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.
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
Annual Testing Services
Test Station Installations
It is going to continue to be exciting times in the midstream market.
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.
This article provides a brief overview of the important role of cathodic protection remote monitoring systems in today’s pipeline operations. We will cover the CP equipment and features that can be monitored and how data is transmitted.
Modern pipeline operations face increasing pressures to incorporate advanced technologies to:
Drive down operating costs
Improve system reliability
Comply with regulatory requirements
Monitor the health of their pipeline networks
Monitor the critical systems that are integral to pipeline integrity
The use of advanced cathodic protection remote monitoring systems has become a critical component in the pipeline operator’s toolbox to meet these challenges.
CP remote monitoring (and control) has proven to be a reliable and cost-effective means to oversee the proper functioning of cathodic protection systems and AC Mitigation systems that are critical to assuring pipeline integrity and the proper protection against pipeline corrosion. Where operators in the past would have to send technicians out to remote pipeline locations to collect snapshot data on a frequent basis, the smart deployment of cathodic protection remote monitoring systems can provide continuous real time data that can be accessed from any cloud connected handheld or desktop device. Additionally, a remote monitoring unit for cathodic protection is well-insulated; this construction affords them excellent protection against lightning strikes. The financial, environmental and safety impact of eliminating hundreds of thousands of windshield hours is staggering across the vast pipeline industry.
Cathodic Protection Remote Monitoring – What can you monitor?
Cathodic Protection Rectifiers – the installation of RMUs with built in interruption capabilities should be standard on all new pipeline installations and retrofitting older units can provide significant cost savings and improve CP system reliability.
DC Cathodic Protection Test Stations – with today’s continuing advances in remote monitoring technology and costs, it is quickly becoming very cost effective to install remote monitoring units on all test stations. When combined with the ability to easily interrupt all of the influencing current sources on a pipeline, regularly scheduled testing of the CP system can be performed quickly and at virtually no cost.
AC and DC Coupon Test Stations – the latest NACE guidelines for AC Mitigation (SP21424-2018*) emphasize that the localized DC current density has a significant impact on AC corrosion and gathering data on both AC and DC current densities at areas of interest/risk is critical to a successful AC Mitigation strategy. Effectively doing so requires the ability to monitor these values over time as AC loads vary during the day and seasonally.
Critical Bonds – monitoring the effectiveness of critical bonds is necessary (and in many cases required by local regulatory bodies) to assure pipeline integrity.
NACE SP21424-2018 “Alternating Current Corrosion on Cathodically Protected Pipelines: Risk Assessment, Mitigation, and Monitoring”
How does a CP remote monitoring system transmit data?
Today’s operators have a range of options to assure that remote monitoring systems can regularly communicate data to their host data collection systems. The availability of conventional cellular networks combined with various commercial satellite systems assures pipeline operators of the ability to communicate with devices in even the remotest of locations. Your monitoring system provider can work with you to select the appropriate communications technology for each cathodic protection remote monitoring unit (CP RMU) location.
In addition to choosing how the communication is to occur, another key factor to consider is whether the communications are to be one way (monitoring only) or two-way (monitoring and control). For test station applications where data collection is the goal, one way transmission of the monitoring unit’s data is all that is required. For rectifier units, the ability to control the system output and/or the ability to initiate an interruption cycle for close interval surveys or test station polling purposes necessitates the ability of the remote monitoring unit to receive and act on communications as well as to transmit data.
Software Interfaces – Installing the appropriate CP RMU hardware is just one step in implementing a successful remote monitoring (and control) program. The data must be collected, stored, and accessible for the operator. Sophisticated cloud-based interfaces have been developed that incorporate critical features including firewall-friendly, password protected internet browser access. These systems allow for multiple client user accounts with configurable permission levels and automated alarm and status information including email and text alerts for designated alarm conditions.
In summary, the use of remote monitoring technology is a key component to the successful operation of any modern pipeline integrity management program. While MATCOR has extensive experience with all of the major RMU manufacturers, we have recently teamed up with Mobiltex, a leader in the field of remote monitoring, to bring state of the art technology to the pipeline and cathodic protection industry. Mobiltex’s CorTalk® line of CP RMU units combined with their CorView interface offers all the features necessary to implement a comprehensive, cost-effective, and highly robust cathodic protection remote monitoring program.
Please contact us at the link below if you have questions about cathodic protection remote monitoring, or if you need a quote for services or materials.
