Whether designing a few above ground storage tanks or performing tank farm design for an entire facility, proper consideration should be given to the adverse impact of corrosion that can occur on the tank bottoms. When addressing the issue of tank bottom corrosion, consider the environment, the tank size and design, and the type of tank foundation to be employed. There are definite advantages in certain materials based on the size and requirements of an above ground storage tank (AST) foundation. By carefully assessing the tank farm surroundings and long-term requirements, costly and potentially dangerous corrosion related tank failures can be avoided. Whether you are relying on a reputable company in the industry or taking on your own front-end engineering and design, there are across-the-board tank farm design recommendations to consider when it comes to corrosion prevention:
In terms of corrosion prevention for under ground storage tank (AST) foundations, is cathodic protection (CP) effective?
For tanks erected on compacted soil or sand foundations, with or without a concrete ring wall, cathodic protection is considered a “good engineering practice” and has been proven as an effective means of addressing tank bottom corrosion concerns. When you compare various methods of corrosion prevention for above ground storage tank bottoms, CP is shown to prevail over asphalt or concrete unless your project involves smaller diameter tanks. The corrosion failure rate is greater for tanks built on asphalt or concrete compared to tanks where a concentric ring cathodic protection system is installed.
In terms of corrosion, when is asphalt or oil/sand acceptable for above ground storage tank (AST) foundations?
Asphalt foundations are not common in the United States, as the mechanical integrity of asphalt can be an issue depending on the AST environment. As well, the use of oil/sand layer designs has been phased out by most tank owners in the United States due to the adverse impact that these oil/sand layers have on tank bottom cathodic protection systems. While historically prevalent in the Middle East and Asia, most larger national oil companies have abandoned this approach because it causes shielding of cathodic protection (CP) current, allowing corrosion to occur. Kuwait Oil, Aramco, and others now prefer clean sand combined with CP as the base material of choice. This is standard in the United States and has been for several decades.
What is a Concentric Ring Cathodic Protection System for above ground storage tanks (AST)?
A. Designed for long-term storage, an AST cathodic protection ring system offers a factory-assembled design whereby the anode rings are ready to install with cable leads that extend past ring wall penetration. Concentric rings sizes are made to order, requiring no onsite welding, cutting, or splicing. The anode locations are marked, rings are laid out, and cabling is placed using a proven labeling system for future monitoring. A mixed metal oxide (MMO) anode is centered among a low-oxygen-generating coke backfill to eliminate depolarization.
Are there some cases where concrete foundations are advantageous for tank farm corrosion prevention?
During installation of above-ground storage tanks, there are some advantages to concrete foundations for tanks when it comes to corrosion—the high pH of the concrete acts to passivate the steel, unless you have an above ground storage tank (AST) liner pad or something that is between the concrete and the tank bottom. If you can effectively seal the chime from the ingress of water and oxygen, the corrosion rates are generally quite small. Unfortunately concrete foundations for larger diameter tanks are not typically practical and can be quite expensive to properly install. Concrete foundations with appropriate AST liners are best for smaller diameter tanks.
In tank farm design for corrosion prevention, what are the best recommendations for above ground storage tank (AST) liners?
Plastic secondary containment liners are largely phased out in the United States and have been replaced by geotextile membranes that serve the same secondary containment purpose as plastic—they are conductive to allow cathodic protection (CP). The general standard in the United States is to have a CP system directly under the tank in order to minimize stray current or current losses due to earthing systems around the tank. Since the tank bottom is a large bare structure and the anodes are closely coupled to the tank bottom, there is usually very little current drain to other structures; the system if properly designed can accommodate modest current drain. While a plastic liner provides isolation from other nearby structures, when a problem arises with the CP system or if the CP system reaches the end of its projected service life, there is no way to install a new CP system without replacing the tank bottom.
Tank farm corrosion prevention is more manageable now than ever before. The MATCOR Concentric Ring Cathodic Protection System™ is just one of many excellent options for protecting your above ground storage tank (AST) from damaging corrosion.
