Development of an Electrochemical Method to Study Top-of-the-line Corrosion

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 (condensation) combined with the low electrical conductivity of the condensed liquid has confined, to-date, TLC studies to the weight loss method which only provides an average over a long period of time information. The onset of localized corrosion cannot be exactly determined, which makes it difficult to determine localized corrosion rates and mechanistic data. The instantaneous monitoring of TLC rates using electrochemical methods is still a challenge for researchers and in the field. To overcome this limitation, a novel TLC monitoring cell has been developed, which is capable of measuring in-situ corrosion rates by electrochemical methods such as Linear Polarization Resistance (LPR), Electrochemical Impedance Spectroscopy (EIS) and Electrochemical Frequency Modulation (EFM). The data presented in this paper have been conducted over 5 days at variable 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. Thus, this paper presents the comparability and limitations of different techniques applied to TLC studies