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Atmospheric and Soil Corrosion Map

We are experiencing increased demand from the largest US utility companies for our corrosion mapping services. SCE and SDG&E, two major California utilities, are now utilizing these maps, and are requesting more for 2019. Recently we were retained by a major company to assist them in developing a corrosion risk assessment map for their service territory.  The genesis of this project started when they found severe below-ground corrosion after a short time in service.  Considering that they had several thousand structures across their service territory, the thought of inspecting each and every one of the structures would be a monumental task.  In consulting with Matergenics it was decided that the best way to approach this would be to develop a corrosion risk assessment map of their service territory.  The map would identify areas of high, medium and low below-ground corrosion risks. As part of this project, we performed carefully selected field inspections in each of the various risk areas.  The data was then used to confirm the accuracy of the corrosion risk assessment map.  Once the map was completed the client was be able to concentrate their resources on structures located in high corrosion risk areas.  The mapping effort has been completed and we have provided the client with a map in ArcGIS which they will put into our GIS system.  They are using the map for many things (operation, maintenance, geotechnical) with regards to other steel corrosion efforts.

Corrosion Risk Mapping

The need to identify areas at higher risk for corrosion becomes more important as pipeline structures and coatings continue to age.  However, a utility’s territory may cover thousands of square miles, and they may need to maximize limited resources to effectively manage its below-ground corrosion issues. The best way to address this situation is to develop a corrosion risk assessment map for areas of high corrosion risk.  A corrosion risk assessment map will combine various properties of soil to identify areas of high, medium, and low soil corrosivity. With this map a pipeline company would be able to deploy its resources most efficiently to specific areas of identifiable high corrosion risk.

Our corrosion maps can be used for corrosion risk assessment, DC/AC interference risk and mitigation, identifying areas that shielding/coating dis-bondment and can potentially cause localized corrosion, leaks, and possible explosions. Examples are provided in the proposal.

We are confident that utilizing corrosivity maps as part of your integrity and corrosion risk program will be instrumental in providing the necessary data to locate high corrosion risk areas high confidence and  with the least amount of investment.

Please find attached the draft proposal for your review. Please let me know your comments and I will send you a formal proposal.  Please do not hesitate to call me if you have any questions or concerns.

Above-grade and Below-grade corrosion is of particular concern to aging, coated pipelines, water/wastewater and  electric utility T&D  in corrosive soils, as the aging structure will react with corrosive soil .  This condition will result in loss in thickness.  Stray AC current interference is another risk for pipelines.  However, consider that zinc anode ribbons used for AC mitigation may exhibit accelerated corrosion in certain corrosive soils.

The need to identify areas at higher risk for corrosion becomes more important as pipeline structures and t&D structures.  However, a utility’s territory may cover thousands of square miles, and the utility need to maximize limited resources to effectively manage its below-grade corrosion issues.

The most efficient way to address this situation is to develop a corrosion risk assessment map that combines various properties of soil to identify areas of high, medium, and low soil corrosivity.  A corrosion map of this kind will allow a pipeline company to deploy its resources to specific areas of highest corrosion risk.  The map uses data collected by the National Resources Conservation Service, and Matergenics’ soil corrosivity data developed with and for other clients.

Technical Approach to construct Above Grade Corrosio Risk Map:

Matergenics’ approach considers the following:

  • Examination of spatial patterns associated with the physical and chemical properties of soil – in order to identify areas of high This evaluation leads to insights on overall corrosion risk, and answers questions on where to locate new pipeline and substation infrastructure
  • GIS identifies the least or most corrosive sites, and also locates access to sites and possible sources of stray current for corrosion mitigation

Some layers that are incorporated into corrosion maps are:

  • Soil resistivity
  • Soil salinity
  • Soil pH
  • Soil type, including the clay content
  • Drainage characteristics
  • Possible presence of stray currents from nearby gas pipelines or other protected assets
  • Corrosivity of the water table

Matergenics project team for the corrosion risk assessment desk study portion and the GIS map development portion of the project will include the following personnel:

  • PhD.-level specialist; NACE-certified in corrosion, cathodic protection, coating, material selection / design
  • PhD.-level Professional Engineer (PE); NACE-certified in cathodic protection (CP2) and coatings (CIP1)
  • PhD.-level Technologist; with expertise in computer-aided design (CAD) and simulation
  • Corrosion Engineer; NACE-certified in cathodic protection (CP2) and experienced in failure analysis
  • GIS mapping scientist
  • Senior soil testing specialist

Technical Approach-Matergenics’ approach considers the following:

  • Examination of spatial patterns associated with the physical and chemical properties of soil – in order to identify areas of high This evaluation leads to insights on overall corrosion risk, and answers questions on where to locate new pipeline and substation infrastructure
  • GIS identifies the least or most corrosive sites, and also locates access to sites and possible sources of stray current for corrosion mitigation

Some layers that are incorporated into corrosion maps are:

  • Soil resistivity
  • Soil salinity
  • Soil pH
  • Soil type, including the clay content
  • Drainage characteristics
  • Possible presence of stray currents from nearby gas pipelines or other protected assets
  • Corrosivity of the water table

Sources of Data

  • Matergenics soil databases
  • Client’s database, if available
  • Soil Survey Geographic Database (SSURGO) – the most detailed level of information for resource management, county planning, etc.
  • USDA database
    • Note that soil data comes in tabular that but can be linked to polygonal attributes/raster file over areas of interest via “map unit key”

The project consists of two phases:

  • In Phase I, the relevant data will be collected, categorized, and analyzed with respect to the project objectives. The information will consist of five distinctive sets of data.
  • In Phase II, a knowledge-based approach along with adequate and accurate equipment, and advanced techniques, will be used to collect, analyze, and verify the Phase I corrosion mapping.
  • Matergenics recommends that investigators should not only consider soil parameters, but also external corrosion sources – such as stray current and AC interference – in order to determine and comprehensively assess corrosion risks.

A proprietary method is utilized in Matergenics’ corrosion risk assessment. The method includes an algorithm to assign a corrosivity index to each location on the map based on soil properties , geological data , and external corrosion factors.  The accuracy of this algorithm has been field tested and proven in several projects.

Matergenics will also include maps for gas pipelines and transmission towers (if available), either of which may be a source for stray current corrosion.

A corrosion risk assessment map will combine various properties of soil to identify areas of high, medium, and low soil corrosivity. With this map a pipeline company would be able to deploy its resources most efficiently to specific areas of identifiable high corrosion risk.

The following  demonstrate various examples of soil corrosivity mapping for utility structures and pipelines:

 

Assessment of the Accuracy of the corrosion map:

In order to assess the accuracy of the corrosion map, selected pipeline sites and sections will be selected from distinctly different service soil environments with varying corrosivity indices.

Field inspections will be performed to investigate soil corrosivity and corrosion risks at selected sites with high corrosion risks as determined by corrosion maps.  Matergenics will perform statistical analysis to determine the appropriate sample size, so as to adequately represent the pipeline service lines in the service territory.

Specific techniques will be used to detect underground corrosion activity, including:

  1. Close-interval potential survey (CIS) is a well-known method to measure the “potentials” of buried pipelines. Matergenics can estimate corrosion penetration based on potentials, predictive modeling and, soil corrosivity.
  2. DC current measurements, if feasible.
  3. Direct current voltage gradient (DCVG) surveys.
  4. Electrochemical technique to assess the corrosion rate based on LPR (linear polarization resistance) on the bare surface of the pipe. The amount of material loss and formation of passive corrosion products on the metal surface affect the values of current and potential in a temporary polarization test, if “off” potentials are less than critical potentials required for corrosion protection. The measurements can be correlated to the current state of corrosion if the age and corrosion potentials are known.

Methods to determine soil corrosivity include:

  1. Soil resistivity measurement (per ASTM G57: Standard Test Method for Field Measurement of Soil Resistivity Using the Wenner Four-Electrode Method), with different pin spacings to perform Barnes layer analysis. This allows calculating soil resistivity at specific depths.
  2. Soil sample collection at shallow and deep burials (if feasible, and depending on site condition) for laboratory analysis. Laboratory tests include the following for soil corrosivity assessment and determination of input parameters for a predictive corrosion rate model:
  3. Instantaneous corrosion rate measurement (for steel) in mils per year (mpy), per ASTM G59; Standard Test Method for Conducting Potentiodynamic Polarization Resistance Measurements, and ASTM G102; Standard Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements
  4. As received and saturated soil resistivity measurement per ASTM G187; Standard Test Method for Measurement of Soil Resistivity Using the Two-Electrode Soil Box Method
  5. Moisture content measurement, per ASTM D2216; Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
  6. Salt contaminations for the following water soluble salts:
  • Chloride per ASTM D51;: Standard Test Methods for Chloride Ion in Water
  • Sulfate per ASTM C1580; Standard Test Method for Water-Soluble Sulfate in Soil
  • Sulfide per ASTM D4658; Standard Test Method for Sulfide Ion in Water
  1. Soil pH measurement, per ASTM G51; Standard Test Method for Measuring pH of Soil for Use in Corrosion Testing

Soil redox potential measurement, per ASTM G200;Standard Test Method for Measurement of Oxidation-Reduction Potential (ORP) of Soil

We perform thousands of soil corrosivity analysis every year and our crews can provide accurate soil corrosivity and confirm the the corrosion map by on-site soil corrosivity risk assessment.

