Principle of clamping diode and its influence on cathodic protection

Clamping diode has been widely used for AC interference mitigation of pipelines. However, its principle is rarely discussed in the industry of pipeline, and there are many misunderstandings on its application. In this paper, based on the internal structure of clamping diode, its mitigation effect on pipeline-ground AC voltage and its influence on the on potential and polarization of cathodic protection (CP) were discussed combined with the field testing data. And finally, the effect of grounding material and pipeline potential difference on the live potential was analyzed in the clamping current drainage. Based on above analysis, the misunderstandings on the clamping diode are clarified. It is indicated that this device does not have the function of DC isolation and its complementary effect on CP shall be investigated further for confirmation. When the clamping diode is used, the on potential of pipelines may present three shift phenomena, i.e., positive shift, negative shift and non-shift, and the shift direction and degree are in close relation with the potential difference between the drainage ground bed and the pipeline.