What Does Potential Survey Mean?
A potential survey is a technique used to measure the magnitude of corrosion of pipelines and detect hot spots where the occurrence of corrosion is severe.
The potential survey is based on recording pipe-to-soil potentials at regular intervals over the pipeline with the reference electrode(s) located on the ground surface. The higher the value of pipe-to-soil potential, the higher the magnitude of corrosion.
The structure-to-soil potentials do not give a qualitative measurement of corrosion. However, they are very useful in the prediction of corrosion when used in conjunction with other data, such as soil resistivity.
Corrosionpedia Explains Potential Survey
The tendency for a metal to corrode can be predicted by its potential in a particular environment. Potential surveys are made to assess the magnitude of corrosion of pipelines and detect special areas and spots where the degree of corrosion is severe.
A general idea of pipeline corrosion severity can be obtained from the average pipe-to-soil potential. Newer pipelines generally exhibit a lower negative potential than older and coated pipelines. For example, a new pipeline may show an average potential of -1.65V when compared to a potential of -1.2V shown by an older pipeline.
The distribution of potential along the survey of earth above the pipeline indicates the location of corroding areas. Different types of soil encountered by the pipe affect the potential of the pipe. The changes in soil resistivity also induce potential differences. The surface potential surveys are made to determine the anodic and cathodic areas on the pipe.
Several methods are used for potential measurement, such as the one-electrode and the two-electrode methods. In the two-electrode method, two Cu/CuSO4 electrodes are placed on a wooden clipboard and connected to each other through a resistance voltmeter. One of the electrodes is in the rear position and the other in the forward. The potential drops at each location are measured between the two electrodes.
The potential difference is recorded and the polarity of the electrode is also noted. This procedure is continued along the whole length of the pipeline. If the polarity of the forward electrode is negative, the potential drop is subtracted to get the final pipe-to-soil potential.
The Coastal Corrosion Control Survey offers computerized potential surveys. The Close Interval Potential Survey (CIPS) technique is targeted at assessing the cathodic protection effectiveness over the entire length of the pipeline.