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Cathodic Protection

Soil Resistivity Testing

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This article discusses the most common soil resistivity testing method and provides some guidelines for properly collecting sufficient data for the cathodic protection system designer.

Soil Resistivity TestingOne of the most important design parameters when considering the application of cathodic protection for buried structures is the resistivity of the soil. Soil resistivity testing is an important consideration for assessing the corrosivity of the environment to buried structures. It also has a tremendous impact on the selection of anode type, quantity, and configuration. Thus, it is critical that the CP designer have accurate data on the soil conditions at both the structure and at any proposed anode system locations. The lack of sufficient soil resistivity data can render a cathodic protection system (CP system) design ineffective and can result in costly remediation efforts during commissioning.

Soil Corrosivity

Soil resistivity is the principal diagnostic factor used to evaluate soil corrosivity. When performing soil resistivity testing, there are numerous factors that can be assessed, including soil composition, moisture content, pH, chloride and sulfate ion concentrations, and redox potential.  These are all common components of a lab or in-situ soil testing program and all have an impact on soil resistivity. While a comprehensive soil testing program may be warranted, especially when performing failure analysis, for most environments the soil resistivity testing data provides an outstanding basis for assessing soil corrosivity. Below is a typical chart correlating soil resistivity with soil corrosivity.

Soil Resistivity (ohm-cm) Corrosivity Rating
>20,000 Essentially non-corrosive
10,000 to 20,000 Mildly corrosive
5,000 to 10,000 Moderately corrosive
3,000 to 5,000 Corrosive
1,000 to 3,000 Highly corrosive
<1,000 Extremely corrosive

SOURCE: Corrosion Basics: An Introduction, NACE Press Book, 2nd edition by Pierre Roberge

Soil Resistivity Testing

Soil Resistivity Testing
Wenner four-pin soil resistivity testing method

While there are several methods for measuring soil resistivity, the most common field testing method is the Wenner four-pin method (ASTM G57). This test uses four metal probes, driven into the ground and spaced equidistant from each other. The outer pins are connected to a current source (I) and the inner pins are connected to a volt meter (V) as shown in Figure 1.

When a known current is injected in the soil through the outer probes, the inner probes can be used to measure voltage drop due to resistance of the soil path as current passes between the outer probes. That resistance value R can then be converted into a soil resistivity value with the formula: ρ=2×π×a×R where “ρ” is measured in ohm-cm and “a” is the spacing of the pins in cm. This value represents the average soil resistivity at the depth equivalent to the spacing of the probes so if the probes are spaced 5 foot apart, the value derived would be equivalent to the average soil resistivity at 5 foot depth.

For cathodic protection system design, it is common to take multiple soil resistivity measurements using this methodology with various probe spacings. For shallow anode placement, it is usually sufficient to take reading readings at 2.5 ft, 5 ft, 10 ft, 20 ft, 25 ft. For deep anode applications, soil resistivity measurements may be recommended at much deeper depths corresponding with the anticipated depth of the deep anode system.

Layer Effects

It is important to note that the soil resistivity values generated from the four pin testing represent the average soil resistivity from the earth surface down to the depth, and each subsequent probe spacing includes all of the shallow resistance readings above it. For cathodic protection design purposes, it is often necessary to determine the resistance of the soil at the anode depth by “subtracting” the top layers from the deep readings. This process of “subtracting” the top layers requires some form of computational adjustment. One popular approach is called the Barnes method which assumes soil layers of uniform thickness with boundaries parallel to the surface of the earth. If the measured data indicates decreasing resistance with increasing electrode spacing, this method can be used to estimate the layer resistivities.

The resistance data (R) values should be laid out in a tabular format and then converted to conductance which is simply the reciprocal of the resistance value. The change in conductance is then calculated for each subsequent spacing. That value is then converted back to a layer resistance value by taking the reciprocal of the change in conductance. Finally, the layer resistivity is calculated using ρ=2×π×a×R.

For the Barnes analysis below, the data shows that a low resistance zone exists between 60m depth and 100m depth.

TEST DATA BARNES ANALYSIS

Spacing a
(m)

 Resistance
(ohms)		 Conductance 1/R
(Siemens)		 Change in Conductance
(Siemens)		 Layer Resistance
(ohms)

Layer Resistivity
(Ohm-m)
20 1.21 0.83 — 1.21 152
40 0.90 1.11 0.28 3.57 441
60 0.63 1.59 0.48 2.08 264
80 0.11 9.09 7.5 0.13 17
100 0.065 15.38 6.29 0.16 20
120 0.058 17.24 1.86 0.54 68

Soil Resistivity Testing Equipment Considerations

Electrically speaking, the earth can be a rather noisy environment with overhead power lines, electric substations, railroad tracks, and many other sources that contribute to signal noise. This can distort readings, potentially resulting in significant errors. For this reason, specialized soil meter equipment that includes sophisticated electronic packages capable of filtering out the noise is critical when taking soil resistivity data.

