Electrochemical Noise Study on Corrosion of Low Carbon Pipeline Steel in Sour Solutions

Abstract

Electrochemical Noise (EN) measurements for low carbon pipeline steel (X52) samples were carried out in 3.5% NaCl aqueous and NACE solutions. Both testing solutions were saturated with hydrogen sulphide (H2S) at 20 and 60 oC, under static conditions. EN data was analysed in the time domain. Parameter such as Electrochemical Noise Resistance (Rn) and Localization Index (LI) were determined from the analysis in the time domain. Also, Rn results are compared with traditional Linear Polarization Resistance (LPR) data. A superficial analysis was carried out by a scanning electron microscopy (SEM) with Energy Dispersive X-Ray analyses (EDX). A good correlation was observed among the used techniques and relevant electrochemical data related to the corrosion phenomena was obtained. According to Rn, the corrosion rate (CR) values of the steel sample immersed in 3.5% NaCl are higher than the CR of the steel samples immersed in NACE solution. The morphology of the corrosion process obtained by SEM was a localized type and this behaviour was corroborated by the results obtained by LI where these LI values are 1 or close to 1.

A novel experimental arrangement for corrosion study of X60 pipeline steel weldments at turbulent flow conditions

“…The results shown in Fig. 3a indicate that at the beginning of the test, the current transients were big and frequent, where these transients correspond to a typical behaviour of a localised process; [27][28][29] after 12 h exposure (Fig. 3b), the transients were reduced to almost disappear and the small current fluctuations were more frequent and trending to a stable value.…”

“…29 In general, the big spikes or big transients shown in the ECN since the beginning to the end of the exposure time, indicate the active behaviour of the steel weld sample, where the pores and ruptures of the corrosion products film that covered the surface of the steel weld sample could provoke a specific localised corrosion form and according to Tamura, the corrosion of the steel under this conditions is crevice corrosion. 28,[30][31][32][33] Figure 4 shows the ECN as a function of the exposure time at turbulent flow conditions (1000 rpm). A similar behaviour was presented in the three different exposure times.…”

“… show the results of the electrochemical current noise (ECN) as a function of the time for ×60 pipeline steel weld immersed in synthetic seawater at static and turbulent flow conditions.Figure3shows ECN as a function of the time at static conditions. The results shown in Fig.3aindicate that at the beginning of the test, the current transients were big and frequent, where these transients correspond to a typical behaviour of a localised process;[27][28][29] after 12 h exposure (Fig.3b), the transients were reduced to almost disappear and the small current fluctuations were more frequent and trending to a stable value. The behaviour presented at T12 should be attributed to the corrosion products film adsorbed on surface of the metallic sample that it can generate a partial protective effect on the metallic surface.…”

“…R n was estimated from the potential and current time records. 20,28,35 Then, CR was calculated by dividing the theoretical Stern-Geary constant (B = 0.120 V) by the estimated R n values. 36,37 Figure 6 shows the CR obtained from EN resistance (R n ) vs. exposure time for X60 pipeline steel weld immersed in synthetic seawater under static and turbulent flow conditions (1000 and 5000 rpm).…”

Electrochemical Noise for Detection of Stress Corrosion Cracking of Low Carbon Steel Exposed to Synthetic Soil Solution

“…Rn was estimated from the potential and current time records 8,33,34 . Rn was calculated according to equation 2.…”