Pipeline cathodic protection design for new pipelines may appear to be a rather easy task for anyone with a basic understanding of cathodic protection. However, as with all design efforts there are a wide number of factors that need to be considered for a sound design that meets generally accepted industry practices.
This article highlights 12 things that the pipeline cathodic protection system designer needs to consider when developing a CP system design. This is not intended to be a comprehensive list as every project has its own unique challenges, but these 12 items would all typically have to be addressed during the design phase. It is assumed that the basic pipeline information is already available to the CP designer including pipeline length, pipeline routing and pipeline characteristics (material, wall thickness, coating type, operating temperature, etc.). Armed with this basic information the CP designer should also consider the following in their design efforts.
12 Things to Consider for New Pipeline Cathodic Protection Design
Soil Resistivity is a factor in many of the design calculations and assumptions (e.g. current requirement, anode resistance, attenuation, AC interference, etc…) Actual soil resistivity data should be collected along the proposed route. Learn about soil resistivity testing.
Design current requirement is selected based on the soil type(s) using some accepted industry guidelines taking into consideration the coating manufacturer’s recommended coating efficiency or other industry accepted guidelines. Additional current requirements for mitigating interference currents should be considered based on the designer’s experience.
Distribution of CP System Stations should take into consideration the total current required, the pipeline attenuation characteristics, the availability of power for impressed current cathodic protection systems, varying soil regimes, isolation valves and other factors to determine how many, what size and where each CP System will be located.
Foreign pipelines and other DC interference sources should be evaluated as part of the CP system design efforts and generally warrant immediate mitigation measures or testing and monitoring provisions for observation and assessment.
AC Interference assessment should be performed to determine if there are one or more high risk categories for AC Interference. Should the initial assessment confirm that there is potential for AC Interference an experienced AC Interference and Mitigation specialist would typically use sophisticated AC modeling to assess the risk and propose appropriate mitigation. From a CP perspective, there is a relationship between DC current density and AC induced corrosion risks where too much cathodic protection accelerates the AC induced corrosion rate so care must be exercised by the CP designer to avoid high DC current densities in AC risk areas.
CP Station design includes the type of anode configuration, anode selection, installation methodology, etc… The CP designer will typically provide detailed Bill of Materials as well as CP System issued for construction drawings and construction details showing the location of equipment and providing installation instructions.
Isolation of MLVs and Stations is a key design criterion that impacts the pipeline cathodic protection system design. Some owners are strongly in favor of isolation of MLVs and Stations from their main pipeline while other owners prefer not to isolate and have to maintain isolation and instead require the that CP system be sized to account for losses to current drains.
Power supply type, sizing and selection is another of the decisions that is determined by the CP designer with consideration given to the pipeline owners specifications and preferences. For most pipeline applications, impressed current systems are typical and these require a DC power source. Electrical AC to DC power supplies (“rectifiers”) are the most common power supply but for remote areas with limited AC power availability, alternate power supplies such as solar, wind, fuel cells, thermo-electric generators or other sources may be required.
Terminal piping is often associated with a new pipeline construction project and the pipeline CP system designer must often provide a supplemental design specifically for the terminal or station piping, or account for these in the primary pipeline CP system design
Use of temporary CP systems is often recommended when permanent power may not be available for some time. These typically involve the installation of galvanic anodes strategically along the pipeline.
Provisions for testing and monitoring are critical components to any successful pipeline CP system design. This often includes the use of remote monitoring systems for all of the system power supplies, specialized test coupons for AC and DC Interference, and numerous cathodic protection test stations placed at the appropriate strategic locations to be able to properly test and monitor the CP system performance.
As noted earlier, this is far from a comprehensive list of all of the factors for a specific pipeline CP System design. Every project may have its own unique challenges; however, the 12 items listed above represent a great starting point for any new pipeline cathodic protection system design challenge.
Please contact us at the link below if you have questions about pipeline cathodic protection design, or if you need a quote for services or materials.
MATCOR provides a full range of AC Mitigation capabilities including AC Modeling and Design engineering services, supply of our proprietary Mitigator® engineered AC grounding system, and an entire construction services organization capable of a wide range of AC Mitigation installation services. Two current projects highlight our construction service capabilities with regards to AC Mitigation. The first project involves several miles of zinc ribbon installation for an AC mitigation system in a congested suburban and urban environment using horizontal directional drilling (HDD) equipment. The second application is in a highly rocky environment in West Texas that requires the use of specialized rock trenching technology for zinc ribbon installation.
