Effect of Alternative Cathodic Protection Potentials on Carbon Steel Corrosion in Brazilian Offshore Condition

Abstract Subsea equipment used in offshore oil production must remain reliable and under adequate structural integrity conditions for many years. Ensuring long-term integrity in deepwater environments is challenging, and cathodic protection (CP) is mandatory to mitigate corrosion of equipment. CP systems in deepwater, typically based on sacrificial anodes, aim to maintain the electrochemical potential of carbon steel (CS) within the range -800 and -1100 mV vs Ag/AgCl. Potentials more negative than -1100 mV may cause hydrogen embrittlement and/or promote cathodic disbondment of coating, while values more positive than -800 mV would indicate insufficient protection, based on common standards criteria (thermodynamic concepts). When CP potentials fall outside this range, anode replacement is recommended — an expensive process involving materials, vessels, and ROVs. This work investigated the corrosion behavior of CS under less negative CP within alternative potentials (-750 to -700 mV vs Ag/AgCl), corrosion rate and CP criteria (-800 mV vs Ag/AgCl) in simulated conditions. Laboratory tests at 0-, 500-, and 1000-meters depth. Field tests, conducted using instrumented buoys, were deployed at 500 and 1000 meters. Results were complemented by inspection data reports from Petrobras subsea systems and equipment. The findings provide technical basis for reassessing CP criteria for offshore assets operating under environmental and operational conditions like those defined in this study.