A coupled multi-electrode array test method has been developed to assess the performance of corrosion inhibitors under sand deposits in sweet conditions. In the absence of inhibitor, the carbon steel under the sand deposit had a more positive corrosion potential than the external carbon steel electrode and acted as a net cathode on coupling (at least in the short time scale of the tests). Addition of the inhibitor to the bulk solution polarizes the external electrode to more noble values compared to the underdeposit steel and initially accelerates the corrosion rate of the latter prior to mitigation as the inhibitor diffuses to the corroding electrodes. Regular replenishment of inhibitor concentration provides a more severe test of inhibitor performance since it is likely to sustain a more noble coupled potential. There was a significant delay in reducing the corrosion rate to the industry acceptable value of 0.1 mm/y, and for one inhibitor, the latter was not attained. Measurement of the bulk solution inhibitor concentration in the tests with regular replenishment suggests that the sand is nearly saturated with inhibitor within 3 days and slow adsorption on the sand is not the primary constraint. The coupled multi-electrode array is shown to be a powerful tool in simultaneous assessment of the impact of electrode precorrosion and, most importantly, in highlighting statistical variations in corrosion rate. In this study, locally high values of the corrosion rate were measured despite an average corrosion rate for the ensemble that was below the acceptable limit. The average value reflects a mix of electrode regions under the sand, including some that are net cathodes, some with low net dissolution rates, and a very few with higher corrosion rates. Such a scenario is possible in service. The coupled multi-electrode system can identify worst-case scenarios that could easily be missed by other test methods and may be considered a more robust qualification test for corrosion inhibitors under deposits.
Novel multi-electrode test method for evaluating inhibition of underdeposit corrosion. Part 1: Sweet conditions
Eine neue Multi-Elektroden-Prüfmethode zur Bestimmung der Korrosionsinhibierung unter Ablagerungen. Teil 1: Süß(öl)-Bedingungen
Corrosion, Houston ; 66 , 4 ; 046001/1-046001/10
2010
10 Seiten, 15 Bilder, 1 Tabelle, 11 Quellen
Article (Journal)
English
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