Measurement And Correction For IR Drop Of Cathodic Protection Of Oil And Gas Pipelines

As an important evaluation index of the pipeline cathodic protection,Impressed current cathodic protection has been widely used in corrosion protection of oil and gas pipelines.Due to the existence of the IR drop in the process of actual measurement, the true potential has not been obtained usually.The test block power interruption is simple and convenient and can reduce the influence of IR drop on protection potential effectively so this paper studying on measurement and correction for IR drop of cathodic protection of oil and gas pipelines has high theory value and application prospect.This paper about cathodic protection system was simulated in the laboratory and 20# steel was used for test blocks.The corrosion morphology of the test block which was tested under different protection potentials was characterized by scanning electron microscope.Off potential and depolarization potential were measured and analyzed comparatively under the condition of different exposed areas,different reference electrode distances,different soil resistivities.Protection effect of test block under different protection potentials was analyzed and judged by the method of corrosion coupons. The experience formula for calculating off potential under a certain condition was summarized.The results show that: Appropriate cathodic protection potential can restrain the ionization of the meta effectively and protect the test block fully.With the increasing of exposed area and reference electrode distance,IR drop is increasing and off potential is positive moving.With the increasing of soil resistivity JR drop is decreasing and off potential is negative moving.The change for IR drop of the test block power interruption is from dozens millivolt to hundreds millivolt. With the rise of cathode protection potential IR drop increases.The equation for IR drop is effective.From what has been discussed above,the test block power interruption method could reduce the measured error of IR drop which produced in impressed current cathodic protection system of oil and gas;only the exposed area of test block match with the breakage of pipeline coating we could ensure the accuracy of the potential measurement.