon Contest”. The contest garnered a tremendous number of very thoughtful entries, but RUSTY was an immediate favorite of the selection committee. Ted will be retiring in the near future, having served the industry well, and we at MATCOR dare say that RUSTY may prove to be one of his great legacies. Thanks Ted!

A very close second place in the naming contest goes to Fernando Villamizar Ariza of Ingacor Colombia, with his name entry of “Cowboy Rust”. Thank you Fernando!

There were many honorable mentions and we thank everyone for the effort and creativity.

AC Interference, Corrosion, Pipeline

Understanding AC Corrosion Criteria

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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.

Contact a Corrosion Expert

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