Local cathodic protection well casings

After a sufficient polarization period, which for the well casing is about a year, for flow lines with a high protection current requirement about half a year, and for flow lines with good coating about a month, the cathodic protection for the flow lines can be verified as in Section 10.4. If the cathodic protection is set up as local cathodic protection, checking is only necessary after a year. 

After measuring the zero profile, AU measurements are carried out with the injection of a cathodic protection current. In contrast to the zero profile measurements, the distance between the individual measurements is 25 to 50 m. Shorter distances between the measuring points are used only at depths where there are unusual AU profiles. Current should be injected at at least three different levels. The protection current density of about 12 mA m obtained from experience should be the basis for determining the maximum required protection current. As shown by the results in Fig. 18-3, the AU profiles are greater with increasing protection current. The action of local cells is suppressed when the AU values no longer decrease in the direction of the well head. This is the case in Fig. 18-3 with a protection current I = 4A. 

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