Corrosion Study of Pipeline Steel under Stress at Different Cathodic Potentials by EIS

Abstract

The effect of different cathodic potentials applied to the X70 pipeline steel immersed in acidified and aerated synthetic soil solution under stress using a slow strain rate test (SSRT) and electrochemical impedance spectroscopy (EIS) was studied. According to SSRT results and the fracture surface analysis by scanning electron microscopy (SEM), the steel susceptibility to stress corrosion cracking (SCC) increased as the cathodic polarization increased (Ecp). This behavior is attributed to the anodic dissolution at the tip of the crack and the increment of the cathodic reaction (hydrogen evolution) producing hydrogen embrittlement. Nevertheless, when the Ecp was subjected to the maximum cathodic potential applied (−970 mV), the susceptibility decreased; this behavior is attributed to the fact that the anodic dissolution was suppressed and the process of the SCC was dominated only by hydrogen embrittlement (HE). The EIS results showed that the cathodic process was influenced by the mass transport (hydrogen diffusion) due to the steel undergoing so many changes in the metallic surface as a result of the applied strain that it generated active sites at the surface.

WC-Co and WC-Co-Cr Coatings for the Protection of API Pipeline Steel from Corrosion in 4% NaCl Solution

“…On another side, the reaction at the anode is the dissolution of metal, which in this case will be the dissolution of Fe presented in the API-2H steel according to the following reaction [27]: The values of the corrosion rate (RCorr), which are mostly expressing the uniformed corrosion and also listed in Table 4, were calculated using the following equation [25]:…”

“…On another side, the reaction at the anode is the dissolution of metal, which in this case will be the dissolution of Fe presented in the API-2H steel according to the following reaction [27]: It is evident that the current shows an active passive behavior for all steel samples but the highest current values were recorded for the uncoated steel, PS sample. The active area results due to the iron dissolution to Fe 2+ and the passivation results from the formation of a corrosion product layer and/or an oxide film onto the steel surface as per the following reactions: The current continues to increase even in the backward direction, resulting in the creation of an area of a hysteresis loop (curve 1 ), which is due the pitting attack that takes place on the surface; the massive area of the hysteresis loop indicates that a more severe pitting corrosion takes place.…”

“…where R Corr (millimeters/year), E W (equivalent weight/grams), ρ (density of the metal or alloy/(g/cm 3 )), and j Corr (µA/cm 2 ). It has been reported that the reaction of cathode for metals and/or alloys in neutral chloride solutions is the reduction of O 2 as per the following equation [26,27];…”

“…On another side, the reaction at the anode is the dissolution of metal, which in this case will be the dissolution of Fe presented in the API-2H steel according to the following reaction [27]:…”

Corrosion and Protection of Metals

“…The work by Galván-Martínez et al on X70 pipeline steel immersed in acidified and aerated synthetic soil solution [14] found a higher susceptibility to stress corrosion cracking (SCC) as the cathodic polarization increased (E cp ). Nevertheless, when the E cp was subjected to the maximum cathodic potential (−970 mV), the susceptibility decreased; this behavior is attributed to the fact that the anodic dissolution was suppressed and the process of the SCC was dominated only by hydrogen embrittlement (HE).…”