Category Archives: linear anodes

Remediation Options for Aging Pipeline Coating Systems

A linear anode system may be an economical alternative to applying a new pipeline coating system or replacing aging pipelines.

by Ted Huck

Introduction: Addressing Aging Pipelines and Pipeline Coatings

aging pipeline coatingExternal corrosion is one of the significant threats facing pipeline operators worldwide. Historically, pipeline owners have employed a two-tiered approach towards mitigating corrosion risks. The primary defense against corrosion has been to apply a pipeline coating system that acts as a barrier, protecting the steel pipe from its environment. Cathodic protection is employed to supplement the coating system by providing protective current to the holidays or defects within the coating system. As with any aging structure, however, time takes its toll – for older pipelines this often results in an older coating system that starts to degrade in its primary function of protecting the pipeline from its environment.

This paper addresses the fundamental issue that many operators will face when evaluating their aging pipelines and pipeline coating systems. That issue is, quite simply, what is the best strategy to remediate an aging pipeline with deteriorating coating systems to maintain compliance with international standards for pipeline integrity. The options are to improve/upgrade the cathodic protection system, recoat the pipeline, or replace the pipeline. Each of these options will be discussed in detail and a decision matrix will be provided to facilitate the operator’s decision-making process.

Pipeline Coating Systems

Coating systems have been used on buried pipelines during the last hundred years and the technology continues to be the subject of significant research and innovation. Pipeline coating manufacturers are continually searching for better coatings to meet the varied needs of industry. Initially, the coatings were simple mixtures of crude pitches and solvents. These early bitumastic/asphaltic systems evolved into engineered coal tar enamel coating systems, which were prevalent into the 1960’s. The introduction of fusion-bonded epoxies (FBE) in the 1970’s quickly captured much of the pipeline market, although polyethylene, polypropylene and coal tar enamels are still used as well. The coatings industry continues to research and develop improved methods of providing more reliable and more economical coating systems.

When evaluating aging pipelines, coating condition is one of the critical issues that must be addressed. The coating provides the primary defense against corrosion and as the coating system ages and deteriorates, then the risks of corrosion increase exponentially. One of the challenges that must be addressed by pipeline owners is properly identifying the type and vintage of the coatings along a given pipeline. In many cases, different sections of pipeline may have different coating systems depending on the age of the pipeline and the standards in place at the time a section of pipe was installed.

Another critical consideration when evaluating aging pipeline coating systems is to identify whether the coating system fails shielding or non-shielding. Coating systems that fail in a non-shielding mode do not inhibit the flow of current making cathodic protection a viable alternative when considering how to remediate these lines. Other coating systems, principally tape coating systems, can fail in a manner that shields cathodic protection current and thus greatly reducing the possible remediation methods available.

Modern, over-the-line survey technologies have proven to be quite effective in evaluating coating quality and finding coating holidays. Technologies such as pipeline current mapping (PCM) which utilize a carrier signal transmitted along the pipeline with a receiver measuring the line attenuation along the pipeline length can accurately pinpoint areas of significant coating degradation even under concrete or asphalt. The information gathered using PCM in conjunction with pipe to soil close interval surveys (CIS) and direct current voltage gradient (DCVG) testing form the basis for identifying critical risk areas along aging pipelines. In-line inspection technologies using smart pigs also provide valuable data regarding coating quality.

Cathodic Protection

Pipeline coating systems are typically augmented by the application of cathodic protection. With a well-coated pipeline, cathodic protection can be economically applied to protect the coating holidays and defects by placing discreet anode beds that distribute current over long distances. In many cases ground beds can be located several kilometers apart and still provide sufficient current distribution to protect the entire pipeline. With some of today’s high technology factory applied coatings, the coating efficiencies are exceptionally high and the groundbed output requirements are very low. These discreet ground bed systems can either be deep anode ground beds or shallow ground beds located some distance off the pipeline.

Several issues must be considered when designing a cathodic protection system. These include coating quality, soil resistivity, available locations for electrical power, ground bed right of way issues, accessibility for maintenance, AC and DC stray current interference, and a host of additional issues. What is critical for aging pipelines is the regular evaluation of the effectiveness of the CP system. Frequently, as pipelines age and the coating quality begins to deteriorate, the CP systems are unable to provide sufficient current properly distributed to meet established cathodic protection criteria. In many cases, simply ramping up the output of the existing system or adding additional ground beds does not prove sufficient to address the problem.