There are two basic types of soil resistivity meters: high-frequency and low-frequency meters.

High-frequency Soil Resistivity Meters

High-frequency meters operate at frequencies well above 60 hz and should be limited to data collection of about 100 feet in depth. This is because they lack sufficient voltage to handle long traverses and they induce noise voltage in the potential leads which cannot be filtered out as the soil resistivity decreases and the probe spacing increases. These are less expensive than their Low-Frequency counter parts and are by far the most common meter used for soil resistivity testing. For CP design purposes, these are frequently used to assess soil corrosivity and for designing shallow anode applications.

Low-frequency Soil Resistivity Meters

Low-frequency meters generate pulses in the 0.5 to 2.0 hz range and are the preferred equipment for deeper soil resistivity readings as they can take readings with extremely large probe spacings. Some models can operate with spacings many thousands of feet in distance. These models typically include more sophisticated electronics filtering packages that are superior to those found in high-frequency models. For CP designs involving deep anode installations, a low-frequency meter is the preferred equipment to provide accurate data at depths below 100 ft.

Field Data Considerations

When collecting accurate soil resistivity data for cathodic protection system design, it is important that the following best practices are taken into consideration to avoid erroneous readings:

  1. Suitability of the testing location. The use of the Wenner four pin testing method requires sufficient open area to properly space the pins to collect data to the depths necessary. For deep anode cathodic protection systems this would require a minimum of three times the anticipated anode system depth.
  2. Avoidance of buried piping and other metallic objects. The presence of any buried metallic structures (piping, conduit, reinforced concrete structures, grounding systems, etc…) provides low current paths that could cause a short-cutting effect that would distort the resistance readings and yield an erroneous soil resistivity reading.
  3. Depth of the probes. It is important that the probes are properly inserted into the earth. For shallow resistivity readings, probes that are driven too deep can impact the shallow readings. Ideally, the pins should be no deeper that 1/20th of the spacing between the pins and no more than 10 cm (4 inches) deep.
  4. Avoid areas of high electrical noise. Soil testing should not be performed directly under high voltage transmission systems or near other outside sources of current in the soil such as DC light rail systems.
  5. Accurately record the test location and conditions. It is important that the location of the testing is accurately recorded along with the soil conditions and temperature at the time of testing. Testing should not be performed in frozen soil, or during periods of extreme drought or abnormally wet conditions.

Summary

Soil resistivity testing with accurate collection of data is the best indicator of the corrosivity of the soil for buried metallic structures and has a significant impact on the design of cathodic protection systems. The most common test methodology for field collection of soil data is the Wenner four pin method. When properly collected, and using appropriate analytical techniques, the soil resistance field data can provide an accurate assessment of soil resistivity values for use in designing an appropriate cathodic protection system.

Learn about MATCOR Soil Resistivity Testing Services

Have questions about soil resistivity testing, or need a quote for services or cathodic protection design and materials? Contact us at the link below.

CONTACT A CORROSION EXPERT

Anodes, News

Matcor Earns Patent for Iron Gopher® Linear Anode

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Iron Gopher® is only linear anode designed for cathodic protection in horizontal directional drilling applications

KENNESAW, Georgia, Sept. 19, 2018 — MATCOR, a BrandSafway company, recently earned a design patent for its Iron Gopher®, a linear anode designed to prevent corrosion through cathodic protection in horizontal directional drilling (HDD) applications. With a braided stainless steel jacket for linear anode protection during installation and a built-in pulling loop for connecting to the drilling head, the Iron Gopher provides approximately 200 percent more pulling strength than traditional anodes used in HDD applications.

It is available in standard and dual-end models, which can both be connected to a DC power source for active cathodic protection with a current. The standard model is used for most cathodic methods, such as roads, streams and property crossings, and the dual-end model is typically used under tank operations or anywhere it is not possible to connect both ends of the linear anode.

“We developed the Iron Gopher with installation costs and timelines at the forefront, focusing on strength to reduce the risks associated with the linear anode breaking during installation,” said Ted Huck, one of the Iron Gopher inventors and vice president of technical sales for MATCOR. “It also makes job sites—and utilities and pipelines—safer by using cathodic protection to decrease the chance of failure due to corrosion that could cause gas leaks or other potentially catastrophic events.”