Zinc Ribbon Installation Using HDD in a Congested Environment
This project in northwestern Ohio involved the zinc ribbon installation over several miles using one of MATCOR’s in-house horizontal directional drilling crews. The project required horizontal directional drilling to minimize surface disturbances due to the congested area.
With any typical AC Mitigation installation there are numerous precautions that must be taken to assure a safe installation. This starts with a thorough pre-construction safety review to develop the project site-specific health and safety plan. Each crew member participates in a daily safety meeting to review the day’s planned activities and address all safety concerns in advance of performing any work. Each crew member is required to have the appropriate operator qualifications and site-specific safety training as identified by MATCOR and the pipeline owner.
Prior to any other construction activities, the first task is to perform a thorough line locating including potholing (excavation of the top of the pipe). This is to physically assure that the location of the pipeline(s) being mitigated is accurately marked to avoid any risks associated with construction activities in close proximity to the pipeline.
Once the pipeline has been physically located and properly flagged, each individual bore must be planned. The route of the bore is assessed prior to boring activities commencing. The bore planning includes:
Identifying entry and exit points
How the bore is to be tracked
Special precautions that might be needed to maintain the bore during the ribbon installations
How the cuttings will be captured, stored and removed
As with any construction project, logistics and project management are key to the successful execution of the project. Working in conjunction with the owner and their designated project inspector to assure that the work is performed safely and in accordance with the AC Mitigation design requirements. For the project in Ohio, some additional complications included difficult weather conditions and working in close proximity to a railroad which requires additional permitting and coordination with the railroad. In some locations, traffic control was also required during the installation work.
Rocky Conditions in West Texas
Another project that MATCOR is currently completing involves the installation of approximately 15 miles of zinc ribbon in West Texas. The original installation plan called for the use of a cable plow to install the zinc ribbon mitigation wire; however, for large stretches of the installation, the rocky conditions forced MATCOR to switch from the planned cable plow to a high-powered rock trencher to cut through the difficult rocky terrain. This project illustrates the importance of using the right equipment to overcome difficult installation challenges. In some cases, being able to adapt to adverse conditions requires a change in construction methodologies and for this project, MATCOR’s ability to react and make equipment changes allowed the project to proceed on schedule with minimal customer impact.
This project also requires the use of HDD for one specific mitigation segment, as the pipeline traverses a cotton field which includes a buried drip irrigation system. The use of HDD is required to prevent any damage to the drip irrigation system during the AC Mitigation zinc ribbon installation. Coordinating the installation schedule around the cotton crop cultivation added another logistical challenge to the project.
Whatever your AC Mitigation challenge might be, MATCOR’s construction teams are able to work with our clients and their project needs to assure a safe and cost-effective installation project.
Have questions about zinc ribbon installation, or need a quote for AC mitigation materials or services? Contact us at the link below.
Overall The US Pipeline regulatory environment is poised to see several new rules implemented to expand the scope and effectiveness of pipeline regulations with a goal to improve the integrity and safety of hazardous material pipeline. These rule changes were all initiated years ago and have been winding their way through the regulatory process, soliciting input from the industry and from concerned citizens, environmental groups and other interested parties.
The Liquids “Final Rule” In January of 2017 in the last few days of the Obama Administration, the Department of Transportation’s Pipeline and Hazardous Materials Safety Administration issued a final rule amending its Rule 49 CFR 195 that among other things expanded integrity management and leak detections beyond high consequence areas (HCA’s). The Final Rule tightened standards and broadened data collection and monitoring requirements for pipeline operators. A few days into the Trump administration, the White House issued a directive to federal agencies to freeze sending new regulations to the Office of the Federal Register (OFR) and withdrawing any regulations sent to the OFR. Thus the liquids “Final Rule” that was 6 years in the making was withdrawn and is awaiting resubmittal by the new administration. While the exact requirements of the Final Rule may be changed, some of the key changes from the withdrawn rule included:
• Assessment of non-HCA pipeline segments every 10 years in compliance with provisions of 49 CFR Part 195. • Increased use of inline inspection tools for all hazardous pipelines in HCA. • Requirement for leak detection systems for covered pipelines in both HCA and non-HCAs.
