This paper reviews five field assessments of the cathodic protection of coated steel pipelines buried in soils of an average resistivity of 4300 Ω cm, performed using the close interval survey (CIS) technique and incorporating the instant off potential (IOP) method to measure any voltage drop. Multiple current sources were identified in the surveys, and simultaneous interruption of all the current sources was achieved using synchronised switches. The results presented here highlight the importance of incorporating the IOP method when performing CIS in order to quantify the voltage drop factor and thus improve the interpretation of potential measurements. Unexpected field situations encountered when performing the CIS technique are discussed and the practicality of using corrosion coupons is analysed.
The authors express their gratitude to Eng. C. K. Meier from Corrosion Control Inc., Rutledge, Ga, USA for the many discussions, and to CICYT, Spain (Project Nº DPI2011-26480) for financial support.
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