Effect of Pulse Cathodic Protection on Corrosion and Electrochemical Conditions under Coating Disbondment of Pipeline Steel

This study investigates the effect of pulse Cathodic protection as compared to conventional Cathodic protection on corrosion and electrochemical conditions under disbonded coating of X-۵۲ pipeline steel. In this regard, a laboratory cell that can simulate the underlying conditions by applying cathodic protection was designed and made. Coupons with dimensions of ۲۰×۱۰×۵ mm, made from X-۵۲ pipeline steel were placed under the simulated coating disbondment while the length and gap size of disbondment was ۲۰۰ mm and ۳ mm respectively. By placing the cell in a simulated soil solution C۲, conventional & pulse CP of -۸۷۰mVSCE was applied to the open mouth (OM) of simulated coating disbondment. For pulse Cathodic protection, frequencies of ۱۰۰۰, ۵۰۰۰, and ۱۰۰۰۰ Hz were utilized. Result showed for conventional CP, potential failed sharply to Open Circuit Potential (OCP) at ۷ cm from the OM of the simulated coating disbondment. For pulse Cathodic protection, at the frequency of ۱۰ kHz, in contrast to conventional CP, no drop in potential was observed under the simulated coating disbondment. In fact, the potential gradient which normally is observed under simulated coating disbondment with conventional CP being applied was not observed. Aslo, investigating the chemical and electrochemical conditions under coating disbondment, showed that there was more uniform distribution of pH and potential with increase in frequency of pulse Cathodic protection, as compared to the conventional Cathodic protection being applied.