Functional relationship between cathodic protection current/potential and duration of system deployment in desert conditions
Introduction
Analysis of the papers published so far regarding the area of the measurements in cathodic protection with overview on the attenuation of the protection current/potential shows that these data are very scanty. Those are mostly periodical records of potential/current [4], [5], [6], [7], or laboratory analysis of the parameters of the CP system [3].
The aim of the paper is to formulate a mathematical model correlating protection current/potential and exploitation time of CP system with galvanic anodes and verify obtained model with data obtained from exploitation of a real CP system.
Development of such a model would create presumptions for more reliable predictions of the behavior of the CP system in some future time intervals. In addition, confirmation of our model could facilitate efficient preventive performance of CP system within projected technical characteristics as long as possible, without direct measurements on the plant.
Our model is based on modified functional correlations for electrode processes and polarization diagrams [1] in addition to a non-linear functional relationship given in [1], [2]. Analysis is done for specific conditions of CP provided to concrete covering prestressing (PCCP) steel wire.
Section snippets
Description of CP system applied to PCCP
Cathodic protection with galvanic anodes is applied on water supply system consisting of reinforced concrete pipes without insulation, having D = 4000 mm. Concrete covering pipeline with prestressed steel wire is buried at average depth of 3 m. Shafts at the ends of sections, are accessible for connecting the cable installation, control – measurement sites and similar. Lengths of individual sections between shafts are 500–700 m. It is ensured that overstretched wires have electric continuity on
Physical model
CP system with galvanic anodes is based on direct electrical contact of two different metals (or their alloys) that have different natural potentials and located in the same corrosion electrolyte. In order to define distribution of the protection current and potential in CP system it is necessary to know the nature of the current of anode and cathode electrochemical reactions.
Fig. 3 shows diagram of polarization model used for analysis of electrochemical reactions on anode and cathode surfaces
Experimental basis and functional correlation
A statistical method that calculates current/potential as functional relationship with time of CP system deployment is introduced. Method is based on field measurements data for CP system on PCCP in desert conditions. Field measurements had been taking place in sections 200 km long CP during period of 22 months. Only characteristic sections with both high and low soil resistivity are presented in this paper. Developed model make it possible to predict the value of protection current/potential at
Conclusion
Extensive and cost – intensive field measurements confirm that there is a substantial reduction of CP current magnitude following initial CP system deployment. Thus, there exists a need for repetitive field measurements in order to establish and confirm the scope of CP protection for the object of interest [4], [5], [6], [7].
The conclusions we have made about changes in protection current values can be used effectively in the periodical recording of cathodic protection parameters in similar
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