Since June 1992, Kortek has focused only on cathodic protection works. Using the expertise of experienced specialists including NACE certified engineers and teamwork of different departments, Kortek provides everything regarding cathodic protection and corrosion control technologies. We assure that our cathodic protection design and applications are safe, on time and efficient.
Cathodic Protection Basics
Cathodic protection is directly related with the polarization of metal surfaces. Cathodic protection is achieved by polarization of all cathode (noble) areas potential to the most anode (active) parts on the metal surface. Normally corroding structures have both cathodic and anodic areas that corrosion occurs. If all cathodic areas can reach the potential of most active anodic area, the entire structure will become a cathode and corrosion will be eliminated.
A potential criteria is based on assumption of most anodic area potential on metal surface is likely to exist on the structure. Criteria depends on type of metal and environmental conditions.
Cathodic protection potential criteria from the literature for;
Iron or Steel in aerobic conditions at 25 ⁰C with respect to Copper Copper Sulphate is “-850 mVDC”
The potential criteria shall not be used without regard to environmental circumstances and operators requirements upon previous experience may differ.
In the application of potential criteria, regardless of structure material, the potential shall be considered as a polarized value (free of IR error) as indicated in current international standards.
Magnesium Anodes:
As a galvanic anodes, magnesium anodes are available in two general alloys, high potential (-1.75 VDC w.r.t Cu/CuSO4) and standard (-1.55 VDC w.r.t Cu/CuSO4). The magnesium alloys have an efficiency of %50 at maximum. This means that half of the metal alloy is consumed in self-corrosion during its life. They may be produced in wide variety of shapes as ribbons or blocks and available packaged with special backfill for maximum possible efficiency in underground use. These anodes are most useful in applications where the soil resistivity is moderately high includes fresh water and most soils.
Zinc Anodes:
The zinc alloy anodes have a nominal potential of -1.10 VDC with respect to copper copper sulfate reference. Its efficiency is relatively high ranging from %90 to %95. Zinc galvanic anodes can be casted and fabricated in wide variety of physical shapes and suitable for different methods of mounting. Zinc anodes with a backfill is used in soils having low resistivity commonly less than 2000 ohm.cm. These anodes is also commonly used as a galvanic anode for marine application on steel ship hulls and to mitigate induced AC on coated pipelines.
Aluminum Anodes:
Aluminum are mainly used in seawater environments. Different alloys are specified in international standards for diffent marine and off shore applications. The potential of aluminium anodes as galnvaic anode is between -1.10 VDC to -1.15 VDC w.r.t Cu/CuSO4 depends on alloy composition and efficiency between %85 and %95.
Potential Measurement: Structure to electrolyte measurements by using a high input impedance (ideally more than 10 Mohm) DC voltmeter, test lead from structure and reference electrode. This type of measurement is main cathodic protection data collection. It is important to consider IR errors and other resistive elements in measurement circuit to collect usable data.
Current Measurement: While it is not a cathodic protection critera, measuring current in the CP circuit is necessary to evaluate system performance. DC cathodic protection current measurements can be applied for galvanic anode, impressed current system output, bond current and current flowing through the structure.
Close Interval Potential Survey (CIP Survey): Basic potential measurements can be conducted on test post locations mainly for pipeline applications. To determine the potential over the entire pipeline requires that the reference electrode to be moved along the pipe route and placed at regular intervals. By using data logger, coper conductor wires and wearable equipment sets, such measurement can be done for pipelines to record complete cathodic protection potential profile of pipeline.
Coating Condition Surveys: Cathodic protection systems are directly related with the coating conditions and holidays should be evaluated with the potential measurement results in many cases. The type of coating surveys are, holiday detection for reachable parts, coating conductance method, Direct Current Voltage Gradient survey (DCVG), Alternative Current Voltage Gradient Survey (ACVG).
AC interference from overhead lines to a pipeline ca be transferred by three possible way, 1- conductive coupling, capacitivie coupling and inductive coupling. Estimating the AC interference effects on structure requires complex calculations or special softwares. Discharge of steady state AC currents from pipeline results with corrosion failures. Corrosion rate on such structures is related with the AC current density discharged from pipeline. Current international standards mention that more than 20 A/m2 AC current density may cause corrosion and corrosion is expected for more than 100 A/m2 AC current density. AC voltage on pipeline may also caused electrical shock hazards and standards have set the maximum allowable induced AC voltage that a person should be exposed as 15 VAC.
Basic type of induced AC voltage mitigation to safe levels of human safety and AC corrosion is grounding. Commonly used grounding electrodes for this purpose are packaged sacrificial anodes and anode ribbons installed in special backfill. Grounding materials that are not directly anodic to the pipeline would affect the cathodic protection system performance therefore such materials