Aging Pipeline Systems

Problem Identification

Aging pipeline systems with deteriorating coating systems suffer from poor current distribution and are characterized by areas of low potentials and exceedingly high levels of applied current density. The challenge with these pipeline systems is controlling current distribution to achieve the prescribed polarization levels consistent with international standards for adequate cathodic protection.

Figure 1 shows a deep well anode system with current output such that some areas are not meeting required off-potentials of -0.85 Volts to meet NACE criteria.

pipeline coating - insufficient cathodic protection

Initial Responses

The typical response to this problem is to increase the overall output of the deep well system (see Figure 2.) This generally does not alleviate the problems of not meeting the off-potential criteria and leads to over-polarizing the piping (potentials greater than -1.2 Volts.) This can result in coating disbondment further exacerbating the problem. The higher output current increases the ground bed’s consumption rate reducing operating life while raising operating costs appreciably. All this occurs without achieving the required levels of polarization to meet cathodic protection criteria.

pipeline coating - increased cathodic protection output

The next step that is taken to fix the cathodic protection current distribution problem is to add additional ground beds to reduce the distance between point sources. This too, proves to be an ineffective solution as the new ground bed provides only limited additional benefit (see Figure 3.)

pipeline coating - additional cathodic protection ground beds

Remediation Options

The problem cannot be economically resolved by the addition of an ever-increasing number of ground beds applying greater and greater amounts of additional current. The pipeline operator is then faced with a limited number of options: recoat the pipeline, replace the pipeline, or install a linear anode cathodic protection system.

Recoating/replacing is the only viable alternative for pipeline systems utilizing shielding type coatings such as tape wrap systems. Recoating costs typically run several hundred dollars per foot in open right of way areas and can be significantly more expensive in congested urban locations (these are ballpark numbers applicable to the United States and can vary significantly.) Recoating, when properly performed, can restore the pipeline coating system to an as new condition greatly extending the service life of the recoated section. The critical issue is to assure that the recoating is executed by an experienced coatings contractor with rigorous quality controls in place. Pipeline replacement is expensive and only performed when extensive third-party damage, significant corrosion or other extenuating circumstances warrant.

An economically attractive alternative to recoat/replace options is to utilize a linear anode configuration in lieu of point anode systems. This option is only viable when the coating system is non-shielding – this would include asphaltic and epoxy type coating systems. The application of a linear anode system typically costs between $20-30/foot in open right of way (again these are general price guidelines and can vary significantly.) In suburban or urban areas, horizontal directional drilling (HDD) can be an effective installation method with minimal surface disruptions. These linear anode systems eliminate the distribution problems experienced by point anode systems; they are in effect an infinite series of point anodes, which provide an optimum current distribution (see Figure 4.)

pipeline coating - linear anode system for optimum current distribution

In addition to confirming that the pipeline coating system is non-shielding and appropriate for the application of linear anodes, the linear anode system design must take into consideration the critical issue of voltage drop and its affect on current attenuation. Voltage drop can have a significant impact on DC power distribution to the linear anode system. Ideally, rectifiers would be located no further than half a mile to a mile apart, however, practical considerations including availability of AC power, right of way issues and other factors can force this to be extended further complicating the system design and affecting the installed cost.

While the design can be complicated by voltage drop considerations, one of the benefits of a linear anode system is that the power consumption is relatively low. Ground bed resistance, as determined by Dwight’s Equation, is significantly affected by anode length and this results in very low groundbed resistance values for linear anode systems relative to conventional ground beds. This makes the linear anode system much more suitable for low wattage power sources such as solar arrays and thermo-electric generators (TEG’s) than conventional ground beds whose wattage could be two or more times that of a linear anode system to achieve the same current discharge.


Aging pipeline systems with deteriorating coating systems present a difficult challenge to pipeline operators. The more the coating deteriorates, the more difficult it is to distribute current further away from the ground bed. The natural response to ramp up the ground bed output does an inadequate job of throwing current further but does result in increased current flow, higher current densities and over polarization near the ground bed further stressing the coating system. Adding additional ground beds also allows more current to be applied to the pipeline, but does not alleviate the current distribution issues. Ultimately, pipeline operators are faced with the choice of recoating/replacing the pipeline, or installing a linear anode system. The flowchart below (Figure 5) provides a decision matrix. Note that aging pipeline systems whose coating systems are determined to be in good condition through indirect and direct examination, require additional investigation to determine why criteria is not being achieved.

Aging pipeline coating decision matrix

For assistance with evaluating aging pipelines or installing linear anode cathodic protection systems, please CONTACT US.

Selecting the Correct Linear Anode for Horizontal Directional Drilling (HDD) Installation

As the world’s leading manufacturer of linear anodes, and the only manufacturer of a linear anode specifically designed for use with horizontal directional drilling installations, we thought it would be appropriate to discuss various anode options for HDD installation.