The Iron Gopher was invented by Ted Huck; William Schutt, MATCOR founder; and Knut Fenner, former director of business development at MATCOR.

“MATCOR is an innovation leader in the corrosion and cathodic protection industry with its ongoing R&D, proprietary products, service and client-focused cloud technology,” Bob Burns, president of Midstream said. “The Iron Gopher is just another example of how we are continually raising the standards within the corrosion industry and ultimately providing the best solutions to our clients.”

For more information about Iron Gopher, visit matcor.com/products/matcor-iron-gopher.

About MATCOR

MATCOR, Inc. is a BrandSafway company and a leading cathodic protection and corrosion prevention engineering design firm, providing environmentally beneficial systems and services to global clients for more than 40 years. An ISO 9001:2015 certified expert in the field of cathodic protection, MATCOR offers proprietary corrosion protection design, engineering, manufacturing, installation, cathodic protection testing, annual surveys, maintenance and complete corrosion protection project management. MATCOR specializes in protecting the infrastructure of the oil and gas, utility, transportation and construction industries. To learn more about MATCOR, please visit www.matcor.com or call 1-215-348-2974.

About BrandSafway

With a commitment to safety as its foremost value, BrandSafway provides the broadest range of services, products and solutions, with the greatest depth of expertise, to the industrial, commercial and infrastructure markets. A portfolio company of Clayton, Dubilier & Rice, BrandSafway offers access, industrial services and forming and shoring solutions to more than 32,000 customers through a workforce of approximately 35,000 employees, who support our network of 350 strategic locations across 30 countries. With its global footprint, rigorous operating processes and extensive service offerings — a full range of work access, insulation, coatings, specialty industrial services and forming and shoring solutions — BrandSafway supports customers’ maintenance and refurbishment needs as well as new construction and expansion plans. Today’s BrandSafway — large enough to leverage economies of scale to increase safety and productivity, while also remaining nimble and responsive — delivers unmatched service with local labor and management.

AC Interference, AC Mitigation, AC Modeling

AC Mitigation Video | Overview of Goals, Strategies and Materials

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We’ve talked about AC Interference and we’ve talked about AC Modeling. The topic of our newest training video is AC Mitigation. The video is about 9 minutes long and we’ve included timeline indicators below so you can easily find your topic of interest in the video.

The goal for AC mitigation is to reduce your fault condition stress values to protect against stress coating damage and arcing potentials (arcing is less common because you need to be very close to the pipeline for arcs to appear). This includes:

  • Reducing current density below your threshold value. Typically in the US we use 20 amps per meter squared for a one CM2
  • Maintaining AC step and touch potential below 15 volts so that people working in and around pipeline areas are not subject to shock due to a fault condition

AC Modeling Aids in Predicting Conditions [0:55]

We use AC modeling to provide predictions and look at the mitigated and unmitigated conditions. Some cases warrant building a model, in other cases we can use “ad hoc” methods (such as experience) to come up with an effective AC mitigation plan.

Learn more in our AC Modeling Video.

AC Mitigation Schemes [1:14]

For our example pipeline application, AC modeling results show some locations to be concerned about where the 20 amps per square meter threshold is exceeded. These locations are indicated below, where the red line is above the yellow 20 amps per square meter reference line. What do we do to mitigate this risk?

AC Modeling Results

In this case, we’re going to put in a gradient control line in the areas of concern next to the pipe. This is a grounding system that attaches to the pipeline so that AC being picked up by the pipeline has a place to go. The coating system is “too good” with only a few small holidays, which means all of the current being picked up tries to rush out of those few small holidays. This is how you end up with AC induced pipeline corrosion.

By putting in a grounding system at strategic locations along the pipeline, we can reduce the AC voltage being picked by discharging it and giving it a place to go.

There are several ways to design an AC mitigation system but they are all basically grounding systems. Our solution in this case is shown as the blue line representing a grounding mitigation line.

AC Mitigation Grounding

Typical AC Mitigation Strategies [2:23]

  • Install a gradient control mat at locations where people can touch the pipeline
  • Maintain safe pipeline to power line separation distances to avoid arcing problems during fault conditions
  • If separation distances are too close, include a shield that picks up current as it is dumped to the earth and deflects away to protect the pipeline
  • Provide grounding of the pipe to the earth to dissipate current being picked up during steady-state conditions

What is a gradient control mat? [3:00]

A gradient control mat is a simple device that is connected to the pipeline to protect workers from step and touch potentials.

It is connected to the pipeline appurtenance where a person can touch the pipeline, and extends out enough so that somebody standing on it will not have that step and touch potential. Since it is connected to the pipeline, the entire gradient control mat has the same potential as the pipe.