For assistance with tank farm design, our Concentric Ring AST Cathodic Protection System™, project management or installation, please CONTACT US.
This presentation explores current tank cathodic protection trends, specifically for above ground storage tanks.
Statistics show owners of above ground tanks often experience external corrosion issues because of limited or poor installation methods. Typical above ground storage tank (AST) methods of the past involve a ring wall foundation that is generally formed with a sand or soil base, or even concrete for smaller tanks. It has previously been acceptable to use a galvanic ribbon anode system (generally magnesium), but this system often fails prematurely due to unstable sand-based foundations and poor connections. For this reason, the industry is moving away from the galvanic anode system and to newer concentric ring tank cathodic protection systems for above ground storage tanks.
Good Engineering Practices
While there are newer designs for AST cathodic protection systems, your first consideration should always be good engineering practices. The proper installation of a high-end tank cathodic protection system begins with known design specifications based on the tank size and diameter. This presentation compares traditional grid anode systems with newer linear anode concentric ring systems for the cathodic protection of above ground storage tank bottoms. In addition, congested terminal environments often lead to interference and less current at the tank bottom.
Grid Anode vs. Concentric Ring Tank Cathodic Protection Systems
Tank Cathodic Protection using MATCOR Tank Ring Anode System for Above-Ground Storage Tanks (ASTs)
While the field-fabricated and field installed grid anode system has been in use for over 20 years, some faults have been discovered. Field installation presents welding challenges for the contractor because the system must first be secured, and it cannot be installed directly over sheet liner. The ribbon anode and titanium conductor bars have to be field cut to the appropriate lengths. At the conductor bar to anode ribbon intersections, a weld is applied. The field assembled grid system is subject to weld failures, the spot welds can be damaged easily during subsequent sand installation, and care must be taken to hold the system in place so that it does not short to the tank bottom. All of these installation challenges can adversely impact the system performance. Additionally, bare MMO in sand is an oxygen generator when used for cathodic protection. Oxygen is a depolarizer and in some instances this can lead to issues with maintaining polarization criteria.
Advantages of the Concentric Ring System
In comparison, newer concentric ring systems for above ground storage tanks include factory assembled anode rings that come equipped with the appropriate cable leads to extend past the ring wall penetration. No onsite field assembly is required. The system is pre-assembled in concentric ring sizes designed for your tank and requires no cutting, splicing, or welding, and the MMO wire is backfilled within a braided fabric sleeve with coke breeze. Anode locations are simply marked, each ring is laid out at the proper diameter, and cabling is extended toward the ring wall. The anode cables are labeled for ease of identification and to allow for monitoring of current to each anode ring. Unlike the grid system, the MMO anode is centered in a coke backfill – this coke environment inhibits the generation of oxygen eliminating the issues with depolarization.
The concentric ring tank cathodic protection system is designed for longevity. A typical under-tank ring system using MMO anodes exceeds a 30-year life, however can be designed to extend life beyond 100 years.
Additional Considerations for Tank CP
Some tank operators opt for a “replaceable” anode system, however time and manpower are required to extract and replace the anodes and backfill and the design life is only 30 years.
Volatile corrosion inhibitors (VCI) are often used in conjunction with cathodic protection systems where CP cannot be installed or may be ineffective, such as ring wall crevices, poor bottom-to-sand contact, and more. It can be pumped under tanks via shielding high-density polyethylene (HDPE) containment liners.
Today, tank owners have more effective choices than traditional grid anode systems for tank cathodic protection. The MATCOR Tank Ring Anode™ System is trending as a high-end solution for above ground storage (AST) tanks.
What is the best way to prevent damage to sled anode cable connections due to rough sea current and waves?
MATCOR marine sled anodes (Sea-Bottom™ Anodes) are designed with the cable connections routed inside a high density polyethylene (HDPE) protective pipe with holes to provide a level of mechanical protection. Then we use concrete weights to help secure the HDPE pipe (with the cable inside) to the sea bottom so that they are not subject to wave or tidal action.