PHMSA anticipates coming out with their revised “Final Rule” in the Fall of 2018.
The Gas “Mega Rule”
On the gas side of the pipeline regulatory environment, 49 CFR Parts 191 and 192, several public meetings have been held regarding PHMSA’s proposed gas rules, often referred to as the Gas Mega Rule. The rulemaking changes originally recommended would have nearly doubled the current number of pages in the regulations. PHMSA has announced that instead of one Mega Rule, the effort would be broken into three separate rules that are expected to be introduced in 2018 and to go into effect in 2019. Part 1 addresses the expansion of risk assessment and MAOP requirements to include areas in non-High Consequence Areas (HCAs) and moderate consequence areas (MCAs.) Part 2 of the rule making focuses on the expansions of integrity management program regulations including corrosion control to gathering lines and other previously non-regulated lines. Part 3 of the gas rule making is expected to focus on reporting requirements, safety regulations and definitions to include expanding into related gas facilities associated with pipeline systems.
Technological advances in horizontal drilling and fracking have changed the oil and gas production landscape that propels the US Pipeline industry. This combined with an increasing demand for natural gas and the promise of larger export markets for both LNG and US crude oil have led to a surge in new pipeline construction. As a result, corrosion prevention, including pipeline cathodic protection design and engineering expertise is critical as the industry adapts to a changing production landscape and new distribution challenges.
Cathodic Protection Engineering Capabilities
MATCOR has been heavily involved in several key engineering projects including pipeline cathodic protection design for new transmission stations. Whether these are compressor stations for gas pipelines or pump stations for liquids pipelines, pipeline owners appreciate MATCOR’s innovative application of linear anodes when designing new construction stations.
Pipeline Cathodic Protection Design with Linear Anodes
The advantages of using linear anodes in a new pipeline station environment include:
Installation in the same trench as the buried piping during initial construction greatly reduces installation costs
Close coupling of the anode to the piping greatly minimizes the current losses of the CP system to the station’s grounding system
Utilizes a low anode gradient / low current output anode system that minimizes interference concerns with other structures and with foreign pipelines outside the station area
Provides exceptionally long anode life using MMO (mixed metal oxide) anodes operating at mA/ft current output.
MATCOR has successfully pioneered the use of linear anodes in plant environments for two decades. With the recent surge of pipeline projects, the use of linear anodes in stations has gained significant traction in the market. MATCOR design engineers and field technical personnel are uniquely qualified to perform engineering, pipeline cathodic protection design, field installation support, commissioning and testing services for these critical infrastructure projects.
AC mitigation is the process of designing and applying pipeline grounding systems to:
Prevent voltage spikes during fault conditions
Reduce AC current density to protect against AC induced corrosion
Maintain AC step and touch potentials below 15 Vac to protect personnel from shock hazards
Pipelines that parallel overhead high voltage AC transmission power systems are subject to AC interference. AC interference has several potential adverse impacts on the safety of personnel and pipeline integrity. Assuming that these conditions exist, there are several measures that can be taken to mitigate the AC interference present on a pipeline. These AC mitigation strategies are detailed in various international standards including NACE SP0177-2014 Mitigation of Alternating Current and Lightning Effects on Metallic Structures and Corrosion Control Systems.
There are four basic approaches to mitigating AC Interference. These mitigation strategies are:
1. Fault Shielding
One of the primary concerns with high voltage AC transmission systems parallel to buried pipelines is the risk that a fault condition at a transmission tower could result in the rapid discharge of fault current near the pipeline. This could lead to direct current arcing in soil – rare but very damaging. More common is the rapid ground potential rise that subjects the pipeline coating to large voltage gradients that result in coating damage. Fault shielding is a suitably designed grounding system that is installed between the tower footing and the pipeline that acts to shield the pipeline and shunt harmful currents away from the pipeline by providing a low resistance path to earth. This typically takes the form of a parallel shielding wire, either copper or zinc, connected to the pipeline.
2. Gradient Control Mats
When high levels of AC voltage are present on a pipeline, either during a fault condition or as the result of an inductive coupling during normal steady-state operations, personnel in close proximity to and/or touching any above ground or exposed appurtenance are at risk for electrical shock step or touch hazards. Installing gradient control mat, which is a system of buried bare conductors, typically galvanized steel, copper or zinc, connected to the structure, provides localized touch and step voltage protection by creating an equipotential area around the appurtenance.
