The Experimental Study Of Measuring The Off Potential Of Buried Pipelines With Test Block Power Interruption Method

The cathodic protection potential is the threshold value of corrosion potential which mustbe achieved to get into the scope of the protection potential. It marks the extent of cathodicpolarization of buried pipelines, is the important index to monitor and control the effect ofcathodic protection. The purpose of measuring the cathodic protection potential of buriedpipelines is to measure the cathodic protection potential of a point on the pipelines, the actualoperation is to measure the voltage difference between the point and the reference electrode.However, as there exists the circuit between the measured point of pipelines and the referenceelectrode, the voltage difference that direct measurement includes the potential drop (IR drop)which is generated by the resistance when the current flows through the metal and theelectrolyte (such as the soil). The IR drop may be up to hundreds of mV, this causes an errorbetween the measured value and the actual cathodic protection potential. The off potential isthe protection potential of pipelines after eliminating the IR drop caused by the protectivecurrent without the existence of interference currents. The test block power interruptionmethod uses the measured off potential of the test block whose polarization degree is the samewith the pipeline at the power interruption moment to approximate the cathodic protectionpotential of the pipeline. It easily measures the cathodic protection potential without IR dropin the main, at the same time, the pipeline and the external power is connective.In this paper, on the basis of domestic and international research, firstly establishing animpressed-current cathodic protection system for buried pipelines in the laboratory, thenworking out the experimental plan, researching the the process of polarization anddepolarization of the test block in the soil by the experiments, the determining methods andrecommended values of key parameters at measurement of test block power interruptionmethod are put forward, the specific steps of measurement process and some problems shouldbe noted are provided, finally, forming the theoretical and experimental basis of test blockpower interruption method measurement. The specific content of this paper include thefollowing aspects:①Summarizing the measurement methods of the cathodic protection potential of buriedpipeline, through the theoretical study, perfect the measurement principle of test block power interruption method;②Carrying out experiment study of the test block power interruption method in a sort ofpipe material and a sort of soil, thus the determining methods and recommended values of keyparameters at measurement of test block power interruption method are put forwardpreliminary. Carrying out experiment study of the test block power interruption method indifferent pipe material and different soil, correcting and improving the previous conclusion;③Carrying out the contrast experiment study including the test block power interruptionmethod and the pipeline power interruption method and the polarized probe powerinterruption method, thus providing the experimental basis for the application andpopularization of the test block power interruption method;④Carrying out field measurement of the off potential of buried pipelines by the testblock power interruption method, perfecting the test block power interruption method andverifying the practicality and accuracy of the test block power interruption method;⑤Programing the data processing software of the test block power interruption method.