Materials Performance Supplements


Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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Volatile corrosion inhibitors (VCIs) are commonly used in various oil systems to prevent corrosion during preservation and in intermittent operation. However, water ingress still introduces the risk of corrosion when water separates and pools at the bottom of these systems. Traditional corrosion inhibitors used in lubricating oils provide good corrosion protection in the oil phase, but cannot offer protection beneath the oil-water phase line due to their typical hydro- phobic nature. It has been determined that the use of proper organic VCIs (which also offer protection in the vapor phase and oil phase) can partition into the water phase and provide additional corrosion protection even in the case of water contamination. Water handling is an important property for lubricating oils in many applications. Even small amounts of water can cause seri- ous damage in a system, decreasing the oxi- dative stability of the oil, increasing depo- sition and contaminants, and reducing the performance of additives. 1 In storage and lay-up, the presence of water can promote surface corrosion on key components inside the system. Over time, each of these factors contributes to shortening equipment life. While operating oils may be replaced, oxi- Corrosion Protection in an Oil System with Water Ingress by Use of Volatile Corrosion Inhibitors John Wulterkens, s en k ang, and Casey h eurung, Cortec Corp., St. Paul, Minnesota, USA dation on metal surfaces may result in cost- lier and time-consuming repairs. Studies and laboratory experiments have previously investigated the effectiveness of oil-soluble/water -dispersible corrosion inhibitors to partition into brine and provide protection to pipeline systems. 2 However, key features of these experiments and the application of these inhibitors is their con- tinuous application into flowing/operating systems. Even traditional efficacy tests of these types of inhibitors, such as the contin- uous wheel test, investigate inhibitor perfor- mance under sheer conditions. 3 This oppor- tunity of mixing dispersion is not offered in stagnant preserved systems where water ingress is slow and inconsistent. Am i n e - b a s e d i n h i b i t o r s , i n c l u di n g imidizolines and aminocarboxylic acids, have been explored for petroleum indus- tries. Inhibitors are carefully crafted to bal- ance a variety of properties for varying sys- t ems. 4 Inhi bitors for preser vation and stagnant applications must be carefully chosen based on the desire for solubility in both oil and aqueous systems. The use of a specific oil-based corrosion inhibitor additive, with the ability to pas- sively partition from the oil phase into the aqueous phase, is investigated here. The effectiveness of partitioning (at various concentrations of corrosion inhibitor in the preservation oil) is evaluated by analyzing the concentration of the nitrogen-based corrosion inhibitors in the aqueous phase through the Kjeldahl Method for determi- nation of organic nitrogen. 5 The corrosion protection capabilities of the partitioned corrosion inhibitor is quantified and com- pared at various concentrations using increasingly rigorous iterations of immer- sion corrosion testing (modeled after ASTM G31 6 ) and el e ctro ch emical imp ed anc e spectroscopy (EIS). Experimental Procedure The evaluation of the corrosion pro- tection provided by a partitioned inhibitor required several different steps. Testing was performed to evaluate the amount of inhibi- tor that will partition into the aqueous phase under varying circumstances, as well as two separate methods to assess the degree of cor- rosion protection provided. Extraction of Corrosion Inhibitor from VCI Oil Additive Determination of Oil/Water Ratio A common practice for preser vation of oil systems includes filling the system with standard lubricating oil treated with a compatible VCI additive. According to the manufacturer's recommendations, VCI oil additives are dosed at 3 to 5% by volume of the base oil inside the system. Other rec- VOLATILE CORROSION INHIBITORS 18 JUNE 2019 MATERIALS PERFORMANCE CORTEC SUPPLEMENT TO MP

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