Effect of scratching on galvanic corrosion in oil and gas environments

Galvanic corrosion behavior in stagnant oil and gas environments, when the metal specimens were mechanically scratched, was investigated by electrochemical methods using material combinations ranging from carbon steels to duplex stainless steels. Galvanic currents and coupled potentials increased rapidly upon mechanical scratching, immediately started to decrease, and finally returned to the values before scratching in sweet and sour environments. Therefore, an increase in the galvanic corrosion rate caused by scratching was negligibly small for the long term, and localized corrosion as a result of mechanical scratching did not occur in these stagnant solutions. The change in coupled potential immediately after scratching was small in sweet environments and large in sour environments. For rapidly forming corrosion films on less noble metals, the galvanic current after scratching decreased rapidly; however, for slowly forming corrosion films on less noble specimens, galvanic current after scratching decreased gradually.