As soon as I step on to that gradient control mat, I don’t have a voltage difference between me and everything else. Even if I touch the pipe, the ground below me is at the same voltage as the pipe, so no current flows through my hand, to my body and into the ground.

It is a fairly significant effort to install a gradient control mat but they protect people close to that appurtenance. Once they are above that gradient control mat, touching or being near the pipeline is not going to cause a problem. Current doesn’t flow unless there is a voltage difference. You can actually be in an environment where there is high voltage all around you, and as long as you are at the same potential (or equipotential), there is not going to be any current flow, and current is what can injure or kill you.

AC Mitigation Case Study [4:33]

In the case study shown, a pipeline runs parallel for 8 km to a transmission line, with the towers next to the pipeline. In this case the towers are too close so we use a zinc ribbon shield wire to protect from fault conditions. The zinc ribbon picks up the current and dissipates it before it can cause damage to the pipeline.

AC Mitigation Reduces Coating Stress Voltages

The chart below shows the effects without any mitigation, where you can see the voltage spike where it goes above 12000 volts of coating stress voltage.

Effects of Zinc Ribbon | AC Mitigation

You can see once various forms of mitigation are added, stress voltage drops below the limits. And depending on the type of coating, there’s a certain voltage limit that coating can withstand.

Pipeline Grounding Methods [5:46]

  • Spiral mat at pipeline valve stem location
  • Anodes in the earth that are connected to the pipeline; these become grounding rods for the pipeline
  • Horizontal ground conductors, connected at various lengths to the pipeline (gradient control line mitigation)
  • Deep anode ground beds

Deep Anode Case Study [6:25]

Deep anode ground beds are a little more expensive, however they a good solution in high resistance areas where you can’t discharge current into the ground effectively near the surface.

We did a project out west in the desert of the United States, where a new pipeline parallel to a transmission line was picking up AC voltage. In the very dry desert environment there was nowhere for this current to discharge. Grounding rods next to the pipeline do not work well in this case because the environment is so dry. We drilled holes 1000 feet into the earth and installed grounding cells. These were run up to the surface and connected to the pipeline to dissipate the AC voltage being picked up.

[7:11] There are a variety of ways to ground a pipeline; AC mitigation is basically how we ground the pipeline effectively.

AC Mitigation Materials [7:16]

The most common materials used for pipeline grounding include:

  • Zinc ribbon laid parallel to the pipeline
  • Bare copper, which is used predominantly in the corrosion industry
  • Engineered copper grounding systems; The MATCOR MITIGATOR® is an example of this type of system
  • Conducrete® systems where conductive concrete is used to enhance the earth’s surface area

AC Mitigation and Grounding Concerns [7:58]

  • Ease of installation
  • Performance
  • Life, how long is it going to last
  • Cost

Optimum AC mitigation [8:12]

  • The AC mitigation system is only as good as the modeling, so it is critical to ensure that modeling is accurate
  • Gradient control lines parallel to the pipeline are the most common grounding system used currently, although there are also quite a few locations using deep anode systems
  • For fault conditions, short lines at tower footings tend to be the most effective AC mitigation strategy
Have questions after viewing our AC mitigation video, or need a quote for AC mitigation materials or services? Contact us at the link below.

CONTACT A CORROSION EXPERT

BrandSafway, Leak Detection and Repair

Leak Detection and Repair

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What is leak detection and repair (LDAR)?

Leak Detection and Repair (LDAR) Programs are put in place to monitor process equipment leaks for fugitive emissions in the petrochemical industry. Solid LDAR programs are critical in controlling fugitive emissions of VOCs, or volatile organic compounds, that cause pollution and safety risks for facility workers and operators, and the environment.

LDAR - Leak Detection and Repair
Leak Detection and Repair (LDAR) Programs are put in place to monitor process equipment leaks for fugitive emissions in the petrochemical industry.

Maintaining refinery process equipment through an LDAR program mitigates these risks. Utilizing leak detection equipment to identify equipment leaks and then repairing those leaks in a timely manner enables operators to prevent most most fugitive emissions occurrences. In addition, successful leak detection and repair programs prevent product loss that impacts facility efficiencies and economics, the health and safety of workers, and the environment.

The article reviews fugitive emissions regulations and lays out a 5-step plan to build LDAR programs that accurately represent your project requirements.

Leak Detection and Repair Program Steps

Step 1: Develop Your Standard Operating Procedures

The first step in developing a successful leak detection and repair program is a cooperative endeavor between you and an LDAR expert to complete, approve and adopt your standard operating procedures (SOP).

