51315-5781-Reduction of Pitting Corrosion Tendency of a Novel Anti-Agglomerate Low Dosage Hydrate Inhibitor on Stainless and Duplex Steels

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Product Number: 51315-5781-SG

ISBN: 5781 2015 CP

Author: Zhengwei Liu

Publication Date: 2015

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Low-dosage hydrate inhibitors (LDHIs) have been used as alternatives to methanol or mono ethylene glycol (MEG) to control hydrate formation. The major advantage is a much lower dosage typically 1-5% compared to much higher volumes required for methanol or MEG. Anti-agglomerants (AAs) as one type of LDHI allows hydrate to form but prevents growth and agglomeration of small crystals.Recently there have been concerns of potential pitting corrosion in offshore umbilical applications caused by an anti-agglomerant. To address these concerns an electrochemical method of cyclic potentiodynamic polarization (CPP) a modified ASTM method and immersion corrosion testing at elevated temperatures was used to evaluate the pitting tendency of AA formulations containing corrosion inhibitors on stainless and duplex steels. From the CPP tests two types of corrosion inhibitors were identified to reduce pitting tendency. One type increases the pitting potential of steels and the other increases the re-passivation potential. The low pitting tendency was also confirmed with immersion testing conducted at elevated temperatures and over a long testing period. The temperature tolerance of the AA formulations with corrosion inhibitors were also identified based on the immersion testing results. The hydrate performance test showed that the additional corrosion inhibitors in the AA formulation have no negative effect on the hydrate inhibition performance.