A New Concept of Corrosion Protection and Integrity of Subsea System in Brazil

Abstract

Abstract Over the past four decades, offshore oil and gas (O&G) production in Brazil has transitioned from shallow waters to deep waters, necessitating considerations for ensuring the integrity of subsea systems in this challenging environment. This study focused on field inspection reports that provided insights into the condition of carbon steel pipelines and subsea equipment, which are protected by galvanic cathodic protection. The findings from laboratory testing and thermodynamic simulations conducted under varying environmental conditions were compared with these evaluations. Additionally, a comprehensive survey of historical shipwrecks, which lacked corrosion protection and had remained on the seabed for decades, was conducted. The preservation and partial integrity of these shipwrecks were inferred from images captured during inspections conducted by remotely operated underwater vehicles (ROVs). By comparing the results of laboratory tests, subsea inspection reports, thermodynamic simulations, and ROV images of shipwrecks, it was observed that the corrosion rate in seawater at considerable depths is significantly reduced. This phenomenon allows shipwrecks to persist on the seabed for extended periods without severe corrosion. Furthermore, the analysis of PETROBRAS technical inspection reports on subsea equipment revealed that components of offshore production systems located in deep waters, which lack effective galvanic cathodic protection, continue functioning without compromising their structural integrity. This analysis supported the investigation of a corrosion protection technique applied to subsea production systems in deep water, based on kinetic considerations that complement existing thermodynamic-based criteria, with minimal risk to structural integrity. Importantly, further investigation is warranted to explore alternative cathodic protection potentials, particularly those exceeding −800 mVAg/AgCl, under high pressure and reduced temperatures. This initiative has contributed to the reduction of CO2 emissions, as there is no longer a need to make two trips to the installation site – one to install the anode skid and another to confirm the reestablishment of the protection potential.