Can any linear anode be used in conjunction with horizontal directional drilling?

An engineer’s favorite answer to any question is “It depends” and this is certainly the case with HDD installations. The important thing to note is that when attempting to pull a linear anode through a bore hole, there is a chance that the pulling forces on the anode will exceed the strength of the anode and cause the anode to break. Even if the anode does not break completely, stretching of the anode can weaken or damage the internal header cable or anode to cable connections.

There are a lot of variables that can impact the success of any linear anode HDD installation. The short answer is yes, with the right bore hole, any linear anode can be pulled successfully. Conversely, with the wrong bore hole, any linear anode can be pulled apart during installation.

What are the key factors to consider when planning an HDD linear anode installation?

The key factors include a site geotechnical investigation, terrain and route mapping, and bore planning.

Site Geotechnical Investigation

Any discussion about HDD installation planning starts with a site geotechnical investigation. Obtaining a geotechnical survey or as much geological information about the respective jobsite is very important. A great amount of record information is available through sources including:

  • United States Geological Society (USGS)
  • National Geological Map Database
  • Publications of the US Army Corps of Engineers
  • Earth Explorer
  • The National Soil Survey Center (NSSC) a division of the US Department of Agriculture
  • State Departments of Transportation
  • Highway Administrations
  • Original construction records

In addition to record information, site-specific investigations (soil bores and soil sampling) by trained geologists and geotechnical service companies can provide valuable detailed data on the planned bore area geology.  The geotechnical analysis should identify several relevant items including:

  • Soil identification along the bore route to locate rock, rock inclusions, gravely soils, loose deposits, discontinuities and hardpan
  • Soil strength and stability characteristics
  • Groundwater

Local drillers with experience in the identified area can often provide valuable insight based on similar projects in the same area.

Terrain and HDD Route Mapping

Collecting accurate topographical information of the bore route is another critical component in the planning phase.  Terrain and HDD mapping includes determining HDD bore hole entrance and exit locations, identifying and mapping elevation profile changes, ensuring that other utilities are appropriately identified and avoided, assessing the need for traffic control, evaluating any environmental considerations or limitations that might impact the use of drilling muds and hole conditioners.

Bore Planning Software

Several commercial bore planning software tools are available to assist in the planning phase.  These programs utilize the soil and geotechnical data combined with the terrain and route mapping information to provide a graphic visualization of the job helping the driller more accurately “see” and perform the job from start to finish.  These software tools help the contractor select the appropriate drill rig, drill bit type and back reamer based on the anticipated soil conditions and the total bore length.  By choosing the drill stem and length, the desired bore path depth, desired minimum cover, diameter and bend radius of the product being pulled, the software plots a proposed bore pitch, calculates setback distances, figures point to point bore paths, estimates hole volumes and calculates pullback time. The software can also provide a fluid–mixing process map that shows how much mud should be used based on soil conditions, drill unit and tooling used.

If a bore planning software package is not used, field calculations should be performed to appropriately choose the correct drill rig, drill bit and back reamer tooling requirements, desired bore path and quantity and type of drilling fluids to be utilized.

What anode should be selected for HDD installation?

MATCOR’s SPL-FBR™ Linear Anode may be suitable for some HDD installations.

MATCOR manufactures two linear anode products (SPL-FBR™ Linear Anode and the Iron Gopher™) that are both, in the right circumstances, suitable for use in HDD installations.  The installation contractor, along with the client, must carefully select the appropriate anode and the appropriate anode installation methodology.  The two generally accepted methodologies are direct pulling of the anode through the properly conditioned borehole by attaching the anode to the backreamer after the initial pilot hole has been drilled.  The second installation methodology involves pulling an HDPE pipe sleeve into the borehole, installing the anode inside the pipe, and then removing the HDPE sleeve.  The tables that follow are intended to assist the installer in selecting the appropriate anode and installation methodology.  The selection of the appropriate anode type and installation methodology is subjective based on a qualitative analysis.

