Materials Performance Supplements

CORTEC 2018

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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† Trade name. VAPOR PHASE CORROSION INHIBITORS should provide effectiveness and good func- tionality in those conditions. The auto-igni- tion temperature for both hydrazine and new VCI is around 288 to 293 °C (553 to 555 °F). However, when the molecules are attached to surface oxides, they are more stable and this temperature is not critical. The research program implemented a closed loop with water/steam circulating through at 90 psi and 118 °C (245 °F). The objectives were to investigate electrochem- ical behavior of CS pipe samples (ASME B31.1 pipes) 26 under the following condi- tions: 1) exposed to the new VCI and a con- trol solution; 2) total immersion in boiling water with new VCI and without inhibitor (control-reference); and 3) in steam/water closed loop system with VCI and without inhibitor (control-reference). Post-test eval- uation was conducted by scanning electron microscopy (SEM)/energy dispersive spec- troscopy (EDS) analysis and x-ray photoelec- tron spectroscopy (XPS) analysis of surface conditions for samples with inhibitor. Experimental Procedure Corrosion behavior of steel pipe samples in the new amine-based VCI in steam/water loops at elevated temperature was investi- gated to explore its inhibiting effectiveness as an alternative for hydrazine. Electrochem- ical polarization behavior was conducted in 50 to 500 mg/L inhibitor solutions. Samples were polished (1.0 µm surface finish), placed in a flat cell, and tested in deionized water solutions containing 50 to 500 mg/L VCI at elevated temperatures. Corrosion behav- ior of CS pipe samples was assessed during complete immersion in boiling water while exposed to the new VCI and without inhib- itor (control sample). Apparatus for testing was similar to that recommended in ASTM G123 27 (Erlenmeyer f lask and condenser, hot plate to maintain solution at its boiling point, Figure 1). These tests were conducted in control solution ( filtered water, no inhib- itor), with 50, 100, 200, and 500 mg/L VCI addition. Test duration was ~700 h. The steam/water loop system included a Chromalox † electric boiler and steel pipe loop. The system is a safe and versatile heat source to produce low- or high-pressure steam (~100 psi). A closed loop system was assembled that can circulate and main- tain steam at 118 °C and 90 psi. Tests were conducted on the control (no inhibitor was used) for a duration of 1,100 h. Test duration for the 100 mg/L VCI was 2,200 h. During these tests, corrosion rate measurements were monitored using electrical resistance (ER) techniques, and the Metal Samples MS3500E † electrical resistance probe system with a data-logger was used for measuring and storing corrosion data. Light microscopy, SEM/EDS analysis, and XPS analysis were performed after cor- rosion tests to verify the extent of corrosion damage on the exposed surfaces after each test, using image analysis and SEM/EDS, fol- lowed by surface chemistry post-corrosion tests using high-resolution XPS analysis. Results and Discussion Electrochemical polarization behavior of the steel pipes in different concentra- tions of corrosion inhibitors at different temperatures are shown in Figure 2. Results indicated that the new VCI is an anodic corrosion inhibitor capable of lowering cor- rosion rate and expanding the passivation range for steel pipe in the working condi- tion of hot steam/water systems. The cor- rosion rate based on the cyclic polarization test results were as follows: for the control, 17.2 µA/cm 2 (7.91 mpy); in the presence of 100 mg/L VCI, 4.73 µA/cm 2 (2.18 mpy); and when a 200 mg/L VCI was added to solution, the corrosion rate decreased to 2.86 µA/cm 2 (1.24 mpy). In general, the boiler industry assumes approximately 1.0 mpy corrosion rate to be an acceptable range for the open circulating system. Corrosion behavior of the steel pipe sam- FIGURE 2 Comparison of cyclic polarization behavior of steel pipe in hot water solution in 100 °C when exposed to control solution, 100, and 200 mg/L VCI. FIGURE 3 Corrosion behavior of steel pipes in hot water solution in 100 °C when exposed to con- trol solution, 100, and 500 mg/L VCI and hydrazine. 1.00E-07 1.00E-06 1.00E-05 1.00E-04 1.00E-03 1.00E-02 -1 -0.5 0 0.5 1 1.5 Current Density, A/cm^2 Potential, Vsce 100 ppm, VCI 200 ppm VCI Ref 0.0 1.0 2.0 3.0 4.0 5.0 6.0 0 100 200 300 400 500 600 700 800 Corrosion Rate, mpy Exposure time, hrs water pH 8.24 Hydrazine 100 ppm pH 9.4 Hydrazine 500ppm, pH 9.96 100 ppm VCI, pH 10.1 500 ppm VCI, pH 11.2 12 JUNE 2018 MATERIALS PERFORMANCE CORTEC SUPPLEMENT TO MP

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