Development of Novel Anti-agglomerant Chemistries with Reduced Localized Corrosion Potential to Stainless and Duplex Steels

Abstract

Abstract Low dosage hydrate inhibitors (LDHIs) have been used as alternatives to thermodynamic inhibitors such as methanol or mono ethylene glycol (MEG) to control hydrate problems. The major advantage of using LDHIs is that they control with a much lower dosage, typically 1 to 3vol% (based on water production volume), thus lowering storage requirements and logistical challenges, compared to much higher volumes required for methanol or MEG. Anti-agglomerants (AAs), as one type of LDHI, allow hydrates to form but inhibit growth and agglomeration of hydrate crystals. Some very effective AAs exhibit a pitting corrosion risk for offshore umbilical chemical delivery systems under certain conditions. An electrochemical method of cyclic potentiodynamic polarization (CPP), a modified ASTM G-61 method at ambient temperature, and immersion testing using a modified ASTM G-31 method at elevated temperatures were used to evaluate pitting tendencies of AA formulations containing corrosion inhibitors on stainless and duplex steels. Initially, these corrosion inhibitors were effective in controlling pitting corrosion in stainless steel only as shown by CPP and immersion testing. After modifying the manufacturing process and adjusting solvent systems, the selected corrosion inhibitors have been shown to be effective for both stainless and duplex steels. Hydrate performance testing showed no performance compromise with the presence of corrosion inhibitors within the AA formulation or from changing the solvent system. Mitigation of pitting tendency was also confirmed by immersion testing at elevated temperatures.