Study of the Top-of-the-Line Corrosion Using a Novel Electrochemical Probe

Abstract

Top-of-the-line corrosion (TLC) is a concern for subsea wet-gas transportation pipelines operating in a stratified flow regime. The insufficient volume of electrolyte at the top of the line combined with the low electrical conductivity of the condensed liquid has confined the majority of TLC studies to the weight loss method which only provides integrated corrosion rate over long period of exposure. The instantaneous monitoring of TLC rates using electrochemical methods is still a challenge for researchers and in the field. To overcome this limitation, this study presents a novel TLC monitoring cell capable of measuring in situ corrosion rates of carbon steel under condensing condition by electrochemical methods such as linear polarization resistance, electrochemical impedance spectroscopy, and electrochemical frequency modulation. The data presented in this paper have been conducted over 5 d at varying condensation rates to evaluate the feasibility and accuracy of the methods applied. In addition, TLC rates have also been measured by weight loss and monitored in situ by measuring the iron concentration in the condensed liquids in order to compare these results with electrochemical methods. Both the electrochemical and non-electrochemical methods provide comparable results, which validates the design and efficacy of the probe. Therefore, the probe appears to be a promising tool for further investigation into the TLC process and its inhibition.

Development and evaluation of miniature electrodes for electrochemical measurements in a CO2 top of line corrosion environment

“…FeCO 3 ) occurs on the steel surface. Otherwise this technique results in the corrosion rate of the specimen being underestimated [8].…”

“…The material considered in this study is X65 carbon steel; one of the most common pipeline materials used in the oil and gas industry [8]. The chemical composition of X65 is shown in Table 1.…”

“…Several different degradation mechanisms are possible with the presence of such species. However, one of the most recent, and perhaps more difficult processes to control is TLC corrosion [4][5][6][7][8][9][10][11].…”

CO2 Top-of-Line-Corrosion; Assessing the Role of Acetic Acid on General and Pitting Corrosion

“…This pit initiation may be associated with the preferential ferrite consumption that is increased due to the development large cathodic areas of Fe 3 C. This phenomena results in a galvanic coupling effect that, along with local chemistry changes, initiates and increases the depth of pits, as suggested in previous studies. 15,17 The localized ferrite consumption is intensified by the addition of HAc, as recorded by the rougher profiles consisting of several peaks and valleys. As already mentioned, such increased preferential dissolution will increase the ratio of Fe 3 C to ferrite over time.…”

“…Furthermore, one of the main parameters that influences TLC rate (and has received little research attention until recently) is T s . Since corrosion is an interface phenomenon, the temperature at the steel-electrolyte interface will undoubtedly influence the steel response to the corrosive environment, as highlighted in recent studies by Islam et al 17 and by De Carvalho et al 10 . The influence of T s on the corrosion rate response is plotted in Figure 4(b) for experiments in the absence of HAc.…”