PR469-183600-R01 The Influence of Solid State Decouplers on Pipeline CP Surveys

Abstract

The objectives of this research are to figure out how solid state decouplers (SSDs) influence the surveys related to pipeline cathodic protection (CP) and provide corresponding field guidelines on how to mitigate the adverse effects of SSDs. Firstly, by combining the classical capacitor discharge theory and the equivalent circuit of the CP system, a four-stage physical model is built to explain how SSDs' discharge current pulse influences the CP related readings. From the physical model, we can obtain the following conclusions: (1) The driving force behind the discharging of an SSD's capacitor, after CP currents are cut off, is the voltage drop in the pipeline; (2)There are two contributors to the CP instant-off potential spikes: self-induced pipeline current and SSD discharge current; (3) The time constant ( and tau;=RC) of an SSD installation determines how fast the SSD finishes its discharging process; (4) The adverse effects of SSDs can be mitigated by making the SSD discharge time constant and tau; small enough (3 and tau; Before performing numerical modeling, some commonly used SSDs are tested for their capacitances in the lab according to the classical capacitor impedance theory. The test results show that the typical SSD capacitance is between 0.15 F and 0.36 F. The target pipeline for numerical modeling is a 50 km pipeline with different levels of coating quality, SSD grounding resistance, and SSD capacitance. An equivalent circuit model with ten parallel branches is built accordingly, and solved by an open-source electrical circuit software module. The numerical modeling results firmly support the primary conclusions drawn from the four-stage physical model. Moreover, the parallel analog circuit tests in the lab further prove the rationality of the four-stage model. Finally, comprehensive field tests are performed to study how SSDs influence the CP install-off potential survey, close interval potential survey, direct current voltage gradient, and alternating current voltage gradient. Practical field guidelines on how to mitigate SSDs' influence are proposed.