3. Lumped Grounding Systems
Lumped pipeline grounding systems consist of shallow or deep localized grounding conductors that are connected to the structure at strategic locations to reduce the AC voltage level along the pipeline. This provides protection to the structure during steady-state or fault conditions from nearby electric transmission.
4. Gradient Control Wire
Gradient control wire grounding systems function the same as the lumped grounding system. With this type of system, long continuous grounding conductor(s) are installed horizontally and parallel to the pipeline. They are strategically located and sized to reduce the AC induced voltage along the pipeline during steady-state or fault conditions from nearby electric transmission.
For mitigating high levels of AC induced voltage along a pipeline, gradient control wires are the most common form of AC mitigation. Hybrid systems that combine lumped grounding systems with gradient control wires are also common. Regardless of the type of pipeline grounding system used, all of these AC mitigation approaches involve installing a grounding device to the affected structure to allow AC induced current and fault current to be quickly discharged off of the pipeline.
Prior to installing an AC mitigation system, it is common to use a complex AC modeling software to evaluate the impact of fault currents and estimate the steady state induced currents that can be expected along the pipeline. This information is used to determine the quantity and location of mitigation required based on numerous factors, including the resistivity of the soil, the physical characteristics of the pipeline, the operating parameters of the HVAC transmission system and the spatial distances between them.
Engineered AC Mitigation Systems
Based on a thorough assessment of the pipeline and high voltage AC transmission system interaction, including modeling results when available, an AC mitigation system is designed by experienced engineers familiar with the mitigation strategies detailed above. This engineered AC mitigation system would detail the quantity and location of grounding installations required for a specific application. MATCOR’s MITIGATOR is an example of this type of AC mitigation system.
Other features of an engineered AC Mitigation system include:
It is quite common to install the grounding conductor in a special backfill material. The purpose of the backfill can vary depending on the conductor material chosen and the type of backfill used. The benefits of various types of AC mitigation backfill include:
Enhanced surface area – conductive backfills such as carbon or conductive concrete are used to effectively increase the surface area of the grounding conductor reducing the overall resistance to earth.
Corrosion/Passivation Protection – some backfills are designed to protect the grounding conductor from corrosion or passivation of the conductor that could adversely affect the life or impede the performance of the grounding conductor.
Hydroscopicity – some hygroscopic backfills readily attract and retain water from the environment, helping to maintain a low uniform resistance around the grounding conductor.
Solid State Decouplers
These devices are almost always used in conjunction with AC mitigation systems and are usually installed wherever the grounding system is connected to the pipeline. These devices are designed to allow AC current to flow off the pipeline during steady-state or fault conditions while blocking all DC current. This effectively isolates the pipeline’s cathodic protection (CP) system from the AC mitigation system, preventing the mitigation system’s grounding conductors from taking CP current from the pipeline.
MATCOR provides complete AC Mitigation solutions including design, supply of materials, turnkey installations and comprehensive testing services.
Have questions or need a quote for an AC mitigation system or services? Contact us at the link below.
Introduction: Addressing Aging Pipelines and Pipeline Coatings
External 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.
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 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.
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.
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.)
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.)
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.
Around the world, the pipeline industry is seeing a growing number of “attenuation deficit disorder” outbreaks along their older pipelines. This is not a disease or a medical condition afflicting pipeline company personnel, but is a reference to a growing global problem with pipeline cathodic protection (CP) systems that are affected by older coatings that are failing. Pipeline operators need a solution for pipeline rehabilitation.
Pipeline Rehabilitation Solutions
Pipeline operators worldwide are grappling with what to do as their 1950’s, once state of the art coatings systems start to fail. In our recent article in World Pipelines, Ted Huck examines two possible solutions for pipeline rehabilitation:
Recoating the Pipeline: At some point in the process of adding more CP stations and increasing the current output to levels that further degrades the coating, it becomes apparent to the pipeline operator that more drastic measures are required.
Rehabilitating the Cathodic Protection System: Under the right circumstances, an attractive alternative to the recoat approach is to consider the use of linear anodes as a rehabilitation strategy.
For additional information about these pipeline rehabilitation solutions, please read the full article in the September issue of World Pipelines. You can access the article HERE.
For assistance with cathodic protection design, MATCOR’s linear anodes for pipeline cathodic protection, project management or installation, please contact us at the link below.