Synergistic effect of erosion and hydrogen on properties of passive film on 2205 duplex stainless steel

Stainless steels have shown great potential in the application of offshore oil and gas industry. However, the internal surface of stainless steel pipeline may simultaneously suffer erosion from the fluid media inside the pipeline and the damage of hydrogen that is generated from the external activities such as cathodic protection. The synergistic effect of erosion and hydrogen on the properties of passive film on 2205 duplex stainless steel was studied for the first time in a loop system coupled with a hydrogen-charging cell. The components, protective performance and semiconductive structure as well as properties of the passive film under different conditions were investigated using in-situ electrochemical techniques, surface characterization and computational fluid dynamics simulation. The results show that the combination of erosion and hydrogen could greatly thin the passive film, furthermore, the Fe³⁺/Fe²⁺ ratio and O²⁻/OH- ratio in the passive film also decrease dramatically under such a condition. Therefore, the hydration degree of the passive film greatly increases, resulting in an increase in active sites and a decrease in the stability of the passive film. Erosion could destroy the passive film through the impact of sand particles and accelerate the mass transfer process of electrochemical reaction. While hydrogen can not only enhance the charge transfer process, but also make the passive film highly defective. Under the combination of erosion and hydrogen condition, erosion could enhance the hydrogen damage and simultaneously hydrogen could also enhance erosion. Therefore, the synergistic effect of erosion and hydrogen could dramatically change the passive film component, decrease the protective performance, and increase the susceptibility of pitting corrosion of 2205 stainless steel in Cl–containing environment.