Importance of Mapping
Digital atmospheric mapping allows one to analyze the relationships between atmospheric corrosion properties and ancillary data (e.g. pollutant deposition and remote/proximal sensing data) through several techniques.
Our corrosion maps can be used for corrosion risk assessment, materials and coating selection, as well as transmission line planning.
The Technical Approach to Constructing an Atmospheric Corrosion Map
Matergenics’ unique approach to atmospheric mapping considers the following:
1) Examination of spatial patterns associated with the physical properties and aerosol deposition of the area of interest. This evaluation leads to insights on overall corrosion risk, and answers questions on where to locate new infrastructure.
2) Identification of the least or most corrosive sites
Sources of Data
1) Client’s Database (if available)
2) National Atmospheric Deposition Program
3) United States Department of Agriculture
4) National Climatic Data Center
5) National Oceanic and Atmospheric Administration
Atmospheric Data Layers
Atmospheric properties contributing to corrosion are individually mapped and a proprietary weighting system is used to compare the layers and develop an overall corrosion risk assessment map identifying areas of high, medium and low corrosion. A few of the properties are listed below. Field surveys are then made to confirm the accuracy of the map. The key to this technology is finding accurate data and the development of an accurate weighting system.
Atmospheric Corrosion Risk Assessment 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. In addition to these properties, Matergenics also considers wind loads.
We 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.
Data Layers Used in Atmospheric Maps
Atmospheric aerosol deposition and wetness play a crucial role in the overall corrosivity of the environment. Our assessment of atmospheric corrosivity is based on international standard ISO 9223. However, in addition to the data used in the standard, we also consider other physical properties of the structure location. While not all of the following layers are used to produce the final corrosion map, an in-depth analysis can be conducted with the extra information.
Sulfur Dioxide Deposition
Time of Wetness
Oxidized Nitrogen
Precipitation
Chloride Deposition
Elevation
Wind speed and direction
Relative Humidity
International Standard ISO 9223
ISO 9223 establishes a classification system for the corrosivity of atmospheric environments. Atmospheric corrosivity falls in one of five categories set by the standard. C1 represents rural environments and C5 represents marine atmospheres.
The corrosivity category of the area of interest provides a basis for materials selection and protective measures with regards to specific application, particularly relating to service life.
The corrosion categories are based on the following three parameters:
deposition of Sulphur Dioxide
Sulfur dioxide plays an important role in atmospheric corrosion in urban and industrial areas. It is absorbed on metal surfaces, has a high solubility in water and tends to from sulfuric acid in the presence of moisture. Sulfate ions are formed in the surface moisture layer by the oxidation of SO2, and their formation is considered to be a corrosion accelerator.
Airborne chlorides
Chlorides are a major component of most salts, which accelerate corrosion due to their hydrophilic nature. When sat attracts water and dissociates, it produces a highly conductive electrolyte. Moreover, chlorides are a main catalyst for pitting corrosion, which is an auto catalytic, localized attack. Chlorides are known to cause hydrolysis ans create acidic chlorides.
Time of wetness
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% and the temperature is above 0 degrees Celsius.
Atmospheric Corrosion Risk Assessment Map
A proprietary method is utilized in Matergenics’ corrosion risk assessment. This method includes an algorithm to weight each data layer and assign a corrosivity index to each location on the bap based on the atmospheric data, wind data, and corrosive gasses by chemical plants.
The construction of an atmospheric corrosion risk map consists of two phases:
Phase 1: Relevant data will be collected, categorized, and analyzed with respect to project objectives. The information will consist of several distinctive sets of data such as chloride deposition rates, sulfur dioxide deposition rates time of wetness, and wind data.
Phase 2: A knowledge-based approach along with adequate and accurate equipment, and advanced techniques, will be used to collect, analyze and verify the phase 1 corrosion mapping at statistically representative selected sites. Matergenics recommends that investigators should not only consider atmospheric parameters, but also corrosion sources such as the presence of chemical plants emitting corrosive gasses, electric generation plants, salt spray sources, wind loads, etc. to determine and comprehensively assess corrosion risks.
