Taking Corrosion Head On.



General Considerations

Description of the DCVG Technique

The DC Voltage Gradient (DCVG) technique is used primarily to locate defects/faults on the pipeline external coating. In addition to the former, the technique enables one to carry out further tests to determine the status of the located defects.

When DC current flows in the soil to or from bare steel/metal in contact with the soil, as in cathodic protection, a voltage gradient is established in the soil. This voltage gradient increases with defect size, pipe depth and soil resistance.

The DCVG method utilizes a sensitive millivoltmeter to measure the voltage difference between two copper/copper sulphate half-cells (probes) placed in the soil across a typical voltage gradient region ie. Near a defect. The half-cells are placed one or two metres apart with one half cell adopting a more positive potential than the other, and as a result the direction of current flow can be established.


General Considerations
Description of the PCM Technique

The Pipe Current Mapper (PCM) technique is used primarily to map current flow on a pipeline with significant benefits in approximating external pipeline coating condition.

When DC current flows in the soil to or from bare steel/metal in contact with the soil, as in cathodic protection, a voltage gradient is established in the soil and a specific current flow pattern is established on the pipeline. This voltage gradients and current flow patterns on a specific pipeline may vary with defect size, pipeline coating and soil resistance.

A current flowing on a buried conductive structure produces a magnetic field directly proportional to the magnitude of the applied current. By resolving components of the magnetic field from above ground, the original current can be determined accurately.

To undertake an accurate close interval potential survey requires modern state of the art equipment and a series of GPS synchronized current interrupters.  All rectifiers influencing the area of the pipeline to be surveyed must be synchronously interrupted to allow the accurate measurement of the rectifier ON and Instant OFF potentials.

GPS current interrupters generally cover a range of 10 amps to 200 amps.  The current interrupters can be installed in either the AC supply to the rectifier or the DC output of the rectifier.  A sufficient number must be installed such that all rectifiers that could influence the potential of the pipeline in the area to be surveyed must be interrupted synchronously.


Cathodic protection comprises the application of both electrical and chemical principles to prevent the corrosion of suitably submerged steel structures.

In simple terms the steel structure requiring corrosion protection is rendered cathodic (negative) and the circuit is completed with an anodic (positive) component. Current flows from the anode to the cathode thereby preventing the oxidation (corrosion) of the steel.


We specialise in the provision of full range cathodic protection surveys such as:
• DCVG (Direct Current Voltage Gradient) surveys, 
• pipe-to-soil
 potential surveys, 
• soil resistivity
• current demand
• stray DC current
 surveys, and 
• AC mitigation
 surveys amongst others.

Our team of experts provide full service management from the conceptual phases of a project through to the final stages of implementation. This would typically include setting out the scope of workbudget estimatesfield surveysreportingdetailed designtenderschedule of rates and quantitiestender processadjudicationtender award and project management.

Paradigm Projects (Pty) Ltd presently manages in excess of 1800km of pipeline network for various clients. This service comprises the total assessment of pipeline networks, existing corrosion protection system assessmentinteraction with other pipeline operators, technical management of other corrosion consultants and implementation of ongoing corrosion system maintenance and capital projects.

Paradigm Projects (Pty) Ltd

Corrosion Engineering Organization

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