A New Understanding of Stress Corrosion Cracking Mechanism of X80 Pipeline Steel at Passive Potential in High-pH Solutions

Abstract

Susceptibilities to stress corrosion cracking (SCC) of X80 pipeline steel in relatively concentrated carbonate/ bicarbonate solutions with different chloride ion concentrations or pH value at a passive potential of -200 mV vs SCE were investigated by slow strain rate tensile test. In order to explore the SCC mechanism and the evaluation criterion for the SCC susceptibility of the steel in passive state, electrochemical measurements were taken. Potentiodynamic polarization curves were obtained at different potential sweep rates, and electrochemical impedance spectroscopy measurements were taken after fast polarization to the passive potential. The effects of chloride ion and pH on SCC behaviors of X80 steel at the passive potential were also discussed. The results showed that the SCC mechanism of X80 pipeline steel was greatly influenced by the passive film formed in these solutions. The SCC behaviors followed the film suppressed anodic dissolution mechanism in these circumstances, because the filming process accounted for a considerable proportion of the overall electrode process. The criteria for evaluating the SCC susceptibility of the steel at passive potential were proposed and validated. Decreasing in the concentration of chloride ion or increasing in pH value resulted in the reduction in SCC susceptibility. The existence of chloride ion greatly lowered the passivation tendency and the film stability, while its concentration determined the dissolution rate of the steel matrix. Higher pH value was responsible for the stable and tenacious passive films and the high repassivation capability. It was also inclined to lower the anodic dissolution rate at crack tips by retarding the cathodic oxygen reduction.

Study of SCC of X70 Steel Immersed in Simulated Soil Solution at Different pH by EIS

“…It is important to point out that despite that the steel exhibit a low susceptibility at these pHs, a few secondary cracks were observed close to the neck region. Similar results were reported by Fan et al [ 54 ]. In their study, an X80 steel showed a low susceptibility to SCC in a carbonate-bicarbonate solution without chloride ion, but shallow and short secondary cracks initiated on the lateral surface.…”

“…For an approximate physical description of the EIS measurements of the steel in NS4 solution at different pH during SSRT test, equivalent electric circuits (EEC) are suggested as shown in Figure 6 . The first EEC ( Figure 6 a) was employed to fit the EIS data in the acid solution (pH 3), in which the R s is solution resistance, R ct is the charge-transfer resistance, L ads and R ads are the inductance and resistance of the adsorption process, respectively [ 22 , 54 ]. The constant phase element (CPE dl ) is an empirical circuit element that represents the non-ideal capacitive behavior of the electrode.…”

Comparison of the Stress Corrosion Cracking Behaviour of AISI 304 Pipes Welded by TIG and LBW

“…This new layer is not stable and starts to dissolve in high-temperature water. At some point, it loses its protective nature and oxidation starts to propagate deeper into the matrix [27][28][29]. Therefore, owning to the positive effect of Cr 2 O 3 on the SCC resistance, the TIG joint containing less Cr 2 O 3 is more vulnerable to oxide rupture and has higher SCC susceptibility in the simulated PRW environment.…”

Tribocorrosion Behavior of 304 Stainless Steel in 0.5 mol/L Sulfuric Acid

“…The electrochemical behavior of stainless steels was studied widely, which is strongly related to chemical compositions and microstructures of stainless steels and corrosive media [27,28]. [29,30].…”