Step 2: Laws Governing Your LDAR Program

In the second step, your LDAR team will research and share comprehensive knowledge of the permits, regulation(s), consolidation agreements, consent decrees, permit(s), and/or binding agreements governing your facility’s LDAR program.

Step 3: Your LDAR Unit Equipment Information Packet

In step three, your team will set up a database of regulations for each unit in your facility. The LDAR team funnels, filters, and identifies congestion overlap and applicable LDAR regulations of varying stringency into a condensed table called a Unit Equipment Information Packet. This is a comprehensive knowledge base for all who need to know more about the LDAR program on a unit-by-unit basis at the subject facility.

Step 4: Facility Process Flow Diagrams

In the fourth step, the LDAR team obtains your facility’s process flow diagrams (PFD’s), piping and instrument diagrams (P&ID’s), the P&ID abbreviations key, material balance sheets, and stream speciation data from the appropriate contact identified in your SOP in Step 1. Smart software is then utilized to highlight or color-code the P&ID’s according to stream state and service. Then the field review begins.

Step 5: Component Inventory Database and Monitoring

In the fifth step, detailed data is collected on a daily basis for affected components. The LDAR team reviews all affected components for accuracy and compliance, and perform necessary correction. All corrections are updated in the database. Monitoring commences as scheduled according to the applicable regulation set up in your LDAR Unit Equipment Information Packet in Step 2. Finally, we initiate a monthly QA/QC process to ensure ongoing compliance.

Many regulations and a lot of detailed data are involved in designing a best-in-class LDAR program to ensure regulatory compliance when it comes to fugitive emissions. It is critical to review all data reports with your facility’s operations and environmental department for understanding and acknowledgement of completion and ongoing compliance.

Why BrandSafway for LDAR Solutions?

BrandSafway offers 150 years of management experience, cutting-edge technology and a highly effective data management system to ensure successful LDAR programs and more, while ensuring regulatory compliance with USEPA Method 21 and other mandated requirements for VOC monitoring.

LDAR Leak Detection and Repair Services

Learn about comprehensive LDAR Solutions from Brandsafway

MATCOR and BrandSafway are committed to being a valuable partner, providing a one-stop resource for industrial work solutions. By bringing together our expertise in both midstream and specialty services, we can better integrate and streamline asset and equipment management solutions for our customers in both the oil & gas and power markets.

Please click the link below to contact us if you have any questions about leak detection and repair, or if you’d like a quote for LDAR services.

Contact a Corrosion Expert
AC Interference, AC Modeling

AC Modeling Introduction Video

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In this video training session we talk about AC modeling. The summary below includes video timeline indicators so you can easily find your topic of interest in the video.

In the previous AC Interference video we talked about the effects of AC interference from transmission lines on parallel pipelines. We discussed three different modes of impact:

AC Interference Recap—3 Issues (0:24)

  1. Step and touch potential-must be below 50 volts AC
  2. Conductive coupling where a fault condition dumps current into the earth, causing potential damage to the pipeline
  3. AC induced voltage from the transmission lines on the pipeline

AC Modeling and Design

Best Guess Approach (0:57)

In some cases you can do a best guess AC mitigation approach, where it might not be worth the effort to put data and information into a model to determine the impact of AC interference on the pipeline.

Example: You have a simple application where you have one mile of pipeline collocated with high voltage transmission lines. You have measured that you’re picking up AC and decide that you’re going to put grounding in from point A to point B and be done with it. It is over-designed, but the cost of AC modeling would exceed the cost of this simple solution. This approach is based on experience in the field.

Complex Pipeline Arrangements Require AC Modeling (1:42)

When you get into more complex pipeline arrangements—multiple pipelines in the same corridor, multiple AC transmission lines coming in and out, multiple towers and circuits—you cannot just throw grounding in the earth and hope it is going to work. You may ground it in one location, and it may push the current somewhere else. In these cases you need to consider AC modeling.

AC Interference Modeling (2:08)

AC modeling is data intensive. And just like any model where we use a computer to predict what’s going to happen, the quality of the data impacts the quality of the results.

At MATCOR, we use a program called Right-of-Way Pro, a software package developed by Safe Engineering Services and Technology out of Canada. It is the leading AC modeling software available today. There are other packages that are less expensive and less accurate, but Right-of-Way Pro is the gold standard for AC modeling software.

AC modeling is a service that MATCOR provides. We have trained professionals with years of experience modeling AC systems in the pipeline industry, and experience with this complex software.

AC Modeling Goals (3:16)

The goals when you’re performing AC modeling are simple:

First, we calculate the fault condition stress values.

What is the worst fault condition that can occur? What is the worst that can happen at each tower and how does that affect the pipeline given the relationship of the pipeline to that tower? How far away is it? How deep is it? What is the resistance in that location? We model every tower along that collocation.

Next, we calculate induced voltage.

This is the impact of having an electrical field with the pipeline running through it and picking up voltage. We model this for every collocation. This can get rather complex when you have multiple pipelines and multiple AC towers in the same corridor.

Then, we predict the AC current density along the length of the pipeline.

In the AC Interference video we talked about AC induced corrosion being a function of how much current is being discharged off small holidays. There is a certain threshold we do not want to exceed or we will be concerned about corrosion occurring.

The model of the pipeline will show where it is picking up current. At every point along the pipeline, the model indicates, given a holiday of a certain size, whether we have a problem with AC corrosion. This will change depending on where we are along the pipeline collocation and what the soil resistivity is around the pipeline in that location. Lower soil resistivity tends to mean higher current discharge, and these tend to be the areas of concern.

Finally, we evaluate mitigation measures.

Where should we put mitigation, how much mitigation, and how effective will it be?

As we are calculating induced voltage along the length of the pipeline, we are looking for areas where we exceed 15 volts because this is a safety concern. We are also looking for areas where a 1 cm² holiday would have more than a maximum threshold of current density. 20 amps/M² is a typical threshold in the US, since that is where corrosion can occur.

AC Modeling Data Requirements (5:50)

We need a lot of data to build the model out, including data on the HVAC transmission line, the pipeline location and characteristics, and the soil resistivity. In addition, we need information about changes in the collocation relationship. These changes are called excitation points; if there is suddenly a change in the pipeline or the high voltage power line, it is often a hot spot in the system and where you will likely have problems.

HVAC Line Data (6:39)

For the HVAC line we want to know the tower geometry, which can change. How high are the towers? How long are the spans? What is the separation of the different phase conductors? AC is always a 3-phase system, with an A, B and a C line. We need to know if there are phase shifts and where they are located for the model. We also need to know the phase conductor arrangement, the conductor height and distances, if shield wire* exists, and current loading information. What is the average current flowing through that line? What is the maximum, or peak current expected? Is there anticipation that the rating will increase in the future? Finally, what are the fault and ground fault currents?

*Shield wire helps in fault conditions; if there is a fault, instead of dumping current to the earth it will travel along the shield wire.

(8:08) Collecting HVAC line data can be a challenge. It is often a combination of going out into the field and physically measuring, and contacting the power company to request information like maximum fault conditions, length of maximum fault, and how quickly will breakers trip to clear a fault. Power companies don’t always like to provide this information and will often ask operators, or consultants like MATCOR, to pay a fee. When this information is not available we sometimes make assumptions, however the more assumption we make the less valid the model becomes.

Pipeline Characteristics (9:12)

We want to know pipeline characteristics, which are generally easier to get. Either they are easier to measure or the pipeline company has good data already.

We need to know the pipeline diameter or diameters, as sometime this can change. A 16-inch pipe may become a 20-inch pipe at some location. This would be an excitation point because a change has occurred. What is the wall thickness and material? What is the coating type, thickness & quality? What is the coating conductance?

(9:52) If your pipeline has an older coating, you probably do not have a big AC problem. If you have a brand-new, high quality coating means you probably have a bigger AC problem.

Depth of cover survey—how does the pipeline change its depth relative to the earth? We need to know the accurate GPS centerline of the pipeline in addition to the location of valves, casings, bonds and foreign pipeline crossings. Finally we need to know soil resistivity at different depths and multiple locations along the pipeline. The AC modeling software has the ability to look at multiple layer effects of the soil.

All of this data must be collected and put into the model. Often the pipeline company can provide the data or we can go out and measure it.

AC Modeling Software Key Features (11:35)

  • Up to five layers of soil resistivity modeling
  • A large conductor database—including most transmission line conductors, all copper conductors and mitigation devices such as zinc ribbon and the MATCOR MITIGATOR®
  • The ability to model large networks with multiple pipelines and multiple power lines along a corridor in the same model

AC Modeling Costs (12:11)

For a relatively simple collocation, you may not need to perform AC Modeling. A very simple AC modeling job might be $20,000. The cost can be well over $100,000 for a project requiring a lot of data collection and modeling effort.

In some cases it may be simpler to put in $10,000 worth of grounding and “overdesign” the AC mitigation system since the cost of modeling would be greater. In other cases, AC modeling is an absolute necessity.