The protective housing is pictured here and called out as item 4 on the drawing on page 3 of our Sea-Bottom Marine Anode Sled brochure. For the concrete weights, you can use a variety of methods from sacks of concrete to custom formed concrete cast weights. Below is a photo of the weights that were locally supplied to us for a recent project in Indonesia. These weights are installed by divers during the sled anode installation.
For assistance with impressed current anode system design, MATCOR’s Sea-Bottom Marine Anode Sleds, project management or installation, please contact us at the link below.
Canister anodes are commonly used for impressed current anode cathodic protection applications. These can be used to protect buried metallic piping in congested plant environments, to protect distribution or transmission pipelines in either distributed shallow ground beds or as horizontal remote ground bed anodes, and to protect other structures such as above ground or buried tanks and piling systems.
MATCOR’s MMP™ Anode provides an outstanding combination of value, quality and proven reliability for use with these types of applications and are often a direct upgrade over other canister anode offerings. Below is a comparison of MATCOR’s MMO canister anode vs. conventional high silicon cast iron anodes, in addition to a real life project example comparing the costs associated with both canister anode types.
MMP Canister Anode Unique Construction Features
Understanding the value of the MATCOR MMP™ anode product, starts with its unique construction features as follows:
HSCI vs MMO/Ti Canister Anode Type
Most canister anodes consist of either a High Silicon Cast Iron (HSCI) anode or some configuration of MMO/Ti anode installed in a large metallic “canister” that is filled with coke backfill. The canister is capped with the anode cable extending out the top of the anode cap. Once installed, the exterior metallic canister housing is part of the anode system and will consume quickly as current is discharged off the anode, through the coke backfill and then off the external metallic housing.
It is important to note that the housing is only intended to survive transportation and installation. Once installed, it is expected to be consumed, leaving behind the anode and coke backfill.
One of the most important considerations in evaluating any canister anode technology is to evaluate the anode technology that is inside the canister anode.
HSCI anode technology is an older anode technology that remains extremely popular around the world. It is popular because it is cheap and readily available from many suppliers. Because HSCI anodes are simply castings of a specific formulation of iron, they are available from a wide range of manufacturers with casting facilities spread across the globe. Any foundry can cast the basic HSCI anode. Testing for anode composition assures that the basic elements are present in the correct ratio, however, the mechanical and more importantly the electrical (anode) characteristics are dependent on a lot more than just having the correct ratio of components. Also critical are the canister anode:
Casting process
Micro-structure
Density and consistency of the casting
Presence of trace elements
Consistency of the grain structure
and more…
Unfortunately, it is very difficult to assess the quality of a particular anode casting batch without extensive long term testing. Even the most experienced and reputable cast iron anode suppliers will admit that HSCI anode quality and anode performance can vary significantly even within different casing batches from the same manufacturer.
This leaves buyers with a real challenge in confirming that the anodes they are purchasing will provide the anode life and current output that they are specifying because of the wide range of casting quality issues that can occur with HSCI anodes and the large number of casting facilities offering this type of product.
Mixed metal oxide coated titanium (MMO/Ti) anodes are also a common anode technology utilized in canister anodes – typically these anodes consist of a titanium substrate on to which a mixture of mixed metal oxides is electro-deposited on to the substrate and thermally cured. The MMO coating typically uses a base of Iridium as the primary catalyst that allows the coating to perform as an anode.
MMO Anodes Easier to Test for Quality
As with HSCI anodes, quality is an issue with MMO/Ti anodes; however, there are some key factors that lead to making MMO/TI anodes easier to QA/QC than conventional cast iron anodes.
First, there are no real mechanical concerns other than assuring that there is good adherence between the MMO coating and the underlying substrate. Because the substrate is pure titanium the mechanical properties are quite consistent (ASTM Grade 1 or Grade 2 Titanium is considered commercial pure titanium and either can be used for MMO/TI anodes). Testing for coating adhesion is a rather simple test that can be performed on a test coupon from the same process or on the anode itself.
