Evolution of Calcareous Deposits and Passive Film on 304 Stainless Steel with Cathodic Polarization in Sea Water

Abstract

Abstract:The change of protective current density, the formation and growth of calcareous deposits, and the evolution of passive film on 304 stainless steel (SS) were investigated at different potentials of cathodic polarization in sea water. Potentiostatic polarization, electrochemical impedance spectroscopy (EIS), and surface analysis techniques of scanning electron microscopy (SEM), energy dispersive X-ray (EDX) microanalysis and X-ray diffraction (XRD) were used to characterize the surface conditions. It was found that the protective current density was smaller for keeping polarization at −0.80 V (vs. saturated calomel electrode (SCE), same as below) than that at −0.65 V. The calcareous deposits could not be formed on 304 SS with polarization at −0.50 V while it was well protected. The formation rate, the morphology, and the constituent of the calcareous deposits depended on the applied potential. The resistance of passive film on 304 SS decreased at the first stage and then increased when polarized at −0.80 V and −0.65 V, which was related to the reduction and the repair of passive film. For the stainless steel polarized at −0.50 V, the film resistance increased with polarization time, indicating that the growth of oxide film was promoted.

Effects of Cathodic Polarization on the Corrosion Behavior of X60 Pipeline Steel in a Simulated Soil Solution

“…If the HER is intensive, it can decrease the crystal growth process on the electrode surface and can induce high porosity in the formed product layer. [ 47,52 ]…”

“…If the HER is intensive, it can decrease the crystal growth process on the electrode surface and can induce high porosity in the formed product layer. [47,52] The precipitation of deposits forms a barrier on the steel surface, which limits the transport of hydroxyl ions out of the steel. According to Barchiche and al., [47] pH 9 favors the precipitation of MgðOHÞ 2 .The measuring of the reversible potential of the hydrogen electrode is a pH measuring, according to Equation (4); the steel potential decreases with the rise of pH.…”

Calcareous Deposits Formed Under Long‐Term In Situ Cathodic Protection Tests

“…After 30 days, deposits had already been formed over the carbon steel surface. According to the literature, the electrochemical formation of CaCO 3 and Mg(OH) 2 crystal deposits in seawater may occur within a few days 12, 17, 19 to months 20, depending on the characteristics of the medium and the applied potential. Such analysis reinforces the importance of seawater characterization when trying to predict the level of calcareous deposition in seawater due to cathodic protection.…”

“…3–5. Even though the species in seawater undergo relatively simple chemical reactions, driven by their solubility product, the formed crystal structures and its extension throughout the deposit are influenced by diverse variables, such as temperature 10, 11, pressure 12, seawater Ca/Mg mass ratio 13, 14, presence of organic molecules 15, 16, applied potential 17–19, and presence of sediments 20. …”

On the evolution and application of the concept of electrochemical polarization

“…A search for the term "potentiostatic polarization" yields hundreds of papers. One can often encounter phrasings such as the electrode is polarized to/at a particular potential in recent papers (a few examples selected from various fields can be found in Refs [16][17][18][19][20][21][22][23][24]). In the description of experiments performed with the control of potential, anodic/cathodic polarization is extensively mentioned as the indication of either the potential sweep direction, the potential range studied as compared to the rest potential of the electrode or the sign of the current hence produced [25,26].…”