FIELD TESTS ON AN ADVANCED CATHODIC PROTECTION COUPON
An advanced cathodic protection coupon design which eliminates almost all of the soil IR drop during current-on potential measurements has been developed. Potential measurements are made through a slot in the geometric center of the coupon,a design sometimes referred to as a concentric coupon. This design greatly minimizes the electrolyte distance between the reference electrode and the coupon, which,in turn, minimizes the IR drop error contained in the measurements. This paper presents results from laboratory and field tests on this advanced coupon design.
1. Concentric CP coupons are a very effective way to substantially eliminate voltage drop error from current-on readings.
2. The effectiveness of concentric CP coupons varies with electrolyte resistivity. In high resistivity electrolytes, using these coupons will eliminate about 90% of the voltage drop error. In lower resistivity electrolytes, virtually all the voltage drop error is eliminated from current-on readings made with concentric CP coupons.
3. The performance of concentric CP coupons can vary depending on their orientation with respect to the structure. Best results are achieved when the coupon is positioned so that it faces the structure.
4. The distance a concentric CP coupon is placed from the structure does not appear to affect its ability to eliminate voltage drop from current-on measurements.However, if it is placed too far away from the structure, the measured potential may be more electro-positive than that on the structure. A compromise position should be sought where the coupon is placed far enough away from the structure so that it is not shielded by it, but not so far away that it is not representative of conditions at the pipe.