Close Interval Potential Surveys

The effectiveness of cathodic protection can be accomphshed by monitoring the pipeline potential using the close interval potential survey (CIPS) method or by using direct current voltage gradient (DCVG) or IR coupon techniques. Also, physical and electrochemical methods can be used to estimate the corrosion rates of a cathodicaUy protected system. 

CIPS (close interval potential survey) Enables detection of defects of coatings, evaluation of cathodic protection effectiveness, CP station current is used. Localization of area with insufficient protection, localization of coating defects, indication of defect size. Requires inspection of whole pipeline, may not show coating disbonding, does not determine corrosion. 

The close interval potential survey (CIPS) and the DCVG (direct current volt-... 

The principle of a close interval potentials surveys (CIPS) is to record the potential profile of a pipeline over its entire length by taking potential readings at approximately 1-m intervals. A reference electrode is connected to the pipeline at a test post and positioned in the ground over the pipeline at regular intervals for the measurement of the potential difference between the reference electrode and the pipeline (Fig. 13.35). The CIPS technique provides a complete pipe to soil potential profile and the interpretation of results, including the identification of defects, is relatively straightforward. 

Close interval potential surveys. Close Interval Potentials Survey (CIPS) refers to potential measurements along the length of buried pipelines to assess the performance of CP systems and the condition of the cathodically protected pipeline. The potential of a buried pipeline can obviously be measured at the permanent test posts (Fig. 11.21) but, considering that these may be miles apart, only a very small fraction of the overall pipeline surface can be assessed in this manner. The principle of a CIPS is to record the potential profile of a pipeline over its entire length by taking potential readings at intervals of around 1 m. 

Pawson, R. L., Close Interval Potential Surveys— Planning, Execution, Results, Materials Performance, 37(2) 16-21 (1998). 

Potential data loggers are now available to undertake close interval pipeline surveys. These increasingly popular surveys, determine a pipeline s pipe-to-soil potential at nominal intervals, of as little as 1 m. Additional information is gained by the recording at each point, of both the pipe-to-soil potential with the cathodic protection system ON , together with the potential some 100-300 ms after the cathodic protection system is switched OFF . This instantaneous OFF potential being devoid of any IR drop component present in the ON potential measurement. 

NACE International has drawn up a Standard Recommended Practice [RP0792-92] for the format of computerized close interval survey data. These guidelines describe a general organization for CIPS data, apphca-ble to both mainframe and personal computers. According to these recommendations, each data file containing the on and off potential values should be supplemented with the following information, in the form of a separate header file or a header incorporated into the data file ... 

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