This paper probes the properties of a novel naturally sourced material for the corrosion inhibition of different carbon steel alloys in the presence of mineral and organic acids as well as for the inhibition of scales. The inhibitor material is a food-grade chemical derived from a plant commonly used in medicinal formulations. It is easily available, nonpolluting, and, being of plant origin, is biodegradable. The inhibitor can be used either as a solid powder derived from the roots or as a liquid derived by means of extraction.
Corrosion inhibition of commonly used carbon steel alloy, such as N-80, was studied in the presence of corrosive media, such as 15% hydrochloric (HCl) acid and organic acid mixtures comprising acetic and formic acids, under pressurized conditions of 1,000 psi over a temperature range of 150 to 275°F. Weight loss measurements were used to evaluate the effectiveness of the inhibitor, and a corrosion loss of < 0.05 lbm/ft was considered passing grade. Evaluation of inhibitor in liquid state as a scale inhibitor was performed using the testing protocol described in National Association of Corrosion Engineers (NACE) test method TM0374-2007. The inhibition tendency toward two commonly observed scales, calcium and strontium sulfate, was evaluated, which are extremely difficult to remove once formed.
The inhibitor chemical has several N, O, and S atoms containing alkaloid structures, which enhances the capacity of the chemical for adsorption and imparts corrosion inhibition properties. At 250°F, a corrosion loss of 0.03 lbm/ft was observed with 5% inhibitor in 15% HCl acid after a test duration of six hours. At 275°F, 15% inhibitor could achieve a passing grade in three hours. With formic and acetic acid mixtures (9 and 13%, respectively), solid powder (75 lbm/gal) was tested, and a passing grade (0.02 lbm/ft2) was achieved at 275°F for six hours. The inhibitor also has certain functional groups that can trap or chelate the bivalent calcium and strontium ions and prevent the formation of scales. At 0.25% v/v inhibitor concentration, 100% inhibition of calcium sulfate and 18% inhibition of strontium sulfate scale occurred. The calcium compatibility of this chemistry exceeds the performance of most commercially available scale inhibitors. For strontium sulfate, the inhibition tendency improved to 29% when 0.5% v/v inhibitor was used.
The details in this paper align with the drive of the oil and gas industry toward greener chemistries and solutions to issues. The unique corrosion inhibition chemistry exhibited by the material is sufficiently robust to function in both organic and inorganic acid environments under challenging conditions. In addition, the same material can function as a scale inhibitor. The results show the potential for inhibiting sulfate scale as well as other commonly encountered scale.