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C H E M I C A L T R E AT M E N T Mitigating Carbon Dioxide Corrosion in Wet Gas Systems FIguRE 3 TAbLE 1 Percentage of corrosion inhibition for different chemicals used Chemical % Corrosion Inhibition Morpholine 23 DEA 6 MEA 40 Proprietary CI 81 adsorption on an iron surface is a prerequisite but not a determining factor in the inhibition of the TOL corrosion. The estimated masses of CI, MEA, and DEA in the condensed water layer were ~18.1, 2.7, and 4.3 µg/cm2, respectively. Corrosion Rate Using Quartz Crystal Microbalance Corrosion rate vs. time in kettle test at 48.9 °C using a 50% liquid hydrocarbon50% synthetic brine in CO2 with 2 ppm of TOL CI. TAbLE 2 Vapor pressure and related parameters of volatile amines/CI Volatile Amines/ Alcohol Vapor Pressure (mmHg @ 20 °C) Vapor Density (Air = 1) pH Boiling Point (°C) Water 17.5 0.8 7.0 100 Morpholine 7.0 3.0 11.8 128 MEA 0.5 2.1 11.8 170 DEA 195.0 2.5 12.5 55 Proprietary CI 0.8 2.7 N/A 157 thickness of the chemically vapor-deposited iron flm measured relative to the height of the reference coating. The flm thickness is verifed by measuring the reference thickness included in the deposition run. In the iron deposition process, the last three runs averaged 1.015 µm. Water Condensation Rate The effect of different chemicals on water condensation on gold-coated quartz crystal showed that morpholine and the proprietary CI signifcantly affect the water condensation rate and subse- 58 MATERIALS PERFORMANCE May 2013 quent film formation, while diethyl amine (DEA) and monoethanol amine (MEA) have little or no effect on water condensation. Inhibitor Adsorption For all chemicals studied, a slight decrease in frequency (~30 Hz) (increase in mass) was observed within 30 min because of their adsorption to the metal surface. Depending on the nature of the adsorbed flm, the adsorption of volatile amines may or may not have an effect on the water condensation or corrosion. The Figure 2 shows the corrosion of ironcoated quartz crystal in a CO2 environment in the presence of a condensed aqueous layer. In this experiment, an iron-coated quartz crystal is placed in the vessel and a water flm is then condensed in a nitrogen environment. The crystal is heated to remove the water layer and CO2 is introduced. The crystal is cooled to induce water condensation. The aqueous flm forms again, followed by corrosion product formation, leading to a corrosion rate of 0.89 mm/y if we assume that the corrosion product layer is iron carbonate (FeCO3).7 The frequency drops were recorded and converted to a corrosion rate. Table 1 summarizes the results of the experiments with the experimentally determined percent of corrosion inhibition. For TOL corrosion inhibition to occur, the inhibitor must be transported to the vapor phase, be absorbed into the water condensed layer, and eventually be adsorbed on the metal surface. The superior inhibition of the CI can be explained by the formation of a hydrophobic flm that has a signifcant effect on both water condensation rate and corrosion. These results show that the amount of the CI adsorbed on the surface was suffcient to inhibit TOL corrosion under these test conditions. NACE International, Vol. 52, No. 5