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Cathodic Protection |
What CP does is not actually to eliminate corrosion. Instead, it reduces the corrosion rate to an acceptable level by transferring it from the structure to be protected to the cathodic protection anode(s), thus making the structure the cathode of an intentional corrosion cell.
For any corroding structure, there are numerous local and microscopic corrosion cells on the surface of the metal. The potential difference between the anode and cathodes of these cells drives the corrosion current. The concept of CP involves reducing the potential difference to zero, resulting in zero corrosion current. CP is accomplished by galvanic (sacrificial) anode systems and impressed current systems.
In impressed current systems, a direct current is forced to flow onto the structure from an external anode which current polarizes the cathode sites in an electronegative direction. By properly adjusting the amount of current flowing, the potentials of the cathodic sites polarize toward the potentials of the anodic site, and corrosion current is reduced.
When the driving voltage of the CP system reach the open circuit potential of the most active anodic sites, the voltage difference between the local anodes and cathodes is eliminated and corrosion ceases.
Cathodic protection is a polarization phenomenon. Polarization of the cathodic sites to the open circuit potential of the anodic sites is the criterion for eliminating corrosion, but to determine the open circuit of the most active anodic site is however impossible. Several criteria have been developed and recommended by National Association of Corrosion Engineers (NACE) International Standard Organization and (ISO) to assist meeting the true criterion for polarization. The polarized potential of a structure is measured to determine the level of protection, and this is the potential across the structure-to-electrolyte interface. This is essentially the potential of interest; – the result is the algebraic sum of all the voltage drops (IR) in the measuring circuit. Our engineers are current with the various levels of NACE cathodic protection (CP) certifications.
CP System Design
· Sacrificial and Impressed Current Anode Systems for all Onshore & Offshore Structures
· Offshore Assets, Harbors, Jetties & Piers, Pipelines, Tanks, DCVG surveys
· Production Well Casings (Oil and Gas Wells, Groundwater Wells, Injection storage wells)
· Transmission Pipelines (Crude Oil, Refined Products, Natural Gas, Large Diameter Water).
· Above-Ground Storage Tanks (External Tank Bottoms, Double Tank Bottoms, Permanent Reference electrodes and Internal Water Storage)
· Gathering and Distribution Piping (Oil and Gas Gathering, Municipal Gas Distribution)
· Power Generation Facilities (Cooling Water Facilities, Power Line Distribution Towers, Plant Piping and Equipment)
CP Installation Services
Galvanic (Sacrificial) Anodes
Impressed Current Groundbeds
Surface Groundbed Configurations
Deep Anode Systems
Test Stations
Installation of Rectifiers and other Power Sources
CP Field Measurements
Current Measurements (Output, Requirement Tests, Line Current Test, Direction and Polarity)
Typical Resistance Measurements
Electrical Continuity Measurements
Electrical Isolation Measurements (Isolation {Insulating Joints)
Structure Continuity Measurements
Accidental Contacts
Structure-to-Electrolyte Potential (Close Interval Surveys, IR Drop).
Electrolyte Resistivity Measurements (Soil Box and Resistivity Probe)
Coupon Measurements
pH Measurements
Diode Bias
Use of Current Interrupters, Data Loggers and Clamp-On Ammeters
Use of Pipe Locating Devices (Conductive and Inductive)
CP System Monitoring and Cathodic Protection Effectiveness
Measurement of Structure-to-Electrolyte Potentials
· Coating Effectiveness Survey
Rectifier Voltage and Current Outputs
Current Output of Galvanic Anodes
Resistance of Groundbeds
Integrity of Rectifiers, Isolating Joints, Electrical Bonds, etc
Internal Electric Logging (Smart Pigs)
Electrical Resistance Probe Test Stations
Structure Examination by Excavation or Divers
Magnitude and Direction of Current through Mitigation Bonds
Coupon test Stations
Close Interval Potential Surveys
Recordkeeping
CP Stray Current Interference
Stray Current Types (Steady and Dynamic Stray Current)
Stray Current Identification
Stray Current Corrosion Control (Mitigation Bonds and Mitigation with CP)
CP Maintenance Services
Troubleshooting
Electrical Isolation
Cathodic Protection Levels
Groundbed Malfunctioning
Rectifier Routine Maintenance and Output Problems
Environmental Factors
Economic Feasibility Studies & Budget Estimates.
Failure analysis
Electrical Short Locating.
Electrical Continuity, Isolation & Resistance Testing.
System Maintenance
CP System Management, Installation Supervision and Testing
· Coating Application and Holiday Detection ((Factory or Field)
CP System Repair
CP System Relocation
CP System Abandonment
CP System Job Safety Analysis (JSA)
· Electrical Equipment (Rectifier) Case
· Lock Out / Tag Out (LOTO)
· Electrical Hazardous Areas
· Explosions or Ignitions
· Cathodic Protection Surveys
· Induced AC Voltages
· Excavations
· Hazardous Materials
· Material safety Data Sheets (MSDS)
· General Precautions
CP System Loss Troubleshooting.
Several factors can affect the level of catholic protection. CMS troubleshoots and investigates the following problems that could affect the level of your cathodic protection system and determine a loss of cathodic protection:
· Reduced Cathodic Protection
· Current Groundbed Malfunctions
· Broken Continuity Shorted Isolation
· Underground Contact to a Foreign Structure
· Shorted Casing
· Stray Current Interference
· Inaccurate Measurements
CP System Instrument and Material Supply House
· DC Rectifiers (Universal rectifiers, J.A. electronics)
· Alternative Power Sources (Hoying Solar Power Supply, Global Thermoelectric)
· Impressed Current Anodes (Treated graphite, Silicon Cast Iron, Mixed Metal Oxide, Platinum)
· Sacrificial Anodes (Hi-Potential Magnesium, Aluminum, Zinc)
· Carbon Backfill (Loresco Products, Asbury Carbon, Great Lakes Carbon)
· Instruments (Borin Corrosion Industry ComputerTechnology)
· Accessories (Cadweld Materials and Equipment, Pipeline Tapes and Mastic, Pipeline Markers, Test Stations, Link Seals, Casing Insulators, Insulating Unions and Flange Kits, Junction and Bond Boxes)
· Current Interrupters
· Data Loggers
· Clamp-On Ammeter
· Borin Reference Electrodes (for all applications)
· High Impedance Multimeters
· Soil Box
· Isolation (Insulating) Joints
· Diode Bias
· Pipe Locating Devices
· pH Meters
· Coupons and Probes
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