Determination of anode resistance to ground is typically an integral part of cathodic protection system designs. However, complications in this process arise when anodes are located close together as mutual interference effects become important, often resulting in significant reduction in effective output. Such considerations can apply for anodes on structures, on sleds and between sleds (if multiple sleds are required such as can be needed, for example, with retrofit installations).
|Contours of current density on the anode surfaces (blue=low, red=high) Chart shows Dwight data (green)for interference ratio of a sled with 3 anodes, with extrapolation to smaller anode spacings. At 1.64 ft (0.5m) spacing, Dwight exaggerates the sled current by 30%|
If you have concerns about the reduction in effectiveness resulting from the need to locate anodes in close proximity to one another, and want to understand how the impact can be readily determined, please contact us.
BEASY paper presented at NACE Corrosion 2019
How to Improve Accuracy of Anode Output Estimated From Field Gradient Measurements
By John Baynham and Tim Froome
At Corrosion 2019, BEASY presented a paper addressing a number of factors that can impact the interpretation of measurements taken during survey with probes incorporating two reference electrodes.
Typical practice is to convert the potential difference between the two electrodes into an estimated anode output. There are, however, risks that those values may be inaccurate if appropriate consideration is not taken of factors such as:
- The stab being taken at a location away from the middle of the anode
- The probe not being perpendicular to the anode surface
- The structure around the anode distorting the electric fields (eg if the structure is not symmetrical)
- Proximity to other anodes
The influence of such factors was explored in the paper and demonstrates how if, for example, measurements are not taken centrally on the anode, the data can nevertheless be used to estimate output.
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