In addition to having a very stable, homogeneous substrate, the MMO/Ti anode performance can be tested using accelerated life testing to provide an evaluation of the performance of the specific coating mixture that is applied. As with HSCI anodes, there are a large (and growing) number of suppliers of MMO/Ti anode materials; however, testing can be used to confirm the anode material quality. MATCOR MMP™anodes use MMO/Ti anode material with a proven track record. Additionally, third party inspection and testing of MATCOR’s MMO/Ti anode material is available for a nominal inspection charge.
Canister Anode Configuration
The actual anode inside the canister can have a wide range of configurations; however, the most common configuration is the tubular anode. All HSCI anodes are cast in tubular (either solid or hollow tubular) configurations and many of the MMO/Ti canister anodes also use tubular anodes.
For HSCI tubular anodes, the brittle nature of the anode must be taken into consideration when transporting, handling and installing the anode as dropping the anode canister can lead to breaking or cracking of the HSCI anode.
MATCOR’s MMP™ Anode is unique in that we utilize a solid titanium rod as our substrate. This provides several advantages over typical MMO/Ti configurations utilizing tubular anodes. The cable to anode connection is easier and more secure when connecting to a solid rod as opposed to trying to connect a cable to the inside of an anode tube. The solid titanium rod is also stronger and unlikely to break should it be bent.
Other MMO/Ti configurations can also be used inside a canister anode including MMO/Ti strips and ribbons. There is nothing inherently wrong with these configurations as long as the anode to cable connection is properly designed. Improper anode to cable connection designs can lead to premature anode failure.
Canister Anode Connection Technology
Typical anode connections used for discreet canister anodes usually consist of some version of a pressure fit mechanical connection with an epoxy sealant covering the anode to cable connection. Anode to cable connection failures have historically been a significant cause of premature anode failure. Depending on the anode type and configuration, the location of the anode connection can also have an impact on performance – especially for HSCI anodes that consume rapidly and may be subject to necking effects– with MMO/Ti anodes that are dimensionally stable (i.e. do not physically consume) this is much less of an issue.
MATCOR’s MMP™ anode utilizes a multi-step welded connection technology to assure the anode to cable connection is mechanically and electrically secure and properly sealed from the ingress of moisture that can lead to premature anode failure. The multi-step anode connection includes a mechanical crimp followed by a welding process. The mechanically secure welded connection then has a layer of non-conductive hot melt sealant followed by a heat shrink sleeve with a second sealant layer on the interior of the heat shrink. This heavily engineered connection technology has proven to be exceptionally effective with hundreds of thousands of connections in service over the past 20 years.
Typical spiral wound 0.7mm thin walled canister
Heavy Duty Canister Anode Construction
Most canister anodes are constructed using a thin walled galvanized steel spiral wound pipe material. This material is commonly used in the HVAC world as a ducting material and is readily available commercially. This material is typically 0.7mm thickness (24 gauge) with a spiral wound construction. This type of canister provides only a modest amount of mechanical strength and must be very carefully handled during transportation and installation.
MATCOR’s MMP™ Canister anode utilizes a thicker walled EMT seamless steel pipe with a typical material thickness of 1.8 mm or 250% times the thickness of typical canister anodes. This additional wall thickness makes the MMP™ anode a much stronger product – you can drive a fork truck or backhoe over our anode and not significantly damage the canister.
Economic Considerations
The actual installed cost of the anodes is an important consideration in selecting the optimal anode solution. As noted previously, the anode system quality and design integrity should also be factored into the evaluation as these factors can serve to reduce the anode system’s life in the field.
Some factors that should be considered include:
Anode Operating Life (Amp-Years)
Every anode has an operating life. For HSCI anodes the calculation of an anode life is complicated by the inherent variability in HSCI anode casting. The nominal consumption rate of HSCI anodes is typically assumed to be between 0.5 to 1.0 lbs/amp-year (0.23 kg/amp-year to 0.45 kg/amp-year) in a coke backfill. This wide range is consistent with the variation in anode consistency and quality inherent in the anode type. The consumption rate can also vary depending on the environment and the operating current density.
