In situ evaluation of the carbon steel corrosion rate under low cathodic polarization in seawater (C2026-00209)

Erwan Diler, Nicolas Larché, Elisa Kassab, Eduardo Alencar, Jefferson Oliveira, Marcelo Schultz da Rocha , Tiago Hofman, Jose Antonio Da Cunha Ponciano Gomes

External corrosion protection for carbon steel offshore structures relies mainly on organic coatings and cathodic protection (CP) using galvanic anodes, designed to last for decades. CP efficiency is monitored via potential measurements, which must stay below the recommended protection potential (Ep). As anodes age and reach the end of their lifespan, the potential rises toward the Open Circuit Potential (OCP), leading to under-polarization and potentially significant residual corrosion.
For deep-sea infrastructure, renewing CP systems is complex and costly, prompting reconsideration of corrosion strategies. If a low residual corrosion rate can be achieved and combined with a corrosion allowance, structural integrity may still be preserved, especially in older installations in cold, deep water.
This study investigated residual corrosion rates under low polarization using two instrumented mooring lines immersed for one year off the coast of Rio de Janeiro (Brazil) at depths of 475 and 1085 meters, alongside laboratory experiments in France. Sensors tracked environmental data, cathodic protection levels, and biofilm activity. Under pseudo-potentiostatic conditions, very low corrosion rates were observed even above Ep in deep, low-oxygen, cold-water environments. These findings offer valuable data to adapt integrity strategies for deep infrastructure, helping cut costs, CO2 emission and save energy