Iron Gopher® Linear Anode for HDD Applications

TABLE 1 – Linear Anode Application Difficulty

EASY• Less than 200 foot pulling length
• Minimal changes in elevation
• No environmental restrictions on use of drilling muds/hole conditioners
• Installation costs and risks are low
MODERATE• 200-500 foot pulling length
• Moderate elevation change
• No environmental restrictions on use of drilling muds/hole conditioners
• Installation costs are modest and risks are low
DIFFICULT• 500-1000 foot pulling length
• Moderate elevation changes
• Some environmental restriction on use of drilling muds/hole conditioners
• Installation costs are higher and risks are moderate
EXTREME• 500+ foot pulling length
• Extreme or multiple elevation changes
• Restrictive environmental limits on use of drilling muds/hole conditioners
• Critical application with high costs and risks

TABLE 2 – Anode Selection Guidelines

 Linear Anode Application Difficulty 1
Earth LoamsFBRFBR/Iron GopherIron GopherIron Gopher*
Sand/SiltFBR/Iron GopherIron GopherIron GopherIron Gopher*
ClayIron GopherIron GopherIron Gopher*Iron Gopher*
Gravel / CobleIron GopherFBR*/Iron Gopher*Iron Gopher*Iron Gopher*
RockyFBR*/Iron Gopher*FBR*/Iron Gopher*Iron Gopher*Iron Gopher*

*Anode is to be installed in HDPE sleeve that is then removed

1Classifying the linear anode application difficulty using Table 1 is a qualitative analysis and may warrant taking into consideration other risk factors that may be appropriate. In general, the more difficult the application, the more costly the installation component, the greater the case to use the higher pulling strength Iron Gopher and the greater the incentive to use temporary HDPE sleeving to assure the lowest risk installation.
2Soil Types based on the US Department of Agriculture Soil textural classification guidelines. Earth Loams would include the broad range of Sandy Clay Loam, Loam, Silt Loam, and Clay Loam.

What contingency planning is warranted for an HDD installation?

Even with proper project planning and an experienced installation contractor, some consideration should be given to contingency plans if something unforeseen happens during the HDD boring and anode installation.

  • Are alternate bits available if needed to complete the pilot hole?
  • Is a larger boring machine available if needed?
  • If drilling is more challenging than anticipated, do we have ready access to HDPE pipe for sleeving if warranted?
  • Does the project warrant having one or more spare anode assemblies in the event of an anode breakage during installation?

While these risks can be greatly minimized with proper planning, asking these questions before mobilizing to the site can help solve problems more quickly, saving time and money.

For assistance with linear anode selection for HDD applications, MATCOR’s linear anode systems, project management or installation, please CONTACT US.

Tank CP Installation – A Drone’s View!

Easy to Install Tank CP System – No Cutting, No Splicing No Welding

Tank CP InstallationWe’re excited to share this aerial drone view of a recent tank CP installation starring MATCOR’s exclusive Tank Ring Anode™ System. Superior to grid anode systems for tank bottom cathodic protection, the Tank Ring Anode System is factory assembled in concentric rings sized for your tank and shipped ready for quick installation.

  • Impressed current anode
  • New and retrofit tanks
  • Ready to install
  • No field assembly required
  • Superior current distribution
  • USA manufactured

Learn about MATCOR’s complete cathodic protection installation services.

Concentric ring anode configuration ideal for tank bottom cathodic protection

Learn more about this newer method of cathodic protection for tanks and its benefits over the more traditional grid anode system—read the full article at HERE.

MATCOR tank app

For assistance with impressed current anode system design for tank bottoms, project management, installation or field service, please contact us at the link below.

Contact a Corrosion Expert

External Tank Bottom Cathodic Protection

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

Concentric ring anode configuration ideal for tank bottom cathodic protection

Tank Bottom Cathodic Protection Article from NACE Materials Performance

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

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


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

Learn more about Tank Cathodic Protection

Video Demonstrates Cathodic Protection System Installation

Iron Gopher® Impressed Current Linear Anode System designed for horizontal directional drilling (HDD) is installed beneath an above ground storage tank (AST)

Chalfont, PA (May 27, 2015) – MATCOR, Inc. the trusted full-service provider of proprietary cathodic protection products, systems, and corrosion engineering solutions recently released a video showing the installation of the company’s Iron Gopher impressed current linear anode system at the site of an above ground storage tank in Texas.

Trenching to install cathodic protection systems may not be feasible for applications such as cross country pipelines, congested industrial environments and under above ground storage tanks. For these horizontal directional drilling applications, a linear anode with superior mechanical strength is required. The Iron Gopher with Kynex® technology is the only impressed current linear anode designed specifically for cathodic protection in horizontal directional drilling applications.

“As another example, Colonial Pipeline installed several thousand feet of our Iron Gopher® linear anode at an HDD project in NE Georgia,” said Ted Huck, VP of Sales for MATCOR. “With its unique design and greatly increased strength, Iron Gopher is superior to anything seen in the market for cathodic protection in HDD applications.”

Learn about MATCOR’s complete cathodic protection installation services.