Investigation on organic pipeline coating effectiveness via electrochemical impedance spectroscopy

High solid thick polyurethane coatings are one of the best choices for pipeline coatings. In this research electrochemical impedance spectroscopy (EIS) has been used to assess the degradation of a high solid polyurethane pipeline coating. Physical and electrochemical properties of coating were interpreted via analysis of equivalent circuits. The mechanism and kinetic of electrochemical systems were assessed by measuring the variations in resistance, capacitance and percentage of water uptake through coating. Electrochemical impedance spectroscopy measurements showed that this coating has very good protection efficiency and after 3 months immersion in 5%NaCl solution, resistant and capacitance of coating reach similar to 10(7) Omega cm(2) and 10(-12) F cm(-2) respectively. Furthermore cathodic disbonding test was carried out in accordance to ASTM G8 for 30 days. After this time duration only 1.53 mm disbonding was observed around the created hole. The coated panels were evaluated in salt fog (ASTM B117) and 100% humidity cabinet (ASTM D2247). After 1000 h exposure in salt fog and 100% relative humidity cabinet no blister, chalking, rust or coating delamination was observed. The results revealed that the coating has very high protection efficiency and could be a very good alternative for conventional coatings in pipeline protection against corrosion.