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1. • CommentAuthorzee
   • CommentTimeAug 10th 2008

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   Circuit Prioritizing Methodology and Identifying High Risk Transmission Lines and anchors for Inspection
   
   Matco has developed a set of predictive protocols by which to evaluate your subsurface assets. Using a combination of desk study, field inspection testing and evaluation of soil formations and corrosivity, Matco will go through your assest inventory and provide an inspection/repair plan which prioritizes the lines at risk based on:
   
   1-Circuit Importance
   
   2-Soil Formations,Topography, Aspect and Soil / Water Table Corrosivity
   
   3-Time in Service (age)
   
   4-Incidents, Accidents, Previous Inspection Reports
   
   4-Materials of Construction, Metallurgy, Coating and Cathodic Protection
   
   First, a desk soil formation study is conducted to predict the likelihood of corrosion taking place at each asset location. The asset inventory is tabulated and the geographic coordinates of each strucure are determined. Along with this data, the materials/coating or constructuion is noted and the age of each system is also listed. Then the local, regional, national and Matco soils data is reviewd by Dr. Gibbon Matco's senior geologist to determine what pertinent information can be found.
   
   Maps are made up within GIS framework so that each corrosion criteion is on an independent layer and can be queried in any combination with one another. Of course since the details of local conditions (topography, aspect , prior construction, etc) control the actual soil charateristics, each location will be placed within a range of predicted conditions. Then, transmission lines can be prioritized for field inspection. Based on the results of the field checks, the predictive criteria are fine tuned and a preventive inspection/maintenance plan (immediate inspection, 5 year inspection and 10 year inspection) is developed to check and protect the entire asset base. This may involve design and installation of cathodic protection systems where necessary in most corrosive sites. The field tier one inspection and tier two inspection methodology includes: Visual inspection, soil resistivity, electrochemical potential field evaluation, corrosion rate determination, ECN and dimentional measurments including pit depth and section loss. The test protocol will provide information as to excavation, repair, or no action.
   
   Field Inspection
   
   Matco Associates, Inc. will initialy assess the towers/poles/anchor rods by completing soil resistivity measurements directly on-site at different depths, therefore including the entire underground portion (including the water table, if present). The electrochemical measurements will identify lattice legs, anchor rods or poles are corroded. The results will indicate if cathodic protection should be installed immediately to prevent further corrosion of the component. The electrochemical corrosion rate determination will provide further information on the life expectancy of the structure and plan future maintenance guidelines. More accurate measurement of the soil resistivity will also indicate the quality of the grounding system. Matco's electrochemical measurements will determine if partial excavation should be considered. If so the following methodology will be performed.
   
   * Visual examination of above grade portions of towers,poles, ground anchors and CP assets; include appropriate digital photographic documentation.
   
   * Electrochemical measurements at towers, poles and each ground anchor which will immediately indicate the genertal corrosion activity and identify any hot spots or areas of extreme corrosion.
   
   * Partial excavation the backfill soil to a depth of three feet to allow for visual examination and thickness measurement on the ground anchors or tower legs.
   
   * On-site soil resistivity measurements at three different depths, depending on the depth or design of the given tower.
   
   * On-site determination and documentation of the moisture content of the soil.
   
   * On-site electrochemical, ECN, potential and polarization resistance measurements
   
   * On-site determination and documentation of the chloride/sulfate/sulfide.. concentration.
   
   * Above ground and underground section loss and member thickness measurements
   
   * The on-site testing will provide information on the life expectancy, frequency of inspection(immediate action, five year inspection or ten year inspection), and plan future maintenance guidelines. The maintenance may include coating, non-corrosive or passive backfill and cathodic protection.
   
   In Matco's approach the testing will be in accordance with American Society for Testing and Materials (ASTM) standards and American Association of State Highway and Transportation Officials (AASHTO) standars. The testing will be perfomed by certified technicians and reviewed by a NACE Certified Corrosion and/or Cathodic Protection Specialist.