Additionally, a utilization factor is typically applied to the calculations as the anode can never be fully utilized – at some point the anode consumption is such that the anode to cable connection is lost prior to fully consuming all of the anode’s mass. For stick anodes with an end connection this is typically 65% (meaning that 35% of the anode mass is unusable) while for tubular anodes with center connections this utilization factor is closer to 85%.
MMO/Ti anodes are considered dimensionally stable anodes and do not physically consume. They are instead electro-catalytic in nature – they cause a reaction to occur that generates DC current flow without actually being a reactant and thus are not consumed. The catalytic component in the MMO coating does; however, have a finite life that is relatively consistent and can be determined based on the accelerated testing performed by the manufacturer.
The challenge with MMO/Ti anodes is that the coating loading is on the order of mg/m2. With such a light coating load, it is often difficult for the anode manufacturer to control the coating loading to exactly the thickness that would be optimal. Most MMO/Ti anodes are supplied with more coating than required to assure that the coating thickness QA/QC spot checks exceed the minimum specified coating loading. MATCOR’s experience has been that the anode coatings tend to exceed that required coating loading by a significant margin assuring even longer life than the stated design life.
Anode Weight
One of the key advantages of the MATCOR MMP™ anode is the low weight over HSCI anodes for a similar current capacity. HSCI anodes consume at a relatively high rate and require significant anode mass to provide the current output and life required. Weight has two key impacts; one is economic as the lower the anode weight the cheaper it is to transport and install, and the second is a safety issue as the heavier the anode the greater the risk of injury associated with the proper transportation and handling of the anode during installation. While the transportation costs are easily quantified, the safety benefit of a much lighter anode to be installed is much more difficult to quantify but should be considered in the anode selection.
Anode Installation Replacement Cost
Another consideration that should be given is the cost of having to replace an anode installation more frequently. This metric is often not considered; however, there is a very real value to having an installation that lasts 25 years versus only 18 years and the additional incremental cost for the additional life has a real value that should be considered in the economic evaluation.
Savings from using fewer, higher output anodes
Another consideration that is often overlooked is the savings that might be achieved by using fewer anodes that are capable of higher output to reduce the overall installation costs. The incremental cost of fewer, larger anodes could result in a significant cost savings over using more anodes that are rated for lower output. When considering the use of fewer, higher output anodes the impact on system resistance could be an issue as the power supply may have to be larger and the operating power higher to overcome the additional system resistance from fewer anodes. Typically power costs are rather nominal and not a major consideration in this type of economic evaluation.
Canister Anodes System Example
Please note that this is a real project example and is intended to show the methodology used to evaluate two different options – one using HSCI anodes and the other using MMP™ canister anodes. The costs associated with this project are not suitable for other applications – each project has its own costs that must be evaluated for that specific project.
Shallow horizontal ground bed rated for 60 Amps using multiple anodes in parallel at a depth of 12 feet and spaced 15 feet from each other. Each hole would be 8” diameter and the hole would be filled with coke around the anode including one foot below the anode and one foot above the anode. System to be suitable for 30 years anode life. Soil resistivity is assumed to be 3000 ohm-cm.
Canister Anode Options
Two anode options were considered as follows:
HSCI Solid Stick Anode
MATCOR MMP™3605
Anode Type
Bare HSCI Anode
Canister MMO/Ti rod
Anode Dimensions
3" x 60"
3" x 60"
Anode Weight, ea
110 lbs
44 lbs
Anode Life, ea
95.3 amp-years*
125 amp-years
Anode Cost
$325
$210
Freight Cost/Anode
$22
$9
* Based on 0.75 lbs/amp year consumption rate and 65% utilization factor for solid stick anode
Additional Costs
Installation cost to drill each hole, install anode and make header cable connection estimated at $700 USD/hole
180 lbs of coke backfill per hole, including freight, estimated at $135/hole
Cable costs for header cable, estimated at $1 per foot
Cable to anode splice kit estimated at $35 per connection
Calculations
Minimum number of anodes required to meet 30 year life operating at 60 amps:
Roundup {(60 amps x 30 years) / Anode life} = minimum # of anodes
HSCI Stick Anode – 19 anodes resulting in 30.19 years design life
MATCOR MMP™ – 15 anodes resulting in 31.25 years design life
Anode System Resistance
Based on Dwight’s equation using an 8” diameter hole and 7 ft coke column in 3000 ohm-cm soil the resistance of a single anode (Ra) is 7.68 ohms. The resistance for multiple anodes in parallel is Ra/Number of parallel anodes
19 HSCI anodes – anode bed resistance is 0.40 ohms
15 MMP™3605 anodes – anode bed resistance is 0.51 ohms
Installed Cost
Based on the cost assumptions the total installed costs are:
HSCI 19 anode system: $23,408.00
MATCOR MMP™ 3605: $16,560.00
Contact MATCOR about your canister anode cathodic protection requirements or learn more about our MMP Anode (MMO) canister anodes.
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
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.
As you watch the evening news or pick up your daily paper you will very likely read about the new Missile Defense Shield in Romania that came on line this week. The Russian response has been loud and indignant. This story will be all over the evening news, cable channels and newspapers.
But did you know that the Deveselu facility in Romania has a MATCOR Cathodic Protection system protecting the buried piping and process tanks? MATCOR VP of engineering Glenn Shreffler made three trips to the site during its construction. So when you watch the evening news and they discuss the “controversial” missile defense base in Romania, we are proud that MATCOR anode systems are hard at work protecting the assets that protect our NATO allies.
Contact MATCOR about your tank and piping cathodic corrosion prevention requirements or learn more about our wide range of cathodic protection products.
MMO anode technology has taken over the cathodic protection industry and MATCOR has been on the forefront for the last 20 years. Ted Huck, our VP of International Sales was interviewed at the recent NACE Corrosion Conference. In this video he discusses MMO anode technology for cathodic protection systems and the importance of reliable anode to cable connections.
MMO Anode Technology
MMO anodes, or mixed metal oxide anodes are the latest technology in the corrosion industry. Mixed metal oxide anodes are lightweight and durable with a very low consumption rate.
MMO anodes are a mix of metal oxide electrocatalysts. In the presence of a DC voltage source they cause an electrical reaction that generates cathodic protection current. Unlike conventional impressed current anodes that physically consume as part of the cathodic protection reaction (at rates measured in kg/amp-year), MMO anodes are dimensionally stable and do not consume. Instead, they have a long and predictable catalytic life. MMO anodes consist of a thin coating of the MMO catalyst over an inert lightweight titanium substrate and are available in a wide range of shapes and configurations.
Why Cathodic Protection Systems Fail
Kynex® Patented, Waterproof Anode to Cable Connection
The most critical component to any cathodic protection anode system is the connection of the anode to the cable that runs back to the power supply. Because the cable is part of the anode system, if it has any nicks or defects or is not water tight, that cable can become part of the anode and will very quickly consume. When that happens, the anode fails. So, with cathodic protection systems it is imperative to have the highest quality connections.
Typically, when a cathodic protection anode system fails, it is not the anode that fails, it is the anode connection that fails. MATCOR has developed a proprietary technology for connecting wire anodes to cable, called Kynex®. Wire anodes are the heart of a lot of our products and this proprietary anode technology is a huge leap forward in the reliability of these connections.
At the end of the day, for our clients, it’s all about delivering value. It’s providing a cost effective solution that’s going to serve them for a very long time. As a designer and manufacturer of cathodic protection anode systems, we are able to specifically address client needs with customized corrosion prevention solutions that provide:
Long life
Great economic value
Superior reliability
MATCOR Products and Services
MATCOR is one of the world’s leading cathodic protection companies. We design, manufacture, install and service cathodic protection systems for clients worldwide. MATCOR provides services to the pipeline, midstream and oil & gas industries, protecting assets such as pipelines, storage tanks, and compressor stations. We also do a lot of work in the power industries, petrochemical, and chemical industries. Anywhere where you have buried steel structures, we are there to stop corrosion. We encourage you to contact MATCORthrough our website where our corrosion specialists and engineers can provide a solution tailored to your needs.
Close Interval Potential Surveys (CIPS) or close interval surveys (CIS) for those in the United States, are an invaluable assessment tool used to maintain pipeline integrity. Close Interval Surveys are frequently mandated by pipeline regulatory authorities.
Keys to a Successful CIPS Survey
Selecting a qualified survey crew
Advanced planning
Selecting the appropriate CIPS Type
Accurate CIPS Data Collection
Expert Data Analysis and Reporting
Learn more about the keys to a successful CIPS survey and other considerations in our recent article appearing in World Pipelines, “Not Just a Walk Along the ROW” by Ted Huck.
MATCOR is here to help. Our experienced and NACE-trained crews are ready to perform close interval surveys to keep your pipeline cathodic protection systems in compliance and operating effectively.
Chalfont, PA (Aug 31, 2015) – MATCOR, Inc., the trusted full-service provider of proprietary cathodic protection products, systems, and corrosion engineering solutions recently announced that the company has joined forces with CP Masters, Inc. The combined company will be known as MATCOR.
CP Masters brings 30 years of cathodic protection technical and system installation expertise to the MATCOR team. In addition to industry-qualified and experienced people, the company maintains one of the industry’s largest fleets of construction equipment.
This move enables MATCOR to execute cathodic protection and AC mitigation projects directly and efficiently. Additional benefits to customers include:
Improved cost-effectiveness
Consistent, high quality construction and installation services
Access to expert, conveniently located survey teams
Turnkey cathodic protection and AC mitigation solutions
“CP Masters and MATCOR have over 70 years of combined name recognition in the industry—with CP Masters known for superior construction and installation services, and MATCOR known for engineering expertise and proprietary products,” said Kevin Pitts, President of MATCOR, Inc. “Now as one company, we are able to offer customers a powerful combination of the best people, services and products in the corrosion industry.”
Cathodic protection, when applied properly, is an effective means to prevent corrosion of underground plant piping. For many underground applications, such as pipelines, cathodic protection system design is relatively straightforward. Plant and facility environments, however, are not simple applications. Plants have congested underground piping systems in a tightly spaced footprint. The presence of copper grounding systems, foundations with reinforcing steel embedded in concrete, conduit, utility piping and structural pilings (either bare or concrete with reinforcing steel) can greatly complicate the task of designing a pipe cathodic protection system.
For simple plant facilities, it is possible to isolate the piping and utilize a conventional galvanic corrosion prevention system. This works only if the plant piping is electrically isolated from other underground structures for the life of the facility. For most plant and facility applications, it is not practical to isolate the piping from the grounding system for the life of the facility. In these cases an impressed current anode system is the only alternative.
3 Methods of Cathodic Protection for Underground Piping and Structures
There are three basic approaches to cathodically protect underground piping and structures using impressed current anodes.
Deep Anode
One method is the deep anode in which high current capacity anodes are installed from the structure in a deep hole drilled vertically 150+ feet deep. This is analogous to lighting a football field with floodlights.
Shallow Anode or Distributed Anode Bed
Another method is to use a shallow ground bed anode design where many smaller capacity ground bed anodes are spaced near the intended structures – analogous to street lamps lighting a street.
Linear Anode
The third method is to place a linear anode parallel to and in close proximity to the piping to be protected discharging current continuously along its length – similar to fiber optic lighting.
This technical bulletin details the advantages of using the linear anode approach for new plant construction projects to protect buried piping in a congested environment. This approach provides the most effective solution both technically and commercially.
Pipe Cathodic Protection Design Issues for Plants & Facilities
Electrical Isolation in a Congested Plant Environment
Electrical isolation is a major concern when designing a CP system for any plant or facility application. Isolating a single cross country pipeline segment from point A to point B is achieved rather simply through the use of electrical isolation flanges/isolation joints that the pipeline operator maintains and tests regularly. The realities of power plant piping networks, on the other hand, significantly complicate electrical isolation. By code, everything above grade in a plant must be grounded, yet it is common to see pipe cathodic protection systems designed based on isolation of the buried piping. Even if electrical isolation is achieved during the plant construction, maintaining electrical isolation over the life of the facility may not be realistic. Given the speed and complexity with which new plants are erected, achieving electrical isolation during construction is no simple task. Once installed, electrical isolation flange kits require regular monitoring and periodic replacement that often does not occur. Piping modifications and other plant maintenance activities can also result in an inadvertent loss of electrical isolation. Cathodic protection for underground piping that relies on electrical isolation should be avoided for plant applications.
Current Distribution – a Critical Issue in Pipe Cathodic Protection Design
Another critical issue that must be properly considered during the design of a CP system for plant applications is the highly congested underground environment and the challenges of achieving thorough current distribution. Buried piping is often located in congested underground areas in close proximity to grounding systems, foundations with reinforcing steel, pilings systems, metallic duct banks and other structures that can shield current from the piping systems that are the intended target of plant cathodic protection systems. It is virtually impossible to assess where current will go in a plant environment – the more remote the anode source, the more difficult it is to assure appropriate current distribution.
Stray Current
When discussing current distribution, it is also important to discuss the potential for stray current. For grounded systems, current that is picked up by other buried metallic structures is merely current that is wasted and not available to protect the intended buried piping structures. For isolated metallic structures, such as foreign pipelines, ductile iron piping systems, and nearby facilities or structures, stray current may be a significant concern. Stray current problems occur when current is picked up on an isolated structure and later discharges off that structure and back to a grounded structure. At the location where stray currents discharge, rapid corrosion may be inadvertently induced on the isolated structure.
The Case for Linear Anode Cathodic Protection System Design
The linear anode solution consists of long runs of linear anode installed parallel and in very close proximity to the piping being protected. The current output is kept very low and is generally consistent across the entire system. A linear anode is in effect a distributed system with an infinite number of anodes spaced continually. This system provides the best technical cathodic protection solution and minimizes the current output required as follows:
Does not require electrical isolation. Because the linear anode is closely located next to the piping being protected, electrical isolation is not a significant concern. The anode is “closely coupled” to the piping and operates with a very low anode gradient that minimizes any losses to nearby structures including grounding.
Assures good current distribution as the anode runs parallel to the piping being protected. The linear anode cathodic protection system design eliminates any requirement for supplemental anodes to address areas where remote anodes may be shielded after the CP system is commissioned. Wherever the piping goes, the linear anode follows in the same trench. This also makes it very easy to adapt the design during piping revisions that may change the piping system routing as the plant construction proceeds.
Eliminates risks of stray current. Close proximity to the piping being protected significantly limits current losses to other structures and virtually eliminates shielding and stray current concerns. This also significantly reduces the total current requirements for the system, reducing the rectifier requirements.
Access issues – the linear anode is installed in very close proximity to the piping that is to be protected. This minimizes the risk of third party damage and reduces trenching required for buried cable. If installed in conjunction with the piping, the anode can be placed in the same trench as the piping affording the anode protection by the piping itself from external damage. This is a very cost effective cathodic protection installation when installed concurrently with the piping.
Ease of installation – when installed alongside the piping as the piping is being installed, the installation is simply a matter of laying the anode cable in the trench.
Our experts are happy to answer your questions about cathodic protection for underground piping.
Whether designing a few above ground storage tanks or performing tank farm design for an entire facility, proper consideration should be given to the adverse impact of corrosion that can occur on the tank bottoms. When addressing the issue of tank bottom corrosion, consider the environment, the tank size and design, and the type of tank foundation to be employed. There are definite advantages in certain materials based on the size and requirements of an above ground storage tank (AST) foundation. By carefully assessing the tank farm surroundings and long-term requirements, costly and potentially dangerous corrosion related tank failures can be avoided. Whether you are relying on a reputable company in the industry or taking on your own front-end engineering and design, there are across-the-board tank farm design recommendations to consider when it comes to corrosion prevention:
The protective housing is pictured here and called out as item 4 on the drawing on page 3 of our 
MATCOR’s 
Learn more about the keys to a successful CIPS survey and other considerations in our recent article appearing in World Pipelines, “Not Just a Walk Along the ROW” by 