 

Atmospheric Corrosion Map

Our  assessment of atmospheric corrosivity is based on international standard ISO 9223. The classification is based on SO2 pollution, chloride deposition and  time of wetness considering wind loads. These results , in addition to geostatistical approach will provide a map of atmospheric corrosion in region of interest.

Corrosion cannot take place without presence of moisture(electrolyte) and corrosive ions . The time of wetness is a measure of how much time the material will be in contact with a conducting solution. Wet surfaces are caused by factors such as dew, rainfall, melting snow, or high humidity. These conditions are estimated by looking at the time during which the relative humidity is greater than 80% at temperatures greater than 0 °C.  Sulfur dioxide pollution is another major cause of atmospheric corrosion, and is more prevalent in industrial and urban environments. Chlorides are a known corrosion risk for several reasons. Firstly, they are a major component of most salts, which accelerate corrosion due to their hydrophilic nature. When a salt attracts water and dissociates, it produces a highly conductive electrolyte. Secondly, chlorides are  main catalyst for pitting corrosion, which is an autocatalytic, localized attack. Chlorides are known to cause hydrolysis and create acidic chlorides. In addition, corrosion products that contain chlorides are typically more soluble than those that contain oxides. We will monitor airborne salts carried by the wind from the ocean. Airborne chloride concentrations are not monitored by weather stations and the models that we use to determine them are only accurate up to a few miles from the shore. As such, most estimates using the model in conjunction with ISO 9223-1992 will be utilized for atmospheric corrosion maps. On-site measurements will be  to obtain more accurate deposition rates for chlides, sulfates and time of wetness per ISO 9223-1992.

These three factors are then combined to determine an overall corrosion environment classification. Based on the classification, the corrosion rates are estimated based on Matergenics existing  data. For example our estimates show that Los Angeles is typically either C3 or C4 (moderate to high corrosion rates). For carbon steel, this equates to 25 to 80 µm/year. For zinc, this equates to 0.7 to 4.2 µm/year. This agrees with data from the American Galvanizers Association (21.4 µm/year for carbon steel and 1.09 µm/year for zinc). It should be noted that this assumes that the structure in question is not too close to the ocean.

Along the coastline, a C5 (very high corrosion rate) can be expected due to higher chloride deposition rates. Concentration of sea salt aerosols, which are the main atmospheric pollutants in coastal regions, gives an indication of the probability of the atmospheric corrosion.  A combination of the results with a geo-statistical approach and modeling wil be used to construct the corrosion map.  The specific environmental conditions, which are affecting the source and distribution of airborne salinity will also be considered in construction of corrosion risk maps.

The construction of atmospheric corrosion risk map consists of two phases:

  • In Phase I, the relevant data will be collected, categorized, and analyzed with respect to the project objectives. The information will consist of several distinctive sets of data such as chloride deposition rates, sulfate deposition rates, time of wetness and wind data.
  • In Phase II, a knowledge-based approach along with adequate and accurate equipment, and advanced techniques, will be used to collect, analyze, and verify the Phase I corrosion mapping at statistically representative selected sites. Matergenics recommends that investigators should not only consider atmospheric parameters, but also  corrosion sources – such as presence of chemical plants emitting corrosive gases, electric generation plants, salt sprays sources, wind loads… – in order to determine and comprehensively assess corrosion risks.

A proprietary method is utilized in Matergenics’ corrosion risk assessment. The method includes an algorithm to assign a corrosivity index to each location on the map based on atmospheric data , wind  data, and  corrosive gases by chemical plants.  The accuracy of this algorithm has been field tested and proven in several projects in California for major Utility companies.

Case Study

Recently we were retained by a major company to assist them in developing a corrosion risk assessment map for their service territory.  The genesis of this project started when they found severe below-ground corrosion after a short time in service.  Considering that they had several thousand structures across their service territory, the thought of inspecting each and every one of the structures would be a monumental task.  In consulting with Matergenics it was decided that the best way to approach this would be to develop a corrosion risk assessment map of their service territory.  The map would identify areas of high, medium and low below-ground corrosion risks.

 

                                   Localized Corrosion Due to Stray Current. Corrosion Map Application

WE VALUE OUR CLIENTS

We are here to help. We respond to all customers promptly by sending a technical proposal to address testing, investigation and the proposal costs. Please call Dr. Zee at 412-952=9441  or Matergenics at 412-788-1263 and let us know how we can assist you..

Looking forward to hearing from you!

 

 

 

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