AC Modeling Software Capabilities (12:42)

AC Modeling Example
(13:17) This is an example of AC modeling with multiple high voltage transmission lines and a pipeline going from one location out to a terminal. We have to model each of those transmission lines as well as the pipeline characteristics
  • Transformers, insulators, substations and other devices
  • Different phasing, pipe diameters and coating type configurations in one model
  • Solid state decoupler sizing
  • 3-D viewing and plotting
  • AC corrosion output
  • Fault modeling

AC Modeling Software Output (13:42)

The output from the software shows you along the length of the pipeline, those areas where you have concerns about steady state touch potentials, from a safety standpoint where it might be above 15 volts.

AC Modeling Software - Touch Potentials
AC Modeling Software – Touch Potentials

It will also provide your 1 cm holiday leakage current density, indicating areas where you are at risk for AC induced corrosion.

AC Modeling Software - Current Density
AC Modeling Software – Current Density

In addition the software provides areas where fault currents can exceed the maximum allowable for your coating stress.

When is AC Modeling Not Required? (14:16)

  • Simple applications
  • When overdesigning AC mitigation solves the problem

In our next segment we will talk about AC mitigation. What do you do once you know where the problems are?

Have questions after viewing our AC modeling video, or need a quote for AC modeling? Contact us at the link below.

CONTACT A CORROSION EXPERT

Infrastructure, MATCOR, Natural Gas, Pipeline, Pipeline Integrity, Regulation, Safety

PHMSA Rule Making Updates – a look at what is ahead on the US Regulatory Front

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See our October 2019 Update on the PHMSA Mega Rule.

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.

Gas, Oil, Pipeline, Piping

Pipeline Cathodic Protection Design for New Transmission Stations

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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, pipeline corrosion prevention, including 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:

  • pipeline cathodic protection design for new transmission stationInstallation 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.

MATCOR also offers a full suite of cathodic protection design and AC mitigation design services for transmission pipeline and oil and gas production pipeline gathering systems.

Have questions or need a quote for engineering and design or materials for your pipeline cathodic protection system? Contact us at the link below.

CONTACT A CORROSION EXPERT

Anodes, Cathodic Protection, Infrastructure, Linear Anodes, MATCOR

Anode Current Ratings and Soil Resistivity

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We appreciate the question: “How does soil resistivity impact current rating.”  The short answer is that resistance has nothing to do with anode rating. Here is a more detailed response:

  1. Anode current rating – all anodes have a current rating based on how long they can be expected to operate at a given current rating.  All anodes have some defined expected life based on current output and time – so many Amp-Hours of service life.  For example a magnesium anode may have an expected consumption rate of 17 lb/Amp-year (7.8 kg/amp) so if a 17 lb anode is operated at 0.1 amps it would have a life of 10 years.  For MMO anodes, they too have an expected life.  For our linear anode rated at 51 mA/m it is important to know that that rating is actually 51 mA/m for 25 years.  So a 100m anode segment with this rating would have an expected life of 127.5 Amp-years.  If this anode were operated at 5.1 amps (full rated capacity) it would be expected to operate for 25 years.  IF it were operated at 2.55 amps (50% of rated capacity) it should last 50 years.  The anode life is generally linear.  Please note that resistance has nothing to do with the anode current rating – the anode current rating merely calculates the life of the anode as a function of how many amps for how long of time.
  2. Actual current output – just because you install an anode rated for 5.1 amps for 25 years (our 100m segment of 51 mA/m SPL-FBR) does not mean that the anode will output this amount of current.  It just means that at that current rating you can expect 25 years of life.  The anode is merely one component of the overall cathodic protection circuit.  The actual output of the anode is function of Ohms Law ( Voltage = Current * Resistance).  It would make sense to note that if the system Voltage were zero (the rectifier were turned off or disconnected) then the anode would not have any current output.  Likewise if the 100m anode segment were installed in a very low resistance environment and driven by a powerful rectifier, the current could be much higher than 5.1 amps which would result in a much shorter life.
  3. Why anode rating is important to the CP designer – the CP designer is tasked with protecting a specific structure for a given period of time (protect this pipeline for 30 years.)  The CP designer then calculates, based on actual testing or established guidelines, the amount of current that should be sufficient to achieve appropriate CP levels to protect the structure.  This results in an answer of some number X of amps required.  If the requirements are to protect the structure for Y number of years, then the anode life required is X * Y (# of amps times # of years).  This defines the minimum amount of anode life that is needed.
  4. The next question the CP designer must address, once it is determined how much current is needed, is how to design a system that will generate that amount of current.  Since Ohms Law dictates that Voltage = Current * Resistance (V=IR) then if we know that the Current = Voltage/Resistance (I=V/R.)  Thus the CP designer must understand how to calculate system resistance (R) and must provide sufficient driving force (V)  Several factors affect system resistance (R) including anode geometry – the longer an anode, the lower its resistance – which in many applications is a big benefit to the linear anode.  One of the great benefits of the linear anode is that because of its length, in most applications the soil resistivity plays a lesser role since the anode resistance to earth is generally low for a wide range of soil resistivities due to its length.  For extremely high resistance environments, linear anodes may be the best option since short anodes will not have a low enough resistance.
  5. There are other factors that go into CP design including current distribution and making sure sufficient current is being applied across the entire structure.

CP Design can be very complicated.  I hope that the above explanation is helpful, but if there is a specific application to evaluate, please contact us with the details.  We are also available, for a reasonable engineering fee, to develop and/or review CP system designs.

Ted Huck

VP, Technical Sales

Jeff Didas, NACE, News

Jeffrey L. Didas Elected NACE International President

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Chalfont, PA (April 2018) – MATCOR, Inc., the trusted full-service provider of proprietary cathodic protection products, systems, services and corrosion engineering solutions announces that senior engineer and pipeline practice lead Jeffrey L. Didas has been elected to the position of president for NACE International (NACE), the Worldwide Corrosion Authority. His term as president is one year commencing at the close of the NACE Corrosion Conference & Expo 2018, taking place April 15-19 in Phoenix, Arizona.

Jeffrey Didas, Practice Lead - Pipelines, MATCOR, Inc.
Jeffrey L. Didas will serve a one-year term as NACE president commencing at the close of the NACE Corrosion Conference & Expo 2018

As NACE president, Didas will advise, govern, oversee policy and direction, and assist with the leadership and promotion of NACE International to support the organization’s mission. He will also serve as chairman of the executive committee and an officer of the association. His responsibilities will include presiding at all official functions of the board of directors and executive committee, including the annual membership meeting of the association and the annual NACE banquet. This position is part of Didas’ five-year commitment to NACE following previous roles as vice president elect and vice president. Following his term as president he will serve one year as past president and one year on the nominating committee.

“I look forward to serving NACE as president over the next year,” said Didas. “My focus will be on member engagement, retention and benefits, moving forward with the strategic plan and our vision for NACE 2030, and promoting the groundbreaking corrosion industry IMPACT Study.”

Didas, an industry expert sought worldwide and active NACE member since 1975, has 44 years of diverse corrosion experience working for pipeline and energy company owner-operators and most recently for MATCOR.

Prior to his executive leadership roles, Didas held a variety of national NACE positions including:

  • Treasurer of NACE International, the NACE Foundation and the NACE Institute
  • Director of the Member Activities Committee – MAC
  • Committee chair for several technical exchange groups (TEGs), including the Corrosion Control Coordinating Committee (TEG 022X), Pipeline Crossings: Steel-Cased, Thrust-Bored, and HDD TEG 208X) and Steel-Cased Pipelines (TG 012)
  • Technology coordinator for technology management group TMG C1 – Corrosion Prevention and Control for Concrete, Land Transportation and Coating Technology
  • Vice chair of the NACE Institute Policy & Practices Committee
  • Member of the Technical Practices Committee – TPC/Technical Coordination Committee – TCC since 1978

He has also served as chair, vice-chair, and general member of several administrative committees over the past 44 years.

Didas received the NACE Brannon Award in 2014 and the NACE Distinguished Service Award in 2001 for his many contributions to the organization. He also received the Appalachian Underground Corrosion Short Course (AUCSC) Colonel Cox award in 2010.

Didas holds the highest level of NACE certification as a Corrosion Specialist and a number of other NACE certifications, including Cathodic Protection Specialist, Coatings Specialist, Chemical Treatment Specialist, Senior Corrosion Technologist, Corrosion Technologist, Corrosion Technician and Level 3 Certified Corrosion Inspector. In addition he is a SSPC (Society for Protective Coatings) certified Protective Coatings Specialist.

Didas graduated from Thomas A. Edison State University in Trenton, NJ, with a BSET in Electrical Engineering. He acquired his ASEE in Electronics Technology from Springfield Technical Community College in Springfield MA.

About NACE

NACE International, The Worldwide Corrosion Authority, serves nearly 36,000+ members in 130 countries and is recognized globally as the premier authority for corrosion control solutions. The organization offers technical training and certification programs, conferences, industry standards, reports, publications, technical journals, government relations activities and more. NACE International is headquartered in Houston, Texas, with offices in San Diego, California; Kuala Lumpur, Malaysia; Shanghai, China, Sao Paulo, Brazil and Al-Khobar, Saudi Arabia.

Visit